Speed at WOT ?

[Hog]

Originally Posted by WVZR-1

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.

OR simply put the tape marker on the inside of the tire.

[WVZR-1]

Originally Posted by Hog

OR simply put the tape marker on the inside of the tire.

Yep!!!

[LancePearson]

Watching the videos it seems to me that the speed each gear runs up to 7-8000 rpms is faster than a 3:45 rear end. I relate since I also have a 2008 TBSS with LS2 that came from GM Performance group with a 4:10 rear end so I have a direct comparison of two over 400 hp engines and a 3:45 and 4:10 rear end. I'd guess you have a 4:10 rear end in the Z from watching the videos of the one that gets to 100 mph in third gear. I get to 125 mph in third gear in my stock 1991 Z with 3:45 rear end. Speed to get through each gear seems more like a 4:10. Check it.

[XfireZ51]

Originally Posted by LancePearson

Watching the videos it seems to me that the speed each gear runs up to 7-8000 rpms is faster than a 3:45 rear end. I relate since I also have a 2008 TBSS with LS2 that came from GM Performance group with a 4:10 rear end so I have a direct comparison of two over 400 hp engines and a 3:45 and 4:10 rear end. I'd guess you have a 4:10 rear end in the Z from watching the videos of the one that gets to 100 mph in third gear. I get to 125 mph in third gear in my stock 1991 Z with 3:45 rear end. Speed to get through each gear seems more like a 4:10. Check it.

w my 3.45s and 17" wheels, I would got through the traps in 3rd gear at ~7000rpm with a trap speed of 118 or so.

[Paul Workman]

My money is on the voltage divider on the cluster board. The divider that biases the op amp for the tach is printed on a ceramic substrate. It is exposed to the air, and over time deteriorates.

By comparing the analog tach reading to the the digital rpm value on a scanner connected to the ALDL, it is easy to determine if the tach is reading correctly.

It is my understanding that over time and exposure to air, the resistance value changes, resulting in the analog tach reading to creap up. (Mine was reading well off the scale when it was at only 7000 rpm.)

Check that first. If tach calibration is the issue, "there is an app for that!"





P.

[XfireZ51]

Originally Posted by Paul Workman

... By comparing the analog tach reading to the the digital rpm value on a scanner connected to the ALDL, it is easy to determine if the tach is reading correctly...

The ALDL datastream has a tach ceiling of 6300rpm which is the limit of the L98
datastream. Granted the rpms change rapidly at that point, but if you want to check tach error v the datastream, do it at a point below 6300rpm. There is raw data for rpms which can be output with a change in the ALDL datastream, but you will need to convert that to rpm.

[WVZR-1]

Originally Posted by XfireZ51

The ALDL datastream has a tach ceiling of 6300rpm which is the limit of the L98
datastream. Granted the rpms change rapidly at that point, but if you want to check tach error v the datastream, do it at a point below 6300rpm. There is raw data for rpms which can be output with a change in the ALDL datastream, but you will need to convert that to rpm.

There is "nothing" that needs to be checked in excess of 6300 RPM - if it's an issue with the tach the display from the scanner will document it in the complete RPM range. It's NOT as complicated as you seem to imply, there is either a tach error there is NOT.

I would guess that likely 95% of the '90 cars if checked likely have an issue OR they've been corrected. How many are aware? Who knows.

[mike100]

stock rev limiter is 7100 rpm. I would suggest revving it until 7100 rpm and then the ecm will cut the ignition. Compare tach reading to known actual rev limit of 7100 rpm.

[WVZR-1]

Originally Posted by mike100

stock rev limiter is 7100 rpm. I would suggest revving it until 7100 rpm and then the ecm will cut the ignition. Compare tach reading to known actual rev limit of 7100 rpm.

There's no need to do that. That would seem to be abuse that isn't required!

[DarkAngel]

Thank you everyone for all your quick answers

for tach limiter, i have a chip so i don't know if i still have the rev limit at 7100
furthermore, i don't really want to hit the rev limit :-S