Thread: MYY Gearbox?

Originally Posted by Bush65

Here, 4BE

Hi John

Yes I did see that painted on. I've hunted down several 4BE1 powered Isuzus for other parts (intake manifolds mainly) and haven't found one with a 6 speed yet. I am still looking though. The trucks imported are often completely different spec to NZ new.

The 4BE1's were the narrow and/or short NKR trucks, all the ones I've found were 5 speed MSA's. My MSA-5G was from a 4BE1 powered 2.5 ton NKR. Approx 92 vintage.

Originally Posted by Dougal

You're just not entertaining enough to be a successful troll. Sorry.

Come back to us when you've got a dyno reading. With your fuel screw removed you're probably only doing 100-110cc.

I will try harder with the entertaining just for you Just actually trying to help

In the meantime some data. Like I said, I look seriously at this box, the ratios and the fitment. I've posted these (or similar to them) graphs before in other threads on torque (or force) to the ground Vs Speed.

Obviously a CVT is best. Then comparison b/n MSA-5G and MYY-6S with the same Transfer Case Ratio.


[IMG][/IMG]

Basically you get an extra gear between 1st and 4th - what your looking for.

Now, primarily it is your 2-3 change that is the problem with the MSA. Ie the area in the graph below.

[IMG][/IMG]

So fitting an MYY simply moves the 2-3 gap to a different point - which may be slightly better, as below.

[IMG][/IMG]

Now do your sums, it's only about a 7% increase in torque required to compensate for this with the MSA in this tiny tiny section of speed. If you not pushing it hard - hardly worth the trouble of fitting a MYY. If you are driving it hard, then surely you can squeeze that extra bit out by upping the output from your engine? Surely a better return for time and money, as you get the benefits across all gears.

Or fit the MSA with splitter to get that extra 7%+ to the ground in that very specific sections of driving.


So yes, to answer your question, they can be made to fit. However given;

1. All the calculations I have done
2. The cost of the box and adapting it
3. Alternatives boxes (and the one you already have)

I would recommend to you not too bother. Does that help at all?

If you would like me to plug in your torque curves in to these Force/Speed graphs I can do so. I mucked around with this a lot, 5/6 speeds and splitters. I though my input would help.... and my conclusion was that a MSA with splitter was the best way to go if you (or anyone else) where looking for more than 5 gears. I could plug the splitter data into these graphs too if you would like? Or different combos of TC ratio.

If my input is 'troll' worthy then I don't know what your looking for

Thanks for the info with the 100-110CC. I think I will get a dyno just to be a poof Will you then show us spinning your wheels?

Originally Posted by the_grubb

If my input is 'troll' worthy then I don't know what your looking for

Indeed.
Force to the ground is not the problem. Graph out rpm vs road speed, highlight the 1500-2500rpm band and it'll be much clearer.

Funnily enough, my gearing calculators are showing my old MSA-5P to be the better 2nd-3rd gear than the 5G. But 3-4 isn't as nice. MXA-6R with a 1.2:1 LT230 looks slightly better than MYY in 6 speed.
But. John has found negative clearance between the MXA-6R to the LT230.

Get 130-140cc of fuel and you can spin your own wheels.

Originally Posted by Dougal

...
But. John has found negative clearance between the MXA-6R to the LT230.

...

Just to clarify that point.

When I first put the 4BD1 + MXA-6R in my bushie, I had a fabricated adapter between the gearbox and transfer.

I pulled the slow revving Isuzu combination when I fitted 6:1 diffs and used it to replace the 300Tdi in my rangie. In the rangie I never had room to move the transfer case back, so the adapter had to shorten up as much as possible. I looked at other options including an LT95 transfer case, but ended up using the Atlas that I had bought to go in the bushie.

Now the Isuzus are in my 120, there is plenty of room to move the transfer back, but alas the Atlas is in the 120 and the LT230, with maxi-drive reduction gears is in Mick's 110 behind an LS1 and patrol gearbox.

Originally Posted by Dougal

Indeed.
Force to the ground is not the problem. Graph out rpm vs road speed, highlight the 1500-2500rpm band and it'll be much clearer.

Done.

LT85

[IMG][/IMG]

MSA-5G
[IMG][/IMG]

MYY-6S

[IMG][/IMG]


There is still a gap between 2-3 on MYY. LT85 actually has the best ratios for what your talking about.

Still begs the question: Why aim for a rally car with a power band from 2000-3200 RPM, but only drive it in the 1500-2500 range?

Originally Posted by Dougal

Get 130-140cc of fuel and you can spin your own wheels.

That's what my truck engine is for. My current car is just a test bed. The doors are nearly rusted off Although I did think the point of 4x4ing was not to spin the wheels

And MSA with splitter (cause I can)

[IMG][/IMG]

Then drive and choose which next gear suits best.

Sure there will be times when ideally you'd like to go from say 2nd high to 3rd low.... however just like all boxes (other than a perfectly efficient CVT) none are perfect. At least there is an option to get to a suitable gear.

Originally Posted by the_grubb

Done.

MSA-5G


MYY-6S

And there we have it. Look at the gear overlaps from 30-80km/h (currrent problem spots) and the MYY is a much nicer spread.

Originally Posted by the_grubb

LT85 actually has the best ratios for what your talking about.

Still begs the question: Why aim for a rally car with a power band from 2000-3200 RPM, but only drive it in the 1500-2500 range?

I'd fit a Puma box or eve a commodore/falcon 6sp long before I'd fit a LT85. Looks like I need to add sarcasm tags.

Haven't forgot your email Dougal I've had no chance to look at it between piggin trips that's all...that'll be the first thing I do once I get back to the car..