Help picking the right shop tachometer -

[Dhopper71]

Hi all. I'm trying to find a tool to test my engines RPMs acurately. I think my instrument panel tach is reading quite low. Now that I've spent so much time getting my boat running, I want to make sure I can track it's performance and keep it that way.

I bought a dwell meter that reads rpms, but is not set up to read 4 cyl motors. I have a '74 140 3.0L. Right now my tach is reading 400 RPM at idle in neutral while on the muffs. The engine looks and feels to be close to twice that IMO. I need to finish going all the way through the current wiring to make sure it's stable, but still want/need a shop tach meter on hand.

Can you all point me in the right direction? Which will work the best on a budget?

Thanks again for all the help.

 

[John_S]

Re: Help picking the right shop tachometer -

I use an old dwell meter from years ago. Are you sure yours doesn't have a 4cyl scale? If not, set it on 8cyl, and multiply by 2. Check on the back of your dash tach. The config setting might have been changed.

 

[Dhopper71]

Re: Help picking the right shop tachometer -

I use an old dwell meter from years ago. Are you sure yours doesn't have a 4cyl scale? If not, set it on 8cyl, and multiply by 2. Check on the back of your dash tach. The config setting might have been changed.

yep. should have checked at the store first. it does say double 8 cyl readings for other uses, but not the tach reading. guess it would work, but i would rather be 100% certain i'm getting good readings. maybe a digital reader or timing gun?

i'll make sure to get behind the dash tach again and look closer. didn't see any way to change settings, but i could have easily missed it as i was mainly checking the wiring connections.

thanks

 

[John_S]

Re: Help picking the right shop tachometer -

8cyl = 4 pulses per revolution
4cyl = 2 pulses per revolution

Multiply be 2 and you will be fine.

I use this tach on my small outboards, but will work on an I/O. While it won't reach the dash, it would provide the piece of mind you are looking for. Maybe you don't have an hour meter, and something you wanted to add.
http://forums.iboats.com/showthread.php?t=503496