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TT w58 diff options - opinions please


Homer

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I'm installing a w58 in my TT and am in two minds what to do about the diff.

 

I have an NA TRD small casing and a UK auto large casing diff (which is already on the car), so am weighing up the best option to go with for the TT

 

The w58 and NA diff are a direct install as the NA one has the small casing. This means I have to replace the UK diff, prop and driveshaft's

The w58 and UK diff will be problematic due to the driveshaft length (I'm pretty certain the UK diff has a different bolt pattern and positioning for the prop), but on the plus side I don't need to change the diff and drive shafts

 

I did some calculations on the gear ratio guide and it looks to me the UK diff with 3.769 ratio is going to be a little too tal, but the UK option allows for lower RPM at motorway speeds. Has anyone done this before or have thoughts on the best approach? I'm thinking the NA TRD diff would be the better option, even though it's not going to be able to do 160mph (which is probably a good thing :D )

 

w58 with NA TRD diff:

attachment.php?attachmentid=177068&stc=1&d=1384467149

 

w58 with UK auto diff:

attachment.php?attachmentid=177069&stc=1&d=1384467149

TT w58 NA diff.jpg

TT w58 UK auto diff.jpg

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I still have the NA A01A in my NA-TT. I'm doing 70mph at around 3100 rpm.

Mines a W58 too :)

 

Ooooh, good to know :) Do you have problems with it being a little too high rpm when at speeds above that (on the track of course ;) )? How is the fuel consumption on the motorway? It looks like it'll be in the 2nd turbo zone in 5th at 100mph so I'm concerned it's going to be putting a lot of long term pressure on the engine and possibly poor mpg.

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On the motorway i can get to Exeter on around a quarter of a tank cruising at 70-80mph, which is 90 miles.

So, motorway driving at 70-80 equals 360 miles to a tank (whatever mpg that is)

 

The second turbo does come on line while getting to 100, but you can hold 100 out of boost (according to the guage)

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On the motorway i can get to Exeter on around a quarter of a tank cruising at 70-80mph, which is 90 miles.

So, motorway driving at 70-80 equals 360 miles to a tank (whatever mpg that is)

 

The second turbo does come on line while getting to 100, but you can hold 100 out of boost (according to the guage)

 

So that's about 25mpg, a bit worse than my old 6spd at BPU (28mpg), I can live with that :) Thanks mate. In reality I'm very heavy footed so it'll probably be a lot less, I'm more concerned about the engine screaming away at high rpm when I'm on a late night drive. I think it'll need that 6th gear eventually.

 

How do you find the gear ratio, do you ever drop off the 2nd turbo when shifting? I like to change around the 6k mark (not on the dial, that would be higher), does it ever drop back below 4.2k rpm when going through the gears on a hard pull? The gear calculator indicates it will drop off at 3rd and above which concerns me.

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we have done loads of swaps with different diffs etc...

the auto tt diff is nice around town etc as it picks up faster but on the motorways its too much!

i would stick the na trd diff in....if you have the shafts and prop from a na its a direct fit too.... with the big casing diff, you'll need to get a custom prop...

 

plus the uk diff and shafts would be worth around £500 to sell on maybe? ;)

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I had an NA-TT W58 with an A01A which I blew and replaced for an A02B (thanks to DavidP for the guidance as to prop flange change and to Keron for supplying it! :thumbs: ). You asked me about my opinion of the change at the time, so here is the quote from my reply:

 

The diff change is a bit difficult to pin down as I changed a couple of things simultaneously! Bumped up from reasonably budget 255/35/18s at the rear to some nice Yoko Advan 275/35/18s at the same time as the swap. So I've never really had a definitive comparison to give in that sense!

 

I haven't noticed much of a difference to be honest as far as gearing goes. Only thing I am conscious of is the difference in RPM > vehicle speed as my speedo has been acting up so I worked out where 30mph in 3rd was etc. Need to back off that little bit more, but not too much really! I haven't given any top speed runs or anything to see how it varies up there. Just acceleration! Still more than fast enough is for sure! More so when I put on my 1st decat (though we'll see how the W58 gets on with that!).

 

I found with the A01A that the acceleration was blistering, though it still is to be fair! In 1st gear with the A01A, the back end NEVER went out, no matter what! Which was a good thing I suppose, just strange! It doesn't hesitate with the A02B though! In saying that, I feel so much more in control now! The traction is improved for sure, though how much of that is down to the tyres is another thing I ponder! It wanted to spin up quite a lot with the ratio from the W58 feeding the A01A, but it still comes on boost (2nd turbo mainly of course) viciously with the A02B.

