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Mercedes 722.6 NAG transmission, and converter mods

Posted: Sat Aug 06, 2016 5:00 pm
by HenrikGM
Hi All;

Im starting to fool around with these 722.6 Mercedes transmissions, and for smaller engines they seem to be a good unit, besides they are the largest i can fit in the tunnel.

The plan is to install the 722.6 behind a volvo 4cyl 16V turbo engine, yielding well above 650bhp. Application is street/drag.

This little engine is very different from the MB diesels, or the V8s, and certainly also compared to the AMGs, so i will get converter issues. I need some 4000rpm to spool the turbo to the traction limit on a manual for comparison, so the stock MB converter will stall the engine way way too early.

I have called around, and most know how to sell me a 3800rpm converter for a 5,7l SRT, but that will likely still be way lower on my low compression-low boost "half engine", and that will kill the 60foot times badly.

Therefore the hunt for converter information has started.
I hate stuff, i dont understand, so im searching for converter information.

I will be looking at modifying the converter from the 2,3 compressor clk assuming this has a higher stall than e.g. the diesel 320cdi would have behind my little "low bottom end torque" engine.

I do have the skills and equipment to modify stuff, including cutting open a converter, and assembling it again, or will just built what it takes to do so, if needed, but i need a few hints to work in the right direction.

I could increase clearance inside, but that will just increase losses. Stall would go up.
I could remove say every other vane on the stator, or curve the blades more, or even build 5 different stators, and test what happends, but i would appreciate some hints on what direction to go, to increase stall significantly. Remember, im looking for a change from some 2000rpm to 4000rpm stall speed.

There is a company selling modifyed converters for 4000rpm on 3,2liter inline6, and judging from the scares information, they simply reduce the windovs in the stator, by welding in material reducing the cross sectional area.

What paramters can i change to a torque converter that will work in the direction of increasing stall speed?
Is there written materials or books that is focusing on performance converters, especially how to increase stall, then im very interested.

Thanks in advance.

Re: Mercedes 722.6 NAG transmission, and converter mods

Posted: Thu Aug 11, 2016 5:07 pm
by HenrikGM
Noone that can tell what changes inside the converter would drive the stall speed higher?

Im thinking:
Smaller diameter will push it higher up, due to less torque arm.
Fluid flow though the stator would affect stall in the way, that lower flow, would raise stall.
Angle of exit from the stator would increase torque multiplication, but high angle of exit would also close the flow window in the stator.
Lower number of blades would raise stall, and allow for more angled exit.

Im just trying to wrap my mind around this, if there are good ideas or litterature, please let me know.

Re: Mercedes 722.6 NAG transmission, and converter mods

Posted: Mon Oct 24, 2016 6:24 am
by naylon
You will have to start with the outer diameter.

Get an 8" converter.

Open the converter and see if the pump's fin angles are at a positive angle or not.

Will you daily drive? Race?

How much stall you need?

You cannot get the correct converter the 1st time. You need to start with a good base converter and get it fine tuned.

I have 2 cars with 722.6 and can help you as much as I can.

Re: Mercedes 722.6 NAG transmission, and converter mods

Posted: Fri Mar 10, 2017 1:35 pm
by HenrikGM
Thanks for the reply, sorry to say i overlooked it initially.

8" converters for the 722.6, i have never seen, do you have a source for those?

Currently, the car is quite brutal and no so much everyday driver, but i will dampen it a bit. Last 60foot was 1,77 on 17" street legal toyo r1r, in a full equipped wagon on street road.

So the plan is to have it as a enthusiastic periodic daily driver, and drive it on friday evenings event, aiming for low 7sek 1/8mile performance.

I think i will need somewhere like 3500-4200rpm stall. The engine is making 680nm at 4800rpm, but something like half of that at 3000rpm. This is also a limit to what i can get into the road.

What base 8" converters are out there for the MB722.6?

I have been looking as possibly moddifying some of the more "mainstream" high stall converters to fit into the MB housing while retaining the lock-up function, but this quickly becomes very time consuming of course.

Re: Mercedes 722.6 NAG transmission, and converter mods

Posted: Wed Mar 15, 2017 9:18 am
by underhead valve
look a AMG transmissions---I recently had one apart, the insides are different, the converter is smaller (i don't know size though), but at the converter rebuilder it took longer because it had a 2 plate lockup clutch they didn't normally have, inside the trans some of the planets were spur gears not helical