M90 Bottom end tear down

[LJ851]

Updates?

[browntown]

Still waiting on some parts and I gotta wait a paycheck or two before it goes to the machine shop. It is hard to watch it sit there, but I don't want to resort to using the credit card and this has been a month of unexpected expenses. I will update when things get moving though

[Doughnut]

m90 is poo.

[browntown]

[browntown]

So, not a lot of progress, but I got some things going to the machine shop over the next couple weeks, and some of the parts are rolling in. Got my kobelschmidt rod and main bearings, picking up the deves swedish steel rings tomorrow at the local german auto shop, my black friday sale haul from Ireland arrived (dual valve springs, retainers, stainless clutch line, steering rack guibo, front subframe weld plates), as well as the ultra-trick goodies from Milos - a overbored throttle body, and spin on oil filter adapter with vdo sending units for the gauges.

It's like christmas!

[BimmerScreamer]

the short stroke is part of what makes the m90 the m90, why change it into another over bored m30.

i have a m90 crank that im keeping just in case i ever build a big six

[Van Westervelt]

Did you ever end up moving forward with this? I know its been a while... :P

[kronus]

hell of a bump


I take back everything stupid 2011 me said about M90s. The block that was in my 635 spent a bit of time in our Lemons car and is now being built for E9 CSL #001.

[Van Westervelt]

hell of a bump


I take back everything stupid 2011 me said about M90s. The block that was in my 635 spent a bit of time in our Lemons car and is now being built for E9 CSL #001.

What combination did you end up trying? I have an m90 in pieces, and two m30b35s complete with all wiring and access. I think I am going to rebuilt the m90, but thinking about using the m30b35 head and intake etc. Or just use the m90 head, upgrade the cam, and at least convert it to motronic 1.3.

[Hooffenstein HD]

I kinda agree, m30 > m90.

How about an M30 with an M90 on the side?

[kronus]

What combination did you end up trying? I have an m90 in pieces, and two m30b35s complete with all wiring and access. I think I am going to rebuilt the m90, but thinking about using the m30b35 head and intake etc. Or just use the m90 head, upgrade the cam, and at least convert it to motronic 1.3.

M90 head is effectively the same as a B34 head with a B35 cam in it.

I've run complete B35s, complete M90, and a few hybrids now. We're currently running a B35 block, B34 head and B35 K cam high-comp hybrid and it's maybe on par or a bit weaker than a full on B35, although I'm sure we're leaving something on the table from lack of high-comp-specific tune and port blending.

In your case, I'd run the M90 with the intake ports blended to match a B35 manifold and 1.3 electronics purely for reliability reasons - L-Jet stuff is ancient and flakey these days and I'm not sure that the bananafold is good for anything other than looking cool.

Depending on the M90 head you have, you might want to upgrade to a B34 head with the hole-type coolant passages rather than the slot type. The changeover was in '82 IIRC.

A B35 head on an M90 is going to lose power.

[Van Westervelt]

Oh heck no, I have the late m90 with motronic 1.1 intake manifold. Just dont know if there is really a benefit of reworking the head to fit the b35 intake mani.