Boosted folks with taller final drives... happy?
 

Gents,

For those of you pushing serious power, have you swapped for a taller ring/pinion set? For the NC's, the 6spd was the stronger transmission, but the gearing is so low as to be nearly pointless.

I'm strongly considering a swap to the 3.72 final drive. Sure, it's only ~10% different than stock, but that's enough to see 60mph in second gear and certainly enough to shave a few hundred RPM off cruise speed. Since my car will spend most of its life as a street bruiser, this seems like a no-brainer.

Thoughts? Flames? Abuse-the-n00b time? :giggle:

You have an NC? I'm not sure what final drive ratio you're coming from.

All the 2009++ NC's have 4.10 final drive.

NC's came with 4.10's... which is 10% higher than 3.72.

As a boosted guy with an NA 5 speed, 1 feels too short and you could probably space the others out a bit to compensate. When/if I upgrade to a 6 speed, I'll go to at least 3.6 or maybe 3.3 rear gears.

Not sure if I'd go so low as 3.3's, but good to hear someone's opinion. Also this thread demonstrates that I need to set up my autosignature...

My setup at 18 PSI, 4.10's are shorter than I'd like with a 6 speed. I think a 3.636 gear would suit this car very well at the power it's making now. It's driveable with 4.10s, but you're shifting a lot. If (when) it has more power I think I'm going to install a numerically lower R&P gear.

When did you last have a revlimiter lower than 8k though? lol

3.3 gears don't exist for NA/NB miatas.

MiataRoadster definitely sold some for a while. Came from a diesel B2000 if I'm not mistaken.

Actually at 7.5K right now. :) Look at me trying to be nice to my engine!

Yeah, the 7500RPM redline in the NC MkII and later helps a little bit. Looks like the 3.72 might be a good way to go.

I had a 4.10 with the MSM 6-speed. It was horrible.

Did the 3.63 over the winter. At just 230 whp I'm happy I did it. When I up the boost I will be even happier.

For people with NA/NB's, it'd be silly to do anything other than the Getrag. I see it this way: I had an MSM torsen, which is easily worth $700. I bought gears for $400 (which was a steal) = 1100. Cost me about $300 to install = $1400. And I now have a spare set of 4.10 gears (worth about $3).

Getrag swap is $1500, plus diff probably another $400 from what I've seen people buying them for = $1900. But then I have stronger axles, and I'm left with a full torsen swap (axles, driveshaft, and diff) to sell (worth about $800-1000, maybe more) making this course of action considerably cheaper than dropping the 3.6 in an existing pumpkin.

None of this applies to you. BUT this thread will come up in searches.

TL;DR... go with taller gears. Tell us what's available in the NC world.

The one that came in the B2000 does not fit in the miata diff, Moti@BlackbirdFab found one and posted about it on the locost7 forums, here is the thread. MR or one of the other vendors tried to get a group buy going to get them made. It never happened though due to cost and quality issues.

Just swapped from 5speed 4.10 to 6speed 3.63 and it is a fine combo. The first 5 gears are similar in ratio to previous but there is about a 300rpm drop in top gear at 80mph versus prior setup. My speedo is off now but I can fix that with a Revlimiter adjusted gauge face.

I've got the Getrag 3.28 swap in my car. And coming from the MSM 4.10 w/6 speed which I pretty much hated once I started making power; I absolutely LOVE it.

Running 20psi ~ 275whp, there's still enough power to smoke the RS3s in 1st if they're not warmed up, second feels a little long, but everything else is great.

I dearly miss the ratios of my 5 spd with 3.9. Even at 220 whp. The 6 sp with 3.9 sux, and I upgraded to 270 whp.
I drove a turboed Focus with ratios close to a miata 6sp + 3.3 and it very very nice.

The above is all about street driving.

street bruiser means you want them as long as possible. so as low as you can go on the fd
over 300 the 6sp+3.6 can light up 1st at ease, 2nd with ease, and 3rd depending on temp and tires

I guess you should also define what "serious power" is to you ;)
Many of us very different perceptions on power

Serious power in my case will be 350-ish at the tires and a wet weight of about 2550lbs.

I think the main problem everyone is trying to solve here is that high power turbo miatas are incredibly slow off boost and incredibly fast on boost and the transition happens about the middle of the rpm band.

