Too much carb?

[03BlkZ]

Hello, I just had my 350 rebuilt. Nothing special but a mild cam and full rebuild. I think I may have ordered too much carb for my engine. I will be running the Edelbrock performer RPM intake and I bought a summit 750 cam carb. After some more reading I think I should have got the 600 CFM version. What are the issues associated with too much carb? I have not installed it yet so I can still exchange it for the smaller version. Thoughts?

[geezer#99]

Tuning!
Bigger primaries can cause a stumble just off idle. It can be tuned to not do that but likely you won’t have the ability to do that. You’d need to play with squirter sizes, pump timing etc. Not the best thing for a novice. I’ve done it but I’ve always liked to play on the edge.
800 dp’s and dual quads on bone stock 350’s.
Normally I’d say a 750 is just right but I’d suggest you drop down to a 600.
A 750 would be better if you plan future big power adders like heads, bigger cam.
I think you want a no-fuss easy to own set up.
Go 600.

Here’s a pic of the dual quad on a bone stock 350. 1250 cfm when wide open. Pulled like a freight train from 90 to 120.

[03BlkZ]

Originally Posted by geezer#99

Tuning!
Bigger primaries can cause a stumble just off idle. It can be tuned to not do that but likely you won’t have the ability to do that. You’d need to play with squirter sizes, pump timing etc. Not the best thing for a novice. I’ve done it but I’ve always liked to play on the edge.
800 dp’s and dual quads on bone stock 350’s.
Normally I’d say a 750 is just right but I’d suggest you drop down to a 600.
A 750 would be better if you plan future big power adders like heads, bigger cam.
I think you want a no-fuss easy to own set up.
Go 600.

Here’s a pic of the dual quad on a bone stock 350. 1250 cfm when wide open. Pulled like a freight train from 90 to 120.

Yep this truck is going to be just a street cruiser with a mild cam. Nothing radical. I want good street manners. I thinkni will run up to summit this afternoon and exchange it for the 600 cfm version.

[CastIron]

Too much intake manifold and carb for a near stock 350. The rpm manifold is for higher rpms than you will likely see. An Edelbrock performer would be a better choice, with a 600 cfm carburetor.

[Redneck Rydes]

X2 on the edelbrock carb, I had a summit carb once,could never get it dialed in,pit on a edelbrock,I have used about 6 edelbrocks over the years,love them, I ran a 750 cfm on my ZZ6 crate engine in my 1970,bit with yours a little more tamer,I would go with the 600

[HO455]

You never mentioned what heads you are running?
What rear end gear ratio are you running?
Is the 750 carburetor a spread bore or square bore?
Stock manifolds or headers?

[03BlkZ]

Originally Posted by HO455

You never mentioned what heads you are running?
What rear end gear ratio are you running?
Is the 750 carburetor a spread bore or square bore?
Stock manifolds or headers?

The 750 is a square bore. The truck has the 441 casting heads that have a little larger chamber. My truck is a 3 on the tree with 373 gears and I do plan to run a mid length header.

[i82much]

i ran an RPM intake on an 041 head 350 many years ago, 216@.050 cam, headers, four speed and 3.90 gears. It was a great combo and I did not notice much difference with a 600 holley vac sec (1850), 750 vac sec (3310), and 650 double pumper (4777).

settled on the double pumper in that application but had some compression, 10:1, was running sunoco 94 back then. and the stick helped. but it ran great with all three carbs.

[garyd1961]

I'm running a 770 Holley with vacuum secondaries on my stock L31-R 350. I have a dual plane intake and dropped down two sizes on the primary jets but run really good. I already had the new 770 when I bought the motor.

[03BlkZ]

Update, I went ahead and made the hour drive yesterday to the summit racing store in Arlington TX. That place is amazing by the way. Anyway I exchanged the 750 for the 600 CFM version. They agreed also I would be happier with the 600. Time will tell.

[72c20customcamper]

Holley has a nice calculator for CFM .

https://www.holley.com/retailer/carbselector/

[BlouDon]

Originally Posted by 03BlkZ

I will be running the Edelbrock performer RPM intake and I bought a summit 750 cam carb.

I am running a Carter Thermoquad (850 cfm) on my 350 and it runs beautifully, starts on the "first spark", hot and cold. These Carter TQs were typically used on Mopar 440s!

The only "issue" which I have found is that, with the secondaries being mechanically operated, I have to demonstrate much restraint when in a hurry, not to floor it until at least 2500rpm, otherwise there is not enough air flow for the secondaries to do their thing (which are MUCH bigger than the primaries) .

The Carter TQ is my carb of choice because it is so fantastically quick and easy to tune it for both primaries and secondaries and idle.

What I'm getting at is that I recon one CAN have "too much carb" but that actually means "too large primary barrels". This would result in lack of control where the tiniest throttle movement would cause huge changes in air flow - perfect for race situations but very bad for street use.

[garyd1961]

If you are running vacuum secondaries you can get away with running a lot bigger carb than what is normally recommended. Depending on heads, cam, compression, ignition, and exhaust you may gain a few more horses.
I'm running a stock cam but I have MSD ignition with a 6al box, a stage 1 dual plane intake, long tube headers and 2 and 1/2 exhaust out the back. I dropped 2 sizes on my primary jets but my L31-R runs great with a 770 holley. I wouldn't change a thing.