mkindypaul
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| posted on 23/8/16 at 03:30 PM |
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God it's a nightmare, I don't think there is going to be any definitive answer it needs a 3:6 and 3:9 to test. The track we used it on was
a short track with just one longish straight and I only put it into 4th for a short period of time and this was from 3rd at about 6200ish rpm so maybe
I was wrong and the 3:6 would be the most practical answer, that way I don't destroy first with such a short diff as a 3:9 and I also bring the
speed down enough with the 3:6 to the point where I needed 4th the engine is gonna be revving harder so once slotted into 4th it's more into the
revs and power band.
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JimSpencer
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| posted on 23/8/16 at 03:41 PM |
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Hi
You answered the question in Post 1 really, as you're running it as a track car cruising ability is irrelevant, so you're looking at the
following scenario:-
On the longest straight you're ever likely to see you should want to hit the rev limiter in 5th just before you get to the point of hitting the
brakes
Or
Around the same point the car hits the aero wall - yes?
Even with a 3.9 in it, you'll not do that you'll either run out of straight well before it gets to the red line or it'll hit the
aero wall - either way out of the choice of a 3.6 or a 3.9 it'll certainly be the latter.
HTH
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mkindypaul
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| posted on 23/8/16 at 04:00 PM |
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Hell Jim,
Basically yes I think it hit the aerodynamic wall in 4th and with the straight not being massively long I ran out of road to pull through but with
more power I'm sure it would of done so. some people reccomend the 3:6 and some say 3:9 so it's confusing. I may just get the 3:9 crown
wheel and pinion off mcerd1 and fit that to my current diff and just take it to a track day at the same one as I used last time, I mean fitting the
3:9 shouldn't hamper the day should it ? Won't be to much that we can't use it
Mcerd1,
Would you be able to remove the crown wheel and pinion to save posting such a bulky item as I don't think I'll use anything else from the
unit itself ?
[Edited on 23/8/16 by mkindypaul]
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Adamirish
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| posted on 23/8/16 at 04:18 PM |
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quote:
Originally posted by mkindypaul
@adamirish
What wheel and tyres size do you run ?
15x6 wheels. 195/50-15 tyres.
A 3.9 diff would do you well. I very much doubt you would use 1st gear much anyway and you would be into 4th well before 100mph. Even if you had a
long enough straight to be flat out in 4th, you still have another gear. At a rough guess with a 3.92 on a standard type 9, flat in 5th is likely to
be around 150mph. With the best will in the world, anything under 250bhp in a seven is going to struggle to get there simple because the aerodynamics
of a 7 are similar to a breeze block!
I do believe there is also a rare 4.1 ratio diff too. Cruising ability would be crap but for track work it would be close to ideal! If I could change
gearbox and diff ratios cheap enough, I would aim for flat out in top to be a theoretical 130mph ish. I don't have the £3k+ to do that
though.
Edited to add, with my 3.62 and 15" wheels, at an indicated 70mph it's doing just over 3000rpm. My rev limit is set to 6800(engine built
for 7.5k though) so with my gearing it's geared for around 160mph. It's a good job it's theoretical as There is no way I would want
to sit in a 7 at those speeds!!
[Edited on 23/8/16 by Adamirish]
MK Indy 1700 Xflow
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mkindypaul
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| posted on 23/8/16 at 04:24 PM |
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Cheers for all the help guys I think I'm gonna go 3:9 route first and see how we get on, I just have one other question though as I've
read on here you can't get a 7" push in shaft lsd diff ? Mine is 7" with push in shafts and on the first page I put a pic up with
the back off?
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mcerd1
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| posted on 23/8/16 at 06:16 PM |
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quote:
Originally posted by mkindypaul
I've read on here you can't get a 7" push in shaft lsd diff ?
you can't get an OE ford LSD with push-in shafts - but you can get any of the aftermarket LSD's 
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mkindypaul
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| posted on 23/8/16 at 06:22 PM |
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quote:
Originally posted by mcerd1
quote:
Originally posted by mkindypaul
I've read on here you can't get a 7" push in shaft lsd diff ?
you can't get an OE ford LSD with push-in shafts - but you can get any of the aftermarket LSD's
Wonder what mine is then ??
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CosKev3
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| posted on 23/8/16 at 06:52 PM |
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Looks after market judging by the difference in materials?
Google the numbers on it
If you can fit 13 inch wheels over your brakes these make for much better track driving than 15's,and you can use the smaller wheels to alter
your gearing too.
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mcerd1
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| posted on 23/8/16 at 07:01 PM |
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^^ my pics above are fords bog standard open diff - so yours looks like an aftermarket of some kind...
doesn't quite look like a tranX one either:
 
Tranx fitted 1
or a quaife atb:
some googling throws up some pics of supposed ZF plated diffs - but they aren't that common (no longer in production) and I don't know
much about them, but I believe they are still quite sought after by some folk
I'm sure someone else will know exactly what it is...
