ass end options
 

I'm finally going to swap out something from the MSM 4.1 torsen I've got. I daily this thing at upper 300s hp, 6-speed and 4.1 is silly.

Has anyone used this 3.3 from MFactory?
MFactory Competition Products - Performance Driveline Components

Or, does anyone have opinions about other options to handle 400hp? Should I be looking at some other swap before spending $800 on the 3.3 (with replacement parts)?

thanks!

https://www.miataturbo.net/suspensio...-92250/page21/

Ted75zcar might be localish to you. He just put a set in.

Check out V8R and Kmiata for big power differential
options. The Getrag from late model GM stuff seems to be popular for lower 3.xx ratios.

The Ford 8.8 IRS pumpkin can be had with a 2.73:1 ratio.

I’m a fan of the 3.9. You’re likely running in the 260 WTQ range too. Easy swap. Wheel hop is the problem and the 6MT would probably give out first. If or when I swapped out the 6MT for a getrag, I would do a different diff as well.

I'm off hunting two options. One, getrag diff at 3.23, which will require a custom driveshaft and half shafts. Or get a 3.63:1 Torsen from UKPrestigeSpares for $700.

Easy button is the 3.63 for sure. But may just be delaying the inevitable of doing some Kmiata BMW swappage of tranny and diff.

And no, not 260 at the wheels. 400 at the wheels is what I'm at. But I'm babying it.

It's important to remember that your numbers are corrected for our elevation. Makes a surprising amount of difference. What were your uncorrected numbers? That's what your drivetrain currently needs to support.

UPDATED QUESTION - I've got an MSM diff. They've got a larger halfshaft and diff center. Does this mean I can't swap the entire thing out with some other 3.63 (Aussie/Brit) diff? (Unless I'm interested in also swapping out the half shafts)

That is correct. New shafts if you swap 3rd members.

I believe the SE (AUDM mazdaspeed) was fitted with a 3.63, but the regular issue NB 6 speed 3.63 would be the regular 1.8 axles.

Ah, thank you for that info. So I have 2 options, swap in new gearset or totally different rear end.

Anyone shredded their rear diff before the 6-speed? I believe I shouldn't worry too much about the rear diff until I've addressed the weakest link (transmission).

I would think you want to swap to a different transmission at the same time. Going to a taller diff will increase the torque seen by the 6 speed, and you're already in gear-shredding territory even though you're babying it. Replace and sell the entire driveline. There are people out there that will pay a premium for the MSM driveline.

I've seen this stated before, but I don't understand how it's possible. How does changing the gearing after the transmission cause the transmission to see more torque? If you could try to explain it or provide a link to an explanation I'd really appreciate it.

It doesn't necessarily increase the max torque seen at the gearbox - an engine provides up to X lb-ft torque, the transmission changes the gearing to increase mechanical advantage to the differential and ultimately the wheels.

A taller rear end (resulting in less mechanical advantage to the wheels) means more torque at the engine required accelerate the car from a dead stop. A taller diff would also increase duration in which the engine is operating in the peak torque as it takes longer to accelerate through gears. Longer duration at high stress could be detrimental to component life.

400 WHP is 280 WTQ at 7500 rpm and 375 WHP is 263 WTQ. That was my point - you are not 400 WTQ unless somehow the universal calculations don’t apply to your build.

TQ peak is not at 7500 RPM on my BP :)

Thank you. That's an explanation I can wrap my head around.

What is your HP, TQ, RPM data point? I obviously know it is a curve. The more HP you have at a given RPM, the less torque it produces. You running a 9000 rpm build or more?

oh I just read WHP as WTQ.

you are getting too pedantic. I just want to get the power down and stop being annoyed by shifting 5 times on my way to the next stop sign. On cold days, I spin the rear wheel in 4th gear. It gets old.

I'd also love to see what kind of 0-60 times I can achieve. I have to shift into third to even get there.

I'm moving forward with a 3.63:1 swap into the existing MSM rear torsen. It'll be fine. I don't need this kind of power, I can't even get it to the ground.

A 3.6 option for your build is a great way to go. Wish I would have gone that way but the 3.9 was an easy solution at the time for us. For daily/city type of driving we generally turn ours down to about 18 psi boost but it’s sure fun to go “north of 4” at 24 pounds even as unnerving as it can be in a light car. Certainly cannot goose it around a short curve or turn.