High RPMS at 55 MPH

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Bad Sport said:
I would say so, I wonder if those factory tachs had the selector switch (4,6,eight) like the aftermarket ones. I haven't a clue.
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No selector switch on the factory ones Bruce. There were 6 cyl ones, but they were a different part # altogether. When we removed Dads and had it redone, I verified the part # as an 8 cyl.
Not happy as Dad spent good $$ on recalibrating it. I will be giving them a call.
 
4spdragtop said:
No selector switch on the factory ones Bruce. There were 6 cyl ones, but they were a different part # altogether. When we removed Dads and had it redone, I verified the part # as an 8 cyl.
Not happy as Dad spent good $$ on recalibrating it. I will be giving them a call.
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Gotcha, I wonder if someone wasn't paying attention and calibrated it to the 6 cylinder. It will be interesting what you find out.

I hope they make it right, they should.
 
Bad Sport said:
Gotcha, I wonder if someone wasn't paying attention and calibrated it to the 6 cylinder. It will be interesting what you find out.

I hope they make it right, they should.
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Are you running MSD or a similar multi spark discharge? Sounds like the mechanical aspects of the drive train are sound, which is always a relief.

I loved 3.23 in my a-body with an EFI 5.9 & 727, but even they were a bit buzzy at higher speeds out on the Western States two lanes out in the middle of nowhere. Looking forward to overdrive and a lock-up converter for those trips in the future.
 
The only thing I see wrong with your calculations Steve is the tire size , I too believed the 245/60/14s where 26.4 in but as Scotty proved they are actually 25.4 and even a little less when calculated as rolling diameter . That said we have the same setup and my numbers are similar to the aftermarket tach you retested with .
 
Sorry to hear that, Steve. In this day and age, GPS is one of the cheapest and easiest ways to check / cross check. Hell I just use one for a speedo!!!

I've bought 3 now, Garmin "Nuvi" off Craigslist and in thrift stores. Paid 15 bucks for one, and about 35--45 for the other two

This is what one looks like with the "speedo" screen up. This was LOL "out testing" the 4 wheel disk brakes

 
Thanks all, paying the $$ to have the "work" done and it not working correctly is one thing. The pain in the arse is getting the tach out!! It will stay in for the summer and I will remove it before it goes to storage...dammit!
 
I've been in and out of my dash so much the past year I can do that swap in about an hour lol , freakin gauges !
 
4spdragtop said:
Ok, finally got a chance to chk things out. Hooked up another tach so I could read it and the factory one in the car at the same time.
Tire size 245/60/15 = 26.5" tire diameter
Rear end gears 3:23= jacked up car turned tire 1 revolution=3.25 approx turns on driveshaft
I "flashed" the stall, and it looks like approx 1800 on new aftermarket tach.
MPH/RPM readings
Idle rpm 1000 factory
500 aftermarket
30 MPH 2300 factory
1600 aftermarket
40 MPH 3100 factory
2000 aftermarket
50 MPH 3700 factory
2500 aftermarket

So to me everything looks good?? Other than dad paying to have the factory tach redone with upgraded electronic board and recalibrated and it looks to be way off.
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Glad to see that the problem has been solved for you.
 
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