the guy i'm buying them of said to ask him for the diff ratio i want. any good ideas??????????????????????

You will need to decide on gearbox and wheel/tyre size first. As a starting point you will have some idea of the donor ratios and speeds thru the gears, then need to match this to the type of engine you have.

no offence, but are you actually building a car??

jag powered, celica powered, diff ratio'd sierra hub'd etc etc??

just a thought

get a calculator out, theres one on quaifes site that's quite good. decide on engine revs, gearbox ratios and rim and tyre sizes and look at what speeds you want to achieve eg loads of acceleration and low top speed, vice versa or somewhere in between.

Ned.

Yeh, i've got a 4.1:1 Cortina axle. On the pinto it'll only do about 120 in top before running out of revs (6500), but bajhesus will it accelerate well in gear. Should be a laugh. Now all ive got to do is build the damn thing...

Ed.

ed,

got any pics of progress on our dearly beloved?

Ned.

Hi,
Diff ratio has a slightly more subtle effect that a pure compromise of speed versus acceleration. You need to consider this from three perspectives and find the best compromise between these taking into account the primary use of the car (Track use, Road Use, Hillclimbs, drag races etc)

1. What top speed do I want and can I cruise comfortably at 70MPH or so without too much "buzz"? For track use on long circuit tracks you probably want to avoid hitting the rev limit in top gear and match max power RPM to top speed. For road use the cruising comfort is perhaps more important.

2. Is my first gear acceleration about right? For example, is it too fierce and provokes uncontrollable wheelspin or could the diff ratio be lowered to gain USEFUL start line wheel torque?

3. Does the main intermediate gear (probably 3rd on a 5 speed g/b) permit rapid overtaking across the 50-75MPH band. Alternatively if 0-60MPH sprints are important then does it hit 60MPH in 2nd gear or do you only get to 55MPH and need another timewasting gearchange...

Unless we are building a new gearbox with user selectable ratios then a compromise between the above three factors will need to be reached.

I want to stress that having a diff with a 5:1 ratio won't necessarily give more start line acceleration than a 3:1 ratio and may have undesirable side effects in the mid range and top end. Also, don't think that just because you don't intend to do 130MPH doesn't mean you shouldn't gear the car to do this speed in top gear as you don't want to end up "cruising" at 70MPH and with 6000RPM on the engine!!

HTH,
Craig.

on TOL

http://groups.yahoo.com/group/locost


there is (or was) an excel spread sheet.


you enter your max revs, gear ratios, diff ratio and tyre size in, and it tells you the speeds thro all the gears.


atb

steve

ps - its in the files area

[Edited on 6/1/04 by stephen_gusterson]

Ive got a spreadsheet for gear calcs.

We could do with somewhere to post techy bits like that where people could get it easily, insted of having to ask each time. Ill see if Chris is up for it or blows my head off

Gordon

quote:

---

Originally posted by Mk-Ninja
Ill see if Chris is up for it or blows my head

---