I am wondering whether there are any handy calculators or spreadsheets out there which I can plug information into to help me work out how my combination of engine, gearbox, differential and wheel/tyre size will interact and what speeds I will get in what gears...?

Basically - I am thinking of mixing and matching between different gearbox/differential and wheels than those which came with my Pinto engined Sierra.

I had intended to keep everything as per the donor to keep the Sierra clocks, but am rapidly deciding that's a lot of faff, just for the sake of saving £150 on an electronic speedo. Especially when my chassis already has a recon diff in it (probably different ratio to my donor), I have the option to use an MT75 over the Type 3 which came with my Sierra and i'm going to pick up second hand alloy wheels which will probably already have tyres on them...

There's a speed calculator in a sticky thread, but you'll have to visit the dark side (otherwise known as the BEC section). It's got bike ratios in it but I think you can substitute your own values.

there are a few around but I like this one:

http://locost7.info/gearcalc.php


quaife have a similar stand alone program, most others run in excel

Cheers - exactly the sort of thing I was after! Now I just need to find out the ratios of the 3 diffs I have and the redline for a 1.6 Emax pinto...

http://www.car-videos.net/tools/speedrpm.asp?Car=Select&Num1=195&Num2=45&Num3=14&AxleRatio=4.1&Ratio1=3.13&Ratio2=2.05&Rat io3=1.48&Ratio4=1.16&Ratio5=0.97&Ratio6=0.81&Ratio7=&Redline=9000&Increment=500&B1=Recalculate

Cracking stuff chaps - looks like the difference between my Emax diff (apparently it's a 3.38:1 but it's still on the car at the moment) and the one which is fitted to my rolling chassis and I assume is a 'standard' ratio of 3.62 makes a reasonable difference at higher speeds. I'm building the car for blatting around the lanes and hopefully some touring - so I think i'll see how easily I can get the longer diff ratio in place :-D

not sure 100% about the Emax but most pinto's are good for 6700rpm, with the conrods being the weakest link (the late/efi 2.0's are safe to around 6900rpm)
but your std. cam will run out of puff before that anyway (i've seen 6000-6300 quoted but I could be worng)




sierra diff's are mostly 3.92 7" (or 3.91 7.5" ) for the 4cyl petrols (pinto, CVH, DOHC....)

and 3.62 7" (or 3.64 7.5" ) for the V6, 1.8D etc...

3.36/3.38/3.14 are rare and mostly found in cars with the old 2.3D

loads more info on the sticky thread: linky
(inc the VIN plate axle codes for each ratio)


if you have got a 3.38 they are worth a bit more as they are good for the BEC and V8's - the 3.6 ratio's are just a bit too low for them



if you've got a type 9 box the best mod you can do is a higher first gear (a few places sell kits / exchange boxes) the standard 1st ratio is so low that its only good for parking !



[Edited on 5/2/2013 by mcerd1]