Carburetor Confusion! What's the Best Setup? | Engine Masters | MotorTrend
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- เผยแพร่เมื่อ 28 ก.ย. 2024
- This test is all about choosing the features you want and need on your carburetor, and how those features affect your horsepower and tunability. Do mechanical secondaries really make any more power than vacuum-power ones? Does a choke horn restrict inlet airflow?
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What about comparison of the A/F curves between carbs? I was expecting to see that presented as the punchline.
well yeah its gonna be different in that no choke brawler that the vac secondary version.
@@KingJT80 Yes, I was expecting them to say that the HP difference was related to A/F ratio differences but that did not happen. They showed there was no difference in actual airflow, so I was left wondering what was the real reason for the significant HP difference.
@@rogermason5833 well they did mess around with the jets too off camera. Vac secondary couldn't make more power
The flow meter there using is not very accurate and even consistent, if it was it would be used as a flow bench
It would seem to stand to reason that if the airflow is the same and the fuel flow is different between carbs, the air/fuel ratio is going to be different. Which begs the question of how much and how much difference the different ratio makes. It's a really odd thing to completely ignore in the video.
The double pumper had the advantage of the air hat. You got the results you wanted by giving the DP straighter air flow.
My thoughts exactly. Air probably had higher velocity before entering the dp carb than it did with the vacuum secondary carb without the air hat. Like the old school velocity stacks, or Weber 8 stack system.
Street gearing and an automatic trans with a near stock converter: Vacuum secondaries. Everything else, double pumpers. I've been building carbs for 40 years.
We all believe you bro.
@@karenthomson9749 hes not wrong tho. double pumpers are great but vac secondary has its place too
I'm diamond 1
Vacuum secondary is fine for mild street applications, but the lag is a killer in racing.
Unless your spending the majority of your time above 5k, go vacuum secondary
For me, in Colorado, we need choke just nature of the beast. Anyway I firmly believe dbl dumper on the track, spread bore on the street. A vacuum secondary just works better in stop and go driving.
I’ve always been a fan of the tri-power setup.
its not enough deference in power to make it worthwhile, I ran a vacuum 780 cfm on a super comp dragster 355 ci with horn still in place worked great interesting listening to it coming up on the brake. what shows up on the dyno is not always track information. thank you love the videos.
that 491 vs 514 is basically you saying you have a 500 HP small block as opposed to to saying yeah it makes almost 500 thats kinda a big difference. if i ran a mechanical secondary on the street (which i might still do) id run a choke. that i do agree theres no real difference vs running a true chokeless race carb even if it's the summer. 780cfm on 355 inches can and should run over 7000 RPM
23 PEAK HP difference on this test is almost a 5% increase, & the double pumper made more torque & HP from just below the test starting RPM all the way to max RPM. That's a pretty substantial difference. Double pumpers have zero disadvantage, "when properly tuned". I've always run them, since 1971 & never had a problem, even in cold weather, without having or using a choke. My current 750 Street HP on an Edelbrock Air-Gap intake & NO heat riser fires up & immediately idles in summer, takes a couple starts & hold the throttle slightly open in the winter, until the engine builds a little heat. My 500HP, 409ci SBC also gets better fuel economy than my computer controlled FI 2004 Tahoe. But, I will add that I've been tuning carbs for over 50 years & learned some big lessons in the early 80s working on highly tuneable Weber carbs, which the Holley HP series tuning is comparable to with their "air correction" jets!
@@bradgriffith4231 This test was done on an engine dyno. A chassis dyno with full accessories and you will never notice that 23 HP.
@@SOLDOZER If you think 5%, or 23 HP isn't noticeable in the vehicle & going down the track, you're very naive or have never raced. Pro Stock guys will spend $10,000 to find 1 or 2 HP with a motor that's already making 1,500 HP! 5% is a BIG pickup! BTW, our ALL MOTOR door slammer has gone 7.97/168 on race gas with 4,000 foot altitude air density, that's 7.70s/172 with 70* sea level air! How's your slug run?
