Oh goodness! I’ve been going over your timing and carb adjustment videos all afternoon. I think I have enough information now to go get myself into trouble with my truck… 😂
Correct! Ported Timing was an early and poor emissions idea, and Manifold vacuum is the right way to go. Before anyone disagrees with that... Go and do some research! Good video.
Incorrect. Ported vacuum was used back to the 40's and was to help with mileage and overall performance when cruising. It wasn't until the late 60's 70's that they reduced or blocked it completely to make cars run hotter and cleaner. This guy has it backwards. Before ported vacuum advance, it was mechanical or manual with a lever on the steering wheel. Manifold vacuum was NEVER used on a stock, early vehicle.
@@gregstahlman1680 WRONG. Ported and manifold vacuum are the same except at idle. Manifold advances at idle, cools the engine and runs more efficient. There is no way ported improves mileage over manifold vacuum.
@@bmclaurinemaybe, but he is right, that ported was used long before emissions, in the 50s and early 60s. Every mid to early 60s Mopar used ported vacuum.
Very good! You did a great job explaining the details and clearing the air! Manifold Vacuum is the correct termination for your Vacuum Advance. Set your Total Advance with the VA unplugged and the Engine RPM a little past where the Mechanical Advance stops Advancing. For a Small Block Chevy, this will be somewhere between 30 and 36 degrees. Then you hook your VA back up to the Manifold Vacuum, and set your Carb Idle and Idle Screws. The only other thing to consider is your Mechanical Advance Curve which is set with the Weights and the Springs in the Distributor and under the Rotor in most cases. You want light Springs for a light car with lots of horsepower, and Heavy Springs for a heavier vehicle with lower horsepower. You typically want your Mechanical Advance to be all there by 3,000 to 3,500 RPM. If you change the Mechanical Advance Springs and/or Weights, you will need to repeat the process to set your Total Advance. Oh... and if you've got issues with a Large Cam Grind bouncing your Vacuum Advance at idle, you might need to cap it off and run without it. Like 289 said, Ported VA will give you too much Total Advance and could cause engine damage. Party on...
I was taught that you set timing with vacuum advance disconnected then you reconnect to ported vacuum so that the vacuum increases as the throttle plates open and engine speed increases creating vacuum above the throttle plates. Connecting to manifold vacuum would bring in the advance at idle and then it would decrease as throttle plates open which reduces advance and decreases power. Is that correct?
@@topfuelr473 You are correct. Ported vacuum was NOT designed for emissions, in fact. they found ways to block it on emissions cars to make them run hotter and cleaner.
It depends on which vacuum canister you have on your distributor. If you've got a "modern" canister that's all-in at say 14", and it's connected to manifold vacuum then vacuum advance drops out during throttle tip-in, that's not good. If you've got an "pre-emissions" vacuum canister that's all-in around 5", then it's designed to be connected to manifold vacuum. So choose the correct vacuum canister and connect it accordingly so it operates as intended.
Agree, manifold vacuum is best if engine will run with it. The 355cu in SBC in my ‘69 Corvette, 600:Holley double-pumper, has full vacuum advance of 14* at idle, which the engine really likes. Ported vacuum didn’t cut it.
Great video as usual 😃👍👍. I actually shipped my Holley 850 out to Max Air Carbs for a total rebuild/custom repainting. A couple of weeks ago, I shut the 455 motor OFF ... fuel was pouring into the intake manifold. 👎👎
This guy seems knowledgeable but made a mistake about ported vacuum stating that it "wasn't used until the late 60's due to emissions." That is completely backwards. I have owned cars back to the early 50's and worked as a mechanic in the 70's and ported vacuum was ALWAYS the factory standard and many times hardwired that way with copper tubing fittings so they couldn't be "accidently" moved. It wasn't until the late 60's early 70's that they found different ways to reduce or eliminate ported vacuum advance by using temperature sensing valves that shut it off or used manifold vacuum "dual diaphragm" distributors that when manifold and ported vacuum were the same, it cancelled out and gave no advance when cruising. Ported and manifold vacuum are pretty much identical when driving, under light accel or WOT. The only difference, as he said, was at idle. The other problem with manifold is, if you think about it, is you are running a lot of vacuum advance at idle and you go to accelerate and the vacuum suddenly drops and your timing retards significantly and can cause sluggish acceleration and sometimes backfire. Where he is correct is in a high performance engine, mechanical advance is your friend! I don't use ANY vacuum advance in my race engines because at WOT, vacuum advance doesn't work anyway. Max advance at 34-36@2800 RPM is a good start. If your cam is lopey enough to cause you to open your idle up to the point where you have a lot of ported vacuum, you would probably be better off with manifold vacuum to smooth out your idle a bit, but for a stock or mild street car, ported was stock and works well.