[Edited on 23/8/2016 by mcerd1]
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mkindypaul
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| posted on 23/8/16 at 07:42 PM |
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My bro googled the last lot of numbers with the s25 and the quaiffe website came up but that's as far as we got, maybe it's a discontinued
version either way it's in perfect working order and fits lol
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mkindypaul
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| posted on 23/8/16 at 08:35 PM |
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Cheers mcerd1 & nickP
Looks like it's a zf Motorsport plated lsd diff, quite a capable unit by all accounts
Mcerd1, did you get my message about your 3:9 bits and if needed whether you'd mind splitting them because I only really need the cw&p
[Edited on 23/8/16 by mkindypaul]
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mcerd1
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| posted on 23/8/16 at 11:43 PM |
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quote:
Originally posted by mkindypaul
Mcerd1, did you get my message about your 3:9 bits and if needed whether you'd mind splitting them because I only really need the
cw&p
did you send a u2u ? (I didn't get one)
I can probably split it, but I'm a bit short of time at the moment (got a new baby due to arrive in a few weeks time) so can't guarantee
how long it'll take me to do it...
[Edited on 23/8/2016 by mcerd1]
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Nickp
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| posted on 24/8/16 at 07:47 PM |
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As discussed here's a pic of my 3.9 Quaife LSD innards. It's got 26 spline push in shafts. U2U me if you want to go ahead.
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mcerd1
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| posted on 29/8/16 at 08:38 AM |
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here's the current state of my spare one:
obviously could do with a clean, not sure when I'll get a chance to split it though
drop me a u2u if your interested
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mkindypaul
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| posted on 29/8/16 at 02:16 PM |
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Cheers mate I'll message you if I need it.
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mkindypaul
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| posted on 2/3/17 at 04:09 PM |
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Well it's been a while I know but I've had the diff changed from a 3:38 to a 3:92 by road and race transmissions which was a really good
hastle free turn around by them, all installed today so fingers crossed at the next track day we notice a difference
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ian locostzx9rc2
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| posted on 2/3/17 at 05:34 PM |
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If it's just for track days then I would fit a 3.9 ratio if you do some road / motorways then 3.6 would be best as said 7s aero is a big issue
so the lower gearing will help to get the most out of it
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snapper
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| posted on 2/3/17 at 06:07 PM |
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I run a 3.9 all the time and it's a good diff for a mid power Pinto
I have a high power Pinto and the higher rev limit makes the ratios feel closer.
I run a V6 type 9 which has slightly higher 1st and longer 2nd & 3rd
But still not ideal
If I had a 2.7 1st that would be ideal for road and track
I eat to survive
I drink to forget
I breath to pi55 my ex wife off (and now my ex partner)
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mcerd1
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| posted on 3/3/17 at 01:55 PM |
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quote:
Originally posted by snapper
I run a 3.9 all the time and it's a good diff for a mid power Pinto
I have a high power Pinto and the higher rev limit makes the ratios feel closer.
I run a V6 type 9 which has slightly higher 1st and longer 2nd & 3rd
But still not ideal
If I had a 2.7 1st that would be ideal for road and track
I really hope my 3.92 is the right choice for me too (probably more road than track for me)
I've got a 2.66 1st gear & 1.75 2nd - but also silly big 245/45 R16 tyres on the back
which pretty much makes my 3.92 diff with the big tyres more like a 3.62 with more normal size 195/50 R15's tyres....
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mkindypaul
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| posted on 28/4/17 at 07:05 PM |
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Well did my first track day of the year in the Indy today after changing the diff ratio to a 3.92 and all I can say is jesus what a difference, its
like a completely different car. Flys up the box now constantly in the power band so thanks to everyone for all your help and info on here.
[Edited on 28/4/17 by mkindypaul]
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ian locostzx9rc2
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| posted on 28/4/17 at 07:22 PM |
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I ran a 3.9 ratio in my striker with a Toyota 4age and I found it the best ratio when it comes to a car which is going to be used for trackdays more
than a cruiser . I've done trackdays at Abingdon for years and that was the ratio which I found best suited.
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snapper
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| posted on 29/4/17 at 01:40 AM |
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You'll soon be looking for a higher 1st gear trust me
I eat to survive
I drink to forget
I breath to pi55 my ex wife off (and now my ex partner)
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mkindypaul
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| posted on 30/4/17 at 07:35 AM |
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quote:
Originally posted by snapper
You'll soon be looking for a higher 1st gear trust me
yeah a gearbox with different ratios has been spoken about already ha ha
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