My tach is off... any fixes?
Thread Starter
Joined: Apr 2006
Posts: 3,910
Likes: 1,158
From: Grand Rapids, Michigan
My tach is off... any fixes? I swapped to 4.10 gears today and haven't reprogrammed my speedometer yet, but I was attempting to guesstimate my MPH through my RPM using f-body.org's gear calculator. I drove past one of those portable radar trailers and my RPM is off by 3-400 rpm, as in it reads 3-400 rpm higher than it really is. I've heard the stock tach is off, but I didn't think by that much. I've been shifting at the track at 6000 RPM, but if it's off that much, I should be shifting closer to 6400. I don't really want to put an aftermarket tach in my car to fix the issue. Does anyone have any experience with this, and if so, what did you do to fix the problem? Also, should I alter my shift points? I heard the rev limiter is set at 6200, so trying to shift higher probably wouldn't work, if the PCM is reading the same values as I am seeing on the tach.
At least it's off in the better direction. Being 3-400 rpm higher than actual rpm is better than being 3-400 lower when your trying to shift at 6200 rpm 
From what I gather the fbody tach in general is not very accurate.
From what I gather the fbody tach in general is not very accurate.
I'm suprised its off that way as well. Usually the tach in the dash is unable to keep up with accelerating engine speeds. I hit the rev limiter once....at like 6k....limiter set at 6500.
TECH Enthusiast
Joined: Oct 2004
Posts: 578
Likes: 0
From: Lincoln, Ne
Originally Posted by Zymosis
I'm suprised its off that way as well. Usually the tach in the dash is unable to keep up with accelerating engine speeds. I hit the rev limiter once....at like 6k....limiter set at 6500.
get a shift light....I always thought our tachs were slow(I know i've hit the rev limiter in 1st when the tach read 5500rpms...hence why i got a shift light..in the ac vent..hidden)..not off. cause I know cruising on the highway and at idle..mine is nearly perfect.
Trending Topics
I've actually got pretty good at shifting by sound. The GMMG makes that a bit easier. I never liked looking down when accelerating hard. I prefer looking at the road. The shift light would probably be a great idea. At least you can see that out of the corner of your eye if mounted in the vent opeining.
LS1 Tech Stories
The Best V8 Stories One Small Block at Time
Gas Monkey Built a 6-Wheel Ferrari Testarossa With a Corvette LT4 Engine
Verdad Gallardo
7 Most Reliable High-Performance Engines GM Has Ever Built
Verdad Gallardo
Amazing '71 Camaro Restomod Is Modern Muscle Car Under the Skin
Verdad Gallardo
6 Common C5 Corvette Failures and What's Involved In Repairing Them
Pouria Savadkouei
Retro Modern Bandit Pontiac Trans AM Comes With Burt Reynolds' Autograph
Verdad Gallardo
Top 10 Greatest Cadillac V Series Performance Models Ever, Ranked
Pouria Savadkouei
Top 10 Most Powerful Chevy Trucks Ever Made!
Hennessey's New Supercharged Silverado ZR2 Has 700 HP
Verdad Gallardo
Coachbuilt N2A Anteros Is an LS2-Powered C6 Corvette In Italian Clothes
Verdad Gallardo
Originally Posted by Mike02Z
I've actually got pretty good at shifting by sound. The GMMG makes that a bit easier. I never liked looking down when accelerating hard. I prefer looking at the road. The shift light would probably be a great idea. At least you can see that out of the corner of your eye if mounted in the vent opeining.