240ZR Posted August 24, 2005 Share Posted August 24, 2005 I if i jammed a Chevy zz4 in and ran a 390 CFM carb what kinda HP am i looking at? will i run too lean and burn up the engine? what if i get EFI can i run 400 NA horse? Engine was rated at 355 HP... Quote Link to comment Share on other sites More sharing options...
Guest zfan Posted August 24, 2005 Share Posted August 24, 2005 My friend has a ZZ4 motor stuffed into a 1975 Jenson Healy. He has a Holley 670 street Avenger carb on it and loves it. He get 15-18 mpg on the highway. Not bad for a car that is carbed ant runs 12.30 at 113 in the 1/4 mile. That carb you mentioned is way to small and will kill your power! Mike Quote Link to comment Share on other sites More sharing options...
80LS1T Posted August 25, 2005 Share Posted August 25, 2005 Think of it this way....the guys that run the 4 barrel set up on the L28(stock 2.8 liter engine) are using a 390cfm carb. So yeah that wont be enough to feed a 355(5.7 liter engine). Running a huge carb doesnt help either, even though some guys seem to think they need a 900cfm carb on a mild small block. Doesnt GM recommend a certain carb for that engine? Guy Quote Link to comment Share on other sites More sharing options...
240ZR Posted August 25, 2005 Author Share Posted August 25, 2005 I see from 650-7500 cfm, but runnign it on the low side like i am will save me gas wont it? and improve low end torque.... I belive Quote Link to comment Share on other sites More sharing options...
John Scott Posted August 25, 2005 Share Posted August 25, 2005 Running a small carburetor on a big engine won't necessarily cause it to run lean. I'm not saying we should run out to the garage and swap the lawnmower carb onto the Z, but for example my old 68 Delta 88 455 came with a tiny 2 bbl. You can jet a 390 cfm to run rich or lean. Performance will suffer over a matched carb and potentially you will use less gas. You might be surprised of the gas mileage the V8s with the "right" size carb and good overdrive transmission can get. Often whats best for performance is best for effeceincy. You might want to consider a vacuum secondary carburetor. They tend to be more streetable, stay in the primaries longer. Quote Link to comment Share on other sites More sharing options...
80LS1T Posted August 25, 2005 Share Posted August 25, 2005 I dont know if you will save on gas but you deffinetly wont gain any TQ with a carb that is too small. Making the engine run the most efficently with the correct sized carb is the best way to make power and get the best MPG. Keeping your foot out of the throttle will help the most with MPG though. Guy Quote Link to comment Share on other sites More sharing options...
Guest zfan Posted August 26, 2005 Share Posted August 26, 2005 GM recommends the 670 Vacuum secondary street avenger that my friend runs on his. That is why he is running it. Very docile build with goobs of torque. You will love it, trust me. Mike Quote Link to comment Share on other sites More sharing options...
American Posted August 26, 2005 Share Posted August 26, 2005 I'd suggest reading these articles regarding CFM vs engine displacement. http://www.carcraft.com/techarticles/56919/ http://www.streetandstripmotorsports.com/charts_guides/charts_carb.htm Some decent Holley tuning tips: http://www.mortec.com/carbtip1.htm This chart & CFM calculator gives CFM based on 100% VE (which is impossible, 80% is a better guideline) but gives you some guidelines. As the article states above this is not totally accurate but will put you in the ballpark. http://www.buicks.net/shop/reference/carb_cfm.htm Hope these will help at least a little. Quote Link to comment Share on other sites More sharing options...
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