The 6sp does have superior gear ratios. Unlike the 5sp the 5th gear in the 6sp is actually an acceleration gear. It also puts you in a better spot in 6th gear after you shift. I have heard rumor TRE is designing a gearset specifically for the 6sp. If they could strengthen 4th gear and allow a larger amount of oil I think the 6sp would be a far superior road racing transmission.

 

Assumes approx 25" overall tire height

JDM RS 0.825 ratio 5th gear with the VIII 4th gear but limits top speed to about 159mph. Going with this gearing and a switch to the 4.11 is 175mph. I think you are up against the power vs rpm drop when you wind out 4th (120 at 8k) and shift to 5th it drops to about 5600 and its "lugging" and has to spend a fair amount of time trying to pull back to peak power.

The 4.11 gear set and stock IX 4th would be up to 132, and with the VIII 4th gear it would be 140. Then when you shift you are only dropping to 6400 which I would think is substantially closer to peak power rpm.

Lots of math to play with.

 

This is not exactly true. 5th gear in the 6-speed is still technically overdrive, it has a ratio of 0.868. Any time you have a gear ratio under 1.0 it's overdrive.

Almost all manual transmissions, whether 5 or 6-speed, strive for close to a 1.0 ratio in 4th with 5th and/or 6th being overdrive.

 

The term acceleration gear is kind of silly. Its all about overall ratio (compound ratio) anyway, it doesnt matter if I run a 6:1 FD and a .5 OD or a 1:1 top gear and a 3:1 FD. Ignoring the frictional loss and pinion speed differences for a minute, its still the same overall ratio

 

Yes but the split between 4th and 5th is short in the 6sp just like from 2nd to 3rd so it is indeed an acceleration gear compared to the 5sp going from 4th to 5th. While technically it may not be considered that it the gears ratios are such that it works like that. This is how many 6sp are...

Also just to point out many 6sp are 1:1 in 5th and use 6th as more of their overdrive gear (ie 350z, Cayman S, Corvette, etc) just to name a few.

 

JB, while true, it's generally not a good idea to combine a high FD and then mega OD to compensate.

Due to excess stress on the drivetrain, OD should be considered a street convenience only when we're talking about customizing a transmission for race purposes.

 

I know I was being deliberate in my exaggeration. Pinion speed, the size of the OD output gear, frictional loss, etc. all go along way as much as the actual gearing. However the fact remains there are Mitsus that were developed using this bassackwards approach to the tranny. They are all DSMs and we know how reliable those trannies can be.

Back to the subject at hand:

What do you think of my gearing strategy?

 

Every Vette I've seen, be it C5, C6, or Z06 has a 1.00 in 4th with overdrive as 5th and 6th.

Cayman S is obviously an exception, being a unique race design and a 7-speed... but this only proves my point. When you build a transmission for race purposes, overdrive is a street convenience only.

 

You failed to address the first point in my post. A vette uses it's 5th for acceleration...what gear is it's top speed reached? How much RPM does it lose going from 4th to 5th? I misquoted it having a 1:1 5th but regardless your suggestion does not hold true in the real world.

Cayman S 6sp has a .97 5th gear...the 350z has a 1.00 5th. I could name many more cars the same way. Even though the 6sp in the MR doesn't it has the same principle. Look at where 5th falls in the powerband...it is NOT an overdrive gear. Like JB pointed out look where your 4th to 5th shift falls in the 5sp...this a large contributing factor to slow top speed in the evo. A VIII 4th and IX 5th helps this but the problem is still there.

 

THIS

Maybe instead of trying to change the gearing or the tranny in the car you could just get a more aggressive tune or a race gas map and you'll have that porsche for breakfast, maybe up the boost to around 30-32psi and see how it feels, should be much better.

 

You might be right. I have installed on my car a Meth kit but I have not used it once because I don't have a tune for it. I will try to tune it soon and see how it works with a bit more boost and timing.
Also , I could try talking to Dave a Shep to see if a closer 5th gear is available.

 

If you are road racing the 6 speed would have been better, shorter 4th and then a taller 5th. Time for a 4.11 final drive it'll really help you out.

 

forget the gearing. you just need more power. run c16 or e85 and tune the car for 30+psi and the porsche will be dead.

 

The evo 8 4th gear results in 4th gear going 130mph+ its a great mod

 

Yeah 24PSi is a WASTE, get up to 30PSI, you are racing, get going.