QUESTIONS ON CRUISE RPM WITH 2:73,3:08 & 3:55 RATIOS

[scottw]

Hi guys,i did a search here on my question but didnt find anything so here go's.

Can anyone tell me what approx cruise rpm would be @ 60 & 70mph in 5th gear with 2:73, 3:08 & 3:55 gear ratios for my 91 5.0GT 5SPD with stock 16" tires?

Also need to know what the correct speedo gear would be for stock oem 2:73 & 3:08 gear ratio too.

Reason i am asking this is i recently bought 91 5.0 that looks to be bone stock but it seems to be running considerably more rpm at cruise speed then i think it should with oem 2:73 or the optional 3:08 ratios.

So i looked at the rear end cover it seemed to have bolts that dont look stock so maybe someone had the dif cover off to change the ring & pinion.

I also did a quick check to see how many times the drive shaft turned for 1 rotation of a rear wheel and it was approx 3.5 turns of d-shaft for 1 tire rotation so i figure 3:55's might currently be in the car.

Thanks in advance for your help.

Scott

 

[broncojunkie]

You're probably correct. 3.55 was a popular upgrade for many years. Late Model Restoration has a calculator to determine the correct speedo gear. You just punch in your info and it tells you which one you need. You can also download a GPS speedo app on your phone. Use it to see if yours is correct or not.

 

[broncojunkie]

Also, you can pull the rear cover and check the edge of the ring gear. The ratio will be stamped there. Not a bad idea to check everything out and go ahead and service it, while you're there. A little fresh fluid and some friction modifier additive always helps keep them working properly. Rear ends tend to get neglected often.

 

[scottw]

Thanks for the reply & your insight/suggestions,it's appreciated!

It's still dead of winter here in upstate NY so i guess i will have to wait and see where cruise rpm is when i get 5.0 out in the spring when all the salt is washed away off the roads.

My 91 Gt 5.0 5spd Covert with 62k original miles on it seems to have not seen salt or winter duty at all because i have been all over and under the car & it has zero rust anywhere to be found,even front areas like AC condenser,lower rad support,lower control arms and shock towers etc have absolutely no rust anywhere on them with same going for the floorboards underneath the body,lower door edge seems and door jams etc too all being clean as heck with not 1 spec of rust.

Guess i ,lucked out when i bought my 1st Ford that just happens to be a hot little high winding 5.0 5spd Muscle car that growls when ya hit the throttle which will be loads of fun to drive on wk ends when the nice weather returns sometime in late May early June.

Till then i plan to do more wrenching on the 5.0 like installing new struts & shock due to being over 28 yrs old and loosing their dampening along with also installing new tries and get an aln done too,already did complete tune up,oil change & filter,changed coolant & had rad hot tanked & cleaner out & tested for leaks along with installing new hoses & t-stat too,everything was original stuff from 1991.

Going to change trans & rear diff diff oil too.

Ok,noiw back to the exterior of the car, i know bumpers were repainted not too long before i bought the car but the rest of the paint is in good cond having a good depth & shine too,all black trim is in good cond with no missing blk paint but some of it needed a quick application of some blk trim bright which i already did which woke up the blk trim making it look good & fresh again.

I may use some Wipe New next time the blk trim gets a bit tired looking but one issue with that is wipe New might make the blk trim look a bit too shiny which isn't the proper look as was the OEM semi & or low gloss blk look for the blk exterior trim which is the reason i may decide not to use the Wipe New on the blk trim on my 5.0.

Don't get me wrong because i found Wipe New to be great stuff for my every day use car that needed some sprucing up ,thats for sure.

My daily driver happens to be an oldy but goody,it's a 98 Nissan Maxima that just turned 56k original miles which was a rust free 1 owner car i bought off the original owner a couple yrs ago when it had 47k original miles on it,you cant kill that gen Maxima,they are rock solid reliable,drive & ride great along with that gen V6 & auto trans running noce & smooth too.

Happy Motoring.

Scott

 

[scottw]

Got it on the road and as i suspected it's got 3:55's in it for sure,it came new 2:73's,must have been kinda doggy even with the 5spd trans & 2:73's.

I think i will stay with the 3:55's for now because the car really zips with the additional gear but still may swap to 3:27's or maybe 3:08's in the future.

That's because 3:55's turn approx 2,750-2,800rpm @ 60mph in 4th gear which is a bit much for long term cruising,but then if i go to 5th gear @ 60mph
to reduce criise rpm a bit it's kinda lugging @ 1,700-1,750ish rpm.

But 3:27's would turn a bit lower rpm of approx 2,500-2,550rpm @ 60mph in 4th gear & 3:08's approx 2,400rpm in 4th @ 60mph which isnt quite as bad
longer term 60mph cruise rpm as w 3:55's.

And then i could go into 5th gear @ 64-65mph with 3:27's being @ approx 1,850-1,900rpm & even 3:08's just might make it being approx 1,750-1,800rpm @ 63-65mph.

Happy motoring to all fellow 5.0r's !

Scott

 

[broncojunkie]

I really liked the 3.55 in my 88gt, but I swapped it for a 3.73 (found a deal on a complete rear end). The 3.73 is just a little too much for highway (although fun from red light to red light!)