When I first got my car I could have swore it hit 97 mph at the top of third gear. Now it only does 92 MPH or so. I used the gear calculators and they all say that it should do 97 as well. What is going on here? The only thing I have changed is the mods in my sig. The performance still feels great and the clutch doesnt seem to be slipping at all but thats the best it will do now is 92.

 

id guess its the testpipes..maybe less backpressure..idk..doesnt make sense but thats the only mod that probably would do some difference in that direction...

 

i was thinking test pipes too... unless you have rims That aren't in your sig.

 

yeah very good thinking!

 

new rims will throw the speedo off....i'm guessing that if he has a SC and test pipes and other mods that he would have rims

 

The SC was on his s2k...not on his Z

 

My Z peaks at about 97-98 with 17's (03 stocks) but with 20's it barely hits 92

 

my bad, i need to read more

 

I dunno....it still pulls harder than when it was stock. Tetspipes shouldnt be making a difference
gearing is gearing.

Even with test pipe. exhaust, and Supercharger on my s2000 the top speed in each gear remained the same. Could anyone explain how this would be different in a Z?

 

RPM, transmission, final drive and tires....

I think you're just imagining things.

 

Did you gain some weight recently? That may account for the lower #s . . .

 

He probably filled up his windshield washer fluid.

 

it has nothing to do with the TPs, which rims do you have ??

T

 

dude havent you heard??? the newly designed testpipes bypass the transmission altogether and engage rocket power!!!

 

I thought I heard somewhere that bigger rims increase top speed but decrease acceleration, which makes sense. If this is true, then your rims should have nothing to do with it.

 

The mph you see on your speedometer isn't accurate. If you changed your wheels then it is wheel/tire setup.

When I had my G35 coupe 19's on my Z, I had a larger tire for the rear which made me trap 98mph in 3rd gear. Now, I have the 18's with the correct tires and i'm hitting 92-3mph in third.

It is definitely your wheel/tire setup.

 

bigger rims throw off the speedo all the time i believe. So if you are cruising at 80 according to the speedo you are probably going more like 83ish

 

First, you need to verify whether or not that the speed showing on your speedo is correct (I.e--someone next to you or passing by one of those speed radars) Tire wear will cost a bit of gearing but shouldnt be that drastic or a 5mph difference. Also, a lot of factory tachs read anywhere from 100-250 rpms higher for safety precaution, so the rpms you are actually at may not be the same as what the gear calculator is at. Make sure there is no tire slippage and the road conditions are sound as well. Also, if you are just barely hitting that certain rpms and then shifting it may have been going to hit that certain speed if it were "held" there, if that makes sense. There are also a few other things that can be throwing it off.

 

Actually, it should be the same with our cars because it works off the speed sensors. The only real difference would be if you have incorrect tire sizes with the aftermarket wheels. That will create + or - % of the stock tire/wheel combination which will affect mph in each gear.

 

98mph @ redline in 3rd gear. stock revup on stock 18s.