I would like to go one size smaller on supercharger pulley. is there any long term problem with doing this?
will be replacing top end gaskets so I thought I would do this. will replace belts anyway.
186K on motor is it worth it?

 

How much knock (KR) does the pcm show the engine has at wide open throttle right now?

If the car currently has any consistent KR, all a smaller pulley is going to do is make more boost / more knock resulting in the pcm pulling even more timing and generally making less power overall.

There are rare occasions that a 3800 will have zero KR on a totally stock engine, but it's fairly unusual. If it was the norm, these would've come with a smaller pulley from the factory. The vast majority of 3800s need supporting mods to eliminate the few degrees of stock KR and buy some additional headroom to be able to run a smaller pulley knock free.


As for the mileage, it's fine to mod at that level. Assuming the engine has been properly maintained, it's not really any more prone to breaking than a low mileage one. The downside to that kind of mileage tends to be that they're more knock prone (ingesting more oil and more carbon buildup on the pistons), so it can take more supporting mods to run the same pulley size. But you won't know for sure how many supporting mods will be needed until you scan it and go for a few WOT pulls.

 

Thats about the mileage I was when I dropped to a 3.4. I was fortunate enough to have (and still do) a KR free engine. I did all the small supporting mods also, though.

Autolite 104s and a CAI would probably keep you safe. Just have to monitor knock. I would also delete the u-bend in the exhaust.