I have a crate 383 stroker in my 77 Monte Carlo that came with mechanical advance. Also installed 700R4 tranny & 3.73 rear gears. The cam Lift: .500 / .510, Duration @ .050: 225 / 231, Centerline: 108, Fair idle The vacuum advance cannister is connected to distributer but crimped (not hooked up to any vacuum). As it is, my timing settings are maxed out for maximum engine output. Car runs perfect! If I hook up vacuum advance to manifold, can I simply leave those timing settings alone?
Thanks for this video. I have a question though. If I want to use manifold vacuum for the advance, what should I set my initial timing at idle at? Should I have manifold port capped off while setting it? I have a mild cam 350 bored 60 over. Doesnt run hot idle is just a little roudy. Double hump heads. Stock hei dizzy. It's in a k10 chevy truck. Thanks in advance.
I have a 66 Mustang with early 80's 302, Holley Ultra 650 DP, and a decent cam that produces vacuum of 12-13 in.Hg. at 850 rpm idle. Timing is 16 degrees initial+20 degrees mechanical advance=36 degrees total at 3200 rpm. I have tried to run vacuum advance, both ported and direct but the engine just doesn't like it. With vacuum advance connected my dial back timing light showed 50+ degrees at 3000 and engine sounded rough. This is a weekend car and I'm not concerned with mpg. Is there any particular reason I should alter the tune just to run vacuum advance?
I know this is an old post but I have exactly the same numbers. 16 to 36 mechanical. I dialed my adjustable canister to 10 degrees. Runs fine but I'm in the same boat as you it hits 57 degrees at 3200 rpm holding the throttle open in the garage.
Where, exactly, is the hose connected for Ported Vacuum? You point frequently to a tap on the upper part of the carburetor, I'll presume that's it. Where do I pick up manifold vacuum? Is it somewhere on the carburetor? On the manifold itself somewhere? Thanks!
A manifold port will be on the lower part of the carb because it gets constant vacuum from the manifold. Ported is higher on the carb because it only gets vacuum when throttled. I hope that helps. Sorry it took 7 months.
Luke, I've been binge watching your carb videos. When did you switch from a manifold vacuum guy to a ported vacuum guy and why? If lean (idle) mixture needs more time to burn, wouldn't manifold be the ticket?I Love the videos.
This was back in the day when i taught along conventionally a cepted guidlines, not based on my own engineer knowedge and what i actually do. Ported is better in most cases due to what it allows you to do with your mechanical timing better matching it to conditions throughout the load range.
The only difference between MV and PV is at idle. If you have a big, lopey cam, a little extra timing at idle from MV can smooth it out a bit and still allow low initial so you can crank it easier to start when hot. Ported vacuum was ALWAYS standard back to the 40's and was NOT designed for emissions, in fact, emissions demanded they lower or completely block ported vacuum advance. That statement about it only coming about for "emissions in the 60's and 70's" is incorrect. I can show you the factory holley on my 58 FE that was hard wired to the dist with copper tubing from the PV port on the side of the metering plate. No emissions then.
@@gregstahlman1680 I don't agree at all with using manifold sourced advance as a crutch for an aggressive cam with an automatic transmission because when you put it in gear the rpm drops, vacuum drops, timing drops, motor don't wanna idle in gear😢 I think the majority of people that advocate relying on vacuum advance for proper idle quality are trying to use a factory stock carburetor, something similar, or don't know how to tune/modify what they have to work on their modified engine. A modified engine will usually require more initial timing(modified distributor) and enrichened carburetor idle circuit(modified carburetor or performance specific carburetor) because a modified engine usually pulls less vacuum at idle speed to draw the fuel through the circuit. It's a matter of having the proper size idle feed restriction and the proper throttle blade setting in relation to the tranfer slot.
@@gregstahlman1680 But, like you, I usually prefer ported sourced advance(when I'm even concerned with vacuum advance). Manifold sourced vacuum advance can work very nice with a manual trans, though.
You say anymore than 24* at idle is too much but you don't explain why, I'm running at 30* and the engine's never run better. in fact, I plan on re-curving my distributor for more advance, Numbers mean nothing, it what the engine wants. "No disrespect" just saying. it's just that some people make statements with no explanation to back it up.
You got that right. It depends on the cylinder pressure that your combination provides. One engine may not even crank over with more than 10° of initial timing and another may not have any punch at all with less than 30.
I set my SBC(auto) to manifold vacuum to improve the idle performance. It worked great! However, I noticed when I decelerated the engine braking resulted in full vacuum advance and that resulted in detonation. Is there any way around that?
