You're spot on about the exhaust port. On our world Superbike spec engines the Akrapovic exhaust systems have this anti reversion built into the head spigots for the exhaust headers. Good stuff Dave. Thank you. We make more power on our Superbike engines usually when we flow the ports and build the floor with epoxy. We make over 225 rear wheel hp with 1000cc four cylinders turning 14-15,000 rpm
@TobiasCat-p6b I agree with you. It's so rare to find a person with such well rounded and complete knowledge of a subject and I believe some folks have confused themselves by listening to many different people that may not have such a complete understand of how to build and tune an engine.
It's a godsend for NA engines with really wild overlap durations. Doesn't make any difference with stock timing events lowered compression and roots blowers like I run.
It's good to hear Jim's name mentioned. He was good friends with my auto shop teacher so I got to meet him a couple times. I was just out of high school when he was working on the old quad four program. He gave a set of headers that he made to my shop teacher that he had used for testing what he called AR cone and they were used on a SBC. I do remember a small improvement in milage and not much gain was felt by the seat of the pants but the shop teacher said it was noticeable when starting to pull a hill. He made the cone the same size of the port al the way around and the expanded the tube at the cone to go around it. I'm not sure if this is coming out right cause I know what I'm thinking but not sure if that's what I'm saying. All that typed it's something I haven't thought about for along time and DV you hit it perfectly what he told me. I hear people saying stuff like we're just old school but sorry this is old news to you and me but valuable new school that work for many. PS I own Jim's old motorcycle dyno. And another PS, when I was racing stockcars I needed a crank for my mopar chrysler called a kellog crank, nobody had one and when jim found out he called Kieth Black who I believe made them and arranged for me to go to his place and pick one up the next day. So that day I sat in kieths office for 15 minutes talk about stockcar racing and left. The price...free thanks to Jim. Anyway you knocked another out of the park
Chevy 6 guys use something similar. The ports are low to the deck surface on both intake and exhaust, causing a huge flow restriction. Their solution is a "lump port" kit. These are a lump of cast iron that fits the port floor on the short side turn. This gives a larger radius to the turn. Then the roof can be ported to increase the area. A hole is drilled through from the rocker area that does not have coolant and through the deck surface. An Allen head bolt secures the lump in place. The hole is taped with a pipe tap from the rocker side to seal the rocker area from the port. I think most V8 heads have coolant above and below the ports, so this would not work.
Wow, that was interesting. I had a 03 Yamaha FZ1 and had installed an Ivan's Jet Kit. Well after some playing around the bike ran well but still had a lot of pops on deceleration. In an effort to reduce this I made a cone (never heard of this before) from some steel pipe to increase back pressure and get rid of the decel pops. I installed it where the four pipes meet as one. After some playing around I had a smooth and fast running machine. More importantly, during taking it apart, adjusting (bending) and putting it back together multiple times, I had accidentally broken one of he four "leafs" of the cone. The broken, or non restricted, area ended up at the bottom of the pipe. I noticed the difference immediately. Only thing is, I had no idea what I had done. Now I know. Thanks David.
This reversion is more evident in larger V8's with large cam overlap. John Kasse made a point to never use old, rusty inside headers. He figured out why his friends were getting oxide in the cylinders and killing their new engines.
Thats why I see so often some rags in the intake port to prevent stuff dropping into it ........but not so often in the exhaust port. Many think : it blows the stuff out... Well.....if the exh valve is open and sonething drops into the port....... drops into the cylinder. Doing its damage before blown out.....
@TobiasCat-p6b its my experience as a pro head porter.... I have seen very often engines in a workshop with covered intake ports ( a folded rag in it , ducktape on etc etc ) ....but exhaust ports open. Than customer explains : no need covering exhaust ports ....its only blowing gases out so no problem. Yeah...right.... but if whatever fell in damages e.g. squish area and top of piston cause it got stuck between that before blown out of the port.... Most of the time ...I get a blank stare.....
This was the entire principle behind GM's "Fast Burn" SBC ports... and they were considerably effective. It allowed you to get big cam revs without excessive duration. The revised exhaust ports alone were worth 10-15hp, and gave an easy 100rpm to the sweep of most street performance cams.
Anti reversion was one of my goals when I created step tube headers back in '83. It enables a smaller first section that boosts velocity off the port while maintaining or even increasing over all flow.
OMG - I just came across this by chance - you sir are an absolute legend! It was your magazine articles and books that got me into engine tuning. After modifying my engine and pulling up at some traffic lights a guy pulled up next to me and said "What engine have you got in that car? It goes like sh*t off a shovel!".
David Vizard has as much knowledge I bet as anyone out there that builds engines like he has in his lifetime. Amazing man. Love for him to build me SBC for my pro 2300 lb pro street car. Thank you David for your hard work and time sharing this stuff with us.😊
After studying engines for years, I learned something today. Thank You! When building my street engines using cast iron exhaust manifolds I have been enlarging the top of the manifold port, creating a lip which I thought would be anti-reversionary. Turns out I should have been doing this at the bottom of the port! Mind-boggling! Thanks again, David. R.
Ahh good idea🏅 I have an adaptor block on my Volvo exhaust to connect a turbo. I know that all doesn't line up quite right. Now I can turn it into an advantage
I have been working on a dato head which had plates added to the floor of the exhaust. Those intake ports look too big for the valve. You can get a good size valve in if you off set the intake by 10 degrees toward the centre of the bore. I have some pics if your interested, it has 47.5mm intake valves. The engine I built is under 2l and it made 150hp at the rear wheels with the rally tires on through a straight cut gearbox! The guy who built the head it used to work with Les Collins, his name is Mark Banyard. I made a few small tweaks like individual spring seats to ensure each of the cosworth springs were nearly binding and kelford made up a special cam. It goes hard, from 4.5k rpm all the way to 9.5K and it only has a 38mm port on the intake.
