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98 vs 99, Manual vs Automatic - turbo behavior question

412 Views 9 Replies 5 Participants Last post by  Rally Man
Hi all. I wanted to ask those who have had numerous P80s a question about turbo behavior and feel. I've had my 98 T5m for over ten years and I'm very used to how it drives. Last year, I bought a 99R Auto and it feels like a completely different animal.

I know that right off the bat there are some notable differences:
  • 4.4 vs ME7 ecus
  • 16T vs 18T (and different wastegate preload settings)
  • Manual vs Automatic

Okay, but when it comes to driving them, the T5m feels like an old school turbo car from the 80s: huge turbo lag as the boost builds. Every gear change, boost is lost because the throttle closes, and it starts over again (doh!). The result is that I can feel a push back in the seat as the turbo hits full boost. Feels good.

Now the 99R Auto - it feels like a NA motor almost. I never hear OR feel the turbo spool. It just constantly surges forward. Of course, because throttle stays open during gear changes, boost is never lost, so that kind of makes sense. But the car just doesn't FEEL as fast as the T5m.

The stopwatch disagrees. The 99R is actually faster than the 98T5m (because I'm not really abusing the clutch), but both are around the 7 second mark from 0-60. The T5m just feels more fun. Almost feels like boost increases in the 98 (from 0-10psi), and boost fades or stays about the same all the time on the 99 Auto.

Is what I'm experiencing pretty common? Or should I be feeling a more pronounced turbo spool in the 99R Auto as well?

I have a boost gauge in the 98, but not in the 99 (can't figure out a good way to mount one - I want to avoid the A-pillar mounts)
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I don't have a ton of experience with the ME7 cars, but I might have a few suggestions for dialing in the '98.

First is play with the wastegate settings. This can make a huge difference. Tightening it up half a turn at a time can be noticeable and reduce turbo lag. I'm pretty sure stock pressure for the wastegate is 4psi, if you have a tool to check.

Also, two other possible things to help driveability on the '98 are replacing the throttle position sensors and the boost control solenoid. There's a youtube video somewhere on the throttle position sensor, and it shows how these sensors lose readings at certain points over time. He says you can clean them up with brake cleaner, but they are pretty cheap new so I just replaced it. This made a huge difference in my manual car, as the power came on more consistently and it was way easier to smoothly engage the clutch. The boost control solenoid is another one that seems to slowly fade out, instead of just dying. Replacing this solenoid with the newer Pierburg one, that has been suggested here many times (hopefully someone else remembers the part number) gave me a lot quicker turbo response in one car in particular, and again it's fairly cheap so it's easy reassurance that everything is dialed in.

For the boost gauge you can get a bluetooth plug-in for the OBDII and then use an app on your phone to read boost, as well as a bunch of other readings. Obviously this route does not give you a true built in gauge, but you can still check boost when you need to.
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I had a '97 850R that the bluetooth readings seemed too delayed and weird to trust, but that might have been 4.3. On my '98 cars with the bluetooth there is a slight delay in the reading on the app, but it seems pretty accurate. As in, you feel the boost hit as you accelerate and then about half a second later you see the number spike on the app boost gauge. I have a vacuum boost gauge in one of my cars that I tested it with, and the overall numbers were the same, just with the app reading slightly delayed.
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