I had my vacuum advance hooked up to my ported vacuum on my carburetor, but it was causing a problem. The problem was, extremely hard starting like the advance timing was too much. Come to find out, when I turn the engine over to start, it was advancing my timing so much, my engine would drag. Now I have no vacuum going to my adjustable vacuum advance. Engine starts nicely every time now
@@trailerparkcryptoking5213 i’m a technician. I’ve been a technician for 50 years. I know how to set timing properly. The problem was heat soak on a holly carburetor and ethanol fuel. I fix the problem
Not possible. Ported vacuum does nothing at idle or while cranking. Sounds like your initial is too high. Something not right with this issue. Kinda like "since I painted my car blue, it runs much better!" Can't argue with results, just how you got them.
Ported vacuum simply doesn’t add any timing at idle where manifold will. Nothing more to it - I prefer to run ported with more mechanical initial advance. Vacuum advance will drop out of the timing equation when you are under high load low manifold vacuum scenarios
@@ThunderHead289 Wait but in the video at 3:14 you said you like to run manifold vacuum, I've watched your newer videos where you say you prefer ported but what made you change your mind from preferring manifold vacuum in your older videos to preferring to run ported vacuum in your newer videos? I enjoy your content a lot but always wondered what made you switch
Greetings, I have a Holley 4150 0-4778C installed in a 1965 Ford 289, I had to acquire an automatic transmission TCI 511200 C4, now the point is WHERE in the carburetor you can connect the hose from the transmission vacuum modulator valve? I see only 1 port that is for the distributor timing, some other videos recommend do not make a share connection in "T", Can you help? #2: For the booster´s hose vacuum, what kind of valve is PCV? I have the intake manifold Street Dominator, but I need you tell me exactly what´s the name of any fitting, valve or device that can be installed in the back of it for the booster´s hose In advance, Thanks for your concern & prompt response
I have a 71' F100 w/302 and C4. All the vacuum for the trans/power brake booster is coming out of a tri-port that goes directly into the intake manifold behind the carburetor. The PCV connects to stock 1" aluminum spacer that is between carb and intake manifold. The vac advance is connected to the lowest port on carburetor. This is an all stock motor....Hope this helps.
MrDLRu Thanks a lot ! x your answer, is exactly what I concluded to do, now I'm quite relaxed, soon I'll finish the restoration & do the start. Have a pleasant New month
i dont believe that would be why a company thats been in business for nearly 100 years would say. they have researched vacuum advance in relation to full manifold vacuum as well as timed port vacuum in great depth. wouldnt you agree ?
+bigpaw64 consider this, all engines were manifold vacuum till emissions. Ported was part of emissions to have less timing at idle. It had to do with exhaust gas temps. Now high lift cam guys have to run a lot of initial timing, so it gets to be a pain. But stock 8 degrees initial, 6 degrees initial. Will run better and more efficient all day off manifold. If you have a look at modern cars, they all run 20 degrees initial. (With my scanner)
im not talking about modern cars or emissions. im talking about holley carbs. ive been buying holleys from the late 60s to present day. these carbs had ported vacuum options on these long before catalytic converters and emissions came along. im alot older then you. all im saying is holley recommends using this for your distributer advance because it works. we all know street cars and race engines have different needs. but for a mid level street car useing a 600 -750 cfm carb , ported is best.
Once the throttle is cracked open there is absolutely difference in the vacuum signal sent to the advance canister whether it is ported or direct vacuum.
Hi there. I have a question about timing my 351 cleveland. Engine had a mild cam, holley double pumper and runs mallory ignition with adjustable vacuum cannister. Engine was built when i got the car but i have been having ignition issues so i have been trying to get it right. And now after adjusting timing and vacuum cannister my timing is at 18 degrees at idle and 34 at 3000 rpm and ported vacuum to the cannister. Car finally runs great and good throttle response. Just wanted to hear if those setting sounds right. Am fairly new to this so i figure it is better to ask for advice.... Dont hear any pinging or knocking so i hope it is okay... Hope anyone can tell me if my settings are okay...???
Oddisto 76 18 might be a bit much.. how does it start when hot, what does your vacuum gauge and temperature say?. is this used for street? what ign. issues
@@danwells7691 . Since i posted the question i retarded my timing down to about 12 degrees. Adjusted the accelerator pumps on the holley since they were way out of shape and now everything seems fine. The issue i was having was that when i floored it while driving it hesitated and backfired trough the carb. But after adjustments on both timing and carburetor it seems the problem are gone. Is 12 degrees still high you think???
I have a 1975 ford f150 when I sick on the vacuum canister it retards the rotor, this leads me to believe I can only run ported vacuum with that style distributor. Plz someone correct me if I'm wrong
I have a 78 Bronco and when I connect the manifold vacuum my rpm increase meaning I advance..I read the vacuum advance canister is adjustable but haven't tried that yet so like you I run ported and it purrs..