I run a modified U20 with larger vavles etc, previously making 142whp before the new EFI. I think a plate system like what he describes would be easy. Would enjoy sharing info. I'm on the dyno July 9 for a final ignition map. I'm expecting 150whp and a flat torque curve coming on at about 3200rpm, 246/50 dur .530 total lift cam, 11 to 1 compression, 40mm Jenvey Heritage TBs on Microsquirt, Ford EDIS ignition, pump gas. Engine is the best ever, easy street runner with no low rpm issues. Cheers!
No useful technical comments. Just the curves that life throws at us if we live long enough (your lovely daughter). Big valves, reground cams and intake runner porting were a must even on my meager salary in 1974 after reading 'Tuning Twin Cam Fords.' Thanks for all your years.
Excellent info. I made up some inlets many years , machined “rimflow” grooves as per Paul Ivy article in C&CConversions, and fitted them to a 649 cammed 1293. Was a lot better at idling, as you say better for getting on cam. The grooves were a little further away from the rim as I was concerned about their “mushrooming’ over. They didn't! Great memories!!!
I've had your book on the pinto engine since I was a wee lad. I still read it from time to time and I remember the antireversion plate in that book, and also the use of the apple port on the intakes. Love your work.
I built AR headers thirty years ago after reading an article by Dean lowery and of course David Vizard. The ones I built followed the work of Jim Fueling with AR cones in the first set I built for FE rail. Later street headers I built I just dropped the bottom of the header away and put a shelf parallel with the port bottom. With close lobe centre cams the engines would rev quite sharply and had a good low rev operation. Step headers do something similar. In the intake manifold the runners stayed very clean I noticed. I think I had to lean the carb or it would run rich with the cones.The magazine was popular hot rodding may 1980. I have followed you David since the English hot car magazine days and have learned a lot from your writings. Thanks.
David, I think this is my favorite video you've done, and super well presented. It also flows nicely from previous conversations about cams with overlap impacting street manners. I wish there was a good way to characterize or score a particular cams low RPM behavior... maybe something like a surge line on a compressor map... but I'm seeing now its not all about the cam.
BMW used increasing diameter steps in their headers to act as reversion dams. Since the exhaust port was the smallest diameter, the ridge from the head casting and the flange made a good dam, then the tube to the flange again had a difference in size, and each tube segment increased in size to help minimize reversion in the exhaust. I have incorporated this technique on all of my ports since learning about it. I stopped match porting exactly on both sides and leave a directional ridge to counter reversion at each flange.
They're not "anti-reversion". They just increase the average area of the headers to increase flow. e.g. If your engine needed 1-13/16" primaries you can make the first half 1-3/4" and the second half 1-7/8".
I'm not sure how they designed it exactly, but regular smooth step-up is usually used for wave tuning and to keep the speed high off the head while still flowing good. Smooth steps could potentially be less sensitive against back pressure for the same reasons, as it would have to work against higher speed and with a pressure drop moving upstream, but it's not the usual reason why it's choosen. Big abrupt steps is usually a crutch as it does a poor job in pressure recovery.
David. In the late 80's I experimented with anti-reversion with some astounding results on my SB chev. My dad's 8hp Briggs & Stratton garden tiller and a friend's SB mud racer also went nuts. Life changes stopped me from continuing. I am so happy to finally see you took this seriously, whereas everyone else has leaned on high-tech for simple solutions. I would love to talk some more.
You know I think I read your article because that’s where I learned about it in the 80s or early 90s but I always thought the ring would be the right way to go. This is very interesting. It changes my approach to how I wanna do it.
There is no substitute for wisdom derived from successful practices. Thank you Sir. Very Respectfully, SKWID Rider’s Shipmate ET1(SS/SW/MTS) US Navy, Ret. Killmonger: 2020 Fat Boy (Stage II+ by Blockhead) SilverBAK: 2021 Road Glide (S&S 129ci/Fueling Race Kit by Rider’s Shipmate)
This channel showed up in my random feed. What he describes is how I built my 345 sv engine 30 years ago. My old boss had a buddy that was an independent machinist. He wrote a program(cnc) to port the heads. He talked about this very thing. Looked at my headder flanges, said "perfect" this engine will rev to the moon. He finished the porting by hand. It does, I run it up to 6500. Factory red line with a stock cam was 3800. 54000 miles later, still pulling hard.
1973. I built a two 8960 over and heard about some fancy new headers called anti-reversion. I believe they were built by Hooker maybe what a screamer couldn’t keep clutches or drivelines in it. Fun fun car.
I remember Grumpy's "Chevrolet Racing Engine"...there was a principle picture of the ditch cut exhaust valve and Vizard's Pinto engine tuning book, where was anti reversion exhaust manifold. I wonder, if the ditch cut would work better with the higher exhaust port and anti reversion exhaust manifold with low exhaust port...
I once owned a 97 Firebird with an LT1 350. It did not run well past 5000 rpm with the stock manifolds so I installed an old set of long tube headers from my stock car on it. The difference in power from that one modification was unreal across the entire RPM range! At that time all you saw was that the D-shaped exhaust ports on LT1 heads needed special D-shaped tubes to correspond to the shape of the port. My headers were regular 1 5/8” round tube. Could the misalignment of the bottom portion of the tube with the flat of the D port have been helping with cancelling reversion? I wish I had ran across David’s books 30 years ago!
