Hi folks I'm running 175x50x13 tyres and I'm using a standard t5 with a standard 3:6:1 cossie diff, the car is flat out at about 115mph at 6500rpm.
My question is would a 3:9:1 diff give me longer gears and a better top end or would it be to long and not pull top?
Any other ratios recomended for my set up? It would be nice to use 1st gear as its pretty non usable at the mo.
Also is the atb quaife diff a worth while upgrade?


Cheers andy....

 

Hi Andy,

The 3.91 would be moving you in the wrong direction Mr. I fitted one to my 2wd, and it knocked a little off the top end but helped the car through the slightly laggy bottom end. I think the Ultima diesel or something has the ratio you want, 3.35 or something, but dont quote me on that specically!

Thanks

Weeksy

 

Hi
Your maths dont add up.
175/70/13 with standard T5 5th (.8) & 3.6 diff gives 20.55mph per 1000rpm this is 133.6mph @ 6.5k rpm. Fitting a 3.3 diff would raise this to 146mph & a 3.9 diff lower it to 124mph.

Cheers Rod

 

My tyres are 175x50x13, I'm going on what it done at the strip the weekend at just under 6000rpm it was doing 110mph.
At 70mph it revs at 3400rpm roughly.
My maths was crap at school anyway. Lol

 

3.14 for a 7''

 

Would that ratio bring it roughly to a standard cossie ratio?

 

I would have thought so mate, maybe rod could do the maths. TT used them as they made more power without wanting to rev higher with the minkers (15'' rims ) .The kit car boys use them as the cars are so light, they are a derv diff ratio from the old 2.3 I think with prob 13'' or maybe 14'' rims.

 

3.14 diff 175/50/13 tyres & standard T5 5th gear will give 153.1mph @ 6500rpm. Thats sounds OK to me

 

Thanks rod, what would the other gears top out at?

And how the fook do you work that out.

Cheers andy....

 

at 6500rpm=
1st = 41.5mph
2nd = 63.1mph
3rd = 91.4mph
4th = 111.4mph
5th = 153.1mph

I made a spreadsheet calculator from scratch back in the early days of excel, Just pump in the info & out it spools. You can get calculators on the web now but not back then. Its basic maths nothing clever.

 

i have a 3.92 7.5" diff with lobro flanges for sale. Its open tho. £40 if of interest? I also have a 3.14 7.5" with lobro flanges but im not to sure i want to part with it.

 

I'm torn between the 3.38 and the 3.14 I'm thinking the 3.14 might to to long in the gears I mean 150mph in a mini would be a sqeaky bum moment for sure.

Just a matter of interest could you work out what the 3.38 would be for me.

Thanks in advance madrod.

 

Mine is a 7" mate, I might be after a 3,38 or 3,14. In a 7" if you know where I can get one from?

I not sure what cars they come out of, granada / scorpio I surpose.

Cheers andy....

 

Your be lucky to find either, they get eaten up by the kit car boys running bike engines. I would grab either or in either size. Its only the rear beam you have to change worse case.

 

Could anyone tell me what my car would top out at in the gears with a 3.38:1 diff.

Its on 175x50x13 and revs to 6500, t5 box.

Cheers andy...

 

I have a 7" diff which I purchased by mistake thinking its 7.5".
I'm not sure in fins drive as I can't make out what's stamped on the tag or crown wheel.
But I can make out 3.62 if that makes any sense.

 

That's what's in mine, I'm looking for a 3,38 or 3,14 but they aren't easy to come by.

 

Can i start with an appology the 4th gear speed on the 3.14 is 122.5mph not 111.4mph as stated on previous post its me being old .
The figures below are correct .

3.14 at 6500rpm=
1st = 41.5mph
2nd = 63.1mph
3rd = 91.4mph
4th = 122.5mph
5th = 153.1mph

3.38 at 6500rpm=
1st = 38.6mph
2nd = 58.7mph
3rd = 84.9mph
4th = 113.8mph
5th = 142.3mph

 

That's superb thanks, in you expert opinion which diff is closest to a standard set up, revs driving at 70mph etc.

I think the 3.38 seems best for track / fast road to me but before I spend out I want to be sure.

Thanks again madrod, are you really mad?

 

No he is not mad just slightly eccentric

 

He most certainly is, M.A.D.

 

what power/engine are you running? i went from a 3.6 to 3.14 and am now currently changing to a 3.38! also on 13'' wheels

 

I'm running 360bhp, I'm going to try the 3.38 and see how that goes I think the 3.14 might be to long it would top out in 5 at 153mph, I don't see me going that quick on many tracks around here.

Are you selling your 3.14 diff

Cheers andy...

 

already sold im affraid they go for fortunes sold the crown wheel and pinion for 400 quid! theres normally a few on locostbuilders.co.uk il have a quick look for you, and yeah id go for a 3.38 aswel youd probably be disapointed in the acceleration loss

 

I've found a company that sells crown wheels and pinions for 3.14 and 3.38 for £300 so £400 is a good sell mate.