 

Again, a combination of both things (tyres and diff) but I feel a lot more confident with the car now! It doesn't seem as wayward! With those BC coilovers fitted, it will be interesting to see what I can do with the handling as the weather begins to improve again! I was thinking about some Titan ARBs as well down the line. Just every little to improve the setup! I don't plan on tracking, but would like to experiment with different arrangements!

 

:)

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So that's about 25mpg, a bit worse than my old 6spd at BPU (28mpg), I can live with that :) Thanks mate. In reality I'm very heavy footed so it'll probably be a lot less, I'm more concerned about the engine screaming away at high rpm when I'm on a late night drive. I think it'll need that 6th gear eventually.

 

How do you find the gear ratio, do you ever drop off the 2nd turbo when shifting? I like to change around the 6k mark (not on the dial, that would be higher), does it ever drop back below 4.2k rpm when going through the gears on a hard pull? The gear calculator indicates it will drop off at 3rd and above which concerns me.

 

It's been a while since I've given her a good hard ragging as such.

From memory though, shifting at high revs you can keep it in the second turbo, but that's shifting at 6500rpm ish.

If you do drop out of the second turbo range though, it's a second before it's online again.

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we have done loads of swaps with different diffs etc...

the auto tt diff is nice around town etc as it picks up faster but on the motorways its too much!

i would stick the na trd diff in....if you have the shafts and prop from a na its a direct fit too.... with the big casing diff, you'll need to get a custom prop...

 

plus the uk diff and shafts would be worth around £500 to sell on maybe? ;)

 

What is it that makes the large case TT diff to much for motorway driving?

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its not large casing diffs in general, just auto tt diffs with 5 speed manual gearboxs on motorways... at 70ish, the revs are higher than using a manual diff... great around town as they accelerate loads better with the auto diffs..i personally prefer the auto diff with a manual 5 speed....(or 6)

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Thanks all, very useful and I think I know which route I'm going to take now... going to go with the NA TRD for now

 

James, I didn't realise it was you that replied all that time ago, I started to wonder yesterday after I posted it. You were the guy that was going to take me for a spin at Japfest a few years ago I think....

 

its not large casing diffs in general, just auto tt diffs with 5 speed manual gearboxs on motorways... at 70ish, the revs are higher than using a manual diff... great around town as they accelerate loads better with the auto diffs..i personally prefer the auto diff with a manual 5 speed....(or 6)

 

Thanks Keron. With the TRD NA diff it's going to be even shorter than the auto, so I am concerned about the RPM at cruise. I guess time will tell and James seems happy with his :) It's going to be bloody quick accelerating through the gears though :D

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its not large casing diffs in general, just auto tt diffs with 5 speed manual gearboxs on motorways... at 70ish, the revs are higher than using a manual diff... great around town as they accelerate loads better with the auto diffs..i personally prefer the auto diff with a manual 5 speed....(or 6)

 

see what you mean, I've got a large case diff at home I'm going to be using in my build with a 6spd box. How can I tell if its an auto large case or manual? And it was sold to me as an LSD so how can I also tell if its one of those? i haven't a clue what model supra it came out of.

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see what you mean, I've got a large case diff at home I'm going to be using in my build with a 6spd box. How can I tell if its an auto large case or manual? And it was sold to me as an LSD so how can I also tell if its one of those? i haven't a clue what model supra it came out of.

 

I believe all large casing diffs are Torsen LSD's, Keron should be able to confirm.

 

A very simple way to check if it's auto or manual is to mark the prop and one driveshaft flange. Rotate the prop making sure the driveshaft flange rotates though exactly one rotation. While doing this count how many turns you make on the prop. It should be 3 and then a part rotation. You just need to work out how many percent of a revolution it does on the 4th rotation. If it rotates approx. 3.2 times it's a manual, if it's approx. 3.5 times its an auto.

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I believe all large casing diffs are Torsen LSD's, Keron should be able to confirm.

 

A very simple way to check if it's auto or manual is to mark the prop and one driveshaft flange. Rotate the prop making sure the driveshaft flange rotates though exactly one rotation. While doing this count how many turns you make on the prop. It should be 3 and then a part rotation. You just need to work out how many percent of a revolution it does on the 4th rotation. If it rotates approx. 3.2 times it's a manual, if it's approx. 3.5 times its an auto.

 

Thanks that's good to know about all large case diffs and will give that a go to work out what type of diff it is. :)

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