Dist vs Gen Tachometer

[Bob S.]

I am changing my '59 to an alternator and will need to change the tach drive to the distributor. What changes, if any, will I need to make to my tachometer? I have heard there is a difference in drive speed. If that is the case, where is the best place to have my tach modified?
Thanks, Sully

[William C.]

Re: Dist vs Gen Tachometer

I don't think you can get the tach modified, but might be able to use the "guts" for a FI tach with your face.

[Bob S.]

Re: Dist vs Gen Tachometer

William, do you know what the difference is? I seem to recall seeing somewhere that one turns at twice the speed of the other but I have no idea if that is correct and if so, which one is the fastest.
Years ago "a friend" had a reducer in his speedometer cable just after the cruise control that cut his odometer reading in half. It was very similar to the tach / speedometer 90 degree adapter that is available from CC and Paragon. If someone knows the relationship an adapter might be made to put in line with the cable at one end or the other. Sully

[William C.]

Re: Dist vs Gen Tachometer

Fi reads twice cable speed, generator driven reads cable speed.

[Tom P.]

Re: Dist vs Gen Tachometer

Not all FI's had a tach drive distributor. Only the solid lifter FI engines got a tach drive distributor.

[Stewart A.]

Re: Dist vs Gen Tachometer

Why change to an alternator. Are you doing a resto mod ? Stewy

[John D.]

Re: Dist vs Gen Tachometer

Not all FI's had a tach drive distributor. Only the solid lifter FI engines got a tach drive distributor.

Tom, You are almost right in your answer. Solid lifter engines in 57 FI cars puts a wrench into your statement. The 889, 905 distributors were typically used with solid lifters.Tach ran off generator.

Solution to the tach problem though is nice Sun Tach mounted on the steering column like the old days. God I miss those. If you didn't have that tach on the column you weren't with it. JD

[Mark P.]

Re: Dist vs Gen Tachometer

If you are not planning to have the car judged you can also buy a electronic tach that is a reproduction of the tach you have and swap it out.

I got mine here and it looks and works well. They run $340.

http://www.corvetteinstruments.com/catalog/53_62parts.htm

[Bob S.]

Re: Dist vs Gen Tachometer

Thanks Mark. That looks like the best solution. I am adding air conditioning so my wife will go with me to see the kids in summer. She likes the top up for the 3 hour drive to Fort Worth so it doesn't blow the hair. (I don't have any left so no problem here.)
The air pulls 30 amps by itself, hence, the alternator. Obviously, with air my plan is no NCRS judging but I still want to keep the original look wherever possible. I am using the Power-Gen alternator which looks like the original generator but won't accept the tach drive. Sully

[Dan H.]

Re: Dist vs Gen Tachometer

I had a gen. drive tach recalibrated years ago to the dist drive ratio, believe Corvette Specialies of Maryland did it. I think any speedo/tach repair place can set it to what ever ratio you need.
Dan