Manual Conversion - Flywheel mod?

[ian2000t]

So, I'm really excited that I will soon be getting an M90 manual conversion so I can get rid of my ZF22 slushbox!

What I wanted to know is, before I put the M90 in, is there any benefit to lightening the flywheel on these?

[745 TurboGreasel]

There is a long thread on this at the VW board, conclusion is it wont make much difference in ET.

[ian2000t]

Cheers mate, did have a look and found a few threads but nothing definite - and no long thread.

No one on here has given it a try before then?

[745 TurboGreasel]

http://www.vwdiesel.net/forum/index.php?topic=21708.0
http://www.vwdiesel.net/forum/index.php?topic=31989.0
http://www.vwdiesel.net/forum/index.php?topic=29283.0

[v8volvo]

I don't know what the ratio is for 1st gear in the M90 but in the M46 it's pretty short (>4:1) so even with a lighter flywheel I doubt you would see too much drawback in driveability (as far as step-off). With that really short first gear you might get some improvement in acceleration off the line too. However, I doubt the difference would be very large, and unless you're planning to do a lot of stoplight grand prix stuff, having a heavier flywheel will probably help the car be more comfortable to drive most of the time. Particularly the case if the M90's low gear is not as short as the tractor setup in the older transmissions.

Are you planning to change the rear end ratio as well? In the US, ZF cars came with a 3.91:1 R&P while M46 cars had a 3.54... Dunno what was the original arrangement for the M90 diesel cars but if their gearing is anything like an M46, I think running with an automatic 3:91 rearend would not be too pleasant... 1st gear is already almost useless as it is, and the motor spins 2500+ at highway cruise. I'd probably want to change to a 3.54 at least, or maybe better yet a 3.31 out of a manual trans gasser...

[ian2000t]

Won't be doing many traffic light grandprix's! At least not with the turbo lag mine's got!!

I was just thinking of lightening to make it more responsive, but really just changing from the auto to manual is going to help that. Over here we have a lot of smaller winding roads so you are always on and off the power/brakes. With the auto box the revs always drop due to the torque converter when you ease off, so when you want the power back after the corner you've got to wind the torque converter up, then spool the turbo up - by which time you're already out the corner. Holding it in a lower gear helps a little.

Think mine has the 3.73 rear end, which I'll be keeping "for now". However, once I can afford some good bushes (poly?) I'll be putting the 3.54 locker I have in. Will have a look see if I can find any D24 M90 ratios anywhere!

[745 TurboGreasel]

It's an Audi motor, gotta brake with the off foot while keeping the other one to the wood

[ian2000t]

Haha, not wrong!!

Keep saying I think a variable vane turbo would transform these engines - just can't get my head round the controlling of it.