I need some help here. I've been working a a friends completely stock 89 IROC with a L98 and 74,XXX miles. He just recently bought the car and wanted a tune-up as the car was running poorly.

Replaced
Plugs
Wires
Cap
Rotor
Distributor
Fuel filter

After doing these things I found the car still running poorly. Long story short it had a large vacuum leak from the intake gaskets at the intake/ head surface. He decided now would be the time to start upgrading and purchased a used HSR. I finished installing the HSR tonight and found I still have the same vacuum leak. I used fel-pro 1204 gaskets and didn't notice any fitment problems on install. The leak is bad enough that after about 15 minutes of run time you could see a slight gray edge around the gaskets I assume from combustion gases escaping. I have no history on this car and can't get any as it was bought from a used car dealer in New York. I'm thinking about trying some Fel-pro 1266's (double thick) to see if that will fix it. Once I get the intake back off I will be checking the heads and intake with a straight edge. I wanted to know if anyone else had any ideas. Thanks.

 

The early HSR base's had fittment (warped) issues. I had a nasty oil leak, blow-by and had to remove it and have it milled flat where it contacts the heads. Then use thicker gaskets.
Mike

 

Sorry I didn't update, but I figured it out the next day. This was an early one and I figured I would have to do exactly what you did. As it turns out when I was laying across the engine installing plug wires that were handed out to me by a buddy, somebody was wrong. When I saw #6 going to the drivers side I knew something was up. Stupid mistake that should have been checked first. Runs like a top now!

 

This did occur with first molds and was talked about on these boards as if it were a wide spread problem. I believed I had the problem but it turned out to be somethig else. Upon talking with the proper people at Holley I was told that there had only been a handfull of intakes that were sent in that verifiably had the wrong angle.