Single Carb or Dual Quads which is better?

[PHM]

I am waiting for my Superformance to come in and trying to decide on the motor options. Its going to be a FE BB but not sure if i should go with the 1 or 2 carbs. I really want the dual quads for the looks but how much trouble are they? Talking to the engine builder he was telling me that the single carb set up actualy produces more HP. If any one could give me there insight on the dual quad set up i would appreciate it.

[Cobrabill]

If you want HP,the single.If you want the "look",duals.

[olddog]

I have read that in a Cobra, the 2x4 actually produces more hp. Not because of the carbs, but because you can get more air through two filters than one filter. Again this only applies to the Cobra due to under the hood space limitations.

Engine sitting on a dyno inside a big room, what has been said is true. After you stuff it into a cobra and fit an air cleaner that will allow the hood to close, it may be a hole different story.

One of the manufactures web site has a big discussion on air filters and explains all this. Might be ERA, not sure. Do some searches on this site for air filter and you should find a link to what I'm remembering. Good luck.

[FWB]

if you compare the factory style intake (dual plane) with vacuum secondary
carbs the dual quad makes more power, this is dyno proven and confirmed by
time slips on the track dating back into my racing log since 1979. the dual quads being sold as factory reproductions (holleys) suck to say the least
they are poor quality castings that require constant fiddling. the distance
between the two carbs on the factory\ blue thunder intake make outfitting
other style carbs quite the project because of the secondary side of the
fuel circuit. if given the choice i would take the less hp single carb, because
the majority of use will be street and the extra couple tenths gained on the track isnt worth the hassle of regasketing the carbs and cleaning the needle and seat because of crappy gas that we all know and love, get the eldeb. single
4bbl dual plane and put a barry grant carb on it and bypass the leak down
and casting flashing problems associated with the holleys....

just my two cents

Fred

[wtm442]

Less problems with a single carb as compared with duals. As CobraBill said, go for the duals only for the WOW factor when you open the hood.

If you want more power, go with fuel injection or add nitrous to the single carb.

[Naumoff]

Originally Posted by wtm442

Less problems with a single carb as compared with duals. As CobraBill said, go for the duals only for the WOW factor when you open the hood.

If you want more power, go with fuel injection or add nitrous to the single carb.

THe WOW factor doesn't hurt either.

[Silverback51]

Either way you will have more HP than you can use under most conditions.

I have duals on mine and love the look and performance. The mechanical secondarys will take a little getting used to however. It does not take much throttle in first and second gear to light the tires up. The switch to Goodyear BillBoards helped with the traction problems considerably. I can now flat foot it in 3rd gear, which I could not do before.

My vote is for the dual 4's.

[Power Surge]

Originally Posted by olddog

I have read that in a Cobra, the 2x4 actually produces more hp. Not because of the carbs, but because you can get more air through two filters than one filter. Again this only applies to the Cobra due to under the hood space limitations.

On original cars, I believe the 2x4 air cleaners were actually each smaller than the single 1x4 cleaner. Together they may still have had more surface area, but it was not two 1x4 air cleaners.

[Naumoff]

Sal, Your rear view mirrors in the wrong place.

I have seen pictures of vintage full comp cars without the turkey pan.
I think a lot of mechanics threw them away. They look like a royal PIA.
I am collecting parts to do a full comp car and I think I will not get a turkey pan just because I have seen original ones without them. But to each there own.

[patrickt]

Originally Posted by Naumoff

I think a lot of mechanics through them away. They look like a royal PIA.

They are... unless you have the foresight to have them fabricated to be easily removable.

[RodKnock]

Originally Posted by patrickt

They are... unless you have the foresight to have them fabricated to be easily removable.

Excellent! How or who did that for you?

[Power Surge]

Originally Posted by Naumoff

Sal, Your rear view mirrors in the wrong place.

I know . But that's not easily changed. And at least it's the RIGHT mirror

[Cobrabill]

Stay away from Barry Grant garbage.Braswell or Proform.They're $$$ but worth it.

Remember the competition cars came with single 4s.The street cars came with dual quads.

The limiting factor is the manifold design.

[Nantucket427]

I changed out the carbs 4 years ago. I like em

[PHM]

any chance of giving me giving you a call and asking some questions? I live in mass as well.

[Silverback51]

If you go with dual 4's, do yourself a favor and go with the Quick Fuel secondary metering plate. This way you can use standard jets to tune it with, instead of buying individual metering plates that jump 4 or 6 jet sizes if I remember right.



http://www.jegs.com/i/Quick%20Fuel/793/34-2/10002/-1

[Naumoff]

I have 2x4 600 with vacuum secondaries.
I find them little problem to set up and I haven't touch them since.

The factory linkage set up is very quick ratio and is tricky to throttle steer with. More like pressure on pressure off.

A single four gives you more pedal movement to throttle steer.

That being said I like the throttle response of the 2x4 very much.

[Excaliber]

The competition cars came with a single carb for ONE specific reason, it's impossible to mount two center pivot float design carbs back to back! At Le Mans when Shelby was looking for more horse power he went with dual carbs. But for a short road course the center pivot floats are a must to avoid fuel slosh under hard cornering G forces. The long straight at Le Mans was the primary concern and for top speed (180 plus) he needed more power. The typical competition car was for short track, extreme low gear ratio and top speed generally not in excess of 130, 150 max (at a million rpm).

Dual fours WILL make more horse power AND can potentially deliver BETTER fuel economy due to a better fuel distribution in the intake. Two small primaries feeding front and back are more effecient than a single larger primary feeding center.

Having said all that... me? I'd go with a single CENTER PIVOT float 750 Holley for better all around street/short course road handling. If I couldn't run center pivot, for what ever reason? Two vacuum secondary carbs abut 450-500 cfm per unit, adjust the float level on the 'low side' and get the power valves to match the cam profile, probably around 8-9" vacuum or so should do it. I think mine are around 6-7" because my cam has a good bit of 'lope' to it. Dual fours here. Max horse power, like someone said, no worries, it will have more than you can handle not matter which way you go.

Single carb would make more horse power than duals IF:
1. Your over carb'd with two, to rich kills the power.
2. The duals are harder to set up and make work together, single is MUCH easier to diagnose/setup.
3. For the above reasons if I was your engine builder I'd highly recommend a single four, just to make life easier on myself.

[Dwight]

Keith Wilson has chromed two four barrels on his 427.

Big in the wow factor anytime you raise the hood. He has tuned his so they run good on the street. Two 390 cfm carbs are best but he has a pair of 600 or 650 because they did not sell chromed 390's. He told us what he did to de-tune them but I'm a Fuel Injected guy so it was over my head. I think Coach Mike understood.
I had talked to buddy of mind who rebuilds carbs last year about smaller jets in a 750 for a 351. He said you would lean out the engine. But he did say a restricter plate would work. You know, like Nascar. You have to keep the air to fuel ratio correct.

Dwight

[wtm442]

Originally Posted by Dwight

I had talked to buddy of mind who rebuilds carbs last year about smaller jets in a 750 for a 351. He said you would lean out the engine. But he did say a restricter plate would work. You know, like Nascar. You have to keep the air to fuel ratio correct. Dwight

My engine is a 351W supplied by Olthoff racing. Supplied with a 750HP Holley. I had the car on the dyno when I got it from the first owner and it was too lean. I upped the jet sizes about 3 step to 70 for primary and 76 for the vacuum secondaries. Runs good. It probably is just a little too large a carb, but I cannot complain. I get about 24 MPG on the highway.