what kind of pistons did you put in? thats the key in your motor. with your list of mods.
if you did not change the piston dimentions, but simply got forged ones, (IE, they are exactly like stock, except they are forged, not made to change compression) you SHOULD run premium. Your compression ratio with PI Heads is now 10:1. Unless you shaved your heads before having them put on. If you had your heads shaved, your compression ratio is HIGHER than 10:1 and you would STILL need premium.
As for a supercharger:
(im writing this post for everyone 96-98, not just the topic starter) also keep in mind this is on pump gas, not race gas. I use the term "premium" for the highest octain you can buy at your location. its 91 here in colorado, 93 lower altitude and on the east coast (FL) ive seen 100+ at multiple stations.
For those who want to do minimal engine work (such as not doing the PI head swap.) Our compression ratio is 9:1. This allows for more boost. The problem is the intake ports can become restrictive. The largest I've heard suggested for stock NPI heads is 14 PSI. This starts to max out the heads. This is suggested mostly for track, run a 8-10PSI on the street. I suggest using a centrifical supercharger (procharger/vortech.)
For those who want to do the PI head Swap, but nothing else. I suggest using a Vortech/procharger. 6-8 PSI street, 8-12 track. The PI heads will RAISE your compression Ratio to 10:1, which is pretty high. I do not suggest having the heads shaved, it will only complicate things for minimal benifits.
For those who want to kick some ass and take some names: I suggest pulling the motor. Rebuilding and forging the lower end with low-compression pistons. Port and polish(optional) P.I. heads (once again, i do not suggest shaving them, but this is the only time i wouldn't yell at you because you can have your pistons customized if needed, and you have a forged lower end.) With a forged lower end, ported heads, and the motor out of the car, i suggest a Kenne Bell SuperCharger. THIS REQUIRES YOU (on 96-98 GTs) TO REMOVE THE RETURN EFI FUEL SYSTEM AND REPLACE IT WITH THE 99-04 NON RETURN LINE EFI FUEL SYSTEM. This is a premium time to upgrade the fuel pump, fuel lines, fuel rails, and fuel injectors as you get rid of that return system.
after your motor is built, i suggest 10-15 PSI for street and 20+ for the track.
A few things to remember: Kenne bell makes 2 kits. the largest is the 2.8L blowzilla. This requires a new hood. stock 94-98 hoods will not fit this (nor will stock strut bars)
the 2.1 is the most common, but is not recomended for boosts higher than 20. Blowzilla takes it further, i believe up to 26? ( i forget the exact boost numbers) the blowzilla is good for 800+ HP.
Kenne Bells are self oiling, buy extra oil with your supercharger, keep it in your car in case of emergencies.
do not port you KB. They are not as common as eatons (03/04 cobra blowers) and you should not trust anyone to port a KB.
KBs come with intercooler kits too, just like centrifical superchargers.
A few more overall notes:
All of these set ups, listed above, require you to move from mid-grade to premium fuel.
TUNE YOUR CAR. (Profesionally might be a good idea) Running rich washes the oil off you cylinder walls, which is terrible, but the problems are only amplified with boost/high compression. And we all know the problems of running lean, because we've all seen that turbo honda bearly running down the road... "i got 15 PSI, WTF???!" :hammer: Also, when you are getting your car tuned YOU CAN TALK TO THE TUNER. My numbers on this forum are ball-park based off the 10000 times ive read kenne bell's webpage and procharger's web page. If you are at sea level, with 103 octain readily available, your tune (and amount of boost) could change than us greenies up here in colorado with 91.
I do not suggest shaving your heads. the added compression can be compensated with higher boost without complications, or extra funds.
remember, if you want a KB on your 96-98, you need to change the fuel system from return EFI to returnless EFI. If you keep the stock return EFI and get a different supercharger (like procharger) i suggest running a fuel cooler, Jegs=$100.00.