4/5/6 speed boxes
Turbo Mini Forums

Okay, so I noticed the ERA ANT posted a wanted for a 5 speed box, and has gotten a lot of downers on the more gears. I figured it would probably be a good idea to start a topic to discuss the benefits/problems with all three boxes. I'm not going to offer to much, other than a few questions.
First, I'm sure the 4 speed box is much stronger, especially for turbo use, but if you're not racing the car, or running it real hard, would it not be fine to have the 5 speed or 6 speed?
Second, a turbo'd car running 150lbft is quite monstrous on any of the gear boxes, but again, if you're not banging through the gears, would they not hold up on the 5/6 speed boxes? and
Third, Let's say you're going for all out top speed, not acceleration, wouldn't the 5/6 speed be better? Top speed on the 4 gear box is what, 130-150? What if you want around 190? Yes fooking flying for a mini, but just run with it, please.

-James

the gears 5 and 6 will be overdriven gears and are weaker by design,
there is a box i have seen that was 5 speed and had a 1:1 5th gear, it looked quite trick and the teeth on the gears was huge, the top speed of this box will be the same as a 4spd due to the 5th being the same ratio as the standard box's 4 gear (ie 1:1)

if you want to go fast you need power and torque, you also need to put this down to the ground, through the gearbox (obviously) even if your not ragging it through the gear box but are say 'croosing' at 140mph how much torque is going through the box? alot...

there is no reason why an overdrive 5/6 spd cant be used but its a bloody expensive problem if you get excited and brake it..
id like one for obvious benefits but there is not enough proof of there strength and ability for me...
an n/a motor every day of the week if i had the cash

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KAD makes a box with a direct fifth.

So you think the n/a box would handle it fine, but a turbo'd car would trash the box with a little excitement? Has anyone run the 5 speed or 6 speed on the forum? Now lets say it's a turbo'd cruiser, constantly doing over 75mph, what would be the best choice? I'm thinking top speed with even a 2.76 diff would be in the 150 range... Again, just roll with the ideas, I'm just trying to get a guage on the pros/cons of all the boxes.

a turbo engine creates power differently to an n/a engine, there is a huge amount of torque in the mid range, its this torque you use to accelerate and cruise (cheers for the spelling). almost all who build a more powerful turbo engine replace the gearset for a stronger set because the standard box is already at its limit,

most the 5 speeds are considered weaker than the standard box
i beleive the KAD box is stronger but it has a direct 5th so is no better for top speed
say you had 250bhp and could legally cruise at 130mph a 2.7diff is still a good choice in my opinion

Yes i moved to the darkside

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But what about acceleration? I would imagine the 2.76 diff is a real pig at acceleration, or does the turbo compensate? And can you get a 2.76 diff for lsd, such as quaife? Wouldn't a 5 or 6 speed get better acceleration with a 3.44 or 3.76 diff?

I had a 3.1FD on a standard 998 and it was still great fun to throw around town. I ersonally don't notice a massive difference in acceleration between different FDs

On 12th Nov, 2009 Paul S said:

I think Gary OS has taken over my role as the forum smart arse

We need JohnK to step in with his tractive effort graphs. I tried knocking one up myself but failed miserably. I got as far as multiplying various points on a theoretical torque curve by gear ratio and FD but got lost after that.

Some graphs and physical data would be great. I'm thinking though that to get a 2.76 diff to perform as effectively as say a 4.-something diff you would have to have 50% to 75% more power than if you had a 4.-something diff?

And something else to think about, if you have so low a diff(2.76) would you have better traction due to less torque, or is it vice versa?

In answer to your question I owned and had to regularly rebuild a JKD 5 speed for a period of some 10 years with a KAD 16V which produced a lot less power and torque than it does now!

I now have a couple of KAD 5 speeders. (1 was a kit and the other was secondhand). The JKD product would not last 5 minutes with the kind of torque youu turbo boys have!

On 5th Sep, 2011 Vegard said:
I stand corrected. You should know

as scruffy says the Kad box is the only one that is going to live with turbo torque,

on the KAD box 1st is a ratio of 2.5, which is the same as the 4 speed straight cut box's, so all you are getting is closer spaced gears, which you dont really want for a turbo lump.

The closer ratios will surely allow you to run a lower final drive, giving a longer first and fith, but second third and fourth would be more like first second and third on a standard gear ratios?

What about the acceleration? I'm gathering that the gear spacing is just to small and parts are too weak for turbo use on the 5 and 6 speed boxes, which is fine, now lets say the car is n/a, would they be fine, as long as the bhp is low down, not a full bore monster?

power low down the revs on an NA engine means its a big torque engine.

The only way to work things out is to sit down and work out the overall final drive between the gear sets you wish to look at.

dont forget that you can change the gear ratios with the transfer gears as well.

Yeah, the transfer gears can make a big difference. What I meant by low down bhp is that it's not a big horse power motor, such as a normal 1275 at 75ish bhp, not a 1460 at 140bhp. Would a 1275 un-modified motor be just fine on the 5/6 speed? And would it be worth it then either, because to get into those gears, you would need power to do it.... And let's say you put in a sccr gear set, with a set of transfer gears that are more for top speed, would it make the engine a real dog?

hi guys didnt even know i had started this topic . my mate has a 6 speed jkd box on his turbo engine that puts out 160bhp and 180 torque and its fine. i would say its the best and most reliable bit of his engine 8-). Also i believe that the jkd 5 speed dog box that fits in the same area as the 4 speed is the same design as the kad? so wont this make them more reliable? or is it the teeth that arnt up to the sudden power dellivery from a turbo engine?

Do it right the first time and make it mint!!!!!!

HAHA about 20 mins ago. lol. yeh thats the figures give or take 1 or 2 and yes he uses it and i have now and again :). are you sure it uses all the box cause on jkd website it says "5 speed involute dog box kit to fit within standard 4 speed box" the bit were the 4 speed gears sit?

Do it right the first time and make it mint!!!!!!

The 'new' kit is a figment of JKD's imagination - maybe if they stay solvent for more than 10 minutes they might get around to making one!

On 5th Sep, 2011 Vegard said:
I stand corrected. You should know

so after all this, are any 5 or 6 speed boxes up to cope with turbo use?

do i take it that the KAD 5 speed box is strong enough?

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heres my KAD 5 speed. Seems to be a bit more compact than the JKD 5/6 spd. Not installed it yet though so would be interesting to see how others fares.

Well mines the jkd 6 speed mentioned above in era ants post. Let me assure u that box gets put through its paces everytime i get in it and is the best part ive ever bought for it and id love 2 see anyone try an break it. Its as era ant said the most relliable bit of my engine by far. Absolutely nothing wrong with 6 speed on a turbo. Mines living proof.