sodaman

Can anyone tell me at 70 mph with 3.73 gears in, where will my rpms be. I am trying to figure out if they recalibrated the speedo. It seems to be like 75mph and feels like 55 or 60. Can anyone verify some rpm/mph data with those gears installed. Thank you.

don_w

I don't have 3.73s, but if you're running stock dia tires, it ought to be ~2350 w/manual trans, and ~2450 w/auto at 75mph. This handy dandy spreadsheet can help with various combinations.


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Glenn

I am wondering what the difference is also. How big of a diff does it make on the speedo? 5 or 6mph?

don_w

Try the spreadsheet I posted.

sodaman

Well I am running the stock polished 18 x 8.5's , so I am not sure that spreadsheet is good for that. I see it says 17. Thanks for the help

don_w

Just change the tires sizes in cells C3:C5 or J3:J5, and the gear ratio in cell C6 or J6 (depending on which trans you have). It will work for any tire/wheel/gear combination.

retfr8flyr

I have 255/45/18 tires with 3.73 gears and turn 2500 rpm at 75 mph if that helps. I think 70 is around 2300 rpm but I am not sure as I cruise at 75.



Earl

sodaman

yah sounds like he didnt change the computer for the speedo. I will be taking it in tommorrow. thanks for the work ups on rpm etc. It was saying about 2000rpm doing 70 or something. According to the worksheet it should be only doing about 61 or so with the 3.73 at those rpms. I will check it out tommorrow. thanks

sodaman

Well I have some bad news and some good news. The bad news is ford cant update the computers any longer with there ids computer system for gear changes. They cant fix my speedo problem. So the good news is that they are probably going to have to order me a procal tool from ford racing to fix it. They did not know there was an issue with 06-07 updating the software. The mechanic forgot to mention that to the service mgr before he left yesterday, so car is back at dealer getting mor attention, and hopefully a new hand held tuner. Yes I can adjust it with my sctx2, but thats not why I paid them the big bucks to do it right. So we shall see what happens. I will report back when I get my car back.

TacoBill

Another spreadsheet for reference... posted by a fellow TMS'er.

Just change tire size and gear ratio to what you want (in red).

pville piper

I was playing around with the spread sheet that DonW posted. It is very interesting what the different gears do. I was wondering what gears I would want to run if I lived back in Jersey with all the 50-55 mph roads. It looked like 4.56 gears would work well with 5th gear and still have enough power unlike the 3.55s. The 3.55s really didn't like the slow speed limits and really sucked the gas. You basically had to run in 4th most of the time as you were down under 1500 in 5th. 4.56 gears would put you around 2000 rpms which would be sweet. Wow... 4.56 on the street and the gas milage wouldn't suck!

sodaman

Well I am getting two different numbers when I try both the spreadsheets. I think don w is closer at least with the auto settings. I am not sure the differences, but easier to change the numbers on his spreadsheet for auto/vs manual. Either way I know they didnt adjust it now. sounds like the 06-07 no longer have the proper software to update computer for gear changes. They did not know ford made changes after the 05. So if I am lucky, they will be ordering me a pro-cal tool for adjusting the gears etc. Again I know I can do this with my sctx2, but I would like to have this tool anyway. So unless they find a cheaper way to adjust the gear ratio, they will be getting me one. I will update when car comes back, they couldnt figure it out today, so that probably means procal tool being overnighted. I am leaving town friday for new orleans. So if I dont hear anything by then I will post when I get back from Mardi Gras. Oh yah I will drink plenty for everyone here. thanks for the help.