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4 bbl carb
Posted by: sekaon ()
Date: January 05, 2018 04:16PM

I am switching from 4 carb to center 4 bbl. what is the best carb I was wondering about a 2bbl vs a 4bbl and what cfm

David Noakes
Nova Scotia, Canada

1968 Corvair 500
140 motor 4 speed

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Re: 4 bbl carb
Posted by: Phil Dally ()
Date: January 05, 2018 04:29PM

You always know what you're going to get from a Holley.


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Re: 4 bbl carb
Posted by: vairmech ()
Date: January 05, 2018 04:56PM

I prefer the Holley 390 manual secondaries and the SBC Quadrajet. I prefer the Quadrajet for street driving.

Ken Hand
Handy Car Care
248 613 8586

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Re: 4 bbl carb
Posted by: jamesolefjensen ()
Date: January 05, 2018 05:51PM


I can’t offer decisive advice so I will spout about my limited experience instead.

I am running a center mount Holley 0-8007 390 CFM. The manifold was part of the deal when I bought the car so I went with it.

My engine is basically a stock 140 HP with an Otto 20 cam. It runs OK with the 4BBL. The upside is that Holley parts are everywhere. The down side is the persistent hesitation; its noticeable at best, an abomination at worst.

The carb set up out of the box is pretty close. I bought a bunch of tuning kits and proceeded to wandered all over the place and ended up pretty much right back where I started with very few significant changes.

Get a big accelerator pump. The 50cc conversion really helped. Just as important is the pump cam. Go straight to the biggest one Holley makes (its orange, I think, and comes in the 50cc kit)

I found slowing the vacuum secondary opening help the midrange. I don’t think this engine needs all 4 barrels until ~5000 RPM. I installed the diaphragm spring quick change kit and am in the medium to heavy range of the spring selection.

I also up the power valve to an 8.5 (opens at higher vacuum than out of the box). This helped tip in at cruise. (I drove around with a big vacuum gauge hooked up to arrive at this number; your results may vary).

Tuning note: this set up likes to run rich. With each step up in jet size, throttle response improved noticeably. However, gas mileage and drivers behind me suffered greatly.

Although this isn’t part of the carburetor, get good throttle linkage. After snapping 2 cables, I cobbled together a solid linkage set up.

65 Corsa

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Re: 4 bbl carb
Posted by: sekaon ()
Date: January 06, 2018 08:24AM

thanks for all the info that will be very help will give a good starting place

Thanks Dave

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Re: 4 bbl carb
Posted by: v8vair ()
Date: January 09, 2018 10:23AM

Just remember a 390 Holley only flows 10 more CFM than 4 Rochester’s.

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Posted by: steve c goodman ()
Date: January 09, 2018 10:57AM

No post

Edited 1 time(s). Last edit at 01/09/2018 10:59AM by steve c goodman.

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