I'm going to say yes, follow along here, a popular swap in the G3 hemi world is to use Eagle heads(09+) on the pre Eagle 5.7(03-08) the exhaust on the Eagle is a D shape, while the 03-08 head it's a square, when we use the round tube headers made for the older head we find a 10Hp/20Ft gain over the later designed headers, now if I weld up and round the top of the eagle head exhaust port to match the round tube header, it's 25Hp/25Ft increase and moves the Power band up a 1k rpms.
Thanks Much DV!!...I've been thinking about this very thing for a little while now and I'm about to fab up some exhaust gaskets for this very purpose....
Hey, sending greetings from Trinidad &Tobago, the part about the datsun head stirrs up memories, i had a L series engine, a N42 block and a N42 head, in the exhaust ports had a funny shaped stamped sheet metal insert, these would become loose and in some cases fall out of the cylinder head and make its way into the exhaust system...never understood its function untill now...thank you Mr. David Vizard.
Those were actually for emissions. They would get hot and help burn off any excess fuel before it got to the catalytic converter. They actually don't have any effect on port flow until you get to making some serious horsepower
You can get those exhaust plates for a 4v big port 351 Cleveland. but that port dives off very steeply on the floor it very well could use another angled bit welded on the end. 🧐
@@Low760 I was referring to the tin plate you put between the header and the head it fils the the bottom of the exhaust floor in Not the alloy block that converts them to a hi-port
I HAVE A 496 CHEVY BIG BLOCK in my 1978 Chevy Suburban which I built for torque and towing. I ended up using peanut port heads as they were what I could afford. A friend gave them to me, and they already had valves in them, so I was not able to port them. I then put a "peanut port manifold on with a Quadra jet carburetor and long tube headers. I am wondering if this idea of putting a dam plate in this set up would help as the headers already have a larger diameter than the exhaust port. i remember reading about Grumpy Jenkins using larger exhaust headers to block back flow and wonder if by putting the larger headers on this engine it accomplished what you are talking about in this video. By the way you look much better than earlier videos (I have a gap in watching your videos due to being able to get back to Thailand to be with my wife). Your skin tone and voice look and sound much improved. Keep up the health as you are one of the greatest minds in the engine building world if not the greatest.
I'd love to hear your comments on the value of cutting an anti-reversion step on the exhaust valve and what the potential if any of the modified valves. Thanks so much for the decades of information - I started following you from 'How to Modify Your Mini' days.
Don’t worry about me, I am 63 and in great condition, never broke a bone. I had a couple crashes at about 8 years old going down a steep rocky hill in a push plastic go cart I made. Crashed at 45 mph on my skateboard, high speed wobbles. Other close calls landing 152 Cessna.
14:50 short side radius... A guy named Birdie ported my alum Edelbrock Oldsmobile heads and he even cut into the intake and had to brass sleeves for the pushrod holes. We didn't make huge flow numbers but one thing i want to point out is he kept the heads forever and kept asking me what cam im gonna run. I kept saying it will be custom based on what you can get out of the heads. We went back and forth on this for months. Then he told me the lift numbers mattereed as far as how much he was gonna roll off the short side exhaust...to reduce reversion. Ultimately i chose a weird hyd roller from crane with LS lobes. I'll give general specs its .620/.620 lift (1.5 ratio rockers) 257/265 duration @.050 and the n/a engine made 620hp/620tq at only 6100 so in the end we did ok. Cubic inch is 462 its a .030 over 455 olds. 4.155 bore with the worst cyl head ever for actual flow. In my mind a 462 set up this way should flow more but it is what it is
Nice tip, i will try to aply on my little 1000cc and 1600cc turbo headers, tinking about litle inserts(flaps/cones) sanduíched btwin header and The exhaust headers
Years ago, I built engines, many of them were air cooled VW engines. We made power on those with higher compression and big round exhaust ports. I built a few Type 356 Porche engines. They had lower compression and weird long rectangular ports, but hey made lots of power. I never knew why. Maybe the 1950's German engineers understood reversion.
So how about designing the surface of the intake/exhuast port and backsides of the valves like shark skin? Its rough in one direction and smooth in the other. It also has a similar effect to golf ball surface.
The ports are already rough in both directions, for the intake its so that the fuel stays in suspension whereas with a polished port you can have fuel pooling in the low pressure areas of the port. I don't see why it wouldn't be worth a try in the exhaust though.
We did the Anti reversion exhaust trick 28 yrs ago on a bbc ski race boat. strangely the intake length had to be 34 inches or the intake charge come out of the trumpets at 4000rpm. I wish i could find the photos.
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Reversion is a big thing with V twin motor cycle engines. They even make anti reversion cones that go into the head pipes to reduce reversion and they actually help[ make more power.
Thankyou Sir, This explains a lot for me as I could understand how an expansion chamber works on a 2 stroke but I never found anything relating to 4 stroke engines other than the length of header pipe. Excellent.
Very, Very interesting vid. enjoyed it. need to watch it again. does the groove cut in the top of the intake valve shorten the life of the valve seat at all?
Thank you for making a video on this subject. One question, could almost the same effect be achieved while port matching? The change would be to leave the floor of the port untouched as long as there is a step down into the exhaust manifold/header. Then, in corollary, if the same technique were used on the intake side from the intake manifold to the cylinder head. Would this give the opportunity for any fuel on the floor to be introduced back into the air stream? This idea is for carb'd applications.