@@bradgriffith4231 Nobody is talking about pro stock race cars here. We are talking about weekend cruisers.
Great job as always, just converted to a choke-less carburetor recently, glad to see, there should be a little bit of a gain!
I use a Quickfuel brawler 850 DP.on my Mopar 500 inch low deck with ported heads...it's also equipped with a ed's Victor single plane intake. I think this setup is bait for a dual feed carb! A vac sec carb can work it's just doesn't have the fuel curve of the DP...also Thompson perf atomizer plates on both ends of the dual feed carb really help in low end torque
These are thing I struggled with early on. Eventually I ran Choke carb tuned for winter. Then a different choke horn delete (sawed off and polished away) carb tuned for summer. This was before you could get a "race" carb with that done already. The double pumper horn delete was for summer. Vac sec for winter. They ran the same in the environments they were tuned for. Nobody knew.
or,
now you can get a chokeless carb with vacuum secondaries!!
I had a 62 nova straight 6 that in winter or summer pump twice and she'd start and idle no chock. With engine hot just turn the key. That car would idle all day and not skip a beat, smoothest carbureted vehicle I've ever had.
Thanks You Guys. There is hope getting my 750 Vac secondary no Choke Horn w. Metering Plate/Jets to work better.
would of been nice to see air fuel ratios of the double pumper to the vac. secondary carb. Great info to see though! Love my double pumper on my Cuda!
This. The primaries are working a lot harder/likely not metering as well as the secondary in the vac carb. I am guessing proper jetting would even these carbs up but ultimately the DP would be making more horses. Have a look at the secondary butterflies on a dyno engine you will see how they open/close depending upon vacuum and the diaphragm/spring setup.
The test with and without a choke horn is not completely accurate. Both carbs would show improvement with a K&N stub-stack, but the same principle would apply with a proper air cleaner base on either carb. The truth is, if you add a wall entirely around the airhorn that forces the airflow to drop straight down into the airhorn instead of entering from around the sides (as with a flat or non-existent air cleaner base), then the airflow is both better in volume and in flow quality. You can see this principle with your sink at home. With water flowing around the drain from all directions, you will get a "vortex hole" in the middle of the drain's flow. If you force the flow to enter from above , it will eliminate the vortex and allow straight-line flow. We do this with the bottom of the carburetor when we add a spacer. It does not just improve performance strictly because of the added plenum volume that may be needed, but by forcing the air through the carburetor in a straight line for a longer section. The longer the air is flowing straight before and after the carburetor's venturis, the better the flow and volume will be. That is one reason why "tunnel-ram" intake manifolds actually do so well. If the only air cleaner that can fit on your carburetor due to hood clearance issues is a small (less than a 3" tall filter), then the carb with the milled off choke horn is going to work better only because it will allow more airflow into the engine, even though it is a less efficient airflow than optimum. If you can, use a stub stack and a filter element top lid for the best performance. Been there, done that many times.
The other issue - double pumper vs vac secondary : the double pumper is better designed for performance engines with camshafts for RPM/HP. Once you cross over a certain cam duration (depends on many variables, but usually around 220 degrees) the engine needs fuel added to the airflow instantly to complement the instant airflow allowed by the rapid opening throttle blades. The double pumper is designed to do that and if tuned correctly is basically a mechanical fuel injection system in operation. Vacuum secondaries cannot do this. They are "reactive" to airflow and always lagging behind the airflow curve by design. Great for torque because they constantly "size" themselves just a little smaller than optimum cfm at all engine speed and load ranges. Just not able to give the engine that maximum airflow upon demand instantly as the DP carb can do.
The dyno numbers are impressive, but it really comes down to seat of the pants results. In my 69 big block Chevelle, vacuum secondaries with a 4-speed and 3.73 gears always gave me steady consistent launches. Switching to a double pumper carb, I only got good throttle response when I switched to a 4.56 rear gear. On the street, the launch was everything! Stop light to stop light never allows you to reach the upper power band. Street tires and the street itself were always the limiting factors as well as local law enforcement.
