Tachy showing too many rpm? • The Dodge Challenger Message Board

by **Martin Mansson (Marangen)** » 17 Apr 2002 11:24

Unsure if previous post worked. My newly rebuilt 440+6 and 3.55 Sure-Grip is ready to hit the road - but I have the feeling that Tachy is showing too many revs, up to 1000 rpm!! New ignition and wiring harness also installed. What can be wrong? Haven´t measured exactly and possibly "hunch" is wrong, but maybe not? Any answers out there?? Martin

by **Dave-R (Roppa440)** » 17 Apr 2002 12:12

Try a keyword search from utilities on the left. We have discussed this a lot and the conclusion is that a high reading factory tach is very common.

by **Martin Mansson (Marangen)** » 18 Apr 2002 10:45

Dave - thanks - but 1000 prm too much also common? It is OK at idle but shoots up to 5-6000
quite easily if I accelerate.....

Any solution - get the tach overhauled? The cable itself cannot be the problem can it?

Many thanks,

Martin

by **Dave-R (Roppa440)** » 18 Apr 2002 13:10

Like I say we have disscussed this already and there are companies that re-build and re-calibrate them. Even then I would not trust it to be accurate. Mine was reading about 7000rpm at only 5000.

by **Tig (Cathtig)** » 10 Jul 2002 22:04

I had this problem when I had the original 318 in . I put the chrome box on a fairly stout 318 (ran 12.8's......ok with nos).Anyway the tach would run backwards for a bit and then go off the scale. At first I thought it was a 6 cylinder one.
but then I put an Autogauge tach in and it still ran backwards but was more accurate once it got going. Putting a big block in fixed it. Maybe thats what you need to do.

by **Johnny D (Johnnyd)** » 11 Jul 2002 10:34

I think Tig is right . . . Put a Big Block in it.

by **Tig (Cathtig)** » 11 Jul 2002 22:32

Whoops it already has a big block in it so thats not the answer. Seriously, the stock rev counter in my car was wildly inaccurate. It must have been at least off by +20%. I couldn't get the car to idle right and found that I was trying to set it to idle at a true 400 rpm, instead of the 700 on the gauge. I know that this is more than 20% but it seemed to become more accurate at higher rpm's. This was confirmed with a Snap-on timing light which has a very precise digital tach built in. I ended up putting in an Autometer 5 inch tach with shift light, this was much better and gave the interior a race feel.