Strongest g/box for MX5

Blue94t · Postby **Blue94t** » Sat Nov 04, 2006 4:52 pm

Hey guys,
Drained the oil out of my gearbox today in preparation to pull it out and got the nasty surprise of a few loose teeth coming out with the oil.
As a result I am now up for a gearbox. I am guessing I broke the input shaft as I have no drive in any gear.
What is the strongest box for the MX5?
Is it worth upgrading to a 6 speed?
Are the later model/6 speed boxes a bolt in or do they require mods?
Does anyone do a kit to put a different box in an MX5, say an RX7 box or something?
My car is 94 model 1.8 turbo and makes around 160rwkw.
Thanks
Jake

Boags · Postby **Boags** » Sat Nov 04, 2006 5:57 pm

The 6 speed gearbox is what you want... The five speed will start to fo at about your HP if you thrash it (much more if you are kind to it), the 6 speed will hold another 100 or so kw before you have to worry about it.

It bolts straight in too. I'm not aware of kits to bolt up other gearboxes, someone else may be though.

Boags

Mr_Q · Postby **Mr_Q** » Sat Nov 04, 2006 6:20 pm

The SE gearbox is the strongest factory MX5 gearbox available, although the regular 5 and 6 speed boxes should hold up. We've a few customers with your sort of power (and higher) who are running the normal boxes.

Blue94t · Postby **Blue94t** » Sat Nov 04, 2006 6:51 pm

Thanks guys,
I blew the standard gearbox up overtaking a truck on the way back to Melbourne from Townsville where I bought the car.
I didn't even change gears, just pulled out in 5th, nailed it, got about level with the cab of the semi I was overtaking and then it let go.
At first I thought I had ripped the centre out of the clutch as the box was not noisy. One second it was fine, the next gone.

How do you differentiate the SE box from a standard box?

What are considered the limits of the different gearboxes?

What are reasonable prices to expect to pay?
EKW quoted me $770 for a 5 spd, $3000 for a 6 Spd. They don't have the 6 speed in stock atm.

Thanks
Jake

Sheck · Postby **Sheck** » Sat Nov 04, 2006 7:33 pm

Those prices are a bit steep especially on the 6 speed, should be paying around half that.

I broke 2 5 speeds in my car (i did abuse them with clutch poping tho) and i've got a 1.6 turbo running 13psi only on a safe tune (bit rich and minimal timing). now i've got a 6 speed and its holding up pretty well! got cams in the motor too and it lasted a drift-a-rama a friday nite session and will be attending another on monday.
It should hold your power quite well.

Dave

Blue94t · Postby **Blue94t** » Sun Nov 05, 2006 6:49 pm

So is there definite documentation that the 6 speed is the stronger box?
I have been looking around the forums and there seems to be a lot of debate about this.
The only reason I would change to a 6 spd is for strength reasons.
Does anyone know where I can get a 6 spd or an SE box?
Jake

Mr_Q · Postby **Mr_Q** » Sun Nov 05, 2006 10:01 pm

Blue94t wrote:So is there definite documentation that the 6 speed is the stronger box?

Depends if by "definite documentation" you mean "people's anecdotes on an Internet forum".

Blue94t wrote:Does anyone know where I can get a 6 spd or an SE box?

Used 6 spds are rare at the moment. It's not really an item that gets upgraded so the used ones are normally from wrecks. They're a popular item for race cars so they get snapped up pretty quickly.

You can get them through Mazda, but I'd hate to think what the price is.

I think the only difference between the regular 6 spd and the SE one is that one or two of the gears are hardened. You can get the gears, so if you already had a normal 6 spd and time for a rebuild ...

