I recently bought my 1990 Iroc Z L98 G92 with 79,000 miles for $1200. I replaced the front calipers, pads, brake hoses, front sway bar endlinks, 1 fog light bulb, belt and battery to pass inspection. I tagged it and took it to the track to see what it would run in the 1/4 mile. I shifted it manually even though it's an automatic. I shifted the car around 5500 not wanting to be too hard on it, but the car did not change gears until the tach read well above 7000 rpms for every gear change. I was a little concerned but kept it on the floor anyway because the track was busy and you only get so many runs. I was wondering what rpm it should be shifting at. I think the tach may be wrong. It reads correctly at idle and does not do anything erradict. The car seems to run fine but if it's on the floor it won't shift until the tach is buried over 7000 even in drive or overdrive. The car ran 14.218 at 97.9 mph street tires with some wheel spin.

 

your tach is reading wrong, it's a common problem on the 90-92 clusters, easy fix and cheap if you know how to solder

https://www.thirdgen.org/forums/elec...meter-fix.html

 

Thanks for the info. How hard is it to get the gauge cluster out? I'm pretty sure my oil pressure gauge is not reading correctly either. I may go with aftermarket.

 

I agree....tach is for sure off....very common....tpi intakes will not flow that rpm...and you 1/4 times seem about right.

 

I read the thread on the tach fix, very helpful, sounds easy and cheap enough I'll have to try it before adding another tach. What kind of rpms should my tpi flow? I believe my Iroc is 100% stock. I never got to talk to the previous owner. I bought it from an estate. I run a small block 350 with a 350thm trans in a Nova with 3.73 rear and the tachometer rpms in drive are about the same as the Iroc Z in overdrive at the same speed. Thats what lead me to believe the tach is wrong. Can I race the Iroc in drive or overdrive or am I better off shifting as far as times go? I prefer shifting the car on the street and I've never tried anything but shifting at the track.

 

a tpi makes great low end power, and really starts dying off early. I'd say you're just about pooped out of power 4500 or 5000 rpm. If your car will shift by itself just leaving it in drive somewhere in that range, I would just leave it in drive. It doesn't matter if you use overdrive or not....the car will not shift into overdrive unless you let off the gas and cruise. Also, top speed of car is done in third gear...the 700r4 can not (in stock trim) run wide open in overdrive it will keep shifting back into third...high speed in overdrive has to be done at part throttle, but doesn't matter at drag strip anyway cause you won't hit fourth gear....just a tid bit of info.