Diff Ratios for Lada

[bzrspeed]

Hello
I need to order diff from supplier to get here in time for car put together. I need advise and guidance, which differential ratio should I get. this is for Gravel based rally car, with 240hp to rear wheels I estimate it should have.
the supplier has given me the following ratios which he has in stock.
3.55:1
4.11:1
4.44:1
5.20:1

Any advice please?

[Dell'Orto]

What gear ratios and tyre diameter do you have? I'd be looking at probably 4.44

[bzrspeed]

ha that would help.
Wheels are 185/60/15 R201 from Hankook
Gearbox
Current ratio options are:
1st 2.2
2nd 1.54
3rd 1.21
4th 1.1
5th 0.89


they also can do a 5.37:1

[RomanV]

What type of motor?

forced induction?

how high does it rev?

IF your engine only revs to 5000rpm or so you'll want the 3.5

However if it zings out to 9000rpm you'll want the 4.4 or there abouts.

Need to know more about the car's setup to give a good answer.

[bzrspeed]

Engine is a 831e5.000 2000cc twin cam. It has Electronic Fuel Injection and is controlled by a computer which has been chipped.
It is non turbo, so is naturally aspirated.
Safe engine revolution is 8500rpm, Maximum engine revolution is 8900rpm

[RomanV]

I'd say your power output to the wheels may be slightly on the optimistic side of things, but yep 4.4 ratio sounds like it would suit that engine best out of those options.

Or the 4.1 if it doesnt have enough top ends speed with those tires.

There are about a million variations of things like this on the net which can help you decide:

http://www.apexgarage.com/tech/gear_ratios.shtml

Got any more information about what's been done to the engine?

I'd say 240hp atw is a bit optimistic if it's been built on a 'chipped ecu' budget.

[fangsport]

running a 15" gravel tyre, would be looking at 4.4 minimum, even with 200hp+

i'm guessing i have around 120- 140hp, and use 4.6/4.8 with 185/70/14 rally tyres.

RWD rally cars don't often get to stretch their legs fully in top gear, so reducing the gaps in the gears with a lower diff will result in better time, at reduced absolute speed.

an Escort i helped to build a few years ago was in the 180hp range, with close gear kit was running 4.4 diff on 13" rally tyres, but was capable of hitting red in top.

[TRD Man]

I'm not a big fan of your tyre size. I'd be looking at a 185/65-15 which are much more common and with taller sidewalls likely offer a bit more deflection (less punctures, more grip etc...).
Also there are truckloads of them available in very good 2nd hand condition, very cheaply. (near new under $100)

On an average 2000cc RWD (around 1000kg) with those ratios and the 65 series tyre I would think a 4.7 or thereabouts would have been ideal so with the 60 series maybe the 4.4 might be spot on.

Why not call Tony Aimers and ask him what he has in his 131.