miyagikarate

Hello-

I have driven a total of three different porsche 944 turbos.

The first two were 88s and had shimmed wastegates, one of which did have a chip and one did not.

The third was a 86 and did not have a shimmed wastegate but did have chips..

I was impressed with the first two and not with the last. The turbo took forever to wind up and It had to be floored to feel it. While the others, I was getting boost without even flooring the car...

Does the shimmed wastegate give that much more power earlier with the turbo??

Thanks

Danno

"Does the shimmed wastegate give that much more power earlier with the turbo??"

Yes, because of the weak spring. Depending upon which boost-controller you have, there's a certain amount of boost-pressure that's always fed to the wastegate. The weak spring cracks open the wastegate early and slows down the boost build-up. Increasing the spring-preload helps spool up the turbo.

Also depending upon the kinds of chips that were installed in those cars, you'd get different low-RPM/partial-throttle behavior as well. In developing the GURU chips, there were some areas of the 3D that didn't make any sense to me whatsoever. The only thing I could surmise about that is those values were intentional turbo-lag programmed into the chips. Replacing those with more appropriate numbers yielded a tremendous improvement in turbo-lag compared to other aftermarket chips. Do a search for "APE GURU chips" and you'll see what I mean.

miyagikarate

Thanks... I just didn't think a shimmed wastegate could make it feel that much different.

hosrom_951

It would DRAMATICALLY

sl951

Danno, what 3D map are you refering too.. Boost, Fuel, or Timing?

awilson40

and how long are you actually in the 3D maps after flooring it. I thought the DME went straight to the 2D maps at full throttle.

Danno

" Danno, what 3D map are you refering too.. Boost, Fuel, or Timing?"

Boost, fuel & timing all work together. Although the KLR only uses TPS-position for the load-axis as opposed to air-flow in the DME.

"and how long are you actually in the 3D maps after flooring it."

You hit WOT maps after having the TPS open more than 65-degrees within a certain amount of time. But what I was referring to was partial-throttle/mid-range response. This could be like cruising on the freeway, then tipping into the throttle slightly to pass someone. With the GURU chips, you don't even have to downshift as the boost and thrust will be available immediately. Also on the way to full-throttle, you pass through the partial-throttle/mid-range as well, and how much boost and torque you have when you hit WOT will be a result of what's programmed in all those previous data-cells you traversed.

SimonK

The interesting question would be: If you have stock chips and you shim the wastgate what happens? Sod all?

hosrom_951

You stock 11psi or so would hold much longer rather than dropping off suddenly.

Basically at redline, boost levels would be 9psi or so, and would start dropping from 11psi to 9ps starting from say 5K rpm (?).

Shimming would just hold or slow down the boost fall, holding it longer (to 5,500rpm or so).

awilson40

Thats cool, how can you tell which cell the DME is using at any particular time? Is it just an educated guess or can you extrapulate by monitoring TPS and AFM voltage??

SimonK

Yeah but wouldn't overboost protection cut in - in high gears - under max load?