My 89 iroc has a b/w rear, supposedly with 2.77s. The last time I was driving it I noticed the tach was around 2250 rpms at 60 mph. That sounds extremely high rpms for that speed. Considering it is a 700-r4 with 245/50-16 tires, I sure something is screwed up. The TCC is locking up in OD and the revs might drop 150 rpm or so. I know it is shifting into every gear, cause the revs jump when I downshift manually. I was wondering if something is wrong with the tach. It seems like it is reading right at idle, but I don't know about the rest. What does your tach say? Thanks

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1989 IROC-Z Original 350 was swapped for a 305! Why, I'll never know.

 

I think I'm around 1800 at 70mph with my 2.77's in OD...either your tach is off, or your speedometer.

Ofcourse someone could have put in 3.70's?

 

Thanks, I don't think my speedo is wrong. I have "paced" other vehicles and it looks like it is fine. How could it be wrong, though? It is the factory tach, so could it be wired up wrong or something? Thanks again

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1989 IROC-Z Original 350 was swapped for a 305! Why, I'll never know.

 

Yes, they can be massively off. Remember, the factory gauges aren't "instruments", they're trim packages.

Pay a tune-up place or something $5 to check the tach against an engine analyer, I'll bet you'll be amused.

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"So many Mustangs, so little time..."
ICON Motorsports

 

how much are they usually off?

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I WOULD RATHER PUSH A CAMARO THAN DRIVE AN IMPORT

1983Z28 350w/ edelbrock performer RPM power package , dynomax shorty headers, 700R-4 with shift kit, 750cfm carb, edelbrock 3" exhaust system, ASCD SS hood, 16" IROC rims.

future mods:
completely done over suspension, black paint with flames, Hurst shifter, dakota digital gauge package, procharger supercharger.