Thread: Adapt-a-tach

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In another thread Imentioned the cost of instrumentation in a modern rod. I am just thinking out loud because in recent trips to a local junk yard I noticed a LOT of nice instrument clusters in late models (junked) which have built-in tachs in an attractive compact layout. I mention in particular the new Saturn, the Ford Ranger, several Buick models etc. Interestingly another note from an up-to-date junkyard is that there are not many V8s in there anymore, mostly V6 and 4-cyl cars! Thus the question is has anyone adapted a digital tach from a late model V6 or 4-cy to a V8? If the unit requires pulses from a digital electronics unit there should be some way to just count the pulses differently and that should be easiest for doubling/halving the pulse count of a 4-cyl engine adapted to a V8 engine. There are many ways to look at this. On the one hand a billet Deuce panel or a reproduction Auburn panel may hold nostalgia for some and indeed look better than just mounting aftermarket gauges in simple holes in a fiberglass dash, but on the other hand if you go back to great looking cars like the AMBR No.1 and other early rods you see innovations based on parts available at that time. Should we not look for innovation/adaptation using modern parts. Of course the main problem may be the speedometer instead of the tach in that the speedometer needs to be corrected to whatever rear ration is being used. Anyway I recall a few Internet sites showing how to retrofit the instrument cluster from a LeBaron with a Tach to another LeBaron which came without a tach. Can that be done only in special cases where the models match closely or are there some cases of a near universal good looking instrument clusters that can be adapted using just the gears in the speedometer cable for a different ratio? Just asking, but when you get a chance peek in through the window of late models and note how many of them have great looking instrument clusters which include tachometers. Anybody adapted one yet?

Don Shillady
Retired Scientis/teen rodder

Well I went back and read a lot of old threads on gauges and tachometers and learned a bit. I did learn that dual point distributors use the setting for a four cylinder engine. That means that commercial tachs have internal circuitry to handle the option of 4, 6 or 8 cyl engines and it should be possible to rig cheap digital logic chips from Radio Shack to convert modern junk instrument clusters (only $20 here) to attractive instrument clusters. The remaining problem is to correct the speedometer but that may not lead to optional gears in all cases so I guess unless someone has a better idea or I figure one out before I cut out the holes in the dash (this winter), I will study the ads in Street Rodder and look over the cheaper gauges at Advanced Auto and the Whitney catalog.

Don Shillady
Retired Scientist/teen rodder

Dual points use 4 cyl. setting? I have a mallory dual point in my mustang and the sun tach is on 8 for the 302, seems accurate. I dunno...

Don
The newer Sun tachs have an rc circuit for the trigger input. I'm in the process of tracing the schematic out on a Sun Super II in an effort to adapt it's circuit board to an older Sun tach. The Super II has an 8 grand sweep whereas the older tach is 9 grand.

About 10 years ago I took a short course in digital electronics and used that info in designing and maintaining some home-built lab equipment. The chips are cheap at Radio Shack and can be simple after you breadboard a few test circuits. I just had the idea that one might be able to use one of the many modern instrument panels from the junkyard that are good looking and rig up a few simple circuits to use the widely available in-dash tachs. Of course one of the problems is adapting the speedometer to a hybrid drivetrain and a change of rear ratio different from the donor car. What I have found is that there are a variety of available tachometers already on the market and of course there are electronic speedometers which are easy to adjust so unless there is some easy example that somebody happens across I guess I will look at the available aftermarket gauges as well as available separate tachs.

Don Shillady
Retired Scientist/teen rodder