I cruise at about 2500 at 70MPH...is that a little high? Feels like my tranny is in 3rd all the time like 4th doesn't exist. I have a 91 L98 Formula by the ay. Thanks.

 

The basic rule of thumb and I quote another Mod from SEThirdgen

 

I think you're in OD, cause if you were in D you would be at least at 2730rpms. Now of course tire height and an inaccurate tach could account for the few hundred rpm difference.

I have 3:73s and at 70mph I'm running 2500 rpms too. Next time you're cruising in OD downshift to D to see if the rpms jump up.

 

I'm at 2000rpm at 70mph, 60mph I'm around 1800rpm. If I shift into 3rd it jumps to around 2500rpm or so. While cruising just try to keep it below 3000rpm, 2000rpm is a good range to keep it at, but if you have an auto and gears well you just have to deal.

 

i'm around 3250 rpm at 70 mph in 5th gear in mine.. which seems way high

and it's susposed to be a 3.08 rear.... so either the rear is way different or the tach is way off...

 

With my 273 peg leg in a 305 TBI I am running 2200 at 80

 

ell, the previous owner told me that he had 3.73's put in the rear,but he doesn't know his *** from a hole...he also thought the car was a "rare Firehawk" so I labeled him as clueless from the start...cruising at 70 in 3rd puts the tach at 3400... what i a trying to figure out is if I do or do not have stock gears by determining if my cruising RPM s are too high for what I am driving at in 4th.

 

Not really related but when I am in 5th at 5000rpms, I am going extremely fast.

 

I have a 91 Z with a ZZ4 tuned port and 700R-4, 3.23 rear and when i'm at 70 it will cruise at about 2400-2500 which is perfect for that motor. So your rpm sounds right, if you have about 3.23 gears.

 

You must have very short tires or an inaccurate tach, because with those rpms at that speed you would have 3:73s.

 

Like Mark said, alot of it depends on tire hight. If you have larger tires you will turn less RPMs for 70mph and if you have smaller tires you will turn more RPMs. The only true way to find out the gear ratio is to pull the covers and post the # stamped on the ring gear, or count teeth.