Page 1 of 1

M90 and M30 hybrid options

Posted: Tue Nov 27, 2012 9:23 pm
by kronus
I'm taking out my early L-Jetronic M90 for a refresh of the internals. I've also got a completely torn-apart M30B35 and a complete B35 harness from an E34 535i in the shop, and have been wondering about clever ways to combine the two to make an engine that is more powerful than either. I don't want to use a B35 crank, though, as the one I have is damaged (the reason the B35 is apart)

From some reading and research I've come up with three alternatives that I'm now deciding between:

B35 cam, front cover and intake manifold, Motronic 1.3 electronics conversion
This would let me keep the M90 head and not lose compression, which is nice, but I don't get the advantages of the B35 head's bigger valves and better port shapes (I'll be using the B35's exhaust manifolds either way, but M90 head + B35 intake manifold = port mismatch)

complete B35 head on M90 block, Motronic 1.3
The main problem with this approach is lost compression, because the B35 head has bigger combustion chambers than the M90 head, as it's designed for domed pistons (B35) rather than flat (M90). However, I get the head's other advantages, including Motronic 1.3, bigger intake valves, better port matching and flow. It is possible to skim the head to bump the compression back up, but that retards the cam timing and needs an adjustable cam gear to fix.

M90 cam and front cover in B35 head, keep everything L-Jetronic
Some people here have mentioned that L-Jet is way more responsive and revvy than Motronic 1.3. I am not sure if that's true or not, but this option is attractive if it's concluded that the conversion to Motronic is not beneficial. I lose compression, but gain valve size and flow. This is not really a great option.

Any thoughts on any of these alternatives are appreciated.

Posted: Tue Nov 27, 2012 11:56 pm
by tschultz
Interesting discussion about the M90 and compatibility. ... hlight=m90

It is my understanding the M90 crank is similar if not the same as the M30B35.
Also, it appears the M30B34 head is very similar to the M90 head, but is depends if you have the early or late style M90 head.

Posted: Wed Nov 28, 2012 12:09 am
by kronus
crank, or cam? I've heard that about cam, but not about crank. It would surprise me if the crank was similar, as people talk about putting B35 cranks into M90s to achieve strokers.

Posted: Wed Nov 28, 2012 12:24 am
fit a m30 86mm crank to a m90 block ,
bore out the block to 95mm custom pistons and then you have a 3.65L , thats what a mate of mine has done for his turbo engine with a e34 535i m30b35 head
i did the same thing with my m88 engine, almost the same block as a m90

Posted: Wed Nov 28, 2012 12:28 am
by kronus
Custom pistons are $$$, I want to do this with stuff I have lying around :(

Posted: Wed Nov 28, 2012 10:48 am
by bgo
Is the B35 a high compression spec?

Maybe just get a B35 crank and use that engine then?

Is essential what I do on mine as well

Mine came with a 2.8l L-jet engine(unfortunately someone swapped the original M90 to that)
So bought a B35 high compression and just use a hot M90 cam on it with cover that I can still have a L-Jet to make it look original.

Re: M90 and M30 hybrid options

Posted: Wed Nov 28, 2012 2:35 pm
by Flash635
Some people here have mentioned that L-Jet is way more responsive and revvy than Motronic 1.3. I am not sure if that's true or not, but this option is attractive [/quote]

It could be more that the M90 has higher compression and a choppier cam than the B34 that makes it go better rather than injection system.

Posted: Wed Nov 28, 2012 3:06 pm
by tschultz
^^ Or maybe even a lighter flywheel.

I'd have to dig back through and see if it's the crank or cam (i searched using the terms 'built m90')

Posted: Sat Dec 01, 2012 4:22 am
by bpoliakoff
Dmitriy, if you stay with Ljet, the most cam you will be able to run is a 280 grind. If you keep the internals of your M90, Schneider Cams in San Diego will regrind your cam for $125 or so. If you convert to Motronic, you can really go wicked with a cam, but that will be unpleasant on the street. What you have to remember is an early car with an M90 will keep up with an American M to about 100mph. The M90 pulls like a freight train and has gobs of torque. I cammed my engine, which is totally modified with a 284 and will probably lose some low end torque, but with the first gear in my dogleg, I doubt it will be noticeable

Posted: Sat Dec 01, 2012 5:35 am
by kronus
Allright, so it sounds like the plan is to fit a (potentially reground) B35 cam into the M90 head and port it out to fit B35 intake and exhaust manifold profiles.

Does Schneider Cams have cores and cam profiles on file? What chip do you use? Any thoughts on Miller MAF/WAR chip?

Posted: Sat Dec 01, 2012 5:46 am
by bpoliakoff
Just run a port matched B34 manifold. If you go with Motronic you will have to run a front driven dizzy. Also you will supply the cam to be reground unless you have then make you a new one. A reground should be fine, but make sure the cam will accept the drive for the rotor in a front dizzy. You can use any cam from an M30 for the regrind. These guys are as good as it gets and do all of Frank Fahey"s cams. You can google them. Best idea is to call them and speak with Jerry. He will help you figure out which way to go.
As to a chip, I can't say as I am running a stock euro ecu which is pretty wide open. If you go to motronic 1.3, I think a war chip is probably the way to go. The guy that really knows the war chip is a fellow called "Oxen" who lives in Seattle. You can find him on bimmerforums. He has done the Motronic 1.3 conversion on a pre 82 car and knows how to do the wiring conversion

Posted: Sat Dec 01, 2012 5:55 am
by kronus
Great, thanks.

Yeah, the B35 cam I have is the Motronic 1.3 type. I want to run a B35 manifold because I have one available, along with the injectors and electronics that conveniently mount to it. I want to keep the bananafold but it's impractical because of the old-style injectors.

Posted: Sat Dec 01, 2012 6:33 am
by Flash635
If you go with a reground cam make sure the engineer supplies the correct eccentrics to go with the reconfigured base circle.

A new billet cam should be ok but enquire anyway.

Posted: Sun Dec 02, 2012 10:39 pm
by bpoliakoff
Schneider Cams will have the proper eccentrics at a totally reasonable price. There was a guy on first fives that kept his bannana rrunners and modified them to take the late fuel rail and injectors. He did it on a home drill press. If you switch cams, you will also need a new front cover for the late dizzy