Street Car with 3071R : 5 speed with 3.9 OK?
 

Trying to figure if the original 57K miles 5 speed will be fine on the street with built 1.8 and 3071R turbo?
About 320whp DJ.
Gentle on transmission and clutch, no drag racing, no full throttle shifts, no 30 minute racing.

I know racers break 5 speeds, and 6 speeds, and it seem to be related to both- loss of lubrication of the gears and thermal overload weakening material: racing without oil cooler causes miniscule amount of gearbox (and diff) oil to get real hot, to the point of not providing nor lubrication nor cooling.

5 speed with 3.9 ratios are very nice for MIata turbo, only matched by 6 speed with expensive 3.6. So I view swap to 6 speed as 6 speed trans + 3.6 R&P, which ends up being a $1200+ upgrade. I know all why yes, but would love to hear if some have actually used their cars on the street with 5 speed without issues, with 300+whp?


thanks

No :)

Mechanical empathy will keep it alive for a little while but eventually it will fail

This is my experience. If you're super easy on it as you say, it will probably work for a while. If you give it hell, you'll kill it. I lost 3rd in my 5 speed the first time I hit 3rd gear hard with 28 PSI on a GT3271.

Mine lasted about a year at exactly 300 wheel and serious mechanical Empathy Street only

3:90 work great with 6spds, I've had both and prefer 3:90's.

Andrew,
Thanks...

I like to prod every technical dilemma, until I exhaust the options.
Reason for considering keeping the 5 speed is that I am over budget- way over - without 6 speed, on this "pushed by pushy MX-5 friends into build". Andrew knows the story, but it started by friend negotiating Codrus sale of our "community AEM ECU" to me...than worse yet buying a VVT Miata to use for core- its actually a nice Miata may I say. Sad to break it.

I enjoy soo soo much MX-5 community and love the modified cars you all produce, that its an incredibly satisfying experience. So the cost of the build is almost like paying dues, to enjoy the "culture". It's my 6th Turbo Roadster.

18PSI, Pat'sMX, thank you.
I can totally understand your experience based on other's friends experience.

Jmann, - you know, I just remember-ed that indeed it's been said that for track the 6 speed with 3.9 and turbo, is actually very good.
I've driven friends (MikeS) 1.9 w/3071 6 speed and 3.9, and never really thought anything other than it worked well together of it. 3.9 was not at all some kind of handicap, too close ratios.Now that I recall the experience.


OK. I guess I have to kiss goodbye more $$.

I didn't like 5 speed and 3.9. Felt slow. My car didn't like it either. 3rd gear went out at ~200ft/lbs.

What the hell is mechanical empathy? Pussies :fawk:

This has been my experience. You can keep it alive for quite a while by being gentle and careful, but it will eventually just die at those power levels. You really have to baby it. Definitely not suitable for track use or drag racing.

I've given in.
Now its decision time, which 6 speed to fetch.
Have choices form $450 to $900.

As long as you only floor it in 4th it'll last forever.

Studying to be like Tony? :)

--Ian

You want one out of an MSM, and a 3.636:1 to go with it. :)

--Ian

I'm running a MSM 6spd and 3.63 gear on the street with a GT 3071 . I went this route after watching a friend gernade two 5 speeds at 250ish hp and no mechanical empathy. Running 12-14 psi you're going to find the first three gears go by awful fast.

Ian,

Tony is 1 of 1: his own customers find him "tight lipped" but I actually have spoken to him at work(his company) and off work a few times and he was quiet outspoken. And informative.

I am not going to indulge into 3.6..we'll leave this setup compromised to track-ability.

You are worse than drug-pushers, ruining a perfectly responsible family man into an emotional wreck filled with missed parts-buying/upgrades opportunities regrets.

6 speed 1600 with 250 whp and 3.9 works great. Your power will be perfect for it.

A bit revvy on the road but track works well.