I've got a problem and I don't really know where to start. I think my tach is off. It works, but I don't think it is accurate. I do have a 383 I built so I shift past 7000 rpm and top out the tach, but still it doesn't seem right...I have 3.73 gears, and in overdrive, to go 55 on a highway, it turns about 4000 rpm. I think it should be about 3400-3600 or so. How can the tach be off by a certain amount? Doesn't it drive off of the distributor? I don't understand how it can be working but off by an amount. Does the computer have any say in what it reads and my chip isn't programmed right? Maybe the tach is right and my overdrive isn't working but I doubt it. The torque converter is a B&M wholeshot 3200 stall with about 2000 miles on it (tranny too)....and I went down a highway at 40 or so and switched from overdrive to drive and it kicked up the rpm's whenit kicked out of overdrive...so I think that's working. Please let me know what you think! Thanks!!

 

is it a stock tach? if so, why? its probably highly inaccurate. just get an autometer tach, i have one and love it. as for the high rpm speed, is your speedo correct? is the gear corect? might be a 4.11

 

Yea, it is the stock tach...by the way...91 Z28...I also like the Autometer tachs but I don't like mounting the big tachs on the dash and stuff...I like the guages all in the guage cluster behind the wheel but then I'd have to do all of them which is 500-700 dollars all said and done...I know the gear is correct cuz I know the guy who owned the car before me (original owner) and all he did to it was put in 3.73 gears and the rest was stock when I bought it. When I put the engine and tranny in, I spun the rear tires while someone watched a mark on the driveshaft, and it was a 3.73...so we verified that...Why do you think the stock tach would be inaccurate? Wouldn't the Autometer one run off of the distributor the same way? Thanks for your help!!

 

anything stock wouldnt be as accuarate as an aftermarket. also, you can custom fab a tach to fit into the stock location, but you would lose the oil pressure gauge. there are also some little tachs about 2 1/4" wide you can hide under the dash by the center vents.

do you know if he changed the gear in the tranny that spins the speedometer? because 4k at 55 sounds like the speedo is slow or the tach is way off. i know a guy with a mustang with 4.10 gears and a 5 speed and he spins 4k at 70 mph.

 

My 92 z28 is all stock

the tach is horribly off.

It always has been, mostly a few thousand RPM off, but as I've driven for the past year, its gotten progressivly worse.

How bad? In 5th gear (its a manual) I redline at 50 MPH. A year ago it was 80...
Its practically useless.

Shift light still works though :P