Ok, so I want around 30 degrees of timing. If my 351w is set for 10 degrees btdc without advance, that should mean that with advance it will be 20 degrees after top dead center. Is that correct?
alright, if you want 30 degrees of total timing, you need to first know how much timing your distributor pulls in mechanically - this would be without the vacuum advance. on a stock 351, you should be at 8 to 10 degrees initial timing BTDC. your total timing will be 30 - 35 BTDC. as your engine speeds up, you need more timing to keep up with the rpm since the flame front of the ignition is basically the same speed. does this make sense??
ThunderHead289 I believe it does, at idle I should have around 30 degrees btdc at idle with advance hooked to manifold vacuum and idle speed set correctly. As rpm increases, so will the advance so the flame front can keep up with the piston. That's how I interpreted it. Thanks for the info, I think I understand how and what now!
Can someone help me with my 454 holley 4 barrel carb on my boat, the secondaries don't open at all it wont go past 3500rpm, runs great, but the secondaries just dont open. I checked the vacuum actuator and it holds good when i push down on the rod and place my finger, the small o ring between the actuator and the body is new, and the hole is clean!
ThunderHead289 Yes i am sure it doesn't open I sat next to the engine I let my friend floor the gas pedal but when its time for secondaries to open it stays at 3500 rpm and they dont open at all!! So i moved the secondaries lever by hand and it went to 4500 rpm!!
WRONG! LOOK IT UP! All you need is any shop manual or Motor manual and you will see, ported vacuum, also called timed vacuum or controlled manifold vacuum, was THE ONLY THING USED PRIOR TO 1968. Don't take my word for it, look it up! Holley, Carter, Rochester, and Ford carbs ALL state to connect ported vacuum to the dist from the factory. The only argument is between Edelbrock and every other factory manual and carb manufacturer out there. Ported vacuum was used as the ONLY type of vacuum advance back to the early 50's and earlier! The only carb company that stated ported vacuum was only used on emission vehicles is Edelbrock, and many have called them out on that and they refuse to reply or change their documentation, even though EVERY shop manual, Motor manual, Chilton manual and every carburetor manual, except Edelbrock, says it's ported vacuum that was originally used from the factory. Like I said, look it up!
wowe did he say vacuum advance canisters are rated in inches of vacuum and will only add timing when the engine produces 15" or more that shit ain't right lol
vacuum canisters are rated in how many degrees of timing they add not at what inch of vacuum they open, for instance a 15 canister adds 15 degrees of timing, you stated a 15 rated canister as not opening till the engine produces 15" or more.
+tron696 here is what I said - most stock vacuum advance canisters add in 15 degrees of timing which is for when you are cruising and the afr is leaner. A lean mixture burns slower, so you need more timing for that fuel charge to ignite at the most optimum time. Consequently when you step on the gas, manifold vacuum drops and you have a richer mixture that burns faster so it doesn't require as much timing. Most stock vacuum canisters drop out at around 15 inches of mercury to where the ignition timing is solely mechanically based. Does this make sense now?
Oh goodness! I’ve been going over your timing and carb adjustment videos all afternoon. I think I have enough information now to go get myself into trouble with my truck… 😂
Correct! Ported Timing was an early and poor emissions idea, and Manifold vacuum is the right way to go. Before anyone disagrees with that... Go and do some research! Good video.
Incorrect. Ported vacuum was used back to the 40's and was to help with mileage and overall performance when cruising. It wasn't until the late 60's 70's that they reduced or blocked it completely to make cars run hotter and cleaner. This guy has it backwards. Before ported vacuum advance, it was mechanical or manual with a lever on the steering wheel. Manifold vacuum was NEVER used on a stock, early vehicle.
@@gregstahlman1680 WRONG. Ported and manifold vacuum are the same except at idle. Manifold advances at idle, cools the engine and runs more efficient. There is no way ported improves mileage over manifold vacuum.
@@bmclaurinemaybe, but he is right, that ported was used long before emissions, in the 50s and early 60s. Every mid to early 60s Mopar used ported vacuum.
Very good! You did a great job explaining the details and clearing the air! Manifold Vacuum is the correct termination for your Vacuum Advance. Set your Total Advance with the VA unplugged and the Engine RPM a little past where the Mechanical Advance stops Advancing. For a Small Block Chevy, this will be somewhere between 30 and 36 degrees. Then you hook your VA back up to the Manifold Vacuum, and set your Carb Idle and Idle Screws. The only other thing to consider is your Mechanical Advance Curve which is set with the Weights and the Springs in the Distributor and under the Rotor in most cases. You want light Springs for a light car with lots of horsepower, and Heavy Springs for a heavier vehicle with lower horsepower. You typically want your Mechanical Advance to be all there by 3,000 to 3,500 RPM. If you change the Mechanical Advance Springs and/or Weights, you will need to repeat the process to set your Total Advance. Oh... and if you've got issues with a Large Cam Grind bouncing your Vacuum Advance at idle, you might need to cap it off and run without it. Like 289 said, Ported VA will give you too much Total Advance and could cause engine damage. Party on...
