Good news guys who want to keep the factory tach after

Heads up all V8 guys wanted to keep the factory tach, after doing a V8 swap.

I found this site, which tell you how to mod the tach on a first gen Mazda RX7,
to read correct rpms for a V8. Hopefully the tach on the RX7 will be close or the same as the B trucks.

Or, you can just send them in your old tach, and they will do it for you for $55.

Here is the link below, but you will have to look under "manuals" then "electrical modifications by circuit".

Thats pretty sweet










-Justin

I don't think the RX-7 tach is going to be similar because the RX-7 gets it's signal from the coils which are batch firing the intake plugs, then the exhaust plugs. I'm just guessing though.

Take a tach from a B and take it apart. Their almost identical.

However, the B truck tach don't have the potentiometer that the RX7 does.

Which will be tomorrows experiment to find out where to put the potentiometer. I guess it would have to go between the signal wire.

MTrain i think you could bring alot of useful knowledge to this forum. You seem to know how to put big things in small holes and make it work haha






-Justin

Well I tested the B tach today with my good full size charger, and the needle went to 1k, not 3.6k like it was supposed to.

The reason for this is that my battery charger is one of those big units that rolls on wheels, were as the article called for the cheapest battery charger made {the link can explain this better than me}.

I found out the potentiometer was bad that I was using so I'm going to have to borrow my son's cheap BC, and head to Radio Shack for another potentiometer.

I got my son's cheap battery charger, and tried again. I still only got 1k on my factory tach., not the 3400 I was supposed to get.

Here is what is on its way tomorrow.

hmm so still no one knows if you can do it to the stock mazda tach?

Sin city local had a thread on mazdatruckin about converting the stock tach for v8 or v6. Maybe pm him or he can do another writeup on it.