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CC volume = BHP??

Introduction to Engine Tuning

Discussion and questions related to the course Introduction to Engine Tuning


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Just wondering if there is a calculation to work out the volume of air that is required to flow to reach set horse power targets.. for instance a 2000cc engine revving at 8000 rpm at 2bar = 16000000cc's (2000 x 8000 / 2 x 2 = 16000000) of air flow. The same engine revved to 8000rpm but ran at 3bar boost has an air flow of 24000000cc's. I am building an engine and at this point I can change almost any of the key figures above, CC, revs, boost and obviously fuels, I want to carry out the above calculation to ensure the engine can reach my BHP targets before starting the build,

Thanks :)

There's a few difficulties here that make it hard to work out a specific power level. First of all the part that you've overlooked in your workings above is the VE of the engine which for the majority of engines is seldom 100% and also varies with rpm. For the hobbyist it's also difficult to estimate accurately the VE when designing an engine on the bench.

The other issue that will affect the ability to simply transfer a specific mass of air into a power value is the octane of the fuel that you're using (actually to be fair there are a variety of aspects that will play into this but I feel octane is probably the major one). What I mean by this is that for a given theoretical airflow you could make potentially 500 hp or 600 hp simply by changing from a typical pump gas to a good quality race fuel or perhaps E85. This is because the high octane fuel can allow the engine to be tuned to MBT which may be impossible with a pump gas.

If you do want a rough approximation however, you'll need around 9.5-10.5 lb/min airflow to make 100 hp.