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carb size vs. HP

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Old Jul 16, 2006 | 08:40 PM
  #1  
greezemonkey's Avatar
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From: The "D"
Car: A Portly 85 Z28
Engine: 4.530 X 4.250 BBC
Transmission: under rated for this application
Axle/Gears: also under rated
carb size vs. HP

I know this question is a shot in the dark sorta, but ball park, what will say an 850 cfm carb support in a N/A motor with a 7,000 rpm limit.... max horsepower ?
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Old Jul 16, 2006 | 09:38 PM
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From: 51°N 114°W, 3500'
Car: 87 IROC L98
Engine: 588 Alcohol BBC
Transmission: Powerglide
Axle/Gears: Ford 9"/31 spline spool/4.86
The HP difference between a 750, 850, 950 or larger isn't going to be very great. How well a carb performs depends on how when the engine operates through the rpm range. Bigger carbs are more consistant however smaller carbs offer better throttle response.

For a street car, bigger isn't better because the engines operate at much lower rpms the majority of the time. A race car such as mine is designed to operate at high rpms where the engine makes it's most power. After I launch, my rpms don't drop below 6000 rpm until the finish line. It's hard to over carb a race engine. I run two 850's on my engine. On the other end of the scale, a NASCAR restrictor plate race has holes in the restrictor plate that would make a 600 CFM carb look good but they still produce 600+ hp and run consistant 180 mph.

While a modest 650 is enough for a typical daily driver 454 BBC, I've also seen two 1050 dominators on a 434 SBC race engine.

Back when I had a 383 stroker and when I still ran a single carb on a 469 BBC, I was taking the engines to 7000 rpm with only an 850DP.
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Old Jul 23, 2006 | 05:52 PM
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850 is more than enough i would go 750

try this free calculator, it is kind of cool
Virtual Engine Calculator Free Download
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Old Jul 23, 2006 | 06:14 PM
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From: The "D"
Car: A Portly 85 Z28
Engine: 4.530 X 4.250 BBC
Transmission: under rated for this application
Axle/Gears: also under rated
Yes, I tried that one, looks like you only get good info if you buy it and know your VE exactly
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Old Jul 23, 2006 | 07:26 PM
  #5  
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From: 51°N 114°W, 3500'
Car: 87 IROC L98
Engine: 588 Alcohol BBC
Transmission: Powerglide
Axle/Gears: Ford 9"/31 spline spool/4.86
Carb calculators are only good for factory style street engines.
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Old Jul 23, 2006 | 09:38 PM
  #6  
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From: buffalo
Car: 85 camaro
Engine: 327
Transmission: 350, 6200 stall, w/ brake
Axle/Gears: soon to be strange 5.14
yeah screw those carb calculators, they'l leaving you scratching your head. i run a mighty demon 750 and rev past 8,000. also depends on your compression and fuel, i run a race/pump mix other wise i was going to go with a 650, however my compression is in a funny place. 7,000 isnt anything crazy for a small block, im sure a 650 will be just fine. keep over carbueration fresh in your mind, too big is bad
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Old Jul 24, 2006 | 09:51 PM
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From: ELIZABETH,PA,USA
Originally Posted by bitchin85camaro
yeah screw those carb calculators, they'l leaving you scratching your head. i run a mighty demon 750 and rev past 8,000. also depends on your compression and fuel, i run a race/pump mix other wise i was going to go with a 650, however my compression is in a funny place. 7,000 isnt anything crazy for a small block, im sure a 650 will be just fine. keep over carbueration fresh in your mind, too big is bad
I wonder alot if I overcarbed my 496 with the 1250 - But I get sick of buying everything 2-3 times.. I figured If I am giving up 10 ft lbs, I'll live with it.
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Old Jul 25, 2006 | 05:25 AM
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From: The "D"
Car: A Portly 85 Z28
Engine: 4.530 X 4.250 BBC
Transmission: under rated for this application
Axle/Gears: also under rated
HAhaaa ... no proplem rpm`ing that one eh?? I think I`m going to stay 4150 for now but ya, your right dominator probably would skip me over one of those stepping stones!
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Old Jul 25, 2006 | 11:19 AM
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Originally Posted by 87_TA
I wonder alot if I overcarbed my 496 with the 1250 - But I get sick of buying everything 2-3 times.. I figured If I am giving up 10 ft lbs, I'll live with it.

I went from a 48 mm TB, to a 52, to a 58, and now I am changing it all again. Should have went right to the big one, and saved some $$$.
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Old Jul 25, 2006 | 03:10 PM
  #10  
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From: miami,fl
Car: 1980 old cutlass
Engine: 305 modified
Transmission: 350 turbo
Axle/Gears: 2.29
cutlass needs help

i went from 2.29 gears to 3.23 just installed and no difference off the line not even a chirp!!!i have a 305 ho .30 ovr pistons holley 650 edle mani big cam th350 tranny ! my buddy's iroc same engine screeches off the line whats holding me back
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Old Jul 25, 2006 | 03:58 PM
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Originally Posted by cutlass80
i went from 2.29 gears to 3.23 just installed and no difference off the line not even a chirp!!!i have a 305 ho .30 ovr pistons holley 650 edle mani big cam th350 tranny ! my buddy's iroc same engine screeches off the line whats holding me back
How big is the cam?
You need heads, intake and headers for cam.............and a converter for sure.
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