QUESTION ... between the vacuum and mechanical carbs you measured the air volume to be exactly the same and measured the fuel flow to be dramatically different ... especially on the secondary side. You put the difference in fuel delivery down to siphoning fuel thru the discharge nozzle .... which is fine.
But given that the volume of fuel ingested looks to be around 20+% LESS at some points, surely this would show up a lean condition in air/fuel ratio ???
So why can't this be tuned out of the vacuum carb ???
Well, I'll I've got to say is, Demonstrates what happens to the power if you only know how to bolt shiny things on out the box.
You guys need to spend more time explaining the fine details on the vac vs mech secondary test. On the surface it sounds alot like marketing for Holley selling more mech sec carbs. Hey, wait, how much $ does Holley pay you guys in advertising?
I hit the thumbs up button several times but it only scores once👍
@@mickangio16 I got your back
I'll save myself some time by just posting this here instead of going through the comments one by one. This is a condensed version of the actual episode on the MT channel. There is a lot more information and they show a lot more of the processes they do to change the carburetors between runs to ensure the results are on an equal playing field. If you want to see that episode you have to pay to play.
Need to compare manifold vacuum for each run. My guess is that the more restrictive carburetor versions will flow the same amount of air, but at slightly higher vacuum. That higher vacuum would sap some of the potential horsepower.
the mech secondary shows more fuel and power over vac sec. can you increase sec jets in vac and make about the same hp as mech?
hey you 2 , how about a dyno run utilizing a correctly cfm rated carb with the exactly correctly rated primary and seconday jets on a 2 barrel then 4 barrel carb
Great episode guys. Informative as always. Thanks.
When I was a kid ,dad pulled the choke blades out of some carbie he had on a 350 Chev.ever since then iv pulled out choke blades on single barrel strombergs,twin barrel webers and on and on until I figured out how to zip tie Rochester primary to the secondaries links all barrels at once lol .Now im tuning Nissan RB motors with a lap top here in New Zealand
the double pumper will also yank your car off the line better because of its near instantaneous hit when whacked wide open.
Perfect group of tests for an old KnN Stub Stack. (I dunno if they were any good)
I used to run a 454 with a Holley 850 with a Stub Stack on. I did The same with a 1050 dominador. Although i never knew if that would increase HP and torque.
They dont. Its a gimmick that faded away
Patrick with PRO Systems can make them work across the band for sure! I've never had an engine run better with any other Carb
Great information! I have to of the same carbs one vacuum and one mechanical. I’m gonna put the mechanical on and try it out
You guys should test out a Weber carburetor setup on a big block. Tune each cylinder and optimize it
i'm with these guys in the opening comments. I had an AFB on my slant six
I wish they would do a Holley vs predator ..I ran every carb possible..not newer than 1997 the predator was wild responsive
have u ever ported the cam bearings to get a bigger cam in a sbc or season a block or polished the inside of the block for faster oil drop or put over sized cylinders in a sbc or use aluminum titanium alloy rods or balance all the parts rods pistons so on then balance the piston and rods to the counter weights then balance the crank with fly wheel and balancer. u guys should try this it will do insane rpms if u try this port all the ports oil water so on then port the heads open up the intake ports and match the new intake ports to the heads but u will need to go bigger on the cam so u will have to go over sized bearing on the cam when we did it back in eary 90's the custom roller cam just the cam was over 1000 bucks and u will need titanium locks on the valves. we did this to a 327 i helped but bell blue printed and built the engine he also went with tunnel ram with 13.5 to 1 compression for pump gas only 92
THANK YOU SO MUCH. I LOVE TO LEARN ABOUT CARBURETORS!!! SO MUCH FUN!!! GREAT VIDEO AND THANKS FOR SHARING!!!! I LEARNED SO MUCH!!!!!
Should have added 85-0200 K&N STUBSTACK AIR HORN to the test
did you even try to fatten up the vaccum secondary carb? gotta play with both carbs not just one.
@@bigboreracing356 Nope and you been corrected 2 times now.
Diaphragm spring change?
I will say also I have a Bugcatcher scoop sticking out the hood so clean cool air is going into the motor going down the road.
