M90 + M30B35 + Motronic = ?

[goodolarchie]

M90 + M30B34 + Motronic = ?

I'm moving to a bigger garage this month which means space to start tearing down the engines in the 3 rigs in my sig :mrgreen:

I've done a bit of research and haven't settled on the best combination to get power to the rear wheels of the E9. Here's my tentative plan:

-Pull E24 M90 and 265CR, finish cleaning and painting the engine bay of E9.
-Refresh bottom end of the M90 (has about 78k on it)
-Refresh the B34 head from e28
-Use the dogleg 265 with a 3.07 side loader (believe the early E24 had this, can't check for a month)
-Could also use the 265 OD with shorter diff
-Deal with Speedo, diff, driveline issues

So that's the laundry list, the goal is use the e28 motronic and keep the M90/265CR since they have so few miles on them and are a joy when paired.

Any issues mating the B24 up to M90? Piston/valve clearance? By my calculation...

575.5 CC per M90 cylinder / 58cc grants a handsome 10:1 CR, still doable on pump gas. If valve clearance is an issue, is a thicker gasket going to fix it?

Cheers

 

[goodolarchie]

Any wisdom on this is appreciated!

 

[Arde]

I think that sfdon, X_atlas, and a few others can offer guidance.

I have little to say but I feel bad that you got no answers, nobody wants to start a thread and have 0 followers, so here it is:

The OD265 is a well tried route and 99% like the result. I love CR on a 4-cylinder E36, and if you already have it on the E24 then you know the outcome.

Looks like three donor cars make up your project, what happens to the carcasses of the other two? Stan may want to tow them to a barn in New Hampshire...


Speedo is doable on the 265 by just adding the mechanical adapter thingy. Differential is also doable per all the 5 speed conversion threads.

 

[goodolarchie]

I think that sfdon, X_atlas, and a few others can offer guidance.

I have little to say but I feel bad that you got no answers, nobody wants to start a thread and have 0 followers, so here it is:

The OD265 is a well tried route and 99% like the result. I love CR on a 4-cylinder E36, and if you already have it on the E24 then you know the outcome.

Looks like three donor cars make up your project, what happens to the carcasses of the other two? Stan may want to tow them to a barn in New Hampshire...


Speedo is doable on the 265 by just adding the mechanical adapter thingy. Differential is also doable per all the 5 speed conversion threads.

Thanks for breaking apart the spiderwebs

The CR dogleg is too much fun to waste! I may change my mind and use an OD

As to the carcasses - the E24 has a lot of Euro parts (bumper, skirts, interior) that I am hoping to sell to help pay for the E9. I will start this dismantling next month.

The E28 will most likely receive a different head and live on as a daily driver. It's in great shape for 243,000 miles.

What I am really wondering about (hopefully somebody around here will have tried this, but I could not find info searching around) is on the clearance and compression ratio when mating B34 to M90, and which engine components will go into the E9? I know there are clearance issues in the engine bay itself (booster)

 

[x_atlas0]

I'm moving to a bigger garage this month which means space to start tearing down the engines in the 3 rigs in my sig :mrgreen:

I've done a bit of research and haven't settled on the best combination to get power to the rear wheels of the E9. Here's my tentative plan:

-Pull E24 M90 and 265CR, finish cleaning and painting the engine bay of E9.
-Refresh bottom end of the M90 (has about 78k on it)
-Refresh the B34 head from e28
-Use the dogleg 265 with a 3.07 side loader (believe the early E24 had this, can't check for a month)
-Could also use the 265 OD with shorter diff
-Deal with Speedo, diff, driveline issues

So that's the laundry list, the goal is use the e28 motronic and keep the M90/265CR since they have so few miles on them and are a joy when paired.

Any issues mating the B24 up to M90? Piston/valve clearance? By my calculation...

575.5 CC per M90 cylinder / 58cc grants a handsome 10:1 CR, still doable on pump gas. If valve clearance is an issue, is a thicker gasket going to fix it?

Cheers

Sorry for the delay, work gets in the way.

As I understand it, the B34 and M90 heads are effectively the same in terms of flow capability, and therefore power. If you want to refresh a head, I would either move it to a B35 or leave the M90 head and use a cam gear to change the M90 to Motronic with some other bits (upper timing cover, valve cover, throttle, intake manifold, etc) but keep in mind that you will be converting to Motronic 1.0, which is a good bit more cantankerous than Motronic 1.3. You will also have to change the bellhousing on the transmission,as the crank position sensor runs off the flywheel on 1.0, and uses some other sensors (cold start for one) that are eliminated in 1.3.

Gains really come if you go with a B35 head and custom pistons to bump the CR backup to reasonable levels due to the improved flow characteristics of the B35. Also, don't forget that you will have to compensate with a tune to get much out of this at all, as the stock Motronic system does not have enough elasticity to deal with these changes.

So, really, the work required boils down to your parts choices: M1.0 with a B34 head for minimal gains and a lot of work, or M1.3 with a B35 head for more money (pistons, B35 head, M1.3 harness/sensors/crank pulley) and more power.

I personally have a B35 system bootstrapped to a B34 with a Getrag 265 OD, and it runs, but not perfectly. A bit on the rich side, actually. (B34 CR:8:1, B35 CR: 9:1) It has been dead reliable for the last few years, though, so I am thrilled with it from that standpoint. Drove to The Vintage without a hitch. I have been meaning to use a WARchip to properly tune the thing, but life keeps getting in the way. (engagement ring, wedding, etc)