Thread: MYY Gearbox?

Originally Posted by Bush65

The place I picked up the MXA-6, removed the original bell housing, because it wouldn't bolt to a 4BD1T flywheel housing and gave me one which would. I never asked what the original bell housing suited, I just assumed 4H, from my limited experience.

One thing I do know is that the ratios 1st to 5th in my MXA-6R are identical to 1st to 5th in a MXA-5R. 6th is tall so I have changed the diff ratio, which has effectively closed the ratios a little. Revs still drop more than what you said you would like on the change 2nd to 3rd, but there is plenty of torque with that amount of gear reduction.

Edit: sorry missed the part about input shaft differences. What gearboxes do you want the differences between?

I had to change the original clutch plate that came fitted to my 4BD1T, to suit the input shaft of the MXA-6R. My engine is an 89, and the clutch plate spline was increased in April 1990 to 29mm x 21 teeth, as specified in the clutch specs.

The MXA-6R ratios work out quite well in the middle, they provide even 2500-1500rpm drops from 1-4th gears and approx 2500-1700rpm for the last two. That would fix the 2-3-4 drivability issue that annoys me. The main question is the second over-drive. Not only whether I can shave enough to make it physically fit, but whether I can actually use a 1600rpm 100km/h cruising gear.
I guess I will know after I get that inertia ring made.

If I couldn't use a 1600rpm top gear, then going back to a 1.2:1 LT230 (which I have, but high mileage) would solve that.

So you only had to change the bellhousing and the only input shaft change was a suitable clutch plate? My current MSA-5G box has the 29mm, 21 spline input shaft and matching clutch already.

Originally Posted by the_grubb

So you do want a race car.

More like a rally car. Group B rangie.

Originally Posted by the_grubb

I rarely go over 2400RPM, as the acceleration between 1500-2500 is excellent, so no need to go higher. I would safely say I easily have 25psi at 2500RPM. No requirement for me for 32psi at 3200RPM (yet).

With no boost reading over 15, how do you know? You could be peaking at 16.
If you were delivering 140cc and had 25psi, you'd bury the EGT gauge with any higher rpm.

Boost gauges aren't expensive. Let us know when you do that dyno run.
For comparison (just one data point, not peak) I had 75kw to the ground at 2000rpm at 800m altitude. On approx 100cc/1000 shots of diesel. You think you're 40% above that, that's a big call, prove it.

Originally Posted by the_grubb

Back to your circumstance.... peak torque (2000RPM) to peak power (3200RPM) (power band), taken from your graphs.

So we have an engine with a power band between 2000-3200, and to make use of that apparently we need more than 4 useable gears.

I am confused again. Your wishing to accelerate between 1500-2500 and so you have the little problem of having to over rev in 2nd (up to 3000RPM) to get into 3rd at 1500. However, that just means you are actually using the engines power band....

Did you want to use the engines power band or not?

I am so confused, you want to match gears to 1500-2500 or to utilize the gears for 2000-3200 where the power band is??

Tell me I am missing something... why not just drive in the range of 1500RPM up to what ever suits?

If we are utilizing from 1500 to 3200 then 4 useable gears is adequate. If you don't want to rev over 2500RPM then why keep talking about peak torque to peak power??

Yes you are missing something. It's the many different ways that a vehicle is driven in many different circumstances?
Some examples: driving through town, open road cruising, winding hills on-road, climbing hills off-road, descending hills off-road, passing trucks uphill on-road etc.

Sometimes you need to be able to go through the gears and still be in the power band on the next one.
Sometimes you want to gently cruise uphill without the engine revving or rumbling.

You know, all the same reasons that all the car makers have for not actually making 4 speed cars and 4wd's any longer.

More gears on one lever with closer spacing make all these situations easier.
More gear levers (splitter) is something Mitsubishi tried in their tredia back in the 80's. The 80's gave us many excellent things. Those tredias however were pox.

I had to modify the bell housing to suit the larger shaft centres in my MXA. The bearings protrude from the front of the case and are used to register the bell housing, so I simply elongated the recess for the lay shaft bearing on the larger centres.

c.h.e.i.f didn't have to change bell housings. So there are some that bolt straight up and some that don't, depending on engine and years most likely.

Originally Posted by Bush65

I had to modify the bell housing to suit the larger shaft centres in my MXA. The bearings protrude from the front of the case and are used to register the bell housing, so I simply elongated the recess for the lay shaft bearing on the larger centres.

c.h.e.i.f didn't have to change bell housings. So there are some that bolt straight up and some that don't, depending on engine and years most likely.