The show is awesome. I'm an old man and I still learn a lot from watching.
Does anybody else think that Dulcich looks exactly like Butthead from the old Beavis and Butthead animated series.
The resemblance is spot on.
I suppose that makes Freiburger Beavis then right?
Such a good show my wife doesn’t agree but she sits there while I watch loved the 6bbl vs hemi. Have had both. Hemi looks better but my 440 on the street is better
Couldn’t just jet up the secondaries on the vacuum carb to make up the difference? Were you just running box stock carbs???
My thoughts too. If (as shown) the airflow graph was (basically) the same. But the fuel flow graph showed less fuel flow. Doesn't take a rocket scientist to figure out it was a leaner mixture. So it was un-tuned. Just out of the box, dropped on, and ran. That's what I saw. Not ideal at all.
what engine was used?
Show us what happens when you change the pump cam profile choose any 3 colored pump cams your choice. Each color has a different profile there are many different colors to choose from and each one has two positions that they can be installed in now Show us what happens on the dyno when you change the pump cam profile
I race my Falcon in vintage races. Holley double pumper.
For my street driven Mustang and Firebird, I've found the most important part I can add to my holleys to make them run correctly is called an.......Edelbrock.
PS.... I have two holley classic 650's for sale.
You guys are amazing 🙌🏻
Using the double pumper when you floor it both throttle plates are open so there's more fuel available for the engine to use
Why not add a secondary pump nozzle to the vac secondary carb, that can be blocked off or used if desired?
quadrajet, my 77 delta 88 never fails. one pump and it fires up, runs right out the gate even on cold mornings.
Also,, it depends on the carb. I once had a 780 vacc that had a rear metering block with a powervalve. Unlike the common 'plate'
The carb was still too big for a stock 400 Ford. Except for top end. A 670 Street Avenger [fitted on a Performer] was far better for low end and mid range power and far more economical as well. Same engine with an overhaul, medium cam with springs and 2 1/4" dual exhaust is even better.
What about testing ambient air temperature vs HP?
Previous test have shown the air hat is better than straight into the carb. So, not an A to B test.
What would happen with the vac sec if you changed the back boosters to a larger size to compensate for the discharge nozzles extra flow
You guys absolutely rock
Would love to see yas do a vintage 6cyl shootout, would love to see yas one up powernation.
I wonder if using a Substack would have helped any?
Great show!
I´d like ro know if the AFR was the same. If it´s "leaking" through the acc pump but the airflow is the same the dp should be a bit richer, meaning the jetting the vacuum carb should put out the same power. Yes?
Exactly ... just asked that question, then thought I'd read some comments and see if anyone else picked up on that .... several have.
AND it only makes sense to me that purposely enriched mixture through a metering circuit designed for the job and dispersed through the booster to atomize correctly would be better and more consistent than fuel "accidentally" admitted into the airstream through the accelerator pump squirter😵💫
What happened to the video you guys did, beating up headers on a dyno engine? I searched for it and can't find it now... got a link?
Ya, at least the double donger won't bog off the line. Personally, i prefer twin 2brl dominators, but not many people use them.
I believe the vacuum secondary will get better fuel mileage too. I personally would rather the extra HP. If I wanted fuel mileage, I'd drive a Honda.
A Holley Carburetor with a properly sized idle feed restriction, electric choke, and tuned will get satisfactory fuel mileage. A double pump carburetor, especially models that aren't equipped with a choke are calibrated rich in the idle system and have smaller size power valve restrictions necessitating bigger carburetor jets that run richer at part throttle. NOT an economy carb fer sure. The vacuum secondary carb can be tuned for economy AND performance.
How you gonna run the vac-sec carb without the air hat, and the DP with it?
I tend to oversized vac secondary for driving, just right sized (big AF) double to try to pull the most for performance. There is such thing as too big for a dp for a lower idle street/strip application. Just my understanding, tell me if I am wrong.
U guys should put a old Quadra jet up against new stuff. 350 or 454 old school vs newest carbs available. See any pros or cons. I’m not into efi for old reliable builds.
