The summer before last my father and I converted my 86 gxl from an automatic to a 5-speed. It was a pain but was well worth it. Lost the reverse lights however but gained ungodly amounts of horsepower. The engine blew 2 months later so I scrapped it. Now I have an 88 gtu(5-speed) and it doesn't have the horsepower or the braking power my gxl had. The gxl had 200,000 mi. while the gtu has 70,000 mi. Does this seem odd to anyone?

 

Run a carfax and make sure that the car really does have only 70K miles on it.

Also check the cats for being clogged and make sure the brake pads are not glazed.

The GTU is a better performance car than the GXL, you should notice a difference between the two.

 

From 88-92 the car had 3,000 mi. on it. I know it has 70,000. I did figure out the hood played a part in it. The hood on the gxl was a hell of a lot lighter than what was on the gtu. So in turn I purchased a tII hood. I was thinking it might have something to do with the rear end gearing. Could it? Also what about the clutch. I put a new one in the gxl and I'm still trying to decide what should be done transmission wise to the gtu. would that be a factor?

 

Also I modified the exhaust on both. No cats, header, mufflers!

 

If anything the rear end gearing on the GTU should be higher (making it faster) as the auto rear end is only a 3.9 while the manual rear end is 4.1. You didn't change the rear end on the GXL when you did the auto to manual conversion right?

Sounds like you may have had an aluminum hood on the GXL for some reason.

And yes if the clutch is slipping you would be down on perceived HP.

Also I would check the compression, if the car sat for 4 years (as it appears to have almost done) the seals may have never set in correctly.

 

I only changed the transmission and the driveshaft. When I did that I put in a new stock clutch and resurfaced the flywheel. I also put in a synthetic transmission fluid.
Well the clutch is not slipping on the gtu, I can just tell by shifting that it needs work. Occasional grinding when I try to shift quickly into third.
So I take it that the 86 gxl wasn't supposed to have the aluminum hood. When I got the car the only modification to it was the split five star rims and red calipers.
When I get the car out again I'll take it to a shop and see what the deal is with compression.