I was taught that you set timing with vacuum advance disconnected then you reconnect to ported vacuum so that the vacuum increases as the throttle plates open and engine speed increases creating vacuum above the throttle plates. Connecting to manifold vacuum would bring in the advance at idle and then it would decrease as throttle plates open which reduces advance and decreases power. Is that correct?
Steven Peruch only decrease when you full open the throtle plates , but distributor stays at total mechanical advance
Both true. Also check your temps at idle. There's a reason u want some advance at idles. Not all cars the same
@@topfuelr473 You are correct. Ported vacuum was NOT designed for emissions, in fact. they found ways to block it on emissions cars to make them run hotter and cleaner.
It depends on which vacuum canister you have on your distributor. If you've got a "modern" canister that's all-in at say 14", and it's connected to manifold vacuum then vacuum advance drops out during throttle tip-in, that's not good. If you've got an "pre-emissions" vacuum canister that's all-in around 5", then it's designed to be connected to manifold vacuum.
So choose the correct vacuum canister and connect it accordingly so it operates as intended.
Agree, manifold vacuum is best if engine will run with it. The 355cu in SBC in my ‘69 Corvette, 600:Holley double-pumper, has full vacuum advance of 14* at idle, which the engine really likes. Ported vacuum didn’t cut it.
Msd speds thousands on research they would know, but ur knowledge is very useful
I'm confused.. I swear you have another video that you say you rather use ported vacuum.. am I mistaken?
Great video as usual 😃👍👍.
I actually shipped my Holley 850 out to Max Air Carbs for a total rebuild/custom repainting. A couple of weeks ago, I shut the 455 motor OFF ... fuel was pouring into the intake manifold. 👎👎
thanks for the positive response! sounds like either a dirty/failed needle and seat or a failed float !!!
This guy seems knowledgeable but made a mistake about ported vacuum stating that it "wasn't used until the late 60's due to emissions." That is completely backwards. I have owned cars back to the early 50's and worked as a mechanic in the 70's and ported vacuum was ALWAYS the factory standard and many times hardwired that way with copper tubing fittings so they couldn't be "accidently" moved. It wasn't until the late 60's early 70's that they found different ways to reduce or eliminate ported vacuum advance by using temperature sensing valves that shut it off or used manifold vacuum "dual diaphragm" distributors that when manifold and ported vacuum were the same, it cancelled out and gave no advance when cruising. Ported and manifold vacuum are pretty much identical when driving, under light accel or WOT. The only difference, as he said, was at idle. The other problem with manifold is, if you think about it, is you are running a lot of vacuum advance at idle and you go to accelerate and the vacuum suddenly drops and your timing retards significantly and can cause sluggish acceleration and sometimes backfire. Where he is correct is in a high performance engine, mechanical advance is your friend! I don't use ANY vacuum advance in my race engines because at WOT, vacuum advance doesn't work anyway. Max advance at 34-36@2800 RPM is a good start. If your cam is lopey enough to cause you to open your idle up to the point where you have a lot of ported vacuum, you would probably be better off with manifold vacuum to smooth out your idle a bit, but for a stock or mild street car, ported was stock and works well.
I have a crate 383 stroker in my 77 Monte Carlo that came with mechanical advance. Also installed 700R4 tranny & 3.73 rear gears. The cam Lift: .500 / .510, Duration @ .050: 225 / 231, Centerline: 108, Fair idle
The vacuum advance cannister is connected to distributer but crimped (not hooked up to any vacuum). As it is, my timing settings are maxed out for maximum engine output. Car runs perfect! If I hook up vacuum advance to manifold, can I simply leave those timing settings alone?
Ported vacuum got them thu the early years of emissions but you could make power with ported vacuum with the right cam/comp ratio setup.
Yes! Thank you for these!!!
Hey thunderhead289 can you use the thermo vacuum switch for ported and manifold to distributor in the back of the intake instead of the front
Is the port vaccum fitting replaceable? I broke mines off trying to mount it to the engine.
Thanks for this video. I have a question though. If I want to use manifold vacuum for the advance, what should I set my initial timing at idle at? Should I have manifold port capped off while setting it? I have a mild cam 350 bored 60 over. Doesnt run hot idle is just a little roudy. Double hump heads. Stock hei dizzy. It's in a k10 chevy truck. Thanks in advance.