David, Great work. Very informative for those well versed in the more advanced aspects of flow. Question: how do tgese principles relate to turbo charging? The intake ridge looks good but the ramp in the header, i winder. Have you any input ?
I would think it would work as well or even better in a turbo application. There would be a bigger back pressure when bumping up against the turbine blades.
I wonder how this plays into turbo engines, like a Subaru EJ257 for example... Just from looking at the exhaust ports in the head it looks like there would probably be quite a bit of flow separation on the short side of the exhaust ports for sure! And I'm guess with it being a turbo engine, the higher exhaust back pressure between the engine and turbo would cause even more backwards exhaust flow back into the cylinders if there is a slow speed flow separation on the short side of the ports...
@David Vizard Could you do a video(s) focusing on workhorse/towing/4x4 truck engines where LOW & MIDRANGE TORQUE is the goal and NOT high rpm horsepower. There are millions of people in that category and there is almost NOBODY doing videos about it. I think the video(s) would be a HUGE success!! I would be forever grateful if you could cover that side of the spectrum. I know you have the knowledge to do it!!! Thank you for everything!
I have always made the manifold about 3 mm bigger in diameter so there is a edge around the port. I would be fun to see if that has a bit of the same effect
I would say next time only go to 3mm on the inside edge where the reversion is. Otherwise you are creating a low pressure turbulence spot where the air wants to flow smooth and fast. And yes this will definitely have an effect. an easy way to do it without making plates although not as efficient
VERY interested in the anti-reversion plate that could be added, as I'm sure my ported Nissan U20 is experiencing the same as the L-series head. Seems relatively "easy" to make... how tall and what angle would such an anti-reversion plate be at in the header? Is its effectiveness highly sensitive to the height and angle? Seems that such a plate would be an easy install between the header and head. I thank you for sharing all your extensive knowledge and hope you're able to comment!
I was told years ago if the header or manifold opening was slightly larger than the head opening it would leave a lip that would reduce reversion. So with what your saying...maybe if you only leave the lip at the bottom it might work better?
11:28 Lunch with Bill "Grumpy" Jenkins.... I sure wish that feller was still around. He would have had a ball with the chevrolet LS platform. Good story too, and i love stories.
You're spot on about the exhaust port. On our world Superbike spec engines the Akrapovic exhaust systems have this anti reversion built into the head spigots for the exhaust headers. Good stuff Dave. Thank you. We make more power on our Superbike engines usually when we flow the ports and build the floor with epoxy. We make over 225 rear wheel hp with 1000cc four cylinders turning 14-15,000 rpm
What we all need is that magic Toyota turbo inlet orifice that changes size with rpm
Amazing. What the team your talking about or if you guys have a TH-cam channel I’d love to see your superbike
Reed valves in two strokes helped.
@@cliffwright9842 Honda used reeds on 450cc single dirtbike 4 strokes too and it worked great Idle to high rpm cammed for the rpm .
What bike motor and what bike did you have 225 hp out of 1000cc bike?
If I learn 1/10th of what this gentleman knows in my lifetime I will be happy.
Do what I did long ago, stay with Mr. Vizard only follow his guidance only and you will NOT ever go wrong.
@TobiasCat-p6b I agree with you. It's so rare to find a person with such well rounded and complete knowledge of a subject and I believe some folks have confused themselves by listening to many different people that may not have such a complete understand of how to build and tune an engine.
if your listening and taking it in youll get there.
I remember an article in Hot rod many years ago with anti reversion cones built into the header flange at the head.
It all made sense.
It's a godsend for NA engines with really wild overlap durations. Doesn't make any difference with stock timing events lowered compression and roots blowers like I run.
0 I'll😊 so@@patrickshaw8595
I read that! Then began learning about sound and pressure waves and exhaust flow.
It's good to hear Jim's name mentioned. He was good friends with my auto shop teacher so I got to meet him a couple times. I was just out of high school when he was working on the old quad four program. He gave a set of headers that he made to my shop teacher that he had used for testing what he called AR cone and they were used on a SBC. I do remember a small improvement in milage and not much gain was felt by the seat of the pants but the shop teacher said it was noticeable when starting to pull a hill. He made the cone the same size of the port al the way around and the expanded the tube at the cone to go around it. I'm not sure if this is coming out right cause I know what I'm thinking but not sure if that's what I'm saying. All that typed it's something I haven't thought about for along time and DV you hit it perfectly what he told me. I hear people saying stuff like we're just old school but sorry this is old news to you and me but valuable new school that work for many. PS I own Jim's old motorcycle dyno. And another PS, when I was racing stockcars I needed a crank for my mopar chrysler called a kellog crank, nobody had one and when jim found out he called Kieth Black who I believe made them and arranged for me to go to his place and pick one up the next day. So that day I sat in kieths office for 15 minutes talk about stockcar racing and left. The price...free thanks to Jim. Anyway you knocked another out of the park
Chevy 6 guys use something similar. The ports are low to the deck surface on both intake and exhaust, causing a huge flow restriction. Their solution is a "lump port" kit. These are a lump of cast iron that fits the port floor on the short side turn. This gives a larger radius to the turn. Then the roof can be ported to increase the area.
A hole is drilled through from the rocker area that does not have coolant and through the deck surface. An Allen head bolt secures the lump in place. The hole is taped with a pipe tap from the rocker side to seal the rocker area from the port.
