Well, I finally got around to getting another dyno done after fixing a couple of things on the car. The first thing was putting in the LT4 Knock Module in place of the LT1 module that came with the stock ECM. Once again I really don't understand why SLP left the stock ECM (including knock module) in these cars when they put in the LT4 engines, but it sure makes for a nice change when you "fix" it. I also had been hearing a "ticking" at startup over the last month or so, and when I finally got a chance to check it this past weekend I discovered a couple of loose exhaust manifold bolts on the driver's side. I don't think the exhaust manifold bolts were loose when I did the previous dyno, so at this point I'm going to say that the big gain over last time (11RWHP and 8TQ) came from the LT4 knock module. This would tend to hold up as I was seeing some knock retard after the last dyno run when I did some monitoring using Datamaster. After retightening the manifold bolts over the weekend I am now seeing ZERO knock retard (both on the dyno and on the street). So, the final gain from the ECM tuning and LT4 knock module at this point are:
29RWHP and 21TQ

This now puts flywheel HP at 366HP, and I'm hoping to increase it a little more as the car is still running a little rich (about 12:1-12.5:1), and by adding a few mods. My goal at this point is to get to 330RWHP so that the 330 HP stickers on the hood actually match up to something!

Once again, the only difference between dynos is a tuned ECM and the LT4 knock module, everything else is stock:

Looking good!

I remember reading that INTMD8 from Speed Inc. in Chicago bought an LT4SS and went from 281rqhp to 304 or something just with a tune. Contrary to what was said about the LT4 fbodies, SLP apparently left the stock LT1 tune in them, which seems nutty to me. Like you said, seems like a no brainer that the LT4 KM would be needed since its the same LT4, noisy roller rockers and all, that was in the Vette.

Looks to be on equal par with LS1 cars....

Man that is a nice gain. It's nice to see some real data from one of these cars.

My understanding is they had to use the LT1 tune or else the car would have to be recertified by the EPA and that just wasn't worth it for such a small production run.

I've got Motortrend TV's test of the 1997 SLP LT4 SS and they say that the computer was re-calibrated...but clearly that was wrong. The EPA thing makes total sense, didn't think about that.

Chris, do you think you could get me a copy of that test, or get me info on where you got it from?? I'd really love to have it.

As to the tuning, it is definitely a bone stock LT1 tune from the factory and had the LT1 knock module.


A little higher actually. We compared it to the shop owners WS6 LS1 with a lid and it was slightly higher across the board on HP, significantly up on TQ on the low end, and pulled to a lot higher RPM. Like I was telling someone else, the HP on an LS1, the TQ of an LT1, and revs past either of them.

I still think I'm running a little rich, but I'm not sure how much more I want to lean it out. It's running 12:1 on the dyno, with O2 numbers around 920-950. But on the open road on a 4th gear pull, the O2s were around 865-890 (must be the Ram Air working).

Anyway, I'm definitely very happy with the results at this point, although I think I may put a Hotcam or something similar in it to see what I can get. The amazing thing to me is that this is through the stock exhaust manifolds, cats and 48mm TB. I may also go ahead and get an offroad pipe (mainly for sound) and a 52mm TB to see if they help out on the power any.

Well as you know, the in-car O2s are not known for their accuracy. What I'd do is tune it on the dyno for 12.5-12.8 AFR, which with a load on the road should be around 13.1, which is usually the sweet spot for naturally aspirated cars. Might pick up another 5-7hp.

I'll search around on Camaroz28.com and see if I can find the thread where INTMID8 tuned that LT4 car.
editI couldn't find the thread, I don't think their archives go back that far, but did find another thread where he mentions picking up 20hp to the wheels by tuning the car. His e-mail is intmd8@sbcglobal.net

the 52 should work fine and add a little as well. we use the one from TPIs with the LT4 conversions. its just a bored out 48 with an airfoil added before boring. not a bad peice by any means, maybe not the flashiest like a holley, but itll work just as good.

if headers and a better y pipe are a possibility, id do those first then tune it again from there. your tune now is safe and good. once you add those two parts youll most like need to make more adjustments to better suit the car.

Yeah, I really didn't want to do headers as they are such a pain, especially since I'd have to convert to mid length 94/95 style or long tubes to really see good gains. However, I keep coming back to the TPIS long tubes for 96/97 cars. They are supposed to have better ground clearance than the other LTs, and have an offroad ypipe available that hooks up directly to the 96/97 style catback. They are a little more expensive than some of the others, but still under $900 for coated headers an ypipe. I think those alone should probably put me over 330RWHP.

Considering FLP's gained 27hp/28tq on my otherwise stock automatic, I think longtubes would get you well over 330, closer to 340.

LT's are the way to go. When I switched from ASM mid lengths to Hooker long tubes I picked up 13/17rwhp/tq with no other changes. (This was on a 396) I was worried about ground clearance with Eibach pro's and the rear isolators removed but, I never hit the headers.

Larry

well we tend to use TPIs headers for various cars. they fit well and work well too. so i think they would be a good investment. random tech offers a dual cat y pipe that will fit those headers and they flow really well incase you don't want to put up with the loud off road pipe. you should be close if not over 330 with LTs. especially if you tune for them