dual 4bbl carbs an good gas mileage

Larry Ruppert · #1 (**permalink**) 01-25-2009, 09:44 AM

Gentlemen I am interested in dual carbs on my 460, I am building a drivable street engine. Is it possible to run two small carbs that would be equal to a single 750 for gas mileage.

Silverback51 · #2 (**permalink**) 01-25-2009, 10:18 AM

When I bought my car it had a pair of 465CFM (1848 Series) Holley's on it. Gas mileage was in the high teens, but performance sucked.

If you are only interested in gas mileage you can give those a try.

Calbullet · #3 (**permalink**) 01-25-2009, 10:33 AM

having a 460 and gas mileage are not used in the same sentence

Rick Parker · #4 (**permalink**) 01-25-2009, 11:12 AM

Calbullet Said: "Having a 460 and gas mileage are not used in the same sentence"

True!

How could you expect anything else???

olddog · #5 (**permalink**) 01-25-2009, 11:35 AM

I think he just doesn't want it to drop from 10 mpg to 5 mpg, from this one simple change.

He likes the look, but isn't willing to take a huge hit on mpg to have it.

From what I have read, the biggest problem with multiple carb set ups is the size of the carbs. If an engine only needs 800 cfm then you need to use two 400 cfm carbs. It's a little harder to find small 4V carbs at the exact size you want. Then tuning them up becomes more difficult, which is the second problem. When propperly set up, I don't see why an 8v set up would be any worse than a 4v on fuel milage, but that is theoretical - not factual.

Tony Aprile · #6 (**permalink**) 01-25-2009, 12:50 PM

Larry...Granted there are many different opinions, I switched from my original setup as delivered with a 750 holley to dual quads with 600 vacuum secondary holley's.

If you step into the throttle alot the dual quads will give you less mileage....no rocket science there....on longer road trips where I was ablle to stay in high gear...about the same using progressive linkage.

Check out Velox's Winter Project:

Winter project

Dwight · #7 (**permalink**) 01-25-2009, 02:51 PM

I've asked this question before. Would two small 4's work?

I think you could take a pair of 500 - 600 cfm carb (easy to find) and make a restrictor plate the same size as a 400 - 480 carb. Thin stainless with 2 gaskets might work. They do it in NASCAR. You need to reduce the air intake to keep the air fuel ratio correct. If you just jet the carb down you will end up with a lean condition. You must decrease the air and fuel together.

Dwight

Silverback51 · #8 (**permalink**) 01-25-2009, 03:26 PM

Quote:

Originally Posted by Dwight

I've asked this question before. Would two small 4's work?

I think you could take a pair of 500 - 600 cfm carb (easy to find) and make a restrictor plate the same size as a 400 - 480 carb. Thin stainless with 2 gaskets might work. They do it in NASCAR. You need to reduce the air intake to keep the air fuel ratio correct. If you just jet the carb down you will end up with a lean condition. You must decrease the air and fuel together.

Dwight

I know people will argue with me, and I'm not going to get into a pi$$ing match, but you need more CFM with dual fours. You do not want two 400 CFM carb's to replace a single 800.

jwd · #9 (**permalink**) 01-25-2009, 03:46 PM

Quote:

Originally Posted by Silverback51

I know people will argue with me, and I'm not going to get into a pi$$ing match, but you need more CFM with dual fours. You do not want two 400 CFM carb's to replace a single 800.

Not to argue but you are wrong. CFM is CFM. I've been running dual fours for 33 years and have installed them on several cars for friends. The best thing is you get better gas mileage with 2 small carbs. vs. one large (assuming you're using progressive linkage) because of the smaller primaries and you'll also have slightly better throttle response.
It's alot of work to get them set up correctly (yours obviously weren't) but once done, they are the best of both worlds and look cool as he11.

Jim