Hand-Held Tachometer recommendation needed. - Hot Rod Forum : Hotrodders Bulletin Board
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Old 01-16-2010, 05:46 AM
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Hand-Held Tachometer recommendation needed.

I am trying to set the ignition on a GM HT 502 crate motor that is in my 69 Corvette. The motor manual recommends setting the ignition timing to 4 degrees BTDC at 650 rpm. The tach in the car is 30 years old and unreliable.

What is a good brand of Hand-Held Tachometer?
I've never used one. How do I use one?

Thanks
~R

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Old 01-16-2010, 06:55 AM
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Sounds to me it's a good excuse to buy a brand new tachometer! Let face it,
you can put the money you spend on a hand held on a new tach AND end up with a reliable tach. JMHO.
I hope no one try's to talk you into more initial timing like I would because being from California you still have to pass emissions testing. Right? Or are you exempt because of the year of the vette?

Last edited by sqzbox; 01-16-2010 at 07:01 AM.
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Old 01-16-2010, 08:52 AM
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The problem with a hand held tach is, holding it makes it harder to shift and steer.
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Old 01-16-2010, 08:56 AM
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Quote:
Originally Posted by sqzbox
Sounds to me it's a good excuse to buy a brand new tachometer! Let face it,
you can put the money you spend on a hand held on a new tach AND end up with a reliable tach. JMHO.
I hope no one try's to talk you into more initial timing like I would because being from California you still have to pass emissions testing. Right? Or are you exempt because of the year of the vette?
No.. this has nothing to do with the day after payday tool buying itch
Yes, pre 1975 cars are smog exempt.

Seriously.. even if I buy a new tach, I've been told that it may not be accurate because the tach is not calibrated for the motor. It's an after market motor. Is this correct?
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Old 01-16-2010, 12:19 PM
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No, not with electric. Might be if it's a mechanical gear drive but I'm not familiar with those. There's nothing special about a 502 crate engine but maybe the ignition. What kind of dist. do you have?
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Old 01-16-2010, 02:29 PM
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I believe 69 Vettes have mechanical gear driven tachs.

The dist I am running is HEI Billet Distributor with melonized steel gears (P/N 93440806)

Last edited by rajsid; 01-17-2010 at 08:47 AM.
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Old 01-16-2010, 05:31 PM
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timing

Many timing lights have tach on them.What was the recommended timing on the crate motor,5btdc may be a little soft depending on the cam and other specs.
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Old 01-16-2010, 08:56 PM
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Quote:
Originally Posted by SDLuck
What was the recommended timing on the crate motor,5btdc may be a little soft depending on the cam and other specs.
From HERE:

Start the engine and adjust the initial timing. If using the HEI distributor P/N 93440806, set the ignition timing to 4 before top dead center (BTDC) at 650 rpm with the vacuum advance line to the distributor disconnected and plugged.

This setting will produce 26 of total advance at wide-open throttle (WOT) when using the HEI distributor P/N 93440806.

The HEI vacuum advance canister should remain disconnected. This engine is designed to operate using only the internal centrifugal advance to achieve the correct timing curve.

That's what I'd call a TRUCK timing curve!

In a passenger car, this can be ignored. I'd run a performance-type curve w/the vacuum advance working.

Cam specs:

--Camshaft: Hydraulic roller tappet
--Lift: .480" intake, .483" exhaust
--Duration: 204 intake, 209 exhaust @ .050" tappet lift
--Centerline: 118 ATDC intake, 118 (BTDC exhaust)

FWIW, mechanical tachs were used prior to the HEI, IIRC- about '74-back.
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Old 01-17-2010, 07:42 AM
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The new vs. old engine is not the critical question; its the type of ignition.

If the distributor has connectors on the cap that are like a stock GM HEI, you can buy a pigtail for the tach connection from Pace, Jegs, etc. Just splice it on to the tach signal wire and connect it to the tach. Then add power, ground and lights, and you will have a working tach. The tach measures ignition pulses, so you do have to set it for 4, 6, or 8 cylinders.

If you are using a special ignition module, you also need to check the documentation to verify that it puts out a standard tach pulse that will drive a stock design tach. Some will not work with a standard tach.

Bruce
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Old 01-17-2010, 08:48 AM
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Thanks all..
I have a GM HEI. I am going to make the stock tach work properly before attempting to reset the timing.
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