I found something interesting on Autosite..... Some of the 2.5l 4 cyls used after 88 are listed as 110hp.

Now I've been able to confirm that they really are the same block etc. What I can't confirm is the internals. Does anyone have access to a parts list for the 2.5 as used in 89-91 Cutlas Calias or 90 Grand Am? I'd like to see if they are using a diferant cam conntecting rod or piston in them. The intake and TBI look the same from what I can see but checking part numbers would confirm it. ((I said connecting rod because the ballancer motor uses a diferant crank. You could compair the cranks if you use 88 Fiero as the reference.))

I have a feeling this may be a PROM programming thing. If it is then it's just an issue of dealing with the VSS if needed.

I'll take another 12HP cheap. Anyone that helps with this project gets first crack at any results.

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Lake Superior? Is that what I stepped in? Sorry.

theogre,

As another owner of a DIS Duke, I am extremely interested in this information. I am skeptical that there are any actual changes. Perhaps it is a paper change similar to the output of the 2.8L Fiero engine. If I remember correctly, the 88 "lost" 5 bhp. Upon closer inspection, one discovers that the "peak" rating was simply not the peak at all. The 135 bhp "peak" rating matched the 85-87 dyno curve perfectly at the new "peak" RPM which had been decreased by 500 units.

I had thought of that posibility. I've always had my doubts about the 98HP number. The DIS motor always seems noticably stronger than the older ones. I also noticed that the same motor, in the same year, has 2 dif HP numbers listed in diferant cars. I forget what 2 cars/year it was just now. I thought that was rather strange. So far the highest HP I've seen listed is 112 HP in an 89 cutless calais.

I'd still like to see if anyone can find any obvious internal diferance. I don't have the time to fool with it myself. It would mean I have to go to a dealer or parts store and talk them into looking it all up.

On the other hand I do have the tools to chip the ECM and diagnose any problems. I've already found that my 87 idles better with a chip from a 88 Grand Am. Problem with that chip tho is the VSS input mode is set wrong. The DIS ECM can read the VSS thru the buffer like Fiero has or the VSS can be connected directly to the ECM. The choice of which source to monitor is made in the PROM.

I'm working on a fake for the ECM if I can't obtain software to change the VSS mode flag. I should be able to tap the VSS feed to the dash and make the ECM think the VSS is direct. Fortunatly I have a spare ECM to try that on. If the fake works then our choices of PROM cadidates increase greatly. (The VSS has to work. Not only do you get code 24 but the TCC will not lock without it.)

I wish I had access to a dyno around here. I'm working with someone to get software setup to program PROMs for these. Mainly I'm after changing the VSS source flag and the Fan activation temperature. If I had a dyno I'd look at some of the other stuff as well but there's no way in hell I'll try it without a dyno. Get a few numbers wrong in the spark or fuel map and you can cook a motor really fast.