I think most V8 heads have coolant above and below the ports, so this would not work.
This is why we watch your videos, thanks DV.
Wow, that was interesting. I had a 03 Yamaha FZ1 and had installed an Ivan's Jet Kit. Well after some playing around the bike ran well but still had a lot of pops on deceleration. In an effort to reduce this I made a cone (never heard of this before) from some steel pipe to increase back pressure and get rid of the decel pops. I installed it where the four pipes meet as one. After some playing around I had a smooth and fast running machine. More importantly, during taking it apart, adjusting (bending) and putting it back together multiple times, I had accidentally broken one of he four "leafs" of the cone. The broken, or non restricted, area ended up at the bottom of the pipe. I noticed the difference immediately. Only thing is, I had no idea what I had done. Now I know. Thanks David.
Why try to increase back pressure? That's steps taken in the wrong f direction buddy
😮
@@AshleyDonald-gr3cmlisten to the video again, you completely missed the point
@@dinadaughtry8993 read the top post. I'm not talking about the video.
This reversion is more evident in larger V8's with large cam overlap. John Kasse made a point to never use old, rusty inside headers. He figured out why his friends were getting oxide in the cylinders and killing their new engines.
Thats why I see so often some rags in the intake port to prevent stuff dropping into it ........but not so often in the exhaust port. Many think : it blows the stuff out...
Well.....if the exh valve is open and sonething drops into the port....... drops into the cylinder. Doing its damage before blown out.....
@TobiasCat-p6b its my experience as a pro head porter....
I have seen very often engines in a workshop with covered intake ports ( a folded rag in it , ducktape on etc etc ) ....but exhaust ports open.
Than customer explains : no need covering exhaust ports ....its only blowing gases out so no problem.
Yeah...right.... but if whatever fell in damages e.g. squish area and top of piston cause it got stuck between that before blown out of the port....
Most of the time ...I get a blank stare.....
Nobody that has any knowledge of 2 stroke understands these ideas.
This was the entire principle behind GM's "Fast Burn" SBC ports... and they were considerably effective. It allowed you to get big cam revs without excessive duration. The revised exhaust ports alone were worth 10-15hp, and gave an easy 100rpm to the sweep of most street performance cams.
Anti reversion was one of my goals when I created step tube headers back in '83. It enables a smaller first section that boosts velocity off the port while maintaining or even increasing over all flow.
OMG - I just came across this by chance - you sir are an absolute legend! It was your magazine articles and books that got me into engine tuning. After modifying my engine and pulling up at some traffic lights a guy pulled up next to me and said "What engine have you got in that car? It goes like sh*t off a shovel!".
David Vizard has as much knowledge I bet as anyone out there that builds engines like he has in his lifetime. Amazing man. Love for him to build me SBC for my pro 2300 lb pro street car. Thank you David for your hard work and time sharing this stuff with us.😊
Tesla Valve principle I guess. Very smart application, thanks for sharing
Tesla valve made effective by large difference between long and short side port velocities.
After studying engines for years, I learned something today. Thank You! When building my street engines using cast iron exhaust manifolds I have been enlarging the top of the manifold port, creating a lip which I thought would be anti-reversionary. Turns out I should have been doing this at the bottom of the port! Mind-boggling! Thanks again, David.
R.
Ahh good idea🏅 I have an adaptor block on my Volvo exhaust to connect a turbo. I know that all doesn't line up quite right. Now I can turn it into an advantage
I have been working on a dato head which had plates added to the floor of the exhaust. Those intake ports look too big for the valve. You can get a good size valve in if you off set the intake by 10 degrees toward the centre of the bore. I have some pics if your interested, it has 47.5mm intake valves. The engine I built is under 2l and it made 150hp at the rear wheels with the rally tires on through a straight cut gearbox! The guy who built the head it used to work with Les Collins, his name is Mark Banyard. I made a few small tweaks like individual spring seats to ensure each of the cosworth springs were nearly binding and kelford made up a special cam. It goes hard, from 4.5k rpm all the way to 9.5K and it only has a 38mm port on the intake.
I run a modified U20 with larger vavles etc, previously making 142whp before the new EFI. I think a plate system like what he describes would be easy. Would enjoy sharing info. I'm on the dyno July 9 for a final ignition map. I'm expecting 150whp and a flat torque curve coming on at about 3200rpm, 246/50 dur .530 total lift cam, 11 to 1 compression, 40mm Jenvey Heritage TBs on Microsquirt, Ford EDIS ignition, pump gas. Engine is the best ever, easy street runner with no low rpm issues. Cheers!
No useful technical comments. Just the curves that life throws at us if we live long enough (your lovely daughter). Big valves, reground cams and intake runner porting were a must even on my meager salary in 1974 after reading 'Tuning Twin Cam Fords.' Thanks for all your years.
The location of the plate is very well explained and makes perfect sense.
Excellent info. I made up some inlets many years , machined “rimflow” grooves as per Paul Ivy article in C&CConversions, and fitted them to a 649 cammed 1293. Was a lot better at idling, as you say better for getting on cam. The grooves were a little further away from the rim as I was concerned about their “mushrooming’ over. They didn't! Great memories!!!
Ditto on my 998 imp 🎉
I've had your book on the pinto engine since I was a wee lad. I still read it from time to time and I remember the antireversion plate in that book, and also the use of the apple port on the intakes. Love your work.
I had that book too, I read it several times cover to cover. Thankyou DV for your books and your YT channel.
