T25 vs T3
Turbo Mini Forums

I've seen a few posts about people who've switched to the T25, and love it versus the T3. Why is this? Is it because of the faster spool? I would think that a well-breathing, hot exhaust engine would do fine with a T3. I'm hoping to, at least, since I can't seem to obtain a T25...

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1967 Cooper 's' Turbo build @ www.drjing.com

Faster spool up time - the T2 series shaft assy has something like 40% of the inertia of the T3 shaft... A significant decrease!!!

Thanks, Dave. That would be a biggie! However, I noted very little lag on the T3 when I drove it. We'll see when I get it together, eh? :)

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1967 Cooper 's' Turbo build @ www.drjing.com

Lag is not the same as inertia...

Lag is the turbo being so large, that for it spin-up, it has to have a lot of exhaust gasses going through it, which requires higher rpm, (and more intake boost), which requires the turbo to spin,, which requires exhaust gasses, which..... well, you get the jist!

The T3 on the Metro can't be accused of suffering from lag as a result of it's compressor / turbine sizes. The lag feel comes from the high inertia (compared to the T2 series)...
Going larger on the exhaust housign will increase the lag a little, but all that's needed would be to drop a cog, plant the throttle, and hey-presto - the 'lag' is gone - as a result of nearly doubling the speed of gasses flowing over the turbine wheel.

My bad. Thanks for the clarification between the two.

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1967 Cooper 's' Turbo build @ www.drjing.com

will a T25 bolt up to the T3 Manifold?

no, a t25 has the same bolt pattern as a t2, well, at least all the ones ive come across do..... will fit a mirage manifold, or look for an adapter plate to fit it to your manifold......

And on the 7th day........... God created turbochargers!