Beater79TA

I recently rebuilt the L98 in our 88 GTA. It is running stock compression with forged internals, AFR 180 heads, and a mild cam (218/224). The air fuel mix is good and the power curve is smooth and moving upward until 3700 rpm where it flatlines until you let off the gas. The peak numbers at 3800 rpm are approx 200hp and 300lb/ft.

The car is running a completely stock TPI intake. Am I correct in thinking my issue with it not pulling any higher into the rpm is I've maxed out the intake and TB?

sccavette

With the combination you have it should atleast pull to 4200-4500.

From your post it looks like you are using a wide band O2 or the car was on a dyno when you see this. When it hits 3700 what is the AF ratio and how much advance do you have at 3700? Are u still running stock injectors and what fuel press? Did you put the cam in straight up or did you retard? advance? it when installing.

if the car was on the Dyno do you have a copy of the dyno sheet you can post?

Atilla the Fun

With an HSR swap your cam and heads should give peak HP at 5500 rpm, and pull well through 6000.

Beater79TA

I'll have to look for the copy of the dyno sheet to get the exact AF ratio from the runs. From memory, it was almost right where the tuner wanted it to be across the band.

The cam was put in per Comps instructions since it is an off the shelf grind for TPI engines. The injectors are new Bosch type III 22lb/hr from FuelinjectorConnection with the fuel pressure set at 50 psi. I have a set of 30lb I could put in but I'd want to do it near the dyno to reset the tune. Based on the AF reading during the dyno run, I think I'm getting enough fuel though.

Another thought... could this be a MAF issue?

sccavette

I think he has another problem. I agree the HSR will allow him to gain a larger RPM range however the stock TPI should be going past 3700. I have a feeling his problem is elsewhere and a intake swap allowing more air is not going to fix it.

Beater79TA

Except the HSR won't fit under the hood on a GTA very well. I put one on my Camaro and had to buy a cowl hood for it. I have a Miniram from a recently acquired parts car that will likely get installed in the next couple of months though.

sccavette

MAF will do strange things however if the MAF is going nuts on the top end you should see it in the AF.

This may sound stupid BUT have you verified the throttle is going full open with the pedal? I have seen this many times.

sccavette

Couple other questions! What ignition are you running and what is the base timing set at?

What exhaust are you running, is the converter still on the car?

Beater79TA

I'll check the throttle to verify this. I'm almost positive the blades are opening all the way but I'll check it anyway.

Beater79TA

The tuner verified base timing was set correctly when he burned the new chip for it. I trust his work on this one since he's been specialized in tuning these since the capability became available.

The ignition is a MSD distributor with a MSD coil. There is not a CD box though.

The exhaust is Edelbrock TES headers (I know but they were on the car when we got it) with a 3 inch hi flow Magnaflow cat and 3 inch catback.

The car feels like it's still building power past 3700 but the dyno chart says otherwise. That's the odd thing. Even the tuner and dyno operator agree on that one.