I wonder though. If thr only difference is fuel wouldn´t bigger jets on the secondary take care of the difference?
I think the same as you, but bigger jets alone may make the a/f ratio fat in some rpm ranges but jets AND air bleed size changes will alter the ratio curve at different engine speeds. It's the engineers' job at Holley Carburetor to accomplish. Are the lower priced carburetors intentionally designed to fall short of potential in order to encourage the user to upgrade to a more expensive model and make another sale? Sorry, Holley, but I believe that is the fact.
I was very disappointed at the end of the video......because it ended! MORE!!!!!!!!
i think the choke horn affects fuel attomisation and distribution to rear cylenders.
9/10 people will always choose the double pumper (i would).
i used to mill my choke horns off because i couldnt afford a race carb and it was a cheap mod.
now brawlers sell those pretty cheap and they have ones that have vac secondary with no choke too. kind like a hybrid
Is a 300 500 eskandarian cam in my Volkswagen sand rail bottom of the page
Hey, I make 1000 cfm HPs run awesome on 318s
Nicely done! Sweet and to the points. Makes u think/wonder about our setups. Thank you!
(. What's a choke? 😂 )
Do y'all have a slant six Dodge 225 to get rid of
Why don't just change the spring in the vac scend dairy to make it open faster and see what the difference is and put a scend dairy meter block on it
I like your really fun to watch if possible I would to see a serie on the v6 yamaha sho and the 2.8 cologne engine yes I know it's not 500 hp but would love to see what you could come up with
Fyi, Vizard put out a newer video claiming 11hp gain in a 4cyl engine by doing a piston flip with a 1mm offset
Can anyone explain to me what "vacuum secondary" means?
Great series!! Can’t get enough!! Curious, would EFI (Terminator, Fitech) beat or match the double pumper?
The carb like efi setups look really nice, imo. However they sometimes have issues with dual plane intake manifolds.
@@nocturnal0072
Yes you’re correct. I believe the fix is either a air gap dual plane manifold or a 1-2 inch spacer. I believe I’ve seen the air gap machined
@@timfarley4485 just run a victor jr with a sniper. i know steve morris isnt a big fan of them. he says go real MPFI or dont do it at all. like edelbrock pro-flo or holley terminator
As usual, testing for race. Different story with finding the best carb for street.
Testing for bench. Not for track.
Living in California helps with the no-choke decision . Try starting a carbureted car in 30 degree weather without one.
I'm not so sure that applies to all well tuned engines. I've never ran a choke, but I don't drop the ignition timing back low just to hear the engine lope either and that seems to make all the difference on cold starts.
Cold starting is no problem with a Holley carb but cold idling and driving is unless your idle fuel mixture is calibrated richer than necessary. In that case you will get lesser fuel mileage than optimum and need fresh spark plugs more often. Some people say that it also washes the oil off of the cylinder walls causing faster wear.
well if im trying to run a car like that in 30 degree weather that needs that type of carburetor, then im driving the car at the wrong time of year. that's a warm weather, hot rod, not a daily driver especially in cold weather
@@KingJT80 yes. You are right. Cars like that usually also have no heat on the intake manifold. When driven in damp, cold weather the carburetor ices up and runs VERY poorly and sometimes not at all. I live in the Chicago where the winters are miserable. In the 1970s & '80s the cars I drove had 4.30 & 4.56 gears and Holley carburetors with no chokes on cold intake manifolds. Those type of cars were my only cars. I drove 'em all year long and VERY seldom ever let me down getting back & forth to work. I only worked about a mile away. Short trips like that weren't that big of a problem but for any continuous use it would ice up and barely run. I used to use bigger idle feed restrictions in the carb in those days that made cold weather operation much better but I would definitly use a choke now days to allow a more proper idle a/f ratio for gas mileage purposes with what gas cost. Also, at the time I didn't realize that I was probably washing down the cylinder walls with gas and diluting the oil. With the gear ratio that I had in my cars I always liked to say "I can't go very far but I can get there pretty fast!".
