GT17 A/R
Turbo Mini Forums

Currently running a standard Metro Turbo setup but looking at building a second fast road car based on a mirage manifold with a GT17 and a Avonbab Ph2 cam. The turbo of choice seems to be the Saab GT1752 with an A/R of 0.47 but I have seen other GT 17 with A/R ranging from .40 to .56 .What is the optinumn A/R for any engine and how far should you variey up or down from it. I know its a general question with many engine variations but did somebody just find the Saab turbo by luck or by calculation.

Is there something wrong with the question or is this an unexplored area.Doing a search the only comparison I can find is were people have had T3 reconditioned from standard .25 to .36 and found it better .More info the range of A/R usable opens the door to using some diesal turbos which I'm finding easier to source secondhand at lower prices.

Changing turbine A/R is largely unexplored. The proven theory is that a lower A/R will reduce the boost threshold but may limit top end power and vice versa.

Personally I think that the higher A/R will work well with higher duration cams as well. The PH2 is a good cam but was developed for use with T3s. Someone should try a 276 with a GT1752 IMHO.

BTW Robert worked out that the GT1752 would be a good turbo for a 1275 based on his long experience with turbos.

Saul Bellow - "A great deal of intelligence can be invested in ignorance when the need for illusion is deep."
Stephen Hawking - "The greatest enemy of knowledge is not ignorance, it is the illusion of knowledge."

I have a GT1752 on a Matty manifold and 1.5 rockers.I found the max torque speed around 5000rpm with a 276 cam.Fitting the ph2 turbo cam brought this down to 4000 rpm AND mysteriously seemed to give more top end power.

'Where does the engine go?'