Built Diff...

[OG Shark]

Originally Posted by SYT_Shadow

haha, but I'm serious man!

285/30 is the widest that fits and you need the lower aspect ratio. If it were 285/35 it would be too tall.

a max speed of 152 sounds really low

what tires are you running?

Ha yeah I know. How are you coming up with 152 though? That sounds low to me, but I definitely could be wrong.

I run 315/30/18 on the rear - for now...

[tsk94]

Originally Posted by SYT_Shadow

I'm basing what fits and what doesn't off dogbone 's thread

275/35 fits perfectly. 285/30 R1 is super wide and requires fender liners to be removed. We'll see how that part works out.

I don't want a 3.45, it kind of feels like what's the point then. But a top speed of 152... WGI and VIR both pass that today

Well you can either go 3.62 and run a taller tire to increase top speed or a 3.45 and the 'standard' tire size. Or save the money and keep the stock final drive.

The real performance advantage comes from the diff itself, the shorter final drive is just the icing on top.

[nicksm3]

Originally Posted by SYT_Shadow

I'd find it hard not to go with whatever James & Phil cooked up with Dan

I'm concerned about the 3.62 though. With a 285/30 tire which I want to run, with a 8400 redline top speed is limited to 152. That is way too slow for the Big Boy tracks.
It's so odd the Schrimer cars run such a short diff in what is probably the biggest big boy track on the planet
3.45 takes my max speed down to 174... more manageable.

As far as coding for the 3.62, Alex@Alpine is able to do it even if you have some else's tune, so that would be my path.

That was my concern actually!

I'm at Watkins Glen 2-3x a year and on the back straight I'm anywhere between 145-149. Can't go faster because of my aero "parachute effect"
Will the 3.62 gearing be too much? Too much for VIR aswell? Should be great for Limerock I'm assuming.

[SYT_Shadow]

Originally Posted by SAMM3Y

Is the coding just for the dct? I never had any coding done for mine... I just slapped it on there OSG custom build with 4.10 6mt. It's awesome.

yes for DCT only

[OG Shark]

Originally Posted by tsk94

Well you can either go 3.62 and run a taller tire to increase top speed or a 3.45 and the 'standard' tire size. Or save the money and keep the stock final drive.

The real performance advantage comes from the diff itself, the shorter final drive is just the icing on top.

Although I'm finding that 3.62 with a ~630mm tire on a DCT ought to top out at 165ish, not 152?

[SYT_Shadow]

Originally Posted by OG Shark

Ha yeah I know. How are you coming up with 152 though? That sounds low to me, but I definitely could be wrong.

I run 315/30/18 on the rear - for now...

Originally Posted by tsk94

Well you can either go 3.62 and run a taller tire to increase top speed or a 3.45 and the 'standard' tire size. Or save the money and keep the stock final drive.

The real performance advantage comes from the diff itself, the shorter final drive is just the icing on top.

Originally Posted by nicksm3

That was my concern actually!

I'm at Watkins Glen 2-3x a year and on the back straight I'm anywhere between 145-149. Can't go faster because of my aero "parachute effect"
Will the 3.62 gearing be too much? Too much for VIR aswell? Should be great for Limerock I'm assuming.

I don't have any aero so top speed is higher

I just wanna go fast

Here are my calculations:

[SYT_Shadow]

Originally Posted by OG Shark

Although I'm finding that 3.62 with a ~630mm tire on a DCT ought to top out at 165ish, not 152?

I friggin hope I made a mistake in my calcs... that would be music to my ears. For whatever reason I'm fixated on getting 3.62

[OG Shark]

Originally Posted by SYT_Shadow

I friggin hope I made a mistake in my calcs... that would be music to my ears. For whatever reason I'm fixated on getting 3.62

I dunno - everything I'm finding actually puts it higher than what I first thought. Around 170ish.

Your stroker with a 3.62 would rip the asphalt up.

[tsk94]

From my calculations, using a 3.62: with 285/30R18 I get an approximate top speed of ~167mph

275/35R18: ~174mph

Calculated at 8300rpm

[SYT_Shadow]

Originally Posted by tsk94

From my calculations, using a 3.62: with 280/30R18 I get an approximate top speed of ~167mph

275/35R18: ~174mph

Calculated at 8300rpm

And with a 285/30?

[tsk94]

Originally Posted by OG Shark

Although I'm finding that 3.62 with a ~630mm tire on a DCT ought to top out at 165ish, not 152?

Originally Posted by SYT_Shadow

And with a 285/30?

Whoops, yeah I meant 285 lol.

So like Jason figured, ~165mph for a 285 - which is almost identical to what I got.