This means that pretty much every first gear that is short enough to not bog off the line will bounce off the rev limiter once boost hits and any first gear long enough to not spin will either bog or eat clutches trying to get off the line fast. If the miata had a flat torque curve from 1500 rpm to redline, everyone would just run 50 mph first gears and call it a day.

The best solution (short of going SC or v8) is probably to just run a shortish first gear and limit power until 2nd/3rd to prevent spin. How hard would it be to rig up a 1st/2nd gear sensor for the miata? Once you have that, lowering the boost would be easy.

edit- I suppose you could just derive gear from the speedo cable- ie, below 30mph turn off boost control or substitute a pulse width of your choosing (selectable with a dial on the dash?)

edit2- wait a second I just remembered the miata uses a cable rather than electronic speedo cable... so where is my ECU getting the car's speed from? Anyone remember where to get a speed signal on the miata for something like an arduino?

1st/2nd gear sensor?
You mean just control boost by gear or boost by speed with the abs/speed sensors?
We've had that for years.

It's not the wheel spin most of us loathe, it's the constant shifting.

Where can I find out more about this rear end. I googled Getrag 3.28 and got stuff about mopar stuff. Sounds interesting.

search his threads. he's got a thread about it

here

https://www.miataturbo.net/suspensio...stalled-83274/

It's awesome, beautiful and amazing. But not exactly what I'd call plug and play. Sorry. Drunk comment is still drunk :)

I've run a 6-speed with 4.10s, 3.909s, and 3.636s.

4.10s are ideal for track cars under 240whp or so. 3.909s work between 270 and 350whp, and north of 350whp, you want 3.636s for better traction in 3rd and 4th. 3.63s are too tall for ~270whp cars - 5th gear feels doggy on track with so much gear.

On the street, 3.636s are great, 3500rpm at 78mph, and you're never beating on the car in 5th on the street (or at least you shouldn't be), and the other gears are short enough that you don't feel like you NEED to downshift to go someplace.

I wouldn't mind a little more rev drop on the freeway with the 6sp/3.63s. A T5 box with G-Force's .75 overdrive will solve that, though.

Speed sensor is very easy. Use the search function. Run a single wire to the ECU for NA6, otherwise its already at the ECU. and profit.

Actually, that's not the problem I'm trying to solve at all....

Foremost, first gear is always going to spin. Nothing we're talking is meant to "solve" 1st gear traction loss. More to the reality, 1st gear is so incredibly short that it's useless for damn-near anything unless towing or a 15% incline are involved. Maybe both.

Also, why are the ONLY two options bog or bounce redline? Are we talking on the strip or the street? Because I'm reasonably confident that a turbocharged application can be reigned in with throttle management. Unless the pedal is pinned to the carpet, I can be reasonably sure of keeping it off the revlimiter.

This seems like a non-sequitur. I'm never going to "launch" at 1500RPM under race circumstances, and if I"m just tooling around on the streets I'm never going to be at such low RPM's unless I've completely stopped. Nobody is asking for a 50mph first gear, unless we're talking about a 250mph Miata here...

Throttle management solves all of this.

The best solution for me is to stretch ALL the gears rather than invoke even more pain with electronic management that further removes me from the decision making. The only place I *might* consider electronic management is in 6th gear, and ONLY because the NC's 6th gear with ~350tq applied tends to rip off all the teeth. Since I have zero interest in EVER going for land-speed records, I have considered using some gear-aware EBC just to ensure I keep it low and slow in 6th.

Based on the other feedback in this thread, it looks like my head is in the right direction. The lowest I've found (native, factory option) for the NC is the 3.72 set, but I can also see other options either with replacement pumpkins or special kits to retrofit other R&P sets.

For what I'm trying to accomplish, the 3.7 is probably fine.

I'm awaiting shipment of Mfactorys 3.33 ring and pinion for my 2.4L ecotec x MSM 6mt setup. Car makes a lot more tq under 4k than probably most turbo miatas and really want to take advantage of that on the highway and any future forced induction plans. Won't get the gears installed till christmas time ish so you'll see me complaining about my 6mt x 4.10 setup for a while.

Megasquirt has boost by gear built right in, NB has the speed sensor in the trans, NA gets it from the cluster.
i went from 3.9 to 3.63 with a 6 speed in my NB and it was a great move with ~250hp. 60mph in 2nd. The shift points were much better at summit point and mid Ohio and will keep me out of 6th gear now that I can get 135mph in 5th.