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Discussion Starter #1
First let me say that I'm new to this Chevy thing. I'm more of a Pontiac man and have a good bit of experience building these engine's, but have very little with Big Chevys, so I'm not too sure how they act, or what they like. Now my question is, I have a 454 in my 71 that is .030" over, with stock unported heads (I'm not sure the numbers off the top of my head, but they are 70-76castings), a Performer rpm intake, 1 3/4 headers, 4 speed, 3.73's, with a mechanical flat tappet cam of 284/294 adv. dur, 238/248 @.050", .567/.589 lift on a 112 LSA. This is a street strip car and I'm not sure which size of a carb I need.Depending on how you do the math, the 750 is fine, or it needs an 850/900. This is where my lack of Chevy knowledge come in, as I have no idea how this engine will want to run, what rpm range it'll want to be in, or what rpm it'll max out at. Thanks.
 

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If you use the conventional formula (RPM x CI)/3456 it dictates about a 750. From experence, I use the following:

Race 3156(Fully ported heads/ High compression)
Street/Strip 3356(Mild ported heads/ low compression)
Street Stock 3456 (stock heads/ low compression)

Assuming you shift at 6000rpm here is what I came up with:
(6000 x 454)/3356= 811cfm
So I would say an 800-850 would be in the ball park.

Here is the biggest problem I think most people have, run a carb to small you give up HP but the car is extremely responsive and tuneable, run too big a carb and it will be slugglish on bottom end due to poor signal related to velocity but HP should be there.
 

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Through my experience, bigger isn't always better. Although it will probably make the most power with the 800-850, seeing that you're going to drive it on the street also, I would stick with the 750. It will be more responsive, probably give you more power down low where you need it. With the small headers, smaller carb, oval port heads and 3.73 gear, you should have gobs of torque. The solid cam will give you an rpm range of around 55-6500, and the small heads will limit you on that. You'll probably still go through the finish line in 3rd gear. You'll have fun. Dave
 

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I recently dynoed a motor for my brother. It's a 454 with iron heads and a rooler, 13 to 1 comp motor. It made 698 HP with the dyno 750 Holley and only made 702 with my tricked up 850 Holley. My motor has better heads and intake than his and mine makes 757 HP with my carb. So the heads intake and cam will usually decide what carb you need. JMHO, RM
 

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Years ago I talked to a guy who had a 454 SS pickup--He removed the injection and started playing with different sized carbs--600,650,750(vac.+DP) and finally an 850 double pumper. He said the car felt a little crisper with the 650, but overall power and driveability was best with the 850.
 

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HotRod mag did a test a few months ago with carbs from 390cfm through 1000cfm. Oddly enough, AF ratio's stayed realitivey constant, and overall there wasn't much HP differenece from a 600cfm-1000cfm. When they over carb the motor, it lost a few lbs of TQ yet maintained the HP.
 

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Discussion Starter #8
Thanks guys, that's alot of help. Like I said, I have no idea how a Big Chevy acts, so I have no idea the rpm range this engine would want to run in, so choosing a carb is a little difficult. Building Pontiacs it's a little easier. It's no problem to run low 11's high 10's in a street car with a 468 and a 750cfm carb(Quadra jet), but these hardly ever rev past around 5600rpm. Just wasn't sure how the 454 Chevy would act with only a 4" stroke and the small heads. I'll stick eith teh 750 for now and see what happens. As for the demon site, I'll stay away from there, with all the problems I had with their carbs, I don't even want to see that name anymore. Thanks guys.:beer:
 
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