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Old 03-31-2002, 07:21 PM
gsxr's Avatar
Join Date: Aug 2001
Location: USA
Posts: 8,069
How to adjust Garrett turbo on 1987 300D?

Hi all,

I tested my boost pressure yesterday, and also timed the car with my G-Tech Pro. The pressure is consistently 12.0-12.5 psi max at full load. I then removed the rubber wastegate hose and plugged it, and went for a drive. The boost would go easily over 15 psi, near ~17 psi or so. I was too chicken to do a redline run to see what the max would be. I also checked my overboost sensor, it engages at 17.5 psi. It did not cut in on the short (1-mile) test drive. Spec per the book is 0.85-0.95 bar, or "13.75-14.25 psi". Is it just me or does that math not add up? Shouldn't that be more like "12.25-13.75 psi", if 1.0 bar is ~14.5 psi? Hmmm.

I then disconnected the ALDA and reconnected the wastegate hose and drove the car. Same 12.0-12.5 psi max boost, even with NO fuel enrichment! That kind of contradicts Marshall's theory, unless I'm missing something? I plugged the MityVac onto the wastegate canister to check the operation. The control rod doesn't budge until 15 psi, which is reaaaally weird... That should make the operational boost 15, not 12, shouldn't it? If not then I guess there is no way to set the boost with the engine off. Bummer! Any adjustment would require a test drive to verify.

So I'd like to increase the boost to ~14-15 psi instead of ~12. AFAICT, I need to shorten the threaded rod from the wastegate can to the valve. It looks like a total bear to access. Anyone BTDT? Any tips?

Oh, yeah - acceleration. Per stopwatch I was getting 11.0-11.5 for 0-60 times. The G-Tech Pro gave me ~10.75 times. With "powerbraking" against the torque converter, it dropped to 10.0. It seems the G-Tech disagrees with my speedometer by 3-4mph and gives optimistic numbers. I do have different wheels/tires, however the circumference is within 1% of stock and I tend to believe the speedo over the G-Tech. I wish I had something more accurate to test with! Oh well...


Dave M.
Sacramento, CA
1987 300D - 229kmi (brake pads on the way, so I'm told)
1987 300D - 237kmi (running pretty darn well with a cracked head)
1984 300D - 208kmi (needs a new turbo - anyone have one for sale cheap?)

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