Same ! Got the a series one first. Both still great books. 😊
I"d never even considered this before! Great information! Thank you, Sir, for sharing. Never stop learning.
Ive learned a lot in this, thank you very much
I built AR headers thirty years ago after reading an article by Dean lowery and of course David Vizard. The ones I built followed the work of Jim Fueling with AR cones in the first set I built for FE rail. Later street headers I built I just dropped the bottom of the header away and put a shelf parallel with the port bottom. With close lobe centre cams the engines would rev quite sharply and had a good low rev operation. Step headers do something similar. In the intake manifold the runners stayed very clean I noticed. I think I had to lean the carb or it would run rich with the cones.The magazine was popular hot rodding may 1980. I have followed you David since the English hot car magazine days and have learned a lot from your writings. Thanks.
David, I think this is my favorite video you've done, and super well presented. It also flows nicely from previous conversations about cams with overlap impacting street manners. I wish there was a good way to characterize or score a particular cams low RPM behavior... maybe something like a surge line on a compressor map... but I'm seeing now its not all about the cam.
This is the wonderful stuff that's found only here. Please keep it coming. It's the reason that I signed
on for in the beginning. Many thanks.
Love all your videos, awesome info, please keep them coming. Now subscribed.
Gday from Australia David Great video as always mate, im hooked
Off the subject but you are the perfect guy to tell Steve Morris the cam specs for his Big Black Hemi, 903 cubic inches. He has a video on it.
You are a great researcher David and have forgotten more than a person like me would ever have learned on this matter
BMW used increasing diameter steps in their headers to act as reversion dams. Since the exhaust port was the smallest diameter, the ridge from the head casting and the flange made a good dam, then the tube to the flange again had a difference in size, and each tube segment increased in size to help minimize reversion in the exhaust.
I have incorporated this technique on all of my ports since learning about it. I stopped match porting exactly on both sides and leave a directional ridge to counter reversion at each flange.
They're not "anti-reversion". They just increase the average area of the headers to increase flow. e.g. If your engine needed 1-13/16" primaries you can make the first half 1-3/4" and the second half 1-7/8".
@@chrisstavro4698 I think I will take BMW at their engineer's word when they explicitly said it was to combat reversion.
I'm not sure how they designed it exactly, but regular smooth step-up is usually used for wave tuning and to keep the speed high off the head while still flowing good. Smooth steps could potentially be less sensitive against back pressure for the same reasons, as it would have to work against higher speed and with a pressure drop moving upstream, but it's not the usual reason why it's choosen. Big abrupt steps is usually a crutch as it does a poor job in pressure recovery.
David. In the late 80's I experimented with anti-reversion with some astounding results on my SB chev. My dad's 8hp Briggs & Stratton garden tiller and a friend's SB mud racer also went nuts. Life changes stopped me from continuing. I am so happy to finally see you took this seriously, whereas everyone else has leaned on high-tech for simple solutions. I would love to talk some more.
I remember reading this in your book "Performance with economy" about 40 years ago!
Excellent video David, the exhaust system will make or break an engine,if the exhaust port is correct you may not need a Merge collector!!
You know I think I read your article because that’s where I learned about it in the 80s or early 90s but I always thought the ring would be the right way to go. This is very interesting. It changes my approach to how I wanna do it.
Thanks DV!
There is no substitute for wisdom derived from successful practices. Thank you Sir.
Very Respectfully,
SKWID
Rider’s Shipmate
ET1(SS/SW/MTS) US Navy, Ret.
Killmonger: 2020 Fat Boy (Stage II+ by Blockhead)
SilverBAK: 2021 Road Glide (S&S 129ci/Fueling Race Kit by Rider’s Shipmate)
Thank you David. Excellent content!
Thanks!
This channel showed up in my random feed.
What he describes is how I built my 345 sv engine 30 years ago. My old boss had a buddy that was an independent machinist. He wrote a program(cnc) to port the heads. He talked about this very thing. Looked at my headder flanges, said "perfect" this engine will rev to the moon. He finished the porting by hand. It does, I run it up to 6500. Factory red line with a stock cam was 3800. 54000 miles later, still pulling hard.
1973. I built a two 8960 over and heard about some fancy new headers called anti-reversion. I believe they were built by Hooker maybe what a screamer couldn’t keep clutches or drivelines in it. Fun fun car.
I always love it when David says "Let me tell you a story...." lol.
Building aerodynamic check valves in addition to the poppet valves is quite a skill.
Exellent knowledge , grumpy used to ditch cut his exhaust valves, but this looks better, many thanks!
I remember Grumpy's "Chevrolet Racing Engine"...there was a principle picture of the ditch cut exhaust valve and Vizard's Pinto engine tuning book, where was anti reversion exhaust manifold. I wonder, if the ditch cut would work better with the higher exhaust port and anti reversion exhaust manifold with low exhaust port...
Had your books for years! Dave, what about stepped headers? Geez, I grew up in the 70s reading Car Craft and Grumpy Jenkins was big back then.
I once owned a 97 Firebird with an LT1 350. It did not run well past 5000 rpm with the stock manifolds so I installed an old set of long tube headers from my stock car on it. The difference in power from that one modification was unreal across the entire RPM range! At that time all you saw was that the D-shaped exhaust ports on LT1 heads needed special D-shaped tubes to correspond to the shape of the port. My headers were regular 1 5/8” round tube. Could the misalignment of the bottom portion of the tube with the flat of the D port have been helping with cancelling reversion? I wish I had ran across David’s books 30 years ago!
