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73-87 Chevy _ GMC Trucks => Performance => Topic started by: Rockin77 on May 05, 2008, 01:03:41 am
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I want a new carb that will give me better acceleration. ;) What is the biggest i can go with a stock manifold??
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Well first, we need to determine what carb/intake setup you have.
If you are going to be keeping the stock manifold, i don't think you're going see too much a gain by switching carbs; Remeber, a quadrajet can flow at least 750-850 cfm's if it needs to.
i finally put new plugs and wires on the truck and i just opened the secondaries last week on my quadrajet for the first time---just to see what it would do. And WOW!
But we're putting the horse before the cart. Tell us more about your setup.
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we also need to know what size engine you are putting this new carb on.
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A rough estimate for the max carb size would be to multiply your engine displacement (in cubic inches) by the max rpm and divide this figure by the constant 3,456.
(engine cid x max rpm)/3456
Using this formula, a 350 with a 5500 rpm redline needs 557 cfm, so by selecting the next larger size you arrive at a 600 cfm carb.
The way Q-jets get away with much higher cfm ratings on smaller motors (without compromising throttle response) is with proportionally much smaller primaries and tuned vacuum secondaries (they only open up when the engine, not your right foot, demands it). So in the case of a Q-jet, 750 cfm would be fine.
Edelbrock/Carter carbs work the same way as the Q-jet, but don't have as much of a staggered size between the primary and secondary throttle blades (in the case of the 750 and 800 cfm models there is no staggering). So, throttle response would be compromised by using a 750 cfm Edelbrock carb on the above engine.