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VDO Tachometer

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I'm fitting a 52mm VDO Vision tacho to my V8 and I'm getting some conflicting advice.

It's regarding the 3 coding switches at the rear of the tacho. These are to trim the tacho for 4, 6, or 8 cylinders.

Now I originally misplaced my fitting instructions within the hovel that passes as my garage. I called John at ETB Instruments to find out what position these switches need to be in for the V8. John very kindly replied to me saying that they all needed to be "on". Fair enough.

However today I happened upon the fitting instructions and according to them it should be 1=on 2=on 3=off.

What to do? Does anyone happen to have a VDO tacho in their V8?

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How are you driving it - from the alternator or from an ignition pulse?

The dip switches are for the ignition pulse (LT side of coil, EDIS module etc) - and this shouldn't need adjusting.

The adjuster wotsit is for if you are driving it from the W terminal on an alternator (eg. on a diesel where there's no coil) - as the pulley sizes for different cars vary, the alternator spins at a different speed, so you have to calibrate the alternator pulse to get the rev counter to read reasonably accurately..

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I just bought one of these, it arrived in a few days. Fitted a tacho today, stuck the reflective tape (x 2) on the crank pulley and fired the laser - ping - instant reading which, when divided by 2, gave me the correct rpm to set the tacho to. (EDIT: Well I assume its the correct rpm!)

Thoroughly recommend it.

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idle between 750 to 850rpm, max revs [no load/not moving] 3850rpm.

Cheers Ralph - it was 760 RPM and a slight increase when warmed up. Useful tool for £10 and will give my 7 year old a heap of fun figuring out rpm's on various things from his bike wheels to the blades of his RC helicopter!

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