mods are "89 corvette motor changed to carbed,650cc holley carb,1.5 roller rockers,zz4 cam,new eldebrock intake,corvette aluminum D port heads, not sure if exhaust matters but shorties into 3inch all the way out the back, i have this in a firebird that was a 305 so the tach shows the car redlining at 5k, and thats what i shift it at should i be shifting higher or not. i know L98s don't rev very high that why i am asking thanks.

 

You don't have a "L98" any more. You have a L98 long block, with a whole other induction system on it. Not the same beast at all.

The thing that makes the L98 a low-RPM, low HP motor is the TPI. You don't have TPI any more. There's nothing about a 350 in general, or the L98 long block in particular, that inherently makes it a low RPM setup, except for the TPI.

Best thing to do is to take it to the chassis dyno, and find out what your torque curve is. Typically you'll want to shift it at near the peak HP RPM, such that it is then at the peak torque RPM when it hits the next gear. Until you know what those RPMs are, anything anybody tells you is nothing but a guess.

My "best guess", based on your description of your combo, would be that you'll want to shift at around 5300-5400, and it should end up at around 3800 in the next gear. 1st to 2nd you might have to let go slightly higher, because of the excessive difference between those 2 ratios.

Factory tachs in these cars are notoriously inaccurate. They tend to read high when they fail. It is rare to find an accurate one. They tend to read high by a percentage; say, 20% or something, that means that the tach reading is always 20% higher than actual, and NOT 1000 RPM high or the like (as people always like to describe, incorrectly). Check that while you're on the dyno.

 

aaahh thanks for the info thats just what i needed to hear, now as for the dyno were not talking about a 800$ dyno more like a 150$ one? because i don't have the money for that at the moment. my tranny is an auto(out of the corvette as well) and i have a lot done to it other than shift kit, if i leave it in drive it will shift at about 5k or 5100 tires chirp and then it will shift at 4500k in second.

 

Last time I ran my car on the dyno, it was $75 for 3 pulls. That seems to be near about the going rate.

Some places do it by the hour; $120/hr or some such.

If you plan on doing any tuning (timing, jetting, etc.) try to get the hourly rate. Take your tuning parts like jets or whatever with you, and every tool you could possibly need (it really SUCKS to watch a $120/hr meter running while some goob is running around trying to find a screwdriver for you). Plan on 2 hrs. If all you want it so see what you've got, the 3-pull deal is probably adequate.

 

Your combo is pretty close to a ZZ4 crate motor. The only real difference is that chevy used 1 3/4 headers, 750 cfm carb and Edelbrock RPM Air Gap intake to reach their numbers. In your case, I'd let the intake powerband be my guide to the proper shift point. The dyno is preferable, but if you don't have the money for it, the intake powerband is a good guide. Shift at the intakes max RPM for conservative driving and about 500 RPM's over that for a more aggressive shift.

 

find yourself an nice open highway, drop it in second and give it to the floor, when you FEEL the car stop pulling hard, take note of the RPM.. drop off about 100rpm and there you have it.. you want to shift right before the power dies.. dont forget to shift into third.. if you know someone with a G-tech, that would be great.. shift a couple 100 rpms over your peak.. you dont wanna shift right at your peak power.. because you still have alot of power on the other side of the curve.. thats how i do it.. all in the butt dyno.. no shift lights, just my ***.. haha

 

5678TA has some good advice for a more aggressive shift pattern. Just remember that aggressive shifting will increase the wear and tear on your parts if it's done frequently. This becomes especially dangerous on unbalanced rotating assemblies turning 6000 rpm or more. There isn't more power on the other side of your peak hp figure as suggested. The benefit comes from being deeper in your power curve in the gear your vehicle has just shifted into. Some pro racer's with high quality engines will actually shift 1000-1500 rpm's above their peak power output.