View Full Version : Does any one have accurate info on gear and diff ratios?

08-06-05, 06:36 PM

Wondering precesely which diff ratio to put on my Cobra with a 383 stroker (approx 450bhp) engine and tremec 600 gear box.

Does anyone have or know where to get the accurate mph per 1,000 rpm for each of the differentials available?


Happy Jim
08-06-05, 06:56 PM
This should do the trick



08-06-05, 07:18 PM
Thanks :-)

08-06-05, 08:09 PM
Using the motormath program to give speed per 1,000 rpm I have made this graph to show the speeds in each gear for the differential ratios of 2.99 3.07 3.31 3.54 with a Tremec TR-3500 gear box with ratios as follows
1st 3.27
2nd 1.98
3rd 1.34
4th 1.00
5th 0.68
and tyres as 255 x 45 x 17"

08-06-05, 09:24 PM
Paul, do a search under Tremec TKO600 and you will find the ratios there.. If not, Ihave them in an e mail somewhere if you want..

There are 2 600 boxes differing in their 5th gear ratios. The streetable version is .64 and the performance being .82.

Now get on the floor all of you and praise to the tech knowledge of PLOD! ;)

08-06-05, 09:29 PM
Now that is a first :finger: I was on the floor and am getting up now but it wasn't in praise it was sheer amazement :angel:

08-06-05, 09:33 PM
That'll do! Not wanting to off topic but I'm sure it can be as an exception, have you sorted your rough running yet Martin, how can I help with that?

08-06-05, 09:46 PM
It's getting there, :thumb: be a pal and pop over with your Laptop and help to programme the Mega Squirt system for me :thumb:

08-06-05, 09:55 PM
It's getting there, :thumb: be a pal and pop over with your Laptop and help to programme the Mega Squirt system for me :thumb:

Yeah I was joking.... :finger: . What's a lap top? ha ha

08-06-05, 10:00 PM
Now there's a surprise :D

09-06-05, 08:43 PM
Good technical info, similar to the one I had

29-06-05, 10:44 PM
Wilburn, I'm having the same problem as you have. Have you found out which diff to choose?

First gear of the TKO600 is quite tall (2.87). I've made some calculations and depending on diff ratio I come to the following max speeds per gear/diff ratio (at 5800 rpm):
DiffTyre sizeTyre heightRim sizeWheel diameterDiffTyre sizeTyre heightRim sizeWheel diameterDiffTyre sizeTyre heightRim sizeWheel diameter3,5424550%170,67683,0724550%170,67682,8824 550%170,6768600 lb-ft km/h 600 lb-ft km/h 600 lb-ft km/h 1st2,87 73 1st2,87 84 1st2,87 90 2nd1,89 111 2nd1,89 128 2nd1,89 136 3rd1,28 163 3rd1,28 188 3rd1,28 201 4th1 209 4th1 241 4th1 257 5th0,82 255 5th0,82 294 5th0,82 313

I'm sorry it's all in km/h, but you should devide it by 1.6 to get view it with miles.

You've got quite a powerfull engine, so I 'm sure that it will pull a long gear. You're choice should be related to quick starts (3,54 diff) or good mpg (2.88 diff). However is there anyone who can say which type of engine can take a tall gear or not?
I've got a Ford 5.0 HO with 225 bhp. Would this pull a first gear to 55 mph?