mathematics...

[deadhorse66]

I have been experimenting with different turbocharger sizing formulas, and found one that should work the way I like, but something doesn't compute. What are you guys using to size your compressors? This is supposed to be the calculation to render required MAP to produce desired horsepower, but I can't make it work. I have been known to suck at mathematics, though. :tongue:

Required Manifold absolute pressure=

actual airflow x (gas constant 639.6)x(460+charge air temp)
divided by
Volumetric efficiency x (peak rpm/2) x CID


I can't get it to to work. I think the math is flawed, but I don't know where. Please realize that I don't have a 3.8, so please don't refer me to a specific compressor map. If anyone has an alternate means to derive this information, please help me. Thanks in advance!

 

[CTX-SLPR]

Compressor maps aren't generated on a specific engine. They map the flow characteristics of the compressor and turbine in combination with the housings. I think one of the problems that you are running into is that on a boosted engine the volumeteric efficiency can cross over into the 100+% range. Some of the best calcuators I've seen are at www.turbofast.com.au

 

[deadhorse66]

Compressor maps aren't generated on a specific engine. They map the flow characteristics of the compressor and turbine in combination with the housings. I think one of the problems that you are running into is that on a boosted engine the volumeteric efficiency can cross over into the 100+% range. Some of the best calcuators I've seen are at www.turbofast.com.au

Thanks for the link. Actually, they are using naturally aspirated VE in the formula. I got the thing from Garretts website, actually--here . Actually, I found the problem. I had printed the document, and was reviewing it in my chair, and could not see the decimal in front of the VE estimation. Sorry to cause the trouble. I know compressor maps aren't generated specifically for 3.8s, but I was afraid someone would refer me to a good upgrade for a GN, and I am more interested in doing a twin setup. Thanks again for the link!