Engine Conversion - Tachometer Issues

[Bob Ashlock]

On the subject of engine conversions.... one of the problems that often comes up after the swap is getting the tachometer to indicate properly. Reasons include different number of engine cylinders, or new ignition signals that are incompatible with the original tachometer design. I had this problem when swapping a 911 engine into my '66 912. Here is a link to a post where I discuss the development of my tachometer adapter that enabled me to use my original tach and have it indicate correctly with the new engine:

Tachometer Adapter

Feel free to contact me for more details.

[tdskip]

If you haven't dealt with Bob before he is great to work with. Highly recommended.

[Flying Toaster]

I agree. Excellent communication and very quick shipping.

I recently purchased the Tach-adapt device for my conversion:

Car: '74 911
New Motor: 5.7L GM small block
Problem: Tachometer was reading significantly higher than it should, as Bob put, 1.33 times what it should be. The needle also bounced erratically as it was unable to handle the HEI signal.
Resolution: Installed the Tach-Adapt device in about 5 minutes, tach reads right on now and the erratic bounce has gone away.

Thanks Bob. - John

[Bob Ashlock]

Check out the latest issue of 9-Magazine (March/April 2012) to see a feature article on my Tachometer Adapter project. To view the magazine article and to see more info, go to my new website Home Page

[prodigyporsche]

im running a vr6 vw motor do you have a setup for that? i have not yet hooked anything up but i would assume that will be an issue

[Bob Ashlock]

Hi, just saw your comments. VW VR6... that sounds like a fun adventure. I'm not familiar with that motor... what type of ignition system does it run? Does it have a Motronics box controlling injection, spark, etc.?

Also important, you didn't mention what car you are putting this VR6 engine into. What year and model (911, 912, etc.)?

Generally, my solution fixes about 90% of the problems that occur, so keep talking and we'll work this thing out.

You can also see info on my website Home

Thanks much ... Bob

[Bob Ashlock]

By the way, just wanted all members to know that since my last post on this thread back in 2012, PELICAN has picked up the TACH-ADAPT product. You can find it under PEL-TA-V3. Hundreds of units are now in service. Thanks to PELICAN PARTS and all my happy customers

[Rumble-Bee]

Superb workmanship & greatly simplified schematic made it easy for me to diagnose the problem after prior owner swapped in a 3.0 to replace the 2.7 in my 74 911. It turned out that I didn't need to leave the unit mounted -- the instructions, schematic, and LED allowed me to diagnose the problem which I was just too scared of "jumping" connections without the tach adapt, for fear of frying my tach. I just wish I had this when I converted 2 914-4's to 914-6's (years ago). Back then I made do with a crude arrangement of resistors after trial & error -- funny thing about that setup was that the tach would start at 0 RPM again and count up again whenever I reached red-line.