cliffyk

Herre's the complete series of formulae to calculate mph, rpm, or gear ratio when you know any two values (assuming OEM tire diameter, and a 3650 in 5th gear):[/align][/align]rpm = mph * gear * 8.38[/align][/align]mph = rpm / (gear * 8.38)[/align][/align]gear = rpm / (mph * 8.38) [/align][/align]Note: In the last formula, if the actual vehicle speed is used the result will be the actual gear; if what the speedometer says is used the result will be what the PCM is programmed for...[/align] [/align][/align]==========================[/align]For a T-45 use 9.06 instead of 8.38...[/align]

mills281e

I think I would have some serious suspicion as to whether someone charged me for gears they didn't put in. Almost worth taking it to a different shop, getting the gears pulled and seeing what's in there. I can guarantee you that any Mustang shop out there has an old set of 3.27's sitting around to show you and say...."here's what came out of your car".

Eventhough gears have a break-in period,you're pretty much dealing withfixed physics that will make your car accelerate faster, as well as tach out quicker....whether they were in for a day or a year.

defconfire

One other thing that may have happened is they could have been shimmed WAY TOO TIGHT and it is making a huge amount of parasitic drag? This actually happened someone i know, the gears were shimmed soo much you couldn't even turn the wheels with the car on the lift and in neutral. Maybe the shop that installed it used every shim in the shim kit or something[8D]


that or he accadentally put the wrong ratio in it?

oldskool04

i dont think he shimed to tight there are stil some left but im going to go to a friends house and jack the car up and see if i have the correct gear

562cobra

when a shop does work to your stang make sure you stay there with her, just to check that she gets her gifts.

later

mvr

i noticed a big difference in rpms between 327 and my 373's, night and day.

02ToRcHgTSLP

it could be your tuner. Install the tune with the changed gear ratio. I had that problem when i tried to install just the gear ratio on the stock tune for the car. there was no difference but wheni installed the tune with the changed gear ratio my speedo was accurate again and so was my rpms.

steve0914

cliffy i have to say you ate the man!

02stallion

going from stockers 3.27 to 3.73 i immediately felt a difference after doing the heat cycles on the gears. as for the speedo correction the rpms stay the same it is just that your mph are off. u sure you are programming your tuner right? and the shop shouldve changed any shims or what not while you had your gears changed. makes no sense in going back. some how the whole story doesnt add up

oldskool04

me and my friend just turned the tires one time and the driveshaft turned just over 4 times, so they are 410s. why would the car be like this, also even if the tuner was wrong i should feel a difference in porformance but if anything id say its slower. is it possible that the shop could have done such a bad install job that performance is messed up. it does whine and make noises but he said he would fix that when he reshims it and retorqes it. i have talked to a couple of my car smart friends and they are just as confused as me.