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73-87 Chevy _ GMC Trucks => Performance => Topic started by: xtreme80 on January 24, 2007, 11:20:00 pm

Title: 750cfm Carb too much?
Post by: xtreme80 on January 24, 2007, 11:20:00 pm

Hey all, I'm in the process of building a 350 bored .060 over with flat top pistons, a mild cam, 194 heads, and an edelbrock performer intake manifold.  I also plan on putting the MSD ignition kit on it.  

Is an edelbrock 750cfm carb gonna be too much for my app?  I know this can be one of the most important parts in building a high performance engine, and I want to get it right.

Suggestions?

Title: Re: 750cfm Carb too much?
Post by: roundedline on January 25, 2007, 01:42:00 pm

Vacuum 750?  If so it will be fine.  If you plan to not spin it over 6000, you won't need more than 650cfm on a mechanical secondary carb.

Chris Lucas
www.73-87chevytrucks.com
www.captkaoscustoms.com
Project Su
Jimmy 2WD Project

Title: 750cfm Carb too much?
Post by: Lt.Del on January 25, 2007, 05:13:00 pm

They put quadrajets on these puppies from the factory...those things are 795cfm if i remember correctly.  

Title: Re: 750cfm Carb too much?
Post by: xtreme80 on January 26, 2007, 11:48:00 am

Yeah it would be a vaccuum secondary carb.

Del, I thought my factory rochester QJ was like 600cfm or something?

Title: Re: 750cfm Carb too much?
Post by: Lt.Del on January 27, 2007, 10:37:00 pm

I bought the edelbrock 1903 qjet carb back in 04 when i put my 383 stroker in, and, after doublechecking, it reads 750 cfm.  The 1904 electric choke shows 795cfm.

Most of the edelbrock performer carbs are around the 650 cfm's.  

I don't even see the 1903 anymore.  I bought mine from  the PAW catalog, and even they don't show the 1903's anymore.  I guess i got mine just in time. I bought the 1903 because it was direct replacement for my 79 w/ egr and all smog stuff and simply bolted right in place and all lines hooked right to it exactly as stock.

750 cfm is not too much for a 350.

SgtDel
aka "Andy"

www.delbridge.net

1979 Big 10 383 stroker
1991 Blu 'Burb 3/4 ton 4x4

Edited by: SgtDel  at: 1/27/07 10:50 pm

Title: Re: 750cfm Carb too much?
Post by: roundedline on January 29, 2007, 01:29:00 pm

Most Q-jets were rated around 750-795cfm, but this is VACUUM, not mechanical.  The engine will only pull as much air as it needs.
Vacuum ratings and mechanical ratings are 2 very different things.  An 800cfm mechanical double pumper is WAY to much carb for a stock motor seeing no more than 6000rpms.
650cfms is more than a stock 350 running at 100% VE needs.  And no motor can run at 100%VE unless is has forced induction.
In general 600cfms are more than enough for a 350.

Chris Lucas
www.73-87chevytrucks.com
www.captkaoscustoms.com
Project Su
Jimmy 2WD Project

Title: Re: 750cfm Carb too much?
Post by: xtreme80 on January 29, 2007, 10:35:00 pm

Good information.  Thanks everyone for the replies.

Title: q-jets
Post by: stepside454 on January 31, 2007, 01:20:00 pm

factory q-jets are rated in the 750-795 cfm range. & yes they work just on smaller engines like 305s & 350s. They work fine because of there spread bore design making them more forging because of the very small primarys.
 I assume with the combo your talking about, this engine well be kept within about 5500 RPMs ( partially based on the heads your using).
With that in mind ,Id run no more than a 600 cfm carb.
A 750 cfm carb will run just fine on that 350 with proper tuning, but overall response will be better with a 600 cfm carb.