Right this might sound stupid but getting there.

I have a Hewland S2 Gearset with very close ratios at the moment.

Havent got a clue what my rear diff is (R180 being a coupe) if it is a 4.1 or what.

Cruising in 5th gear @ 80mph is 4500rpm.

If I do have a 4.1 diff (How can you tell by looking?) then can I put a 3.9 rear diff in or 3.54 diff in to lengthen the gears if you see what I mean.

I wouldnt mind sacrificing a bit to cruise at lower revs and have longer to change between the gears.

Am I making sense? LOL!

 

Do you have a DCCD or viscous centre diff car? If you have DCCD, you have an R180 rear diff. If car was bought with viscous centre, rear diff will be an R160. However, that's just the physical type of the diff, the reduction is a separate issue.

The only way to tell for certain what the reduction of the diffs is is to disassemble them and count the teeth on the drive and ring gears, as well as the number of teeth on the drop gears at the back of the centre diff. If you tell us what model of car you've got, we'll be able to tell you what the final drives should be, but of course this assumes that they haven't been altered at some point in the car's life. If it's got an aftermarket gearkit installed, it's always possible that the diff ratios may also have been changed.

Yes, you can change the overall gearing by lengthening the final drive, but changing the rear diff alone is only half the job. You'd also have to change the front diff to match.

You're making sense, but it's a more involved job than a simple rear diff swap.

 

Yes I have the DCCD at the moment, wanted to keep so went for the stronger gearset.

I have an STI3 Coupe at the moment 1997 model.

So if I change the front diff and rear diff to 3.9 then I will have lengthened just the final drive or all the gears?

Appreciate the help, got some cash to spend on it so might as well do it properly!

 

In a nutshell yup. Would do the same as you but I've got this minor problem of having short gears and a 3.9 diff which means that i have your gearing.

 

Jon, the correct diff that should be in your car (STi Type R coupe ] is 4.4:1 teeth count 9 - 40 you can prove it through the drain plug hole by tippex -ing a tooth for the start point and rotating the crown wheel.

In a JDM car - as you almost ceratinly know the diffs are the same front to rear.

By fitting a 4.1 pair or a 3.9 pair you will use less revs for the same road speed.

David API

Just had second thoughts if your car is a version 3 STi then I think I'm right in saying that you will have a 160 size diff. I am sure they changed to 180 with the V4 and the body facelift.

 

you will "lenghten" (increased speed in each gear) the gears by doing the mods suggested, however the "closeness" of the gears will stay the same (i.e. the "drop-off" in revs when changing gear)................
cheers

 

I think stockcar is right, the gearshifts will still come thick and fast!
Just what is the difference between a 160 and 180 diff? The rear diff on my Stiv3 and an early RA diff (4.44 and 4.11 respec) are the same casing/drive shafts.
911

 

Stockcar is right 911, but the shifts won't come quite as thick and fast as they otherwise would do. If you lengthen the final drive by 10%, the time between shifts will also increase by 10% if you're accelerating flat out.

 

what are you wanting to achieve?

buy a different 5th gear from hewland if its a crusing issue?

David

 

Perfect! Thats exactly what I want to know. I am NOT just lengthening the 5th gear, each gear will be 10% longer effectively.

Have a feeling I already do actually. 1-4th gears are very quick where as 5th steps down a touch more if you see what I am getting at. 80mpg at 4500rpm. 120mph at just over 6000rpm.

Anyone got a contact for Hewland at all?

Thanks for all the help

 

Oh and one other point. So I have a R160 diff then?

This might make it easier!

Any ideas what 2 4.11 diffs are worth then?