@@KingJT80 I'm driving this engine in my pic here now. Fall is a great time to drive. We still have car shows out here in the midwest. I'm looking forward to a Trunk or Treat Halloween show on the 29th. Expected temps on the 29th here? High of 52 meaning its going to be colder at 9:00am. I drive it until the salt hits the ground then its garaged for the winter. The first salt hits typically anywhere from about Mid November to mid December.
Carbs dont like cold starts on motors with decent hp.and will eventually foul plugs.. holley sniper starts off the key every time.
A good engine setup on a dyno is set up warm Af in perfect. On a cold start its lean and pumping fuel into the thing to get it started and running will foul plugs.i have 7 sets of good plugs that are all over time wet and black. They cant be cleaned. Do you think race teams clean their old plugs...no.
YOU need Sniper😁
We all know, well, I do. 4150 will do absolutely amazing things.
Dulcich always looks like he's getting ready to go over the edge...
I want to know if a single 750 Elderbrock is too big for a stock 350?? Can someone tell me that??
It should be fine with it's adjustable secondary air door.
It pulls fuel?
I stopped using carburetors all together
EFI better and doesn't cost as much as it use to
Love my proform dp ..
Now you Need to test 4150 vs 4500 flanges
Next on Mullet Masters.....
the numbers are so close together. if you aren't at the strip does it really make much of a difference? just use whatever you have and what's in your budget.
They are helping Holley to sell their more expensive product and to get customers to "upgrade" from what they currently own.
How the heck did you get a 318 to run on a 1000cfm carb??????
Went through this with my 393W stroker with several different Holley carbs in different sizes, with and without choke horns, etc..... ended up on the 780 double pumper just like I thought I would in the beginning. I've always heard the theory that the horns cause turbulence in the venturi air which affects the fuel atomization into the chambers so the burn isn't as efficient but I'm no expert. I still need to do a bit of tuning and jetting to get max out of my engine, but my hot rod is so light and my hp ratings are higher than I need already so I'm in no hurry to make my car even more uncontrollable...
Why not release more
Full episodes onto TH-cam? The ad revenue will for sure pay off
The choke horn interferes with the signal to the air bleeds, that is why is makes less power.
Actually, the choke horn improves the Primary venturi bore mixture quality and the carburetor would benefit from a "Horn" or wall if it entirely circled the entire airhorn. The principle is seen with a K&N stub-stack or similar effect with an air cleaner base that forces the incoming air to drop straight down into the airhorn rather than circle its way in as it does without one. Picture a sink drain. When the water flows down a drain, it is actually slowed down by the fact that it has unlimited approach angles from the sides and that is why a circular vortex flow pattern develops and leaves a "hole" in the center of the drain flow. When you force the water to approach from directly above (think velocity stack) it must flow straight down and will not develop a vortex with the space wasting "hole"in the center.
@@reason2gether So tell me do you have dyno numbers to back up this theory?
@@racerd9669 Better. I have timeslips.
@@reason2gether So here is what you really need to do to prove you theory. Go to the track run the car 3 times w the choke horn on it, then remove the choke horn on that carb, streamline the entry and then run it 3 more times. That will be the best way to prove what works best.
@@racerd9669 Right! And then if by chance it ran better with the choke horn on, just put it back on! Oh wait.....ummmm.... well shoot.....😬 Duct tape. Where's the duct tape. Fixes everything......
You need to do a show comparing long tube headers with "equal length tubes" to long tube headers with "shortest path tubes"...also the advantage of shapes inside the collectors.
They did that already
Go big
What cracks me up is my buddies and me figured most of all this stuff , you guys talk about and test on all your shows. In the late 60s early 70s. All of use trying different things the hard way , racing each other, one step at a time. the drag strip times was our dynamometer. Really miss those times,we still talk about them, those of us still alive😢
It was all trial and error back then.
Strip tells the real story.
If the vacuum secondary carb flowed less fuel in the secondary, was the AFR leaner? Would increasing the jets help the power?
@@bigboreracing356 Brawler series does.
@@bigboreracing356 - There are jets in the secondaries. However, there is no accelerator pump.
