Daniel Dudley

Well I took my 89 GT to Musante Motorsports yesterday For some dyno runs. It was pulling about 275 RWHP but the air fuel was extremely lean over most of the lower rev range, at around 15 to 1. I'm open to suggestions as to why this would be. Now 275 is a respectable number, but further investigation reveals that my GT isn't a GT. It has an S4 engine and transmission. What really gets me is that I had a PPI by one of the big Porsche dealers who have a factory trained 928 mechanic and they told me to Absolutely buy this car as it was a rare 89 GT and worth the asking price. Ouch! Yes I have verified the engine and transmission as S4 myself, only too late. So caveat emptor boys and girls. I will be hooking the car up to a bosch hammer on the sixth of june, but in the meantime I don't want to drive it too much in a lean mode. The car has a K&N and Autothority chips, otherwise stock. On a positive note, I followed a real GT over to the dyno. He couldn't shake me at full throttle to 105. I just don't want to be doing that again until this problem is sorted out.

Garth S

While I've never been convinced of any merits of a K&N vs a stock filter, why not try the latter?
If you do not have the stock chips to try, a set of GT chips can be readily had and inserted to replace the after market ones: I've put the GT EZK in my S4 with no ill effects - and have the LH unit to go in soon.
No, this will not make it a GT, but may provide a little boost in a safe A/F ratio zone.

John Speake

What was the A/F at WOT ?

Lagavulin

I'll bet your WOT switch is broke and your engine is running closed-loop.

Jim_H

Sorry to hear that.

Maybe you have GT cams!

Tom. M

True..keep the faith..perhaps the PO. had the block swapped but kept everything else. One way to tell is the idle speed..GT should be around 775...100 higher than the S4...at 675....The idle speed is tough to tell though.

Another one is the shape of the peaks on the torque curve. If the torque curve looks like double hump..with both humps being about the same size and height with the second peak just a bit taller....it may have GT cams. The GT makes maximum torque at around 4500 (second peak)...and the S4 makes the most torque at the low end (first peak) at 3500rpm..

What was the build date and vin of your car?....

EDIT..just read the post again..how do you know you don't have the GT tranny?....
later,
Tom
midlman@rennlist.net
89GT

Jfrahm

How do you measure AF on a dyno with cats? Do you have a wideband before the cats, or are you using the sample tubes? I would suppose cats thow off a tailpipe AF reading.

Rich9928p

The dyno HP looks good. As others have said, check the WOT switch. The next thing to check are the fuel injectors. Pull them and have the flow and spray pattern checked.

morganabowen

Can't you recognize a GT from an S-4 by the VIN

Cameron

Go and get your $250 back from the shop that did the PPI.

Rich9928p

No ... the 1989 GTs are determined by option code (M637 = GT) and engine type number M28/47. I think for model year 1990-91 all 5 speeds were GTs.

Tom. M

In 89 as a rule of thumb....vins >1000 could be GT's....build dates starting in march of 89 are also an indication..as well as the others...engine number..tranny code, M637, CS rims etc..but as always with Porsche...plenty of exceptions to the rule...

later,
Tom
midlman@rennlist.net
89GT

John Veninger

Daniel,
Sorry to hear you thought you had a GT when in deed it's an S4. You have an M28/41 motor. Still a great car, but you paid a GT price.
Have Dave check the WOT switch and see if you can get yourself a set of stock chips. Run some fuel injector cleaner in the next few tanks.

A GT won't shake you until about 150

Chuck Z

Actually, with more research I have come to the conclusion that the 89 GT probably started production with VIN 1100 and not 1000 as previously stated. I know it still says 1000 (at least until I get done typing this post) on my web site but the earliest I have is # 1107.

Ketchmi

Ours "was" (sold yesterday to a gentleman from Las Vegas) #1174. Most certainly a GT.