With current 850cfm carburetor engine runs best at 8100rpm.Question is: If I were to change to a 500cfm 2 barrel carburetor what rpm should it run best?
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With current 850cfm carburetor engine runs best at 8100rpm.Question is: If I were to change to a 500cfm 2 barrel carburetor what rpm should it run best?
If I wanted the answer to this question, the person I would ask is Perfconn, so now, I don't know what to do.
I know what the engine is capable of,I just don't know what the carburetor is capable of.
Their is some calcs that can help you their i don't remember the math off the top of my head. Also i believe 2bbl and 4bbl are rated at different inches of water so the cfm ratings are not apples to apples. But wen we'r ran Keith dorton 500's our steel head roller 358 saw 7200-7400 . 7600 -7800 with same combo and open 600 c&s aerosol. This same engine turns 8000+ with a open 750 4bbl. And needed 20-30 points more gear on the 2bblQuote:
Originally Posted by perfconn
1000 rpm less is what I'd shoot for.
My experience running 2 barrel stuff usually best around 6400-6700. By this I mean motor pulled the whole way.
It'll depend a lot on how good the 500 is.
If big track I'd figure gear to run about 7,200. Small track gear it to get up off corner, 7,400 or so.
We run 2 different series with a good Competition Carb 500 for one that is gauge legal and flows 587 cfm and the other with one of Bob's very good 750 4 barrels. Turn 'em both in the 72-7400 range and they do well with both and estimate something like 50 horse difference. And, like jk24 said, we go 20 points lower with the 500. The trick is finding a cam that is compatible with both sizes & it took us a lot of experimenting to find one.
cam shaft selection has a lot to do with the different carbs , if your trying to optimize power out put with each carb . if your engine is running its best at 8100 with the 850 cfm , the same cam will not generate optimum power from the 500 cfm at 7200 rpm .