dual 4bbl carbs an good gas mileage

[Larry Ruppert]

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]

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]

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

[Rick Parker]

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

True!

How could you expect anything else???

[olddog]

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]

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]

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]

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]

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

[69boss429]

I've been running the dual holleys from carl's ford parts advertised as 715's for the 427's on my Boss 429 for over 5000 miles .
Works great,throttle response is wonderful,and mileage is between 12 and 14,but who's counting!

[Dwight]

silverback

I'm not a carb expert.

I was told that a motor is a air pump. 427 cubic inches of air in and 427 cubic inches of air out.

Could you please exlain how you would need more air with with two carb's vs one.

Thanks Dwight

[SuperHart]

As you probably expected, there are many different opinions about dual quads. First, you need to calculate the air volume requirement of your engine. A 460 cid engine at 6000 RPM uses approximately 800 cfm of air assuming 100% efficiency (which most engines are not). There are several calculators online, one being on the Holley web site. Once you calculate the air requirement you can choose carbs. Using vacuum secondary Holley carbs is always a good choice for the street since the secondaries will open on an "as needed" basis. This characteristic should lessen the risk of "bogging" with banzai pedal mashing. In addition, vacuum secondary carbs allow you a little more wiggle room when choosing carb cfm size. You could probably do very well with a pair of Holley #8007 390 cfm or #1848 465 cfm carbs. The #1848s from Price Motorsports ($775 for the pair) come with the Ford style throttle arms and proper secondary vacuum covers for dual quad usage. Either the 427FE low riser or medium riser linkage should work well. The #8007 carbs are usually available used for less money and work well when set up properly (1-2 steps richer primary jetting and vacuum pot covers for dual quad use). Top off your setup with a pair of Stellings and Hellings air cleaners for the original Cobra look.

As correctly stated by jwd you can actually get better gas mileage with two smaller carbs using progressive linkage on the street because most of the time you will be running on the primary carb only. You will love the look of dual quads sitting atop your engine and they really aren't difficult to keep in reasonable tune.