Learn where to set total timing! Initial timing is for dummies that don’t know how to tune!
Ported vacuum was factory Setup long before emissions in the 50s and probably before. Every mid to early 60s Mopar used ported vacuum.
I have a 66 Mustang with early 80's 302, Holley Ultra 650 DP, and a decent cam that produces vacuum of 12-13 in.Hg. at 850 rpm idle. Timing is 16 degrees initial+20 degrees mechanical advance=36 degrees total at 3200 rpm. I have tried to run vacuum advance, both ported and direct but the engine just doesn't like it. With vacuum advance connected my dial back timing light showed 50+ degrees at 3000 and engine sounded rough. This is a weekend car and I'm not concerned with mpg. Is there any particular reason I should alter the tune just to run vacuum advance?
I know this is an old post but I have exactly the same numbers. 16 to 36 mechanical. I dialed my adjustable canister to 10 degrees. Runs fine but I'm in the same boat as you it hits 57 degrees at 3200 rpm holding the throttle open in the garage.
Are you connected to ported vacuum? Sounds like it. Connect to manifold vacuum, you need 50* at idle, less as you hit the throttle and vacuum drops...
Please make a video on vacuum signal and how to improve it.
Where, exactly, is the hose connected for Ported Vacuum? You point frequently to a tap on the upper part of the carburetor, I'll presume that's it. Where do I pick up manifold vacuum? Is it somewhere on the carburetor? On the manifold itself somewhere? Thanks!
A manifold port will be on the lower part of the carb because it gets constant vacuum from the manifold. Ported is higher on the carb because it only gets vacuum when throttled. I hope that helps. Sorry it took 7 months.
@@robpitthan7497 Thanks. I figured it out a while ago and got the thing dialed in nicely.
Awesome! I think it might be an issue I'm having with my '76 Dodge van.
I always have used a mechanical advance distributor. My blower motor will not tolerate a vacuum advance distributor.
Luke, I've been binge watching your carb videos. When did you switch from a manifold vacuum guy to a ported vacuum guy and why?
If lean (idle) mixture needs more time to burn, wouldn't manifold be the ticket?I
Love the videos.
This was back in the day when i taught along conventionally a cepted guidlines, not based on my own engineer knowedge and what i actually do.
Ported is better in most cases due to what it allows you to do with your mechanical timing better matching it to conditions throughout the load range.
The only difference between MV and PV is at idle. If you have a big, lopey cam, a little extra timing at idle from MV can smooth it out a bit and still allow low initial so you can crank it easier to start when hot. Ported vacuum was ALWAYS standard back to the 40's and was NOT designed for emissions, in fact, emissions demanded they lower or completely block ported vacuum advance. That statement about it only coming about for "emissions in the 60's and 70's" is incorrect. I can show you the factory holley on my 58 FE that was hard wired to the dist with copper tubing from the PV port on the side of the metering plate. No emissions then.
@@gregstahlman1680
I don't agree at all with using manifold sourced advance as a crutch for an aggressive cam with an automatic transmission because when you put it in gear the rpm drops, vacuum drops, timing drops, motor don't wanna idle in gear😢 I think the majority of people that advocate relying on vacuum advance for proper idle quality are trying to use a factory stock carburetor, something similar, or don't know how to tune/modify what they have to work on their modified engine. A modified engine will usually require more initial timing(modified distributor) and enrichened carburetor idle circuit(modified carburetor or performance specific carburetor) because a modified engine usually pulls less vacuum at idle speed to draw the fuel through the circuit. It's a matter of having the proper size idle feed restriction and the proper throttle blade setting in relation to the tranfer slot.
@@gregstahlman1680
But, like you, I usually prefer ported sourced advance(when I'm even concerned with vacuum advance). Manifold sourced vacuum advance can work very nice with a manual trans, though.
You say anymore than 24* at idle is too much but you don't explain why, I'm running at 30* and the engine's never run better. in fact, I plan on re-curving my distributor for more advance, Numbers mean nothing, it what the engine wants. "No disrespect" just saying. it's just that some people make statements with no explanation to back it up.
You got that right. It depends on the cylinder pressure that your combination provides. One engine may not even crank over with more than 10° of initial timing and another may not have any punch at all with less than 30.
Very informative. Thanks
I set my SBC(auto) to manifold vacuum to improve the idle performance. It worked great! However, I noticed when I decelerated the engine braking resulted in full vacuum advance and that resulted in detonation. Is there any way around that?
I have never of an engine detonating or preigniting (there is a difference) during deceleration.
I meant never heard of.
