I am installing a Edelbrock Flow-Pro EFI systems and HEI ignition in my 69.

I am trying to decide how best to upgrade the tach to electronic as well. I found several references to modifying a working 75-77 electronic tach with the faceplate from an earlier model. This is option 1 and it seems fairly simple but you end up with $150 in a 40 year old tach. I am considering a few other options as outlined below.

Option 2 - Has anyone had success modifying one of the 75-77 reproduction electronic tachs with an earlier faceplate? I can't tell how the back side is made so thought I would ask. These tachs go for around $180 and would be new.

Option 3 - I also noticed several threads referencing swapping the guts out with an Isspro tachometer, one referenced a model R85100. The specs on the R85100 are 6000 RPM with 270 degree sweep. The original gauge is 7000 RPM with a 300 degree sweep, so I am not sure how that bolted right in and worked as stated in the thread. Is there another model with the correct sweep? I called Isspro and they were really no help.

Option 4 - Use a standard 270 degree sweep gauge and have a faceplate reprinted to match. I am not sure this would this be a viable and cost effective solution, if you have information on this please advise. You can get an Isspro 8000 RPM tach which will bolt in to the same holes as the original for < $100 new.

Option 5 - By far the simplest is to drop $250 to have mine done at one of the instrument shops or $290 to purchase a new one ready to go with a the correct faceplate.

Any guidance or suggestions would be greatly appreciated.

 

The Isspro is my conversion. I jut had a couple spares on my shelf.
The 0-6000 rpm 270 degree sweep on the Isspro is the same as the 0-6000 rpm 270 degree sweep on the vette tach. You just don't get the last1000 rpm. And if my engine hits 7000 rpm, the last thing I'm worrying about is tach accuracy.
Like I said earlier, even the 2 little screw holes in the faceplate matched the Isspro tach mounts.

 

I did it w/ a under $100 Autometer gauge. Simply matched the RPMs- seems to be pretty accurate till 4K- then is not that much off.

Drilled the faceplate to match- countersunk the screws on the Autometer faceplate and put the needle back on- then tested against the BMW's tach.

 

Here's my thread on converting my '71 from mechanical to electrical. It was pretty easy. I was able to find the base, needle (very important), and back housing for around $60 knowing that I'd be putting on a new board from Willcox.

Note that the early needles won't fit on the 75-77, here's my run around with that.