Thanks.
The MXA-6R did come factory fitted to a 4BD2T in mid 90's NPR's, but was also fitted to the 4H engines. I found a wrecker today who has one 4BD2 MXA and I've spoken with others who have had them, just not currently. I understand the 4BD2T wasn't sold new in Aus, so maybe Cheif's box was imported used.

The info is in c.h.e.i.f.'s thread, I just don't remember, it was a 4B??, but not a 'D'.

Originally Posted by Bush65

The info is in c.h.e.i.f.'s thread, I just don't remember, it was a 4B??, but not a 'D'.

Item G525 on this stock-list: Wymer Brothers - Stock List

G525 94 NPR65 4BD2TC MXA-6R

4H application is also listed there:

F496 96 NPR71 4HG1 PARTS MXA-6R

These parts have all been sold BTW. Their website gets outdated pretty quick.

Originally Posted by Bush65

The info is in c.h.e.i.f.'s thread, I just don't remember, it was a 4B??, but not a 'D'.

Here, 4BE

Originally Posted by Dougal

More like a rally car. Group B rangie.

Ok, first step... we've finally achieved to know what you want to achieve...

Excellent!

Originally Posted by Dougal

With no boost reading over 15, how do you know? You could be peaking at 16.

My numbers stop at 15 on the guage, the needle keeps going. I can assure you it is not peaking at 16.

Originally Posted by Dougal

If you were delivering 140cc and had 25psi, you'd bury the EGT gauge with any higher rpm.

I never said I was pokeing 140CC in - you did. Higher RPM than what? My 2400? In all my driving, never above 650C.

Originally Posted by Dougal

Boost gauges aren't expensive. Let us know when you do that dyno run.
For comparison (just one data point, not peak) I had 75kw to the ground at 2000rpm at 800m altitude. On approx 100cc/1000 shots of diesel. You think you're 40% above that, that's a big call, prove it.

Umm I never said I am 40% above anything - where do you find this data to put in my mouth? I have no idea how much fuel I am putting in - I can prove that.

I can also prove that with my set up I can easily keep up with traffic and not look like a tosser revving the guts out of my engine in too lower gear or shuddering in too higher gear quite sufficiently with my 5 speed box. Most of the time I am stuck behind traffic

I fail to see how you can't do the same. If you have more torque and power than me then you should be able to do it easier. If you have less power and torque then perhaps you could increase it to make it more driveable. Simple as that. That is all I have been trying to point out. I've made no big calls... seems you are making them for me.

Originally Posted by Dougal

Yes you are missing something. It's the many different ways that a vehicle is driven in many different circumstances?
Some examples: driving through town, open road cruising, winding hills on-road, climbing hills off-road, descending hills off-road, passing trucks uphill on-road etc.

Err Derr - thanks for sharing that. I never knew cars where driven in the real world...

Originally Posted by Dougal

Sometimes you need to be able to go through the gears and still be in the power band on the next one.

Feel like beating my head against the wall. Isn't your power band from 2000-3200? However you want to drive between 1500-2500? If your happy with as low as 1500 and maintaining thru to 3200 (in the power band) then a 5 speed does your job. Someone build a wall with bigger bricks please.

Originally Posted by Dougal

Sometimes you want to gently cruise uphill without the engine revving or rumbling.

What kind of hill are we talking? There is no such thing as 'cruising' up the side of a cliff unless you have momentum....

Originally Posted by Dougal

You know, all the same reasons that all the car makers have for not actually making 4 speed cars and 4wd's any longer.

More gears on one lever with closer spacing make all these situations easier.
More gear levers (splitter) is something Mitsubishi tried in their tredia back in the 80's. The 80's gave us many excellent things. Those tredias however were pox.

I agree, more gears makes it easier - the maths proves that.

6 gears is 20% more than 5 gears. I can do all the scenerios you describe above comfortably with 5 gears. 6 gears would make it nicer, so would a splitter on the 5 speed.

Don't go comparing with some crappy Mitsubishi. For all I know it was heavy and underpowered. I could pull out some example of a truck with a splitter that went well... Umm like the NPR with the Turboed 4BD1....

Two extremes;

1. Underpowered/narrow power band requires lots of gears to keep the torque to the ground at all speeds. ideally a CVT

2. Perfect engine with copious torque from idle that revs out to infiinity. No gears or gear box would be required.

Obviously limitations in the real world so all cars are somewhere in between. With a wider power band, less gears are required. Would more gears make it better - sure. Are they actually needed - no.

I'm still baffled why you make no mention of your power band in your driving and gear ratios, just only 1500-2500? Or you can keep trying to distract from the point by telling me I need to prove things that you say I have

Thing is, a man of your intelligence know this. Why the bull?

When I sell another 327 adapters to pay for it, I'll buy a Boost gauge and get a dyno and let you know