90MPH 3K RPM?

[paxton350]

I cant seem to change my sig, but my new setup is an automatic 94 z28 with new motor and rebuilt tranny. On the highway im cruising anywhere from 70mph to 90 mph ( im in florida) and im in overdrive but the RPMs are at 3k and the exhaust sounds good but seems a little excessive for only 90mph. Im used to a manual which in 6th gear i used to be at 1500rpm so im not sure if theres something i should adjust or if this is normal. torque converter is stock , exhaust is pacesetter headers to single 3" exhaust to dual out flowmaster. rearend is stock and we just did a BMR suspension 1inch drop.
I think i shoulda stuck with my old 6 speed lol

[Joe 1320]

I cant seem to change my sig, but my new setup is an automatic 94 z28 with new motor and rebuilt tranny. On the highway im cruising anywhere from 70mph to 90 mph ( im in florida) and im in overdrive but the RPMs are at 3k and the exhaust sounds good but seems a little excessive for only 90mph. Im used to a manual which in 6th gear i used to be at 1500rpm so im not sure if theres something i should adjust or if this is normal. torque converter is stock , exhaust is pacesetter headers to single 3" exhaust to dual out flowmaster. rearend is stock and we just did a BMR suspension 1inch drop.
I think i shoulda stuck with my old 6 speed lol

First, the signature can be changed via the "quick links" to the right in the same toolbar.

next, Auto trans cars will rpm quite a bit higher than a 6 speed which contains a double overdrive. Compound that with the flowmaster that tends to develop a big resonance above 1800 rpm to the 3000 rpm range and you get what you've got. As a comparison, my ws6 had 3.73 gears, headers and a 4" mufflex system with the flowmaster. Cruising at highway speed could get brutal. Below 1800 it was great, perfect for a stock geared 6 speed car. Cruise rpms would be well below that rpm threshold and no resonance.

To get rid of the resonance, I think you'll need to change out the flowmaster.

[Rob B (shoebox)]

Sounds like you might have 3.73s. 3000RPM in 4th gear would be 88 MPH.
Stock 3.23s with an auto would be 101MPH.

[ConElite]

At about 2800rpms im doing 120+mph. (I checked)


What gearing do you have. Yeah 3000 seems excessive but could be your stall, and gears. I drove my buddies 49 Chevy (Gray car)with a SBC and a 3800 stall w/ like 4.11 gearsnand I mean that thing was insane loud at 60mph but it was only a 3 speed.
Took a little getting used to but I managed.

[paxton350]

thanks joe ill change my sig i usually went to user cp.. Im under the assumption that the gearing on the rearend is stock, however i got the car a 94 camaro z28 with a rebuilt auto tranny and a knocking lt1. since then i replaced the motor and did the suspension/exhaust however im under the assumption the rearend is stock, is there a way to check without pulling it apart (rearend)? The invoice says they did a "shift kit" in it too but i dont think that would affect highway driving like that right? I mean im dead on 3k at 85-90mph in overdrive.

[ConElite]

So do you still have the 4l60e trans in there?

[Rob B (shoebox)]

thanks joe ill change my sig i usually went to user cp.. Im under the assumption that the gearing on the rearend is stock, however i got the car a 94 camaro z28 with a rebuilt auto tranny and a knocking lt1. since then i replaced the motor and did the suspension/exhaust however im under the assumption the rearend is stock, is there a way to check without pulling it apart (rearend)? The invoice says they did a "shift kit" in it too but i dont think that would affect highway driving like that right? I mean im dead on 3k at 85-90mph in overdrive.

It ain't stock if that is what you are getting (or you have some serious slip happening). The highest gears an auto would have had is 3.23s and I already gave you the RPMs and speed for those.
I am assuming you are running some close to stock diameter tires.

Check for yourself: http://www.f-body.org/gears/

Jack up the rear of the car, rotate the wheel one turn and count the number of turns the driveshaft makes. 3.75 turns would be ~3.73s. 3.25 turns would be ~3.23s.

[Injuneer]

My own gear calculator, set up specifically for the 4L60/60E shows that with 3.73 gears, and a tire ranging from 25.6-26.0" you would be turning 3,000rpm somewhere between 88-90 MPH. The stock tach does typically read 100-200rpm higher than actual engine RPM, so you get more accurate results if you read the RPM directly off the PCM with a scanner.