Which rear axle/diff for my 3500 V8 Kit car

stuartl · Post by **stuartl** » Mon Apr 13, 2009 7:34 am

Hi all, I have a Robin Hood S7 kit car, originall built using a Sierra donor vehicle.

Once I have the V8 shoehorned in am I right in thinking it will destroy the old Sierra diff/axle very quickly? If so, what is a suitable replacement....one from a sportier Sierra such as a 4x4?

Thanks in advance!

Stuart

topcatcustom · Post by **topcatcustom** » Mon Apr 13, 2009 10:10 am

I don't think it will destroy the diff as quick as you think, apart from the extra torque from the RV8 (I'm assuming fairly standard spec) the power is not massively more than a well tuned sierra, though the torque is the issue! Your car will only weigh about half a ton so it will break traction before the diff goes bang- the only thing is that if you don't have an LSD and are constantly spinning the rear wheels (or 1 of them) then the diff may not last long- but by using an LSD you should get over that prob pretty easy.

I am using a 7.5" LSD in my mx5 with a supercharged 4.0 and have been told it should be fine- plus the car weighs about a ton, so you should get away with a std diff or 7" LSD!

TC

stuartl · Post by **stuartl** » Mon Apr 13, 2009 10:54 am

Thanks TC, that is good news.

Actually, the car with a pinto engine weighs in between 750-800kg, a lot more than my old Sylva Striker that came in under 500kg so hopefully it will give it a bit more traction. I guess avoiding first gear could be a way round wheelspin until I get the ratios fine tuned. There is a guy on our owners forum with a 3.9 Rover in the same car but mine will be the 3500 in standard form running twin Su's.

The gearbox ratio is an issue also. theV8kid has a sherpa box for sale which sounds great but I need to check that the ratios are suitable for my car.

It will never see a track but I would like it to be a comfortable cruiser as well as having good acceleration.

This forum is fantastic for such info!

JC. · Post by **JC.** » Mon Apr 13, 2009 3:50 pm

The Hoyle MGB IRS system uses a narrowed siera axle.
Apparently they are good for 350bhp. You aren't going to be making that on an NA 3.5 litre.

seight · Post by **seight** » Tue Apr 14, 2009 3:13 pm

Hello,

Barry Ashcroft 'only' had a Sierra 7.5 diff in his Chevy Westfield with a genuine 450+bhp.

He's got a profile on here somewhere.

AFAIK all the Westfield V8s use a Sierra diff either 7" or 7.5" and most are probably around 650kg - 750kg depending on exhaust/gbox/rad etc.

Mike