I'm going to say yes, follow along here, a popular swap in the G3 hemi world is to use Eagle heads(09+) on the pre Eagle 5.7(03-08) the exhaust on the Eagle is a D shape, while the 03-08 head it's a square, when we use the round tube headers made for the older head we find a 10Hp/20Ft gain over the later designed headers, now if I weld up and round the top of the eagle head exhaust port to match the round tube header, it's 25Hp/25Ft increase and moves the Power band up a 1k rpms.
Thanks Much DV!!...I've been thinking about this very thing for a little while now and I'm about to fab up some exhaust gaskets for this very purpose....
,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,great to see an energizing new presentation..........,,,,gonna build some ramps in my header tubes as outlined.......
I love this guy. I’ve made good power. But I wanna make all the power
Think I remember this from your Ford Lima book. Great stuff.
Hey, sending greetings from Trinidad &Tobago, the part about the datsun head stirrs up memories, i had a L series engine, a N42 block and a N42 head, in the exhaust ports had a funny shaped stamped sheet metal insert, these would become loose and in some cases fall out of the cylinder head and make its way into the exhaust system...never understood its function untill now...thank you Mr. David Vizard.
Those were actually for emissions. They would get hot and help burn off any excess fuel before it got to the catalytic converter. They actually don't have any effect on port flow until you get to making some serious horsepower
I was a big fan of Jim Feulings anti-reversion seminars at the Super Flow convention I studied his video like a bible.
You can get those exhaust plates for a 4v big port 351 Cleveland. but that port dives off very steeply on the floor it very well could use another angled bit welded on the end. 🧐
At that point an aftermarket 3v head works better.
Hi port conversion
@@Low760 I was referring to the tin plate you put between the header and the head it fils the the bottom of the exhaust floor in
Not the alloy block that converts them to a hi-port
I HAVE A 496 CHEVY BIG BLOCK in my 1978 Chevy Suburban which I built for torque and towing. I ended up using peanut port heads as they were what I could afford. A friend gave them to me, and they already had valves in them, so I was not able to port them. I then put a "peanut port manifold on with a Quadra jet carburetor and long tube headers. I am wondering if this idea of putting a dam plate in this set up would help as the headers already have a larger diameter than the exhaust port.
i remember reading about Grumpy Jenkins using larger exhaust headers to block back flow and wonder if by putting the larger headers on this engine it accomplished what you are talking about in this video.
By the way you look much better than earlier videos (I have a gap in watching your videos due to being able to get back to Thailand to be with my wife). Your skin tone and voice look and sound much improved. Keep up the health as you are one of the greatest minds in the engine building world if not the greatest.
I wish David could be my grandfather, wasn't that a great lesson!
I'd love to hear your comments on the value of cutting an anti-reversion step on the exhaust valve and what the potential if any of the modified valves. Thanks so much for the decades of information - I started following you from 'How to Modify Your Mini' days.
Amazing information.
Always lerning some thing new! 👍
Good. Learn how to spell 🤣
So cool, the Fiat multi-Air won design awards thanks to the big intake air increases.
Thank you so much for your time DV!
Don’t worry about me, I am 63 and in great condition, never broke a bone. I had a couple crashes at about 8 years old going down a steep rocky hill in a push plastic go cart I made. Crashed at 45 mph on my skateboard, high speed wobbles. Other close calls landing 152 Cessna.
🔔😎
Brings to mind the port plates that were used on the Cleveland heads.
Any comments about such DV ?
Intake tongues. They were wonderful items. The big speed hump on the clevos floors
14:50 short side radius...
A guy named Birdie ported my alum Edelbrock Oldsmobile heads and he even cut into the intake and had to brass sleeves for the pushrod holes. We didn't make huge flow numbers but one thing i want to point out is he kept the heads forever and kept asking me what cam im gonna run. I kept saying it will be custom based on what you can get out of the heads. We went back and forth on this for months. Then he told me the lift numbers mattereed as far as how much he was gonna roll off the short side exhaust...to reduce reversion.
Ultimately i chose a weird hyd roller from crane with LS lobes. I'll give general specs its .620/.620 lift (1.5 ratio rockers) 257/265 duration @.050 and the n/a engine made 620hp/620tq at only 6100 so in the end we did ok. Cubic inch is 462 its a .030 over 455 olds. 4.155 bore with the worst cyl head ever for actual flow. In my mind a 462 set up this way should flow more but it is what it is
@williamstamper442
The top engine guys will tell you that flow numbers do not equal power.
Lower flow can make more power.
@@bobirving6052
Yes I suppose ...lower flow numbers at max lift can have a bunch of flow below on the curve at half lift
I would enjoy seeing exactly how you use the manometer to measure the port velocity.
Nice tip, i will try to aply on my little 1000cc and 1600cc turbo headers, tinking about litle inserts(flaps/cones) sanduíched btwin header and The exhaust headers
I like the information you shared with us thank you 💯💯💯💯🇺🇸🇺🇸
Tuliped valves probably accomplish the anti-reversion. I would suspect you could see that on the flow bench.
You are a true Master Craftsman.. and don't mind letting some secrets out..Sir you are a true gentleman..
Spot on with early Harleys, I have experienced reversion to the point of contaminating the opposing cylinders intake charge.
Thank you for the knowledge.
Has anyone ever measured the electrical exchange inside the chamber during the compression cycle before the spark plug sparks?
Haven't seen any oems do this yet except for two strokes, but I was contemplating a header with a power valve for a big port engine at some point.