[OG Shark]

Originally Posted by SYT_Shadow

And with a 285/30?

Right at 170 - unless there is some secret voodoo at work on that size that knocks it down to 152

Edit - ha somewhere between 165 & 170 per Trevor & my calcs. But you going to need some big boy tires to take advantage of all them gains from the diff

[SYT_Shadow]

Originally Posted by tsk94

Whoops, yeah I meant 285 lol.

So like Jason figured, ~165mph for a 285 - which is almost identical to what I got.

Originally Posted by OG Shark

Right at 170 - unless there is some secret voodoo at work on that size that knocks it down to 152

Edit - ha somewhere between 165 & 170 per Trevor & my calcs.

That makes more sense guys! I'll review my calculations! Thank you

3.62 is back on the table!

[nicksm3]

Originally Posted by SYT_Shadow

That makes more sense guys! I'll review my calculations! Thank you

3.62 is back on the table!

[tsk94]

So in conclusion, I think it's safe to say that a 3.62 final drive for a DCT car provides plenty of top speed potential. Even if we figure ~165mph at the low end of things (could be higher with a bigger diameter tire), surely that's plenty for any tracks here in NA?

OP, I would go 3.62!

[SYT_Shadow]

Originally Posted by tsk94

So in conclusion, I think it's safe to say that a 3.62 final drive for a DCT car provides plenty of top speed potential. Even if we figure ~165mph at the low end of things (could be higher with a bigger diameter tire), surely that's plenty for any tracks here in NA?

OP, I would go 3.62!

Yes, for sure. 170mph sounds great so you're not redlining 7th

Lower gearing also means more shifts, more shifts means more heat... interesting to see how the dct will handle that

[OG Shark]

Originally Posted by tsk94

So in conclusion, I think it's safe to say that a 3.62 final drive for a DCT car provides plenty of top speed potential. Even if we figure ~165mph at the low end of things (could be higher with a bigger diameter tire), surely that's plenty for any tracks here in NA?

OP, I would go 3.62!

I would listen to this man - he knows of what he speaks

Originally Posted by SYT_Shadow

Yes, for sure. 170mph sounds great so you're not redlining 7th

Lower gearing also means more shifts, more shifts means more heat... interesting to see how the dct will handle that

So far so good. It really hasn't translated into that many more shifts for me either. What you add on going up a gear in some parts you can lose by not needing to drop down as much in others. Will definitely keep an eye on that & share though - but my DCT cooler setup is going to be quite a bit different moving forward so might not be a good example.

[//steve\\]

I also know Schirmer also tends to add an external cooler to the diff as well. Most of the cars I see from them are setup to run the Nurburgring so a fairly high average speed.

[ThunderMoose]

Originally Posted by SYT_Shadow

I'd find it hard not to go with whatever James & Phil cooked up with Dan

I'm concerned about the 3.62 though. With a 285/30 tire which I want to run, with a 8400 redline top speed is limited to 152. That is way too slow for the Big Boy tracks.
It's so odd the Schrimer cars run such a short diff in what is probably the biggest big boy track on the planet
3.45 takes my max speed down to 174... more manageable.

As far as coding for the 3.62, Alex@Alpine is able to do it even if you have some else's tune, so that would be my path.

I have a 3.91 and only a 5 speed and can hit 145 on 245/40/18's at 8200. I would think a 3.62 and 7 speed would still be >165, but I haven't done the math. What is the ratio of 7th gear? Diameter of 285's?

[nicksm3]

aprreciate all the info here, great stuff and what a learning curve for me.

[OG Shark]

Originally Posted by //steve\\

I also know Schirmer also tends to add an external cooler to the diff as well. Most of the cars I see from them are setup to run the Nurburgring so a fairly high average speed.

Good point on the diff cooler, we run one as well.

Originally Posted by ThunderMoose

I have a 3.91 and only a 5 speed and can hit 145 on 245/40/18's at 8200. I would think a 3.62 and 7 speed would still be >165, but I haven't done the math. What is the ratio of 7th gear? Diameter of 285's?

Yeah > 165mph - we're just helping Danny work through some fuzzy math. Trying to do it nicely so he doesn't get mad and take me out at Laguna Seca tonight (when he laps me )

7th is 1.000, we're using ~630mm for the diameter

[SYT_Shadow]

Originally Posted by OG Shark

Good point on the diff cooler, we run one as well.



Yeah > 165mph - we're just helping Danny work through some fuzzy math. Trying to do it nicely so he doesn't get mad and take me out at Laguna Seca tonight (when he laps me )

7th is 1.000, we're using ~630mm for the diameter

LOL!

I was clearly using some fuzzy math. This is great news overall though!