Hello All,
So the story goes like this. I run with an odd group of vehicles that usually consists of:

• BMW x5M
• C5 Vette - High compression built motor - 650whp
• SRT4 Stage 2 - a bit of a freak creation that's faster than it should be
• C6 Z06 Twin Turbo - Ridiculousness

Last summer my car- a 2002 1.8 5 speed: 4.30 Diff - was a stock bottom end, XEDE managed and at 14 PSI it probably made 270whp. The SRT4 and I were just about neck and neck. If I had someone in my car he would inch out and vice versa.

Now my car is fully built running on 20PSI with 310@the wheels with a 6 speed and the same stupid 4.30 rear end. Last weekend the SRT4 and I hopped on the freeway and I quite clearly pull on him in every gear but the gears are so short that I actually don’t gain any ground on him. I get ¼ to ½ a car on him through a gear and then I shift and he is door to door with me again.

My power starts at mid 3000RPM and holds solid until 7500, but I shift at 7500 and my RPM’s only drop to 5500-6000 leaving me with less than 2000RPM of useful power…

My fear is that going to a 3.909 rear end is just going to increase the speed at which I am changing gears, not the frequency. Is the 6 speed simply too close of a gear ratio or will the diff help me?

 

I had this same issue. Absolutely hated the 6speed so much that I went back to the 5 and bought a spare for when it would blow.
What about a ford t5, rx7 t2, or a quaife or other custom dogbox?

 

3.63 is the way. You're still going to shift frequently, but you'll have gearing out to 161mph.

 

That doesn't remedy his situation.
But I agree, 3.6 is the awesomeness

 

Right - So I'm debating. It really might make all the difference in the world to go to a different gear ratio.

The rear end in theory will multiply the length of each gear but not by much. I've come this far with the build - Just knowing it's potential and not being able to use it is too frustrating for me.

 

The 3.6 will spread the speeds out a bit. If they don't work, switch to a 7.5 ford rear end with a 3.42 or 3.27 gear.

 

What's my best source for a 3.636? Just a ring and pinion? Where should I start looking?

 

626 I believe. PM Cueball1, and read his thread about it:
https://www.miataturbo.net/suspension-brakes-drivetrain-49/626-3-63-r-p-swap-trouble-urgent-60305/

 

Mazdaspeed, you'll never find a 3.63 rear end in a junkyard.

 

TSE has them as well:
http://trackspeedengineering.com/sto...2104a03cbbb1ba

 

I do not know how easy it is to flat foot shift a 6 speed, but with my 5 speed, it takes just a little bit of practice to get the shifts right. It should shift like an automatic with no hesitation at all.

If you are unable to flat foot shift, then you need to change to a different tranny oil. I know for a fact that when I used the wrong oil I was not able to have quick shifts, making a switch was all it took to get it back to no hestitation. That could be the majority of your problem.

Gearing should be for what ever you use the car for, or for your driving pleasure.

 

I'm sure I can flat foot shift the car. However - I doubt it with the trans oil that I went with. RedLine MT90 is usually my weapon of choice, however the 6 speed is not happy with it. The Adaptronic is already setup for flat foot shifting so maybe I should give it a go.

 

zxtex and I believe prospero both had it on their cars and it worked flawlessly on the adap.
and I dont think the redline will make that much of a difference, the 6speed is pretty much always notchy and not as smooth to shift as the nb 5sp. you could always switch to the motorcraft stuff we were all raving about a year back. worked pretty good on my 6sp

 

I've always wondered about using gears from S2000 or RX8 transmissions in the 6 speed to set up wider ratios.

 

Any tips on setting it up? We just set a limiter at like 7200 rpm so I think when the clutch is depressed my ignition cuts and aims for 7200. My redline/where I shift is 7500.

 

You should try Amsoil gear oil in your 6 speed. Shoot me a pm and I will get you contact info for who you can get it for cost from.

 

https://www.miataturbo.net/showthrea...t=wot+shifting

 

what is the difference in going to a turbo 2 transmission. Are they more long winded ?

i know it would require a trans mount and all but if it gives a longer run out then why not.

 

Your power doesn't start at "mid 3000rpm". If each shift dumped 3000rpm off the tach, I promise that your car would be way, way slower than it is now. You want to keep the revs high so the engine is producing as much power as it can for as long as it can. If you are shifting too much, you don't need longer gears - you need a longer rear end.

Thankfully the laws of physics still apply to your transmission, despite what the rest of this thread says. Switching to a 3.636:1 rear end will stretch every single one of your gears by 18% without affecting the output produced by the motor (longer gears = more rev drop = less output after each shift). IIRC, a 6sp/3.636 combo has a very similar gearset to a 5sp/4.30 combo, only with a taller 6th for cruising.

What you really want is a lighter clutch, BTW - that's the secret to silly fast shifts. I can shift the 6-speed in Theseus fast enough that the MAP sensor never falls below 100kpa, and I don't use flatshift.

 

we need a gearing calculator link in here pronto lol
plug in the numbers, get the mph readouts = make a smart decision on which fd you need.