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Using Randy's Ring & Pinion calculator and a 27" tire I get 66 mph with the 3.55 at 3000rpm and 60 mph at 3000 with the 3.91. Auto tranny.
With typical tire sizes the 3.55 really is the compromise gear, doing both tasks adequately but not optimally. The 3.91 are far better around town (for performance driving) but they do poorly on the highway on long trips.
Quote:No way are you going to turn that kind of RPM's with those gears and tires and no way would there be a difference with the same size tires and gears. even with a 4.88 gear at 4000 you should be in the area of 65 MPH with a 27 inch tire. With the same height tire and rear end gear ratio the RPM's would be the same no matter what the conditions, engine size, aero of the car or truck etc. Engine RPM per gear ratio and tire size will not change as long as both transmissions have a 1-1 out put drive which most did unless OD equiped which was not an option on those cars.
but are general, and can't compensate for real world conditions, such as air drag, HP, aerodynamics of the car, smblk, BBlk, etc,.......my Challenger T/A with 3:91's with a 27 " tall tire, would do about 60 MPH at about 4000 RPM,......my 70 SuperBee with 3:91's with a 27 " tire, and 440 would do about 60 MPH at about 3800 RPM,...
Quote:Let the good Lord help you if you have that much converter or transmission slippage. Either one would be toast.
Torque convertor slippage must be taken into account.
Quote:I guess the auto manufacturers were wasting their time when they went to the trouble of designing lockup convertors. I do agree with you that Dayclonas rpm seems high for 60mph. From my own personal experiance, going from a 11 inch 2500 stall, to a 10in 3500, to a 9.5 in 4500,every one has run a little more rpm on the highway than the last.yet after years of driving and thousands of miles, my tranny is not toast. I do have before me an excerpt from the july 95 issue of Hot Rod. In it a nova with 3.00 gears had its 11 inch convertor swapped for a 10 inch.The rpm cruising at 60 mph rose from 2600 to 2950. With the rearend gears changed to 3.25, rpm at 60 was 2900 with the 11in and 3100 with the 10 in.Quote:Let the good Lord help you if you have that much converter or transmission slippage. Either one would be toast.
Torque convertor slippage must be taken into account.
Quote:No not at all but the slipage warrented for this was very abnormal. Or a bad tachometer. There is no way to turn either one of the RPM's listed with the speeds listed.Quote:I guess the auto manufacturers were wasting their time when they went to the trouble of designing lockup convertors. I do agree with you that Dayclonas rpm seems high for 60mph. From my own personal experiance, going from a 11 inch 2500 stall, to a 10in 3500, to a 9.5 in 4500,every one has run a little more rpm on the highway than the last.yet after years of driving and thousands of miles, my tranny is not toast. I do have before me an excerpt from the july 95 issue of Hot Rod. In it a nova with 3.00 gears had its 11 inch convertor swapped for a 10 inch.The rpm cruising at 60 mph rose from 2600 to 2950. With the rearend gears changed to 3.25, rpm at 60 was 2900 with the 11in and 3100 with the 10 in.Quote:Let the good Lord help you if you have that much converter or transmission slippage. Either one would be toast.
Torque convertor slippage must be taken into account.
It's an option.
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I'm in a similar situation trying to decide between 3.55 & 3.91. I DO plan on driving the car long trips on the interstate though, which leans me towards the 3.55, but I will also be installing a Gear Vendors overdrive, which leans me towards the 3.91.
Which one should I pick?
Tav