I've seen some guys do antireversion seat, you could take it to the next level and make it into antireversion seat-cone.
It's amazing. Something so simple is not thought about in production cars.
Years ago, I built engines, many of them were air cooled VW engines. We made power on those with higher compression and big round exhaust ports. I built a few Type 356 Porche engines. They had lower compression and weird long rectangular ports, but hey made lots of power. I never knew why. Maybe the 1950's German engineers understood reversion.
Muchas gracias por compartir tan buenas experiencias
I have a few intake valves that have that groove cut into them l thought they were defective
By adding this grove do you see any failure of the intake valve braking the outer edge off over time?
I used this tractor pulling and had no ill effects - As Long As I Didnt Cut the Valve Too Thin !!!
@bobgyetvai9444 how long did the engine last? I'm looking at street driving and high miles.
So how about designing the surface of the intake/exhuast port and backsides of the valves like shark skin? Its rough in one direction and smooth in the other. It also has a similar effect to golf ball surface.
The ports are already rough in both directions, for the intake its so that the fuel stays in suspension whereas with a polished port you can have fuel pooling in the low pressure areas of the port. I don't see why it wouldn't be worth a try in the exhaust though.
This is what the Americans used in the early 90s 80s? in the American cup yacht race. It worked for them they won then the technology got banned.
Great video thanks
We did the Anti reversion exhaust trick 28 yrs ago on a bbc ski race boat. strangely the intake length had to be 34 inches or the intake charge come out of the trumpets at 4000rpm. I wish i could find the photos.
Reversion is a big thing with V twin motor cycle engines. They even make anti reversion cones that go into the head pipes to reduce reversion and they actually help[ make more power.
Fluidic Diode
Hell yeah another performance focused video.
What about turbo and supercharged engines ? Same ?
Thankyou Sir, This explains a lot for me as I could understand how an expansion chamber works on a 2 stroke but I never found anything relating to 4 stroke engines other than the length of header pipe. Excellent.
Very, Very interesting vid. enjoyed it. need to watch it again. does the groove cut in the top of the intake valve shorten the life of the valve seat at all?
Thank you for making a video on this subject. One question, could almost the same effect be achieved while port matching? The change would be to leave the floor of the port untouched as long as there is a step down into the exhaust manifold/header.
Then, in corollary, if the same technique were used on the intake side from the intake manifold to the cylinder head. Would this give the opportunity for any fuel on the floor to be introduced back into the air stream? This idea is for carb'd applications.
David,
Great work. Very informative for those well versed in the more advanced aspects of flow.
Question: how do tgese principles relate to turbo charging?
The intake ridge looks good but the ramp in the header, i winder.
Have you any input ?
I would think it would work as well or even better in a turbo application. There would be a bigger back pressure when bumping up against the turbine blades.
I wonder how this plays into turbo engines, like a Subaru EJ257 for example... Just from looking at the exhaust ports in the head it looks like there would probably be quite a bit of flow separation on the short side of the exhaust ports for sure! And I'm guess with it being a turbo engine, the higher exhaust back pressure between the engine and turbo would cause even more backwards exhaust flow back into the cylinders if there is a slow speed flow separation on the short side of the ports...
@David Vizard Could you do a video(s) focusing on workhorse/towing/4x4 truck engines where LOW & MIDRANGE TORQUE is the goal and NOT high rpm horsepower. There are millions of people in that category and there is almost NOBODY doing videos about it. I think the video(s) would be a HUGE success!! I would be forever grateful if you could cover that side of the spectrum. I know you have the knowledge to do it!!! Thank you for everything!
This is NEEDED BADLY !!!
Outstanding video.
This was an article in Classic bike mag in the 80s an anti reversion dam on motorcycles headers.I think Royce Creacy was the author.
I have always made the manifold about 3 mm bigger in diameter so there is a edge around the port. I would be fun to see if that has a bit of the same effect
I would say next time only go to 3mm on the inside edge where the reversion is. Otherwise you are creating a low pressure turbulence spot where the air wants to flow smooth and fast. And yes this will definitely have an effect. an easy way to do it without making plates although not as efficient
Velocity map to the rescue....I was a little surprised at the variance found on the Datsun head.
VERY interested in the anti-reversion plate that could be added, as I'm sure my ported Nissan U20 is experiencing the same as the L-series head. Seems relatively "easy" to make... how tall and what angle would such an anti-reversion plate be at in the header? Is its effectiveness highly sensitive to the height and angle? Seems that such a plate would be an easy install between the header and head. I thank you for sharing all your extensive knowledge and hope you're able to comment!
Thank you Mr.DV for the explanation about the anti-reversion! I wonder could a raising of port floor function as a anti-reversion plate?
King David Vizard:)
The Party Continues…
More High Quality Instruction:)
I was told years ago if the header or manifold opening was slightly larger than the head opening it would leave a lip that would reduce reversion. So with what your saying...maybe if you only leave the lip at the bottom it might work better?
you also have a bit in the BMC 1275 book on this i think - i seem to remember one of the UK valve manufacturers making anti reversion valves
11:28 Lunch with Bill "Grumpy" Jenkins....
I sure wish that feller was still around. He would have had a ball with the chevrolet LS platform. Good story too, and i love stories.
David, how are you able to observe and measure these pressure waves? Is there a way to negate or eliminate them, and if so, should you?
My concern is Cutting that groove in the intake valve won’t the sharp edge of the groove get hotter than it would without the groove?
THANKS David....!!!!AWESOME!!!!