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Changing Rear Ratio for Track

Grant 302

basic and well known psychic
See my first post in this thread:

Also note that there is some confusion about the T-2/Boss/T-2R Torsens. The Boss is also a T-2R design, just with the 2.7 bias . The FR-500 or 4.0 bias unit is also a T-2R, but often the only one referred to as a T-2R.




Spotting an assembled "R" should be easy and see the Thrust Plate differences:



JMO, but I'd get the 4.0 bias T-2R for AutoX or tight courses. Boss T-2R for track.


TMO Addict
Should get a tune with the LTH
I have an AED Kooks tune now. Definitely wakes the car up. But at a track day this year I chatted with a local drag racer who was running his GT350 with our group. He also happens to have a performance shop and told me I was missing out on big HP by not having a CAI. I was under the impression that a CAI was only good for a handful of HP. He tells me to specifically get the JLT as he has dynoed all of the popular brands and that makes the best HP. With a custom tune (cam phasing?) he is telling me I can see 35-40HP gains. For less than $300 for an intake plus a few bucks for a tune that's money well spent. Guess I will see if he is right. I will post dyno results once I have it done.

Mad Hatter

Gotta go Faster
Santiago, Chile
Hmmmm....... Having the LTH in first makes the CAI useful.... Not much point till you improve the exhaust side of the engine.... Always hear about CAI adding massive hp but never seen it... I Think my airaid CAI plus accufab 84.5mm TB with a tune probably gave me 15rwhp.... I really really doubt that its more.... I think the PMAS CAI (tune needed version) is one of the best right now (but ugly)... And I think the Airaid is better then the JLT from what I have seen.... Lots of CAI's don't do a dam thing. And when they say....NO TUNE NEEDED, then you know its just window dressing.

As far as tuners go..... I would just go with what Shaun from AED says... He lives and breaths Coyotes (cam phasing?? alarm bells went off)


TMO Addict
And I think the Airaid is better then the JLT from what I have seen
Boy I hope that's not the case. I went with his recommendation. He said he has tested them. I got the new version JLT that was released but I have no idea if it really is any different. I still think 15 RWHP is worth a CAI and tune cost but I was stoked about 30-40. Maybe my interpretation of the conversation is a bit off but he seemed very confident about what he has seen and what he can do. He was aware of the difficulties in cracking the Coyote computer but said he has worked with the experts and has it down. Guess the dyno will tell...…or a blown motor :eek:

Grant 302

basic and well known psychic
I'm not sure the semantics make any difference in the end but Torsen seems to differentiate between the T2 and T2R. In addition to the link I provided in post #4 Torsen also differentiates them in the attached
Quoted the wrong post before...this was actually the one that clarified that the Boss Torsen is a T-2R unit. From their website:

"(T-2R) differentials are in the 2nd generation of design, now employing Equvex II parallel-axis gears, which make use of Split-Gear technology. Split-Gear, first introduced for the 2012 Ford Mustang Boss 302, uses a helical spline coupling to the side gears. This gives the model tunable friction characteristics, allowing it to meet OEM customers’ specific needs in a way no one else in the industry can."


This helical spline 'update' is a good reason IMO to go with the Boss unit. Probably also the main reason it costs more.


TMO Addict
Philly Metro Area
3-5 Years
Got it, thanks! I wish Torsen would be consistent in their terminology.

In any case the Boss Torsen is very strong and possibly better suited to our cars - especially those with power adders - than the other T-2Rs.

Norm Peterson

Corner Barstool Sitter
Coz, I see you are in my area so if you know NJMP you know what I mean. On both Lightning and Thunderbolt main straights I am needing 5th gear at half to 3/4 length which really kills the acceleration. Same thing happens at Pocono (probably can't prevent that one) and on the fastest hillclimb I run in Reading which again kills progress. So if I can stay in 4th I will be in a much better position when it comes time to brake. I don't remember going down to 2nd so I don't think that's an issue.

As for the T2R, maybe I am not understanding the bias difference between the Boss Torsen and the FR500 but additional torque to the weighted tire sounds like a better traction situation, especially with a 315 width. But if my interpretation is off please weigh in.
Don't know if you've solved your dilemma yet or not . . . NJMP is my home track. Or will be back to being my home track once I get the car back to being ready for it.

What I can tell you is that at either of the NJMP courses that you pay for being able to stay in 4th down the straights with a 3rd gear that's a bit out of the powerband coming out of T5 @ Thunderbolt and T7 over on Lightning (they're sub-60 mph turns on 285/35 MPSS tires and 18x11 wheels)

You should be a good bit above 130 down either main straight with a bone-stock 5.0 if I'm in the mid-120's with a stockish 4.6. I think I'd gear the car to put upshift rpm a few mph above that or 300 or so rpm below upshift.

One caveat that may or may not apply to Coz's tables depends on whether they were built around mfr-listed tire revs per mile or computed from diameter or nominal size information. The calculated speeds in gears will typically be 3% to 3.5% too high, because circumferential tire tread compression in the contact zone is not being considered. Most times this doesn't matter very much (i.e. speedometer accuracy), but I can see where here it could well make the difference in your gearing choice.

Basically, 130 calculated from diameter/size is really about 125, 135 about 130 . . .

At Thunderbolt, the straight is long enough that you'll either be on your upshift rpm in a lower gear at the end of the straight or close to upshift rpm in the next lower gear going through T12. Lightning isn't quite as fussy but could be the faster of the two peak-speed-wise.

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TMO Addict
Don't know if you've solved your dilemma yet or not
I won't know until I do the Track Night at NJMP is June I think. Joe Aquilante said they use the 3:31 ratio in their cars as well. I'm sure they can swap out gears anytime they want to depending on the track but at least I feel I'm going to be close. If the 3:31 is too low I have no problem trying another ratio (3:42, 3:55 ??) until I get the best compromise. I won't make a decision until I run all the tracks and hills and see where I end up.

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