Garrett GT35 turbo ?

[elias11]

Hey Ive been looking around here for a while getting some info for an M42 Turbo swap into a 2002. I was just wondering has anyone used a GT35 turbo on their M42 ? Ive seen the GT30's done with heaps of success, but was just wondering if the slightly larger 35 is still compatible with our engines.

The cars going to be a weekend toy, so everyday drivability isnt really an issue.

[rob_e30]

I suspect you would get a ton of lag.

[m42oh2]

I realize this is an older thread, but it's so relevant to my current build that I thought I'd chime in, just in case you haven't progressed since you last posted..

I've been researching turbo sizing for a M42 turbo 2002 project I'm working on and have also been zoning in on the Garrett GT3571.  71mm, 52 Trim, 0.50 A/R.  Running around 23psi boost with 8.5:1 C/R.  With the M47 crank and slight overbore (84.5mm), overall displacement is just under 2 liters.  This setup should be good for around 300 HP.  There's a website where you can evaluate compressor maps at various RPMs based on your engine (http://www.squirrelpf.com/turbocalc/index.php).

This option would reach full boost at 3800 RPM, and would be around 13psi boost around 3400 RPM.  Also, with this setup, the turbo operates between 72%-76% efficiency (76% is peak) from 3800 - 7000 RPM, which means it stays around peak operating efficiency for most of the boost range.  This setup never crosses the surge line, nor does it result in undersizing (when you see efficiency drop off significantly at higher RPMs, i.e. below 60%).  Furthermore, from 3800 RPM to 7000 RPM, you stay at full boost (PR just over 2.5) and the turbo is spinning between 113,000 - 123,000, which is a nice constant range.  Other turbos will have a much greater range of turbo rpms from this 3800-7000RPM engine speed, which is harder on the turbo.  This is a very attractive sizing for a 2.0L.  I've looked at dozens of pressure maps for this setup, and if you try to make boost kick in below roughly 3400, the turbo would be so small that it would run out of pressure above 5500 or so RPM.  

Here's the map I'm looking at with the GT3571:


http://www.squirrelpf.com/turbocalc/graph.php?version=4&pr0=1&pr1=1.07&pr2=1.8&pr3=2.53&pr4=2.53&pr5=2.53&pr6=2.53&pr7=2.53&airflow0=2.2&airflow1=7.3&airflow2=13.8&airflow3=21.6&airflow4=25.7&airflow5=28.2&airflow6=32.9&airflow7=36&product_id=41

Maybe boost kicking in around 3400 and fully engaged at 3800 is considered turbo lag by some, but to me that sounds like a reasonable expectation for a street performer where the turbo will continue to feed 23 psi up to redline at full efficiency..