As the name implies, I got a 92 Z 5.7. The engine has not been internally mod; only the exhaust. I am interested on modifying the air induction. I was wondering if the SLP runners are just a simple bolt on or do I need to anticipate any other adjustments. Also I was going to port the plenum at the same time, but keep my 48mm throttle body. Should this be a reasonable option and what realistic hp gains could I have from this???

 

should see some gains...especially from the ported plenum

while you have it out...i would port the TB openings

 

The runners alone are worth 10-12hp I think. Not sure about porting.

But if your not going to go with a bigger tb you should get the tb airfoil. This add claims the airfoil adds another 5.8hp
http://www.holley.com/120-140.asp

EDIT: they claim 20 extra hp w/SLP http://www.lmperformance.com/1748/7.html

 

I ported the inside of the plenum to get rid of those walls on the bottom. Siammesed the holes on the side so they look like a number 8 without the middle line. Matched the runners and all opening to the gasket size, possible a little bigger and made the gasket bigger also. Doing this and shifting 1-2 at 5500 instead of 5000 netted me my biggest gains. I think I went from 15.20's to 14.40's 3mph increase roughly. It's probably 20+HP.

 

Thanks for the replies. I expected a modest gain around 15-20 total. I think im going also for an adjustable fuel regulator as well. After this its all internal in the future.