Originally posted by Frank@AMS
While I do agree that a GT30R would spool up sooner, Garret does not make a T4 hot side GT30R. I can most likely get one specially machined, but at the same time, the turbo would really run out of breath in the top end.
When Yermancars converted to the smaller turbo he is running now, there was a small loss in power however, it spooled up so much sooner, and the power band expanded. The car felt quite a bit faster than before, even though its down a few horsepower from the GT40.
Also, the ball bearing turbos are nice, however, you will have to run and extra oil line through the water passages.
Standard journal bearing turbos, with updated housings, are a better way to go with the air cooled boxer motor in my opinion.
Frank, Greg's original posts suggested he was after a LOW BOOST setup on a naturally aspirated motor, so I'd assume he's looking at running only about 0.7bar. The GT30R would suit that application nicely and not run out of breathe up top. It's rated to 500HP and a 0.7bar bolt on setup on a 3.2 would yield ~400HP. BTDT
Also, I run my GT35R oil cooled only. I left the water passages open. I use a -3AN oil feed, NO RESTRICTOR (as advised by Garrett dealer) and drain to the oil sump plug. I've had no problems to date, however, it's only been on my car for a couple months now. Time will tell. The key to making these live is to exercise proper cool-down procedure and to keep the oil clean and fresh.
The idle oil pressure on 911 engines is relatively low (~1.5bar) compared to Japanese cars, which is why the Garrett dealer suggested no restrictor is used. Also, oil pressure does not exceed 70psi under load, so that's another reason why they suggested no restrictor.
The turbo will let you know if a restrictor is required or not as it'd start leaking oil and smoking. Mine's been fine
'89 911 Turbo Cab
Protomotive MAP ECU, Twin Plugged Heads, GT2-EVO CAMs, 3.3L fully finned P&C's, ARP fasteners, C2T head gaskets, Titanium Retainers, Turbo spec valves, springs & guides, 964 splash valves, GT35R BB turbo, GSF Stainless Headers, Magnaflow Exhaust, Full bay Intercooler, TiAL 46mm w/gate, TiAL 50mm BOV, Apexi AVC-R EBC, SPEC Stage3+ Clutch kit, Crane CDI Ignition