Speed at WOT ?

[DarkAngel]

Hello

Just wondering,
I've drived my 'Z a little hard this week-end, and i remark that i could only reach 100mph on third at ~7000rpm

Refering to this table, it should be 120mph with stock 3.45 (at 7000 on third)

My car is totally stock (except B&B catback)

On this video (not from me), the guy reach also 100Mph and not 120
http://www.youtube.com/watch?v=E0Egyp4N-uA

My car works fine i think and it revs until 7000
but do i have to worry about something ?

Is 100MPH on third at 7000 normal or not enough ?

[BigJohn]

Tire Diameter would make a differance!!!

[XfireZ51]

Based on the chart and assuming your speedometer is correct, it looks like you have a 4.10 gear. I wouldn't be surprised by that since 4.10 gears are a popular upgrade for the ZR-1. Have you checked the accuracy of your speedo?

[DarkAngel]

the tires are same as stock
315/35/17 and the speedo is accurate (tested with GPS)
i don't know about gear ratio but i guess it has not been changed

[WVZR-1]

You don't mention the year of your Z either. If it's a '90 and has a tachometer error then yes you would be convinced that the Z has had a rear gear installed. Use a scanning tool and check the RPM's from the ALDL to confirm tach operation. All years could have the tach error but it's frequently found on the '90 and less frequently the '91.

I'm guessing that's your error situation!

Drive it with the scan tool attached and do the same or similar runs!

Check the rear axle ratio. It's discussed in this thread and I mentioned a couple different ways to calculate it and the latter using degrees or minutes of rotation was confirmed by the OP.

http://www.zr1.net/forum/showthread.php?t=21653

[We Gone]

http://www.youtube.com/watch?v=ktdywT5EsiQ

[DarkAngel]

Originally Posted by WVZR-1

You don't mention the year of your Z either. If it's a '90 and has a tachometer error then yes you would be convinced that the Z has had a rear gear installed. Use a scanning tool and check the RPM's from the ALDL to confirm tach operation. All years could have the tach error but it's frequently found on the '90 and less frequently the '91.

I'm guessing that's your error situation!

sorry, i forgot to mention the year
it's a '90 ZR1
but i've checked the speed with a GPS and it seems pretty accurate

i don't have all the history of the car but it has been kept for a long time in a private collection ; it has really few milleage (17000miles) so i would be surprised that the gear ration would have been changed

[WVZR-1]

Originally Posted by We Gone

http://www.youtube.com/watch?v=ktdywT5EsiQ

Had he understood what exactly what he was doing he had it solved with his "first" drive-shaft rotation. With a locking differential the one tire revolution and counting the pinion rotations is used most frequently. While rotating the drive-shaft if a person is doing it by himself you have to do the crawl a couple times. Marking the pinion deflector and using the degrees or minutes it can be done by one person with just a reach under for the marking of the pinion deflector.

[WVZR-1]

Originally Posted by DarkAngel

sorry, i forgot to mention the year
it's a '90 ZR1
but i've checked the speed with a GPS and it seems pretty accurate

i don't have all the history of the car but it has been kept for a long time in a private collection ; it has really few milleage (17000miles) so i would be surprised that the gear ration would have been changed

I'll wager the "tach error" !

I have never used the C68 display to check for tach error but I would guess it could be done. Drive at a known display on the C68 and see what the tach displays. Will that work? I would think but I've never tried.

I believe you would do X 25 for the C68 display in 6 for RPM's. A C68 display of 80 would be 2000, 120 would be 3000, 160 would be 4000. I believe that's correct. I'd appreciate knowing.

Access is shown in the C68 section of the FSM but I believe you just depress fan up/down (same time) to access the display, fan up or down until you get to 6 and then press the "auto" button for the display of that parameter.

[We Gone]

When I bought the 90 ZR-1 I had I got a great deal on it as the owner thought it had serious issues with the motor due to lack of power. Only problem the tach was just over 2k rpms off....