No. Both carbs would be providing the same air/fuel ratio and adding more fuel to either would just cause an over rich mixture ratio and possibly lose power. The DP carb is pro-active in that it squirts the required amount of fuel into the incoming air ahead of the curve which is why it allows better performance to begin with. The air and fuel enter instantly and are predetermined by tuning. No restriction equals maximum air/fuel inducted into the engine. The vacuum secondary design is a reactive design that restricts the airflow to an always less than maximum so that it can use the throttled engine pressure differential to initiate and maintain fuel flow to match the airflow. This can give good torque and is easier to tune to prevent "bogging" but it comes at the cost of limiting the engine to always less than maximum induction for any given load and RPM condition.
@@reason2gether you did not watch the video carefully nor do you understand how this works.
@@bigboreracing356 LOL - still wondering what the AFR differences were.
Are you saying you couldn't increase the secondary jetting to help the secondaries flow more fuel?
Odd that you didn't try that.
I must be missing something.
@pinkysgarage4517 there’s a lot more to this episode, this is just the highlights. Use the app, watch the episode. The AFR’s were very close, the difference in fuel flow has to do with the quality of airflow. Bottom line, if you’re wide open all the time, a DP makes more power.
Like any great engine builder will say, fuel injection is for fuel mileage, carburetors are for horsepower.
Meh, you ran the vac sec secondaries lean.
I don't get something though.. the Vacuum carb is flowing less fuel, couldn't you just jet up the rear jets and make it make the same power and give you the vacuum secondaries if you want them?
There was one I'd like to see in addition to this - that is how much bigger do you have to go in vac secondary carb size to negate the double pumper advantage?
Why? The HP loss is negligible from a street to strip application. Use what the application calls for.
@@joshtheking1772 Oh I see, because you don't see the need for a test like this then it doesn't need to be done.
If the double pumper is adding more fuel (via siphoning through the a/p discharge nozzles) to the same air volume, the mixture is richer. Why not enlarge either the main jets or the power valve restriction in the vacuum secondary carb to achieve the same fuel/air ratio?
While that would have been worth testing, it seems their criteria at the onset was to test apples to apples from the factory instead of fiddling with them whatsoever. I bet you could compensate a bit for what the vacuum one lacks in and probably pretty easily so it’s disappointing they didn’t test for that.
The problem is distribution in the Vacuum Carb vs the DP. It's more than just the volume of fuel added by the siphoning. It's also distribution. You've got 4 separate barrels in both carbs. All the same size and physically in the same spot geographically speaking on the manifold to which they are bolted. This is where the similarity ends though. While air flow is the same in both the ability to atomize and mix fuel is different. ALL THE FUEL supplied in the two primary barrels of the Vac Carb must mix with air supplied by all 4 individual barrels of the carb. The front two will supply a little bit richer mix to the cylinders supplied most by the air coming from the front of the carb and the cylinders mostly supplied by the rear bowls will be just a tad leaner. It's a trade off you accept for the drivability on the street. The mechanical carb supplies fuel to each of all 4 barrels and this no doubt gets you a much more even distribution of air and fuel both to every cylinder.....while not perfectly even you can bet it's far closer to even than the Vacuum carb will ever be capable of. As Steve B points out: you could richen up the primary circuit of the Vac carb but you'd lose all you drivability in the attempt and it still wouldn't work as well because while you may actually resolve "lean" in some cylinders it'll almost for sure enrich, past ideal, in those that were properly supplied before you richened up the primaries. Bottom line: This is why computer controlled injectors above each cylinder are how it's done on modern engines. With a Carb you can't have both. You gotta pick. Street or Strip one carb is going to be vastly superior to the other depending on your priorities. The vac carb can't match the WOT performance of the Mechanical and of the flip side the Mechanical will never be able to match the street manners of the Vacuum Carb. You gotta know which is more important to you ahead of time.
I enjoy the stellar information and the banter. You guys are great.
The double pumper is always the way to go if you're willing to put the time into tuning it
Agreed .
Double pumper waste of time for street application.
@@SOLDOZER depends on the combination