I had my vacuum advance hooked up to my ported vacuum on my carburetor, but it was causing a problem. The problem was, extremely hard starting like the advance timing was too much. Come to find out, when I turn the engine over to start, it was advancing my timing so much, my engine would drag. Now I have no vacuum going to my adjustable vacuum advance. Engine starts nicely every time now
Learn how to properly set up timing! Something is wrong in your system!
@@trailerparkcryptoking5213 i’m a technician. I’ve been a technician for 50 years. I know how to set timing properly. The problem was heat soak on a holly carburetor and ethanol fuel. I fix the problem
Not possible. Ported vacuum does nothing at idle or while cranking. Sounds like your initial is too high. Something not right with this issue. Kinda like "since I painted my car blue, it runs much better!" Can't argue with results, just how you got them.
@@gregstahlman1680 I’ve already fix it
@@gregstahlman1680 but yes it shouldn’t
Good video.. I been trying to find more info to set my car.
So let me grab the concept here. Ported vacuum basically will pull more vacuum vs manifold vacuum, thus causing premature vacuum advance?
Ported vacuum simply doesn’t add any timing at idle where manifold will. Nothing more to it - I prefer to run ported with more mechanical initial advance.
Vacuum advance will drop out of the timing equation when you are under high load low manifold vacuum scenarios
@@ThunderHead289 Wait but in the video at 3:14 you said you like to run manifold vacuum, I've watched your newer videos where you say you prefer ported but what made you change your mind from preferring manifold vacuum in your older videos to preferring to run ported vacuum in your newer videos? I enjoy your content a lot but always wondered what made you switch
@@crankemtv3907 I wondered the same. So yeah, would like to know as well
Greetings, I have a Holley 4150 0-4778C installed in a 1965 Ford 289, I had to acquire an automatic transmission TCI 511200 C4, now the point is WHERE in the carburetor you can connect the hose from the transmission vacuum modulator valve? I see only 1 port that is for the distributor timing, some other videos recommend do not make a share connection in "T", Can you help?
#2: For the booster´s hose vacuum, what kind of valve is PCV? I have the intake manifold Street Dominator, but I need you tell me exactly what´s the name of any fitting, valve or device that can be installed in the back of it for the booster´s hose
In advance, Thanks for your concern & prompt response
I have a 71' F100 w/302 and C4. All the vacuum for the trans/power brake booster is coming out of a tri-port that goes directly into the intake manifold behind the carburetor. The PCV connects to stock 1" aluminum spacer that is between carb and intake manifold. The vac advance is connected to the lowest port on carburetor. This is an all stock motor....Hope this helps.
MrDLRu Thanks a lot ! x your answer, is exactly what I concluded to do, now I'm quite relaxed, soon I'll finish the restoration & do the start. Have a pleasant New month
holley themselves tell you to use ported vacuum for your dist, so thats good enough for me
That's because it's easy for people.
i dont believe that would be why a company thats been in business for nearly 100 years would say. they have researched vacuum advance in relation to full manifold vacuum as well as timed port vacuum in great depth. wouldnt you agree ?
+bigpaw64 consider this, all engines were manifold vacuum till emissions. Ported was part of emissions to have less timing at idle. It had to do with exhaust gas temps. Now high lift cam guys have to run a lot of initial timing, so it gets to be a pain. But stock 8 degrees initial, 6 degrees initial. Will run better and more efficient all day off manifold. If you have a look at modern cars, they all run 20 degrees initial. (With my scanner)
im not talking about modern cars or emissions. im talking about holley carbs. ive been buying holleys from the late 60s to present day. these carbs had ported vacuum options on these long before catalytic converters and emissions came along. im alot older then you. all im saying is holley recommends using this for your distributer advance because it works. we all know street cars and race engines have different needs. but for a mid level street car useing a 600 -750 cfm carb , ported is best.
Once the throttle is cracked open there is absolutely difference in the vacuum signal sent to the advance canister whether it is ported or direct vacuum.
Hi there. I have a question about timing my 351 cleveland. Engine had a mild cam, holley double pumper and runs mallory ignition with adjustable vacuum cannister. Engine was built when i got the car but i have been having ignition issues so i have been trying to get it right. And now after adjusting timing and vacuum cannister my timing is at 18 degrees at idle and 34 at 3000 rpm and ported vacuum to the cannister. Car finally runs great and good throttle response. Just wanted to hear if those setting sounds right. Am fairly new to this so i figure it is better to ask for advice.... Dont hear any pinging or knocking so i hope it is okay... Hope anyone can tell me if my settings are okay...???
