I pulled the original 305 from an 84 camaro and put in a new 350. Everything works great except for one thing. The tach now reads about 2 times to high. My brother did the same swap in another 84 camaro and had the exact same result. All the parts in both swaps are original (same distributer, carb, etc.)
Both cars run great and don't throw codes. I don't want to have to put in a second tach and make it look like crap. I'd like to use the original tach if it's possible. Any help with this would be great!

 

Wow!

If you re-used your original distributor I don't see where the problem could be... That is the place that the tach hooks up..

Are you by chance running an MSD box that multiplies the number of coil firings? Any spark box will throw off the tach at the coil signal. You usually have to run a filter or tach adapter with those boxes.

 

I'm not running any after market parts in the ignition system. And I unpluged the computer to see if the computer had an effect, it didn't. As far as I can tell the distributor runs right to the tach. It's interesting though that the tachs in both cars are off by the exact same amount. One is a z28 and the other is a sport coupe.

 

I just took the RPM reading

Tach Actual RPM
4000 = 2400
2000 = 1200

Exactly 60% to high
I used a timing gun with a RPM Gauge on it.

I was thinking that maybe either the tach went bad or the distributor and it might be a coincidence that it happened in both cars during the engine swap. I'm going to do the same engine swap in a 86 sport coupe in the next couple of weeks and hopefully the same thing doesn't happen again.

Any thoughts on the matter would help alot. Thanks

 

I don't know about yours but i still had the stock 305 in my car and before i got the car the engine was removed and re installed (had work done) none of the emissions gear was put back in when it was done but i was told the tach went weird since then. it is reading the exact same as what yours is.
I was thinking it may be the jump from CC-Distributor to non CC-Distributor?