Tachometer accuracy
Thread Starter
Team Owner
Joined: Sep 2003
Posts: 25,393
Likes: 2,741
Tachometer accuracy
Just checked cluster against a GM Tech1 for gauge validation and it seems the analog cluster tach is about 30% high! When using the analog readings on the cluster vs mph it can give some unusual rear axle ratio values. I assumed the car I bought was stock with a 3.45 but when using tach values and mph from cluster it appeared to have possibly a 4.09 or so gear. Using the Tech1 values it indeed appears to be "unfortunately" a 3.45!
I had done a couple measured miles to confirm the odometer and they were on the button. Now I'm back to shopping for the 4.09 or maybe just a 3.73 or so rear.
Here's a link to some very interesting calcuator programs:
http://www.angelfire.com/fl/procrastination/rear.html
I had done a couple measured miles to confirm the odometer and they were on the button. Now I'm back to shopping for the 4.09 or maybe just a 3.73 or so rear.
Here's a link to some very interesting calcuator programs:
http://www.angelfire.com/fl/procrastination/rear.html
Instructor
Joined: Jun 2001
Posts: 151
Likes: 0
From: wilm de
Tach acuracy
I discovered this many years ago and posted the answer in the old Legend. While on a trip with Ray Raskin to Summit point we discovered my tach was off at 80 mph compared to his. After talking with Jerry Watts at the Corvette Action Center he put me in touch with a orvette engineer at BG. The specs for the Tach, he told me is +/- 250 from the actual readout as the tach is like a printer. I then checked my findings and the tach was 250 rpms high at all readings on the odometer. I was going to swap out the tach, but deceided not too as it could have resulted in a rattle or whatever which I did not have then. Hope this helps. Garth
Thread Starter
Team Owner
Joined: Sep 2003
Posts: 25,393
Likes: 2,741
Garth,
Summit Point is right around the corner and I used to live about 2 miles down the road from them. Did a good many Caprices and Impalas for the driving school there! They were quite tough on the sheetmetal! I've not been there for a good # of years. Forgot the real equipment was the older Malibu's.
Back to the tach! This seems to be a percentage variance similar to what you would get with a speedometer gear mismatch. If it were an engine with a distributor, a tach filter might correct it. The car has a prom of "someones" in it with a few mods and I don't know if it could be related to the "tune" or not. I spoke to a cluster rebuilder today and + or - 5 to 10% seems to be acceptable.
I've got a new service prom and thought I'd maybe try it first or maybe post in the tuners forum and see if it could be related! Any ideas or suggestions would be appreciated!
Dave
Summit Point is right around the corner and I used to live about 2 miles down the road from them. Did a good many Caprices and Impalas for the driving school there! They were quite tough on the sheetmetal! I've not been there for a good # of years. Forgot the real equipment was the older Malibu's.
Back to the tach! This seems to be a percentage variance similar to what you would get with a speedometer gear mismatch. If it were an engine with a distributor, a tach filter might correct it. The car has a prom of "someones" in it with a few mods and I don't know if it could be related to the "tune" or not. I spoke to a cluster rebuilder today and + or - 5 to 10% seems to be acceptable.
I've got a new service prom and thought I'd maybe try it first or maybe post in the tuners forum and see if it could be related! Any ideas or suggestions would be appreciated!
Dave
Last edited by WVZR-1; Sep 7, 2004 at 09:04 PM.
Melting Slicks
Joined: Jun 2001
Posts: 3,031
Likes: 1
From: Republic of Texas
Originally Posted by drmcar
I discovered this many years ago and posted the answer in the old Legend. While on a trip with Ray Raskin to Summit point we discovered my tach was off at 80 mph compared to his. After talking with Jerry Watts at the Corvette Action Center he put me in touch with a orvette engineer at BG. The specs for the Tach, he told me is +/- 250 from the actual readout as the tach is like a printer. I then checked my findings and the tach was 250 rpms high at all readings on the odometer. I was going to swap out the tach, but deceided not too as it could have resulted in a rattle or whatever which I did not have then. Hope this helps. Garth
