Tachometer accuracy? (My comparison)
Thread Starter
Melting Slicks
Joined: Oct 1999
Posts: 2,581
Likes: 14
From: Tolar Texas
Tachometer accuracy? (My comparison)
This is pretty trivial stuff but I thought someone might find it interesting.
While taking another look at my timing curve last night, I decided to record the Car Tach vs. Timing Light Tach data for comparison. Here are the results:
CAR tach vs. Timing Light tach
1000.............850
1500.............1350
2000.............1850
2500.............2300
3000.............2800
3500.............3300
It appears that the OE tach reads about 150 to 200 rpm higher than the timing light (+/- 1% accuracy claimed). I don't know if I trust either one too much. Based on my speedometers indicated road speed vs. tach readig, I think that the car tach is indeed reading high (~200 rpm).
While taking another look at my timing curve last night, I decided to record the Car Tach vs. Timing Light Tach data for comparison. Here are the results:
CAR tach vs. Timing Light tach
1000.............850
1500.............1350
2000.............1850
2500.............2300
3000.............2800
3500.............3300
It appears that the OE tach reads about 150 to 200 rpm higher than the timing light (+/- 1% accuracy claimed). I don't know if I trust either one too much. Based on my speedometers indicated road speed vs. tach readig, I think that the car tach is indeed reading high (~200 rpm).
Le Mans Master
Joined: May 2000
Posts: 6,493
Likes: 6
From: Bloomington MN
Cruise-In II Veteran
Re: Tachometer accuracy? (MIKER)
That is an electronic tach, correct? I am interested because I am putting a 75-77 tach in my 69 to work with the HEI. Is there a way to get them calibrated, or would an aftermarket electronic tach work better? I think the old cable driven tach was pretty accurate.
AC
AC
Thread Starter
Melting Slicks
Joined: Oct 1999
Posts: 2,581
Likes: 14
From: Tolar Texas
Re: Tachometer accuracy? (A C)
Yes, the car has an electronic tach. I suppose they could be calibrated but I'm not sure who (vendor) performs calibrations.
Being off a couple of hundred rpm probably isn't that big of a deal.
Loosely related, seems like someone posted a link to a product that added a "Memory" feature to stock tachs. After a hard run, you could push a button and the tach needle would point to the highest value it recorded on the last run. Kinda neat if you liked drag racing.
Being off a couple of hundred rpm probably isn't that big of a deal.
Loosely related, seems like someone posted a link to a product that added a "Memory" feature to stock tachs. After a hard run, you could push a button and the tach needle would point to the highest value it recorded on the last run. Kinda neat if you liked drag racing.
Race Director
Joined: Jan 2000
Posts: 13,014
Likes: 2,257
From: Corsicana, Tx
2020 C2 of the Year - Modified Winner
2020 Corvette of the Year (performance mods)
C2 of Year Winner (performance mods) 2019
2017 C2 of Year Finalist
Re: Tachometer accuracy? (MIKER)
Better than my rebuilt/calibrated mechanical one in my midyear. During chassis dyno testing I told them I was going to take it to 6800 rpm or so. It sure seemed like it took a LONG time to climb from 6000-6800 relatively speaking. Turns out 6700-6800 was actually 7500 according to the Dynojet tach!
Oops!!!
JIm
Oops!!!
JIm
Instructor
Joined: Jan 2000
Posts: 163
Likes: 0
From: Fullerton CA
Re: Tachometer accuracy? (427Hotrod)
My experience with the electronic tach was similar. I noticed that once I got the engine warmed up, the tach would slowly creep up, and end up indicating 200-300 RPM high, as compared to my calculated RPM at speed given the 3.07 rearend. Ensured that the clutch wasn't slipping, then decided to pull the tach, and replace the circuit board. Actually a pretty easy job (done it twice now. live & learn). Tach now agrees with MPH, as it should. Guess 20+ year old electronics finally had given up the ghost.
Tom
Tom
Melting Slicks
Joined: May 2001
Posts: 2,812
Likes: 4
From: Gig Harbor Wa
Re: Tachometer accuracy? (av8vito)
Abbot http://www.abbott-tach.com/era.htm makes an Electronic Ratio Adapter that wires in with your tach(I know it says it is for a speedo, but it works for the tach, too.) There are a bunch of dip switches that can be adjusted to correct any error in the signal.
[Modified by 70 LS1, 8:53 PM 6/24/2002]
[Modified by 70 LS1, 8:53 PM 6/24/2002]
