Originally posted by ssmumich00:
I'm rambling. . .but since this has become kind of a cool tech forum on upsizing turbo's on 2.5L engines, out of curiousity, how do you calculate the INEFFICIENT point where the heat from compression reduces power put to wheels. . .like in my case, with a 2.5L t3/t4, nothing beyond 15psi as Keyser said?


Well that all depends of your power goals, shape of the curve you want and how fast you want to get to maximum boost.

It is easy to plot a specific engine combination on a compressor map and see where your desired boost level (per rpm) puts you in it's efficiency range.

Depending on the factors I listed in my previous post certain turbo's offer more surge area (needed running a T3/4 on a 2.5L), faster spool up (really a moot point - see later), high boost capability, low boost efficiency, etc, etc...

You can play with trim and A/R sizing to get a proper medium.

For instance Tom is using a T3/4 60-1 trim (on his 3L, NOT 2.5L) with larger turbine wheel. (.83 A/R IIRC) He generates full boost around 3500rpm which is easily soon enough and has plenty of room to grow on the top end.

IMO the worst thing you could do is use a large compressor like a 60-1 trim and then castrate it with a small turbine wheel. (still talking 3L as the 60-1 is too "large" for a 2.5L - I.E. surge)

You end up with the worst of both combinations.
Poor low boost airflow, slightly sooner spool time (but in real world driving that's completely moot and you'll need a dual stage boost controller anyway because of traction), but then no top end airflow because the exhaust compressor is already over spinning because it is so damn small. Don't even think about high boost. (Serious heat air)
That leaves you with a turbo that under performs at both ends.


So what are you "goals"???

2000 SVT #674 13.47 @ 102 - All Motor! It was not broke; Yet I fixed it anyway.