The Jalopy Journal
Discussion in 'The Hokey Ass Message Board' started by Wicked50, Oct 9, 2009.
What is the horsepower difference between running a single 4 barrel carb to running dual 4 barrel?
That is a very loaded question. It depends on many different factors such as Intake Manifold Design, Cam Selection, Carb Selection, etc.
That is like your wife asking which dress she looks better in.
Answer she looks good in both, but the little red dress probably isn't appropriate for Grandma's Funeral.
Ok I have a stock Buick 401 with a single 4 barrel intake and am thinking about upgrading to a stock dual 4 barrel intake with 500cfm carbs
Horse power may end being the same and you might end up loosing a lot of throttle response and low end torque. Don't give your engine more carb than it needs. Unless of course looks and being cool is more important than driveability. On the other hand if you have big cubic inches and an engine that needs more cfm than one carb can give you and your engine is set up to run in rpm ranges where it can take advantage of a dual quad set up horse power gain might be significant in higher rpm's. It all depends on your engine combo, intended use and so on.
oh boy.. just had a huge thread similar to this on tunnelram dual quad vs. single quad. Uhm.. like frozen merc said, depends on engine internals mainly. your cam choses everything from gear ratio, to transmission/ torque converter, to pistons, heads, intake, and CARBS.The most important thing that determine's CFM's is your camshaft. pretty much when you breach .400 lift and about 250 duration youll be looking at 750 cfm and then once you get to .500 lift and 280 duration you start looking at 850-900cfm which is dual quad country (or gigantic single four barrel). Then also along with high duration comes high rpm ranges(power band) and this may not only require a bigger carb but also possibly a high rise intake or tunnelram application
My Cadillac was 300 HP with single carb and 325 with the 2/4s advertised factory.
although this cadilac gained 25 horsepower with another 4 barrel, doesnt mean this is a scale you should go by. just putting that out there. This cadillac probably was tuned from the facctory for the dual quads and they just put the single quad on for the option, thus bolting on the proper application would increase power.
for example, you wouldnt put a 650 holley on a stock inline six? youd be fouling plugs left and right and would probably lose 25 horse power in doing so. its all about proper application and tuning. but also you could detune the dual carbs for looks, but as far as power increase i stand by my previous reply
I really think that was a factory embellishment, in 57 advertised HP was a sales gimmic. just threw it out for comparison.
could be! good thought and point though. just didnt want him to be misled, but your response is a direct and perfect answer to the thread topic
nope didnt sound like a dick i was worried i sounded like one! haha hopefully our colaborated information will be the answer to his carburetion problem. and its ok youre definitely more experience than I am. you have been working on cars for over 10 years before i was born! Im only 19
Well, I'm a 19 year old stuck in a 63 yrae old body. Enjoy your evening.
Depends what you use the car for.
If it is a streeter with factory cam and gearing, it may make very slightly more top end power, but may also make it truly horrible to drive, and THIRSTY.
A little bit of everything is a lot better than a huge carb on a dead stock engine.
A bit more compression, and cam, exhaust, and a slightly larger four barrel, with some head work would make for a really nice package.
you wouldnt put a 650 holley on a stock inline six? youd be fouling plugs left and right
Fouling plugs? maybe not.Too much carburation often results in a lean part throttle condition,the air velocity through the carb venturis can be too low to pick up fuel. A 650 Holley on a stock inline will likely unsuitable of course.
really, dual quads are not necessary to make more power. it's been proven that single quad setups can easily match and in may cases outperform dual quad setups, and do it more efficiently. there is no practical reason to run dual quads on a street motor other than it looking a lot cooler than a single carb setup. to make power with any engine, you have to match the carb size with the engine's combo, not just cram as much air and fuel down it's throat as possible.
here's a pretty decent read on the subject:
I learned the hard way a long time ago...too much carb and too much cam leads to not much performance!
Good discussion here:
Read the whole thread.
Lotta good stuff in there.
Quote from Carbking - who really knows what he's doing....
the stock dual 4 will make more power and does not sacrifice drivability. Buick had it very well thought out. Are you looking at a complete factory setup or just the manifold and you're gonna do the rest? The two 500's are about perfect. There should be a couple of Nailhead threads that talk about this.
Did you look at what he's running? It is necessary for him to run dual quads to make more power. There are no aftermarket single 4 manifolds. The factory ones are mediocre at best. The best being the 66 quadrajet manifold and the dual 4 outperforms it.
i didn't actually, i just read his first post and commented.
if he HAS to run dual quads on an aftermarket intake or a single quad in the factory intake, i would have thought the answer would be obvious.
I'll take a dual 4bbl carbed setup over a single carb any day, if only for the looks of them.
To those who 'think' a dual carb-setup is less responsive; have you ever driven a car with such a setup (with non-progressive linkage that is)?
The key (today) is to use carbs with a secondary airvalve so the motor only gets the amount of mixture what it wants.
The non-progressive linkage will move the total of 4 primary butterflies at once, in effect doubling the amount of air that enters the engine at the same throttle-pedal position. This makes the engine feel more responsive. It's a mechanical thing.
Very well said, think AFB's, not Holley 660 tunnel ram carbs for a street machine and you will do well.
Buick made the dual-quad setup work by mating it with a switch-pitch TH400 transmission. I had this setup in a '65 Skylark GS with 3.70 posi rear and it was a screamer. Not so much when the switch-pitch was not employed, however.
I'm running dual 600 Edelbrocks on my 390 FE and absolutely love them. no tinkering with any adjustments and the car is very fast. plus under nomal street driving, I still get 14+ MPG's
That's half the problem, people commenting without reading the thread. He was going to use the stock dual 4 manifold as well and not an aftermarket one.
Worked great without the switch pitch as well, and even with a dynaflow.
So, is this the reason why some engines, big block chevies for example, don't have many multible carb manifolds avalible?
Because the rat works better with one large 4-bbl? Also, school me on what happens if you don't have ENOUGH CFM's in your setup.
The engine will run and idle fine, and it would seem to me that around town where RPM's are down low a small carb would be the setup, no?
Something to remember........Multi carburetion was the answer to a problem posed by small carburetors. In the days when the factory did duals, a real big carburetor was around 550 cfm. Most engines were using 150-350 cfm carburetors. Most hot V8s require 650-850 cfm to make max hp.
Follow the timeline to where multi carb originally fell out of favor and you'll note that it follows the availability of 650-850 cfm carbs.
If you want multi carb, run it. Definitely cool. But don't expect any more power than if you ran a large mechanical secondary 4bbl. Good luck with the project
Good info here. As for having not enough CFM, remember that the engine is an air pump. It will pump more air (rated at Cubic Feet per Minute or CFM) as the engine speed increases. Also, a 4 stroke engine pumps it's displacement every other revolution. There are formulas, but unless you are increasing the RPM, increasing the displacement or both dramatically, the stock carb will be fine up to 70-80 per cent of the stock RPM. How often are you driving the car at that RPM?
So how does the number of carbs affect performance? tri-power (3 2 barrels) makes 85-90% of the power of a dual four - I guess you weren't thinking of the Mopar Six Pack or 427 chevy tri-power.
Making blanket statements like that doesn't make me think he knows what he's doing.
Separate names with a comma.