Blue94t · Postby **Blue94t** » Mon Nov 06, 2006 12:53 pm

After researching as much as I could I have ordered a late model 5spd from Mania. They where the cheapest around, even after factoring in freight to Melbourne.
I could not find any solid evidence that the 6 speed is a stronger box so I was not prepared to spend the money on one.
I will rebuild my original box and will be looking in to all the options for making it as strong as possible.
However I don't want to go to a dog box because it is still a street car and must be drivable.
Thanks for all your help

Jake

CT · Postby CT » Mon Nov 06, 2006 4:41 pm

The SE box has a factory shot peened gearset which makes them much stronger than normal 6sp gears. The 6 speeders also have a stronger case which helps to keep the internals together compared to the 5 speeder.

Blue94t · Postby **Blue94t** » Mon Nov 06, 2006 7:43 pm

CT,
I found that in my research. However finding a SE box is a bit like finding rocking horse sh*t.
I will be looking at getting the gears in the box I rebuild hardened. I guess I will probably go through a box every now and again too.

Might have to look in to other options.
Anyone know if the 350z box is an Aisin box?

Jake

Sean · Postby **Sean** » Tue Nov 07, 2006 1:17 pm

butters wrote:if you are really chasing strength and want to do the job properly once. i'd be getting onto ppg and seeing if they do stronger gear sets.

this is what most of the rex boys have to do when they double their power.

PPG used to make them for MX5s, but last time i spoke to them they had ceased production.

I believe PAR are still able to produce a dog set for the 5 speeders.

Blue94t wrote:Might have to look in to other options.
Anyone know if the 350z box is an Aisin box?

Jake

Not sure on the 350z, but the late model 200sx has an aisin 6 speed that shares the internals with teh 6 speed mx5.

I know a guy in sydney who has made an adapter to run a s5 rx7 box, but it's still not a simple bolt in affair.

MX5-SP · Postby **MX5-SP** » Thu Nov 16, 2006 9:04 pm

Blue94t wrote:My car is 94 model 1.8 turbo and makes around 160rwkw.

I find it interesting you are thinking about a 6-speed g/b with that much power on tap. I've often wondered why the SP has a 6-speed (yeah, yeah...I know the answer) instead of a 5-speed as I think the ratio between 1st, 2nd and 3rd is too close. I mean, 1st revvs out so quickly that some extra road contact time would be preferable - (and i've got 25rwkws less than you).

If you haven't already done so, I suggest you try out either a 6-speed SP or SE before plunging in. I kinda think a 5-speed would have more traction time - but before you suggest swapping my 6-speed for your 5-speed - forget it, I'm not that keen to see if it makes a difference.

I also note the Bullet SS runs a 5-speed g/b...but that has a 'bit more grunt too'.

rhysk · Postby **rhysk** » Thu Nov 16, 2006 9:50 pm

The 6 speed in Blue94t's car would be even shorter than yours, Mr. SP.
Yours will have a 3.6 diff ratio versus a 4.1 or 4.3 in the 5 speed MX5s.

StanTheMan · Postby **StanTheMan** » Thu Nov 16, 2006 10:01 pm

Blue94t was talking about changing the diff ratio to 3.6 recently as well.

MX5-SP · Postby **MX5-SP** » Sun Nov 19, 2006 2:17 am

StanTheMan wrote:Blue94t was talking about changing the diff ratio to 3.6 recently as well.

Again I'll say it. I think a 6-speed box in such a powerful car is a waste of time changing gears. If you have the grunt then use it...why waste time flipping gears unless you have to?

Look, a good example is my wife drives a VT Commodore. It has 4 forward gears. I occasionally ride a push bike. It has 12 gears (these are all forward gears). Which is quicker off the blocks...? The answer is not me.

Honestly...It's almost embarressing having to switch cogs 20 metres after take-off (er, I'm not on the bike now...in the SP...in case you didn't realise the subtle shift in saddles).

With the turbo on tap...I can't recall the need to drop down to 1st in tight bends unless I'm too close to Jules...which is sufficient reason to back off anyway. And I have way less power on tap than Blue94T.

Just my tuppence....