Pick up the phone and ask a master engine builder what he thinks….
Terry Tinney
livermore California
Terry Tinney
livermore California
bmw m90 questions
- Thread starter bavarian
- Start date
So the only real pluses to an M90 are
Nostalgia and maybe bragging rights to getting more HP the hard way?
John
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I’m curious why the choice matters unless you are doing a super low budget build (B35 wins), or a vintage race motor where you are supposed to use the correct motor, you are limited on displacement and ready to spend $$$ to find every last HP.
John
John
gazzol
Well-Known Member
Can't answer about the m90 head cracking, you can't use the s38 head gasket as the engines use different timing chain casings and moreover good quality performance gaskets aren't that expensive. You can use moronic on an m90 if you change the upper timing cover and the camshaft to a moronic one (to take the rotor arm in the end of the cam) or alternatively lock the distributor so it doesn't advance anymore otherwise you will end up with too much ignition advance. You will need a crank signal to run motronic too. As for power be prepared to be disappointed. The engine is stock apart from a marginal increase in compression so there will be a marginal (if any) increase in power. The m30/m90 never makes big power natrually aspirated in road trim.and even with a lot of money thrown at them 260-270 at the flywheel is all you can get with the standard inlet manifold without forced induction. Having said that a good m90 with a fast road cam is a nice tourqey motor and plenty quick enough.
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gazzol
Well-Known Member
Who said anything about more horsepower? All the power is made by the head not the block, the block just deals with it and sends it to the transmission. Your theory about bragging rights is pretty accurate though
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One way race motors product more power is via tuning for operating at higher RPM (at the cost of longevity). Comments I’ve seen here suggest the M90 is more friendly for that purpose.
gazzol
Well-Known Member
Maybe the m90 is a better casting and is therefore stronger or can be bored out more but like I said the block doesn't make any power at all it simply deals with it, cramming more air and fuel in is what makes a bigger bang. If you bore an m30 to 93.4mm and put an 84mm crank in it assuming everything else is the same in both engines then give it take a little they will produce the same power.
gazzol
Well-Known Member
Very interested to know more about that thermostat housingA bit of LH Owen M90 Eye Candy for you!View attachment 145292
Both the M90 and the Eurospec M30 10:1 engines are great to install and drive.
We do a little of everything with the M90 engines- from stock to 10:1 custom pistons mated up to B35 heads and bored to 94.5mm with M rods. We emphasize low rpm’s and high torque in our builds.
Last weeks Dyno of a 10:1 euro spec “dirty motor” with a Schrick mild street cam.
We do a little of everything with the M90 engines- from stock to 10:1 custom pistons mated up to B35 heads and bored to 94.5mm with M rods. We emphasize low rpm’s and high torque in our builds.
Last weeks Dyno of a 10:1 euro spec “dirty motor” with a Schrick mild street cam.
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bavarian
Well-Known Member
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its more rev happy due to the shorter stroke , the motor mounts are all bolt on when installing in a e9 chassis while the b35 motor mount on one side will need to be modified , all the old e9 engine components will bolt up to an m90, its pretty much carb conversion ready . performance wise the block isn't much different besides being better than the old motors but not better than the new ones , m30b34 has a tougher block than a m30b35. the m106 block in my opinion is the best m30 block due to piston cooling jets, getting harder to find nowadays. if i had to build the perfect m30 it would be a 3.7 stroked and turboed with a m106 block, a m30b35 ported head with a twin scroll top mount turbo on 15 psi flowing into a s38b36 intake manifold and itb's , with this platform you can achieve 500-700 torque easily and reliably
Are those DBilas intake manifolds?A bit of LH Owen M90 Eye Candy for you!
For reference only, 87/88 b35 motors have the passenger side bosses for a b30 motor mount.
gazzol
Well-Known Member
My old m90 and my new m30 (86mm crank) both rev to 7K rpm. Ironically the m90 produced more torque than my m30 due to the milder cam and inlet plenum verses itb's. I'm currently getting a b35 head done by a renown race engine builder and I'll be hoping for close to 280 bhp.
reedreed
Well-Known Member
Could I contact you to find out more about this project and how realise it Europe were I'm based?
ScottAndrews
Well-Known Member
The bore and STROKE of the M90 are different, so it is very difficult (impossible?) to convert an M30 to a faux M90. Need to bore the block, and that may or may not be possible, depending on the cooling passages of the M30. You might just go right through the cylinder wall. You would also need to source a SHORTER stroke M90 crank. Once you are that far in, you might just as well source a real M90.
IIRC Paul Cain stroked an M90 and created a beautiful 3.8 liter engine... That made more sense than starting from an M30. Not sure if he used an M30 crank, or something more custom.
M90/M88/S38:
Bore 94.3 mm, stroke: 84mm
M30/B32 ("3.3" liter) (added)
Bore: 89, Stroke: 86mm
M30/B35: (corrected)
Bore: 92.5, Stroke: 86mm
The larger bore of the M90 means that the cylinders, are very close together (only 6.6 mm apart). A typical failure mechanism in these engines is head gasket blow-by between cylinders (AMHIK). This also results in different water passages in the block. It is common to look for the side water passage on the block as an M90 identifier, and this was the case for early M90 blocks. it is my understanding that the later incarnations of this block did not have that. The M88/S38 engines used different pistons and (obviously) a different head, and they also used a dual row timing chain, since there is a lot more valve train to drive.
The M90 was originally an offshoot of the M49 racing engine. It was the block developed for the M88 engine using in the Euro M635. The M88 and it's later incarnation as the S38 (in the US M6) used a DOHC head, and higher compression pistons. Apparently the BMW Motorsport folks wanted to test the integrity of the new architecture (specifically that close web spacing between the cylinders), so they fitted an SOHC head to the new block, and this became the M90. It was used on the early E12 based 635's (all Euro cars).
The M90 is notable for its very strong and wide torque curve. I have raced ("spirited driving") many M6 cars in the hills above Silicon Valley in my M90 powered 1980 635, and obliterated them on uphills and in the twisties. The car is light, and it just powers out of turns and up hills. Out on coast highway, they passed my like I was driving a Yugo. I once traded cars with an M6 owner (Pete Kelly) on a group drive. My observations supported my experiences in the hills. The M90 torque comes on almost immediately, and holds on to redline. The M6 (S38 engine) is pretty pedestrian until about 3500 RPM, at which time it feels like you have lit the afterburner. Very definitely different engines..
I have attached an interesting and detailed history of the M49, M88, S38 and M90 engines that was published many years ago on the FirstFives site.
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Isn't it:
M90/M88/S38
Bore 93,4mm, stroke 84mm
M30B35
Bore 92mm, stroke 86mm
The rare E3 M30B33 has the "stroker crank" with 88,4mm stroke.
Agree on everything else!
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ScottAndrews
Well-Known Member
Yes, sorry. I wrote that from memory. Corrected the post above!!Isn't it:
M90/M88/S38
Bore 93,4mm, stroke 84mm
M30B35
Bore 92mm, stroke 86mm
The rare E3 M30B33 has the "stroker crank" with 88,4mm stroke.
Agree on everything else!