944 timbo

Is it best to pick a redline and then a turbo that runs out of air right after that? Whereby you would have the smallest posible turbo to reach your target PSI and RPM?
-or-
Go with a bigger turbo that supplies much more air than you need keeping the wastegates busy. And the compressor wheel spinning slower thereby reducing heat and increasing longevity while giving you the possibliity for more power later?

ealoken

Hello, what are your HP goal?
The turbo alone does not dictate boost by rpm, camshaft, intercooler, exhaust size, tuning etc all makes some differences.

Our 4syl M44 will never! make a lot of umph on 2500 rpm, but will wake up from 3500, this is dictated by the engine design.

Frank@Work

I would look for the rpm range you expect to run your engine in mainly and find a turbo which can deliver the required amount of boost within that range.

944 timbo

I think I am phrasing the question wrong, sorry. Strickly speaking about airflow and not hp, lets say at 7000 rpm, turbo A delivers 920cfm @ 20 psi with a 58mm wheel and tubo B delivers 920cfm @20 psi with a 110mm wheel. Which would you choose and why?

Nowanker

Sizing the turbo is a science....
Calculate the airflow requirements, and choose one with the best compressor map (highest efficiency) to match.
Not my field of expertise, but I am aware of the process.

ealoken

There is a number of things that dictate the turbo size.
What are your goals?

GPA951s

For these types of questions you need to contact the guys who are professionals.. call charlie at evergreen turbo. He knows his stuff..

951TurboRS

Once you know how much boost and air your engine needs to meet your hp goals find a turbo with a compressor map to suit. Ideally you want a turbo that will be in its efficiency range from midrange rpm to max rpm.

Ideally yes you should always run the smallest compressor you need to meet your hp target. A caveat to this is if you’re running pump gas you want to be within the most efficient islands of the compressor map. You may need to step up a size of turbo in this case. On E85 you can run a small turbo all the way to the choke line and make up for the loss of efficiency from the E85’s cooling effect.