carburetor size

Underdog · Post by **Underdog** » Fri Jul 10, 2009 4:58 pm

Can I use a 995cfm carburetor for my 396ci sbc engine???

norm · Post by **norm** » Fri Jul 10, 2009 5:02 pm

i would say yes, but with that little info,who knows? is it 8 to 1? 13 to 1? got 305 heads? if it is a decently built engine,yes.just may need some tuning..

Robbie DeVane · Post by **Robbie DeVane** » Fri Jul 10, 2009 5:33 pm

need some information about the motor before anything can be said.
www.devanecarbs.com

Troy Patterson · Post by **Troy Patterson** » Fri Jul 10, 2009 7:30 pm

What venturi diameter and what booster?

Troy Patterson TMPCarbs.net TMP Carbs

Rick1999 · Post by **Rick1999** » Fri Jul 10, 2009 7:47 pm

No you can't!!!!!!!

Sorry it's Friday night and I'm stuck at home, bored. More info needed.

Drag Chevette · Post by **Drag Chevette** » Fri Jul 10, 2009 8:34 pm

I use a 750 on the 1/8th and a 1050 Dom for 1/4.....

both on 355 sbc.....dom is faster in the 1/4, small carb is more consistant in the 1/8th.

new engine builder · Post by **new engine builder** » Fri Jul 10, 2009 8:56 pm

Rick1999 wrote:No you can't!!!!!!!
Great,now I feel like acting up also.
I'm stuck at home also.
All the dirt track racing is rained out.

Sorry it's Friday night and I'm stuck at home, bored. More info needed.

Troy Patterson · Post by **Troy Patterson** » Fri Jul 10, 2009 9:07 pm

I've have a number of customers running 1000+ CFM carbs on 350 / 351 cid inch engines, and 900+ cfm carbs on 289 / 302 cid engines, street and strip, consistently.

One, ran a '69 Mach 1 with a .030" or .040" over windsor with Vic Jr. heads in the heavy car launching at 2800 - 3000 rpm. Oh, did I say he also runs at between 8600' and 9000' DA?

True, you can't expect to do this with a stock carb Holley or not, but you can go bigger than most people think with good annular boosters and further still with a good tune in the carburetor. When I say tune, I mean fuel curve that is correct for the engine in the vehicle.

Troy Patterson TMPCarbs.net TMP Carbs

MadBill · Post by **MadBill** » Fri Jul 10, 2009 10:18 pm

To restate Troy's position: Big carbs are much more tricky to tune and are likely to be a power plus only if set up very precisely. If you can't make that happen, a conventionally sized carb {rated CFM = [(peak power RPM /2) x displacement]/1728} will be nearly foolproof but at a cost of significant lost power potential.

Underdog · Post by **Underdog** » Fri Jul 10, 2009 10:36 pm

Here is my set-up:
Bottom End = 396ci LT1 motor fully forged (4.030 Bore) 3.875 Stroke, and 5.850" Rods, and 11.1 cr

Top End = GM#867 Pontiac Heads raised runners, 60/40 valve spacing 2.10 intake valves 1.60 exhaust valves, 64cc chambers, 235cc intake ports, heads flow over 330cfm @(.600/.700?) lift. Cam is a solid roller 262/272 @.050"
.424"/.424" Lobe Lift
112 LSA
GM bow tie raised runner intake #10051103

I don't want to buy an 850 carb and then find out that I needed to go a bit bigger. By the way the 995cfm is a king demon with interchangeable venturis which I already have.

Underdog · Post by **Underdog** » Fri Jul 10, 2009 10:48 pm

yes madbill I agree with you that your formula is the safe way to go but most healthy combinations can get away with multiplying 1.2 or 1.5 to your formula's result. Im I right?

MadBill · Post by **MadBill** » Fri Jul 10, 2009 10:59 pm

Or more. My street/strip 495" BBC is going together with a pair of annular booster 970 CFM actual dry flow Holleys. The Formula would call for ~1,000 CFM total @ 7000 RPM.

Robbie DeVane · Post by **Robbie DeVane** » Fri Jul 10, 2009 11:07 pm

[quote="Rick1999"]No you can't!!!!!!!

Sorry it's Friday night and I'm stuck at home, bored More info needed.

hahaha!!!! That's funny, How about some vehicle information what is the weight of your car, how tight are you going to turn the motor, what trans and what stall. Everything that is why I have a 45 question spec sheet on my web sight you have to take all of this into consideration plus sum.
www.devanecarbs.com

Underdog · Post by **Underdog** » Fri Jul 10, 2009 11:47 pm

Robbie the car weights 3100lbs and it has a 6 speed manual transmission, I'll be shifting at 7200.

Post by **jmarkaudio** » Sat Jul 11, 2009 1:42 am

I've picked up with a Dominator with less than you run, yours will be fine.