Oddisto 76 18 might be a bit much.. how does it start when hot, what does your vacuum gauge and temperature say?. is this used for street? what ign. issues
@@danwells7691 . Since i posted the question i retarded my timing down to about 12 degrees. Adjusted the accelerator pumps on the holley since they were way out of shape and now everything seems fine. The issue i was having was that when i floored it while driving it hesitated and backfired trough the carb. But after adjustments on both timing and carburetor it seems the problem are gone. Is 12 degrees still high you think???
hey buddy awesome videos ... Question.. on my 302 with a Holley 600 where would i put my transmission (c4 modulator hose) vacuum hose and thanks
Manifold vac.
@@mtnman6278 what would happen if the c4 modulator hose is connected to carburetor timing vacuum port?
I have a 1975 ford f150 when I sick on the vacuum canister it retards the rotor, this leads me to believe I can only run ported vacuum with that style distributor. Plz someone correct me if I'm wrong
I have a 78 Bronco and when I connect the manifold vacuum my rpm increase meaning I advance..I read the vacuum advance canister is adjustable but haven't tried that yet so like you I run ported and it purrs..
Msd says above throttle plates
Ported vacuum
And MSD KNOWS😊
See an update about 4 -5 years later
Ok, so I want around 30 degrees of timing. If my 351w is set for 10 degrees btdc without advance, that should mean that with advance it will be 20 degrees after top dead center. Is that correct?
alright, if you want 30 degrees of total timing, you need to first know how much timing your distributor pulls in mechanically - this would be without the vacuum advance. on a stock 351, you should be at 8 to 10 degrees initial timing BTDC. your total timing will be 30 - 35 BTDC. as your engine speeds up, you need more timing to keep up with the rpm since the flame front of the ignition is basically the same speed. does this make sense??
ThunderHead289 I believe it does, at idle I should have around 30 degrees btdc at idle with advance hooked to manifold vacuum and idle speed set correctly. As rpm increases, so will the advance so the flame front can keep up with the piston. That's how I interpreted it. Thanks for the info, I think I understand how and what now!
@@bairfamilyfarm1336This post was 1 year ago, how did that work out for you?
3D print a clear plastic Vacuum advance cannister perhaps.
Can someone help me with my 454 holley 4 barrel carb on my boat, the secondaries don't open at all it wont go past 3500rpm, runs great, but the secondaries just dont open.
I checked the vacuum actuator and it holds good when i push down on the rod and place my finger, the small o ring between the actuator and the body is new, and the hole is clean!
How have you determined that it doesn’t open?
ThunderHead289
Yes i am sure it doesn't open
I sat next to the engine I let my friend floor the gas pedal but when its time for secondaries to open it stays at 3500 rpm and they dont open at all!!
So i moved the secondaries lever by hand and it went to 4500 rpm!!
I thought they only use mechanical secondary carbs on boats just for that reason.
My street avenger manual says to connect advance to ported. So that is what I am doing. !984 460 e350 RV,
WRONG! LOOK IT UP! All you need is any shop manual or Motor manual and you will see, ported vacuum, also called timed vacuum or controlled manifold vacuum, was THE ONLY THING USED PRIOR TO 1968. Don't take my word for it, look it up! Holley, Carter, Rochester, and Ford carbs ALL state to connect ported vacuum to the dist from the factory. The only argument is between Edelbrock and every other factory manual and carb manufacturer out there. Ported vacuum was used as the ONLY type of vacuum advance back to the early 50's and earlier! The only carb company that stated ported vacuum was only used on emission vehicles is Edelbrock, and many have called them out on that and they refuse to reply or change their documentation, even though EVERY shop manual, Motor manual, Chilton manual and every carburetor manual, except Edelbrock, says it's ported vacuum that was originally used from the factory. Like I said, look it up!
Uncle Tony’s garage
Bryce Madden Thunderhead289’s .... Garage 😂
Looks like your hand is talking !!
He does good videos but talks to much, 10 minute videos and 2 minutes of information.
wowe did he say vacuum advance canisters are rated in inches of vacuum and will only add timing when the engine produces 15" or more that shit ain't right lol
Aside from saying "inches of vacuum" this is entirely true - what do you not agree on?
vacuum canisters are rated in how many degrees of timing they add not at what inch of vacuum they open, for instance a 15 canister adds 15 degrees of timing, you stated a 15 rated canister as not opening till the engine produces 15" or more.
+tron696 here is what I said - most stock vacuum advance canisters add in 15 degrees of timing which is for when you are cruising and the afr is leaner. A lean mixture burns slower, so you need more timing for that fuel charge to ignite at the most optimum time. Consequently when you step on the gas, manifold vacuum drops and you have a richer mixture that burns faster so it doesn't require as much timing. Most stock vacuum canisters drop out at around 15 inches of mercury to where the ignition timing is solely mechanically based.
Does this make sense now?
Manifold vacuum all the way for me