Are the LT1 tachs off?
Thread Starter
Burning Brakes
Joined: Oct 2000
Posts: 1,183
Likes: 0
From: Tulsa OK
Are the LT1 tachs off?
I got a program from Shark ssn591 (thanks) that shows rpms and mph at different tire sizes, gear ratios, and trans. It is showing 75mph@1768rpm for 2.59s. The tach in my car shows 1950-2000rpm@75mph :confused:
BTW, for 3.07s the program shows 75mph@2105rpm.
BTW, for 3.07s the program shows 75mph@2105rpm.
Thread Starter
Burning Brakes
Joined: Oct 2000
Posts: 1,183
Likes: 0
From: Tulsa OK
Re: Are the LT1 tachs off? (93Polo)
Torque converter slippage tire sizes not exactly the same and other things can make the speed different.
Melting Slicks
Joined: Apr 2000
Posts: 3,198
Likes: 2
From: Northern CA
Re: Are the LT1 tachs off? (RichS)
If you can read the tach signal on the PCM or coil directly, that will be a much better judge of how inaccurate your tach is. If you are using vehicle speed to calculate things, you've introduced the tire size variable. Keep in mind that different tire brands/models will vary a bit in actual size...tread depth makes a difference, etc etc etc.
Direct comparison between PCM and tach is the best way.
Direct comparison between PCM and tach is the best way.
Le Mans Master
Joined: Apr 2001
Posts: 7,411
Likes: 253
From: Little Elm TX
Re: Are the LT1 tachs off? (JasonL)
At idle on the dyno it reads 750rpm (like it's suppose too), but the tach reads 1000rpm. They were shifting at 5500rpm and the tach was almost to 6000rpm. :rolleyes:
Thread Starter
Burning Brakes
Joined: Oct 2000
Posts: 1,183
Likes: 0
From: Tulsa OK
Re: Are the LT1 tachs off? (R94 LT 1)
At idle on the dyno it reads 750rpm (like it's suppose too), but the tach reads 1000rpm. They were shifting at 5500rpm and the tach was almost to 6000rpm. :rolleyes:
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Melting Slicks
Joined: Jan 2000
Posts: 3,418
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From: NW Chicago Suburbs
Re: Are the LT1 tachs off? (jay17)
The error is an offset, not a percentage error. If your tach is off by 500 RPM at 2000rpm, it'll be off by 500 RPM at 5500 RPM. The cause of this error is that GM has a big problem with getting the needle on correctly. It's not easy with the present system. The Flint plant looked at fixing the problem in the early 90's, but it was decided that nobody really cares. Would have cost ~$0.50 per car to fix this (another great decision by GM managment).
Eric
Eric
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Re: Are the LT1 tachs off? (jay17)
PURE JUNK. :mad