Accuracy of 69 tach - Team Camaro Tech
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post #1 of 10 (permalink) Old Jul 5th, 15, 08:12 PM Thread Starter
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Accuracy of 69 tach

I just discovered that my tach is reading 400 rpm's higher at 60 mph than the calculated rpm should be. I contacted the shop that just rebuilt my tach and they said it is within spec! Is this true? I used to flat shift my new 69z at 7200 at that the track,(back in 1970) if this is true, what was I really shifting at?

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post #2 of 10 (permalink) Old Jul 6th, 15, 05:21 AM
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Re: Accuracy of 69 tach

6,700? Still pretty high revving. Maybe that saved your engine.

I have noticed that my factory tach reads higher than actual. A couple of hundred at idle. I didn't think it was compounded at higher revs, will have to test it to see the difference.

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post #3 of 10 (permalink) Old Jul 6th, 15, 10:06 AM Thread Starter
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Re: Accuracy of 69 tach

I'd appreciate your feedback. I used a calculator based on gps and tire size to reference what rpm's I should be at. I thought this tach should be a little closer. By the way, I was told by the my engine builder to shift at 7200.......it was pretty scary but AAAwesome!

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post #4 of 10 (permalink) Old Jul 6th, 15, 10:28 AM
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Re: Accuracy of 69 tach

My '69 factory tach is dead on at idle. Not sure at 6k.
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post #5 of 10 (permalink) Old Jul 6th, 15, 10:47 AM
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Re: Accuracy of 69 tach

Back it the day (1970) with my Z I launched at 7200 and shifted 1st to 2nd at 8100

I had changed the pistons to 12:1 the cam to a sig erson, intake to edelbrock, headers

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post #6 of 10 (permalink) Old Jul 6th, 15, 02:32 PM
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Re: Accuracy of 69 tach

Quote:
Originally Posted by reelknots View Post
I'd appreciate your feedback. I used a calculator based on gps and tire size to reference what rpm's I should be at. I thought this tach should be a little closer. By the way, I was told by the my engine builder to shift at 7200.......it was pretty scary but AAAwesome!
I bet it was Aaawesome!! I'm too chicken now to try that much. I've had my engine up to 7k a few times and it does tend to excite a person.

Quote:
Originally Posted by Vega$69 View Post
Back it the day (1970) with my Z I launched at 7200 and shifted 1st to 2nd at 8100

I had changed the pistons to 12:1 the cam to a sig erson, intake to edelbrock, headers
How much below 7,200 did it initially drop? How much above 8,100 did it rev before you found 2nd gear? You must have had some really steep rear gears. Did you ever miss 2nd?

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post #7 of 10 (permalink) Old Jul 6th, 15, 04:17 PM
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Re: Accuracy of 69 tach

Mine reads about 100 rpm low at idle. The issue is that they will not keep up going down the track or wot, I did not notice it until I installed a shift light. I think it was at least 3-400 behind

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post #8 of 10 (permalink) Old Jul 6th, 15, 06:07 PM Thread Starter
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Re: Accuracy of 69 tach

Mine reads 100 high at idle, but 400 high at 60 mph. Should read 2700 but it's 31-3200! I can live with it now that I know how far it's off.

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post #9 of 10 (permalink) Old Jul 6th, 15, 08:17 PM
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Re: Accuracy of 69 tach

Quote:
Originally Posted by Andrew69 View Post
How much below 7,200 did it initially drop? How much above 8,100 did it rev before you found 2nd gear? You must have had some really steep rear gears. Did you ever miss 2nd?
These motors were made to Rev and I had built and re-balanced it.

Dump the Clutch and it would drop to maybe 6500. Climbed fast back to 8000 and I'd powershift into 2nd. About 7800 in 2nd then 3rd and 4th. At least that's the best I remember 45 years ago anyway.

Yeah I missed a shift once in a while. Didn't hurt the motor though

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post #10 of 10 (permalink) Old Jul 6th, 15, 09:10 PM Thread Starter
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Re: Accuracy of 69 tach

OK, Ok , enough reminiscing. I launched at 7200....sometimes missed 3rd but only hit low 12's at 120. Had slicks, hookers, lunati cam, 5:13 rear and a COOL CAN made from a large coffee can and copper tubing curled inside. Had to take a cooler full of ice to cool down the gas. Had a blast back then, now my biggest concern is matching rpm to mph!! Wow, what 45 years will do to your priorities.

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