bmw m90 questions

HBChris: We thought the same thing re. the red paint when we first saw it, but we decided to leave it as is, not least of which reason being that the ITB’s will . The block is ‘79 / head ‘86 / w/ larger ports and the water jacket.

As for Motronic, the reason it’s set up that way currently is because that was the only option available when we got the cam. However, Don pointed out that with the help of a special nut he has, that it can be converted to a distributor. Long story short we can have it either way. Once it’s back from upholstery we’ll jump back in to the engine bay.

Reference pics:
 

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Thumbs got in the way…

“ ITB’s might be more interesting anyway than the red - lol! “
 
OCCoupe said:
Yes, I was able to source one from BMW. It created a few problems since it used a different harmonic balancer with a 4 bolt setup.
Click to expand...
So did you have to find a s38b38 harmonic balancer or make an adapter?
 
I don't have a M90 block to tell, but perhaps the group here can tell me; are there any structural differences in the M90 block that make it a preferred option instead of boring out a M30B35 block? M90 blocks are pretty thin on the ground these days.
 
The bore and stroke of a b35 are different than a M90 block.
The water passages are different at deck of block of M90
The head gasket is different because of this.
The water outlet on a b35 block is missing
you want more :)
 
x_atlas0 said:
I don't have a M90 block to tell, but perhaps the group here can tell me; are there any structural differences in the M90 block that make it a preferred option instead of boring out a M30B35 block? M90 blocks are pretty thin on the ground these days.
Click to expand...
in my opinion the abundance of b35 blocks make it a way cheaper better option, heads breathe better on a b35 and if you bore it like an m90 you'll have more hp as long as compression stays the same but forged custom pistons are expensive but you would be able to bump up compression a bit, to use a old style distributer on a b35 you'll need a timing cover a dizzy rod and an adapter nut from the older engines
 
x_atlas0 said:
I don't have a M90 block to tell, but perhaps the group here can tell me; are there any structural differences in the M90 block that make it a preferred option instead of boring out a M30B35 block? M90 blocks are pretty thin on the ground these days.
Click to expand...
Shameless hijack, so apologies, but I have a couple of M90 block and crank combinations to clear. One is a non-extended water jacket type, and another with the extended water jacket. Also have a few heads / sets of pistons/rods etc if someone is keen.

UK based but ok to ship
cheers
 
sfdon said:
The bore and stroke of a b35 are different than a M90 block.
The water passages are different at deck of block of M90
The head gasket is different because of this.
The water outlet on a b35 block is missing
you want more :)
Click to expand...

The bore and stroke of a b35 are different than a M90 block.

Yep, that's why I was asking if there's system interactions vs boring the B35 to M90 spec. Meaning, are there M90 block changes to specifically allow the bore vs the B35's bore capacity? (Mains changes, webbing modifications, etc.) Could I bore out a B35 block and have it be functionally identical to the M90, or are there advantages to the M90 block?

The water passages are different at deck of block of M90

Right, that's the holes vs oblong shape coolant passages, right? Is the extra head cooling needed, given the B35 hits the same power figures with the modified passages?

The water outlet on a b35 block is missing

You're talking about the one on the back of the head, right? The one that goes to the heater core? Is there a reason you wouldn't use the B35 upper rad hose (or make your own) that includes this outlet? What other system problems does this create?

Basically, is the extra work of finding a M90 block worth the effort vs boring/stroking a B35 block, particularly if you plan to go with custom pistons + rods anyway?
 
M90 engines have a water outlet on the side the block.

There are twin cooling passenges between the bores on a m90
 
B35 has the best flowing head out of any m30 period. With custom pistons it’s a no brainer , unless your going for insane rpms aftermarket aftermarket rods are very expensive and not needed, I know turbo guys doing 585whp on stock bottom end m30s
Wanna be safe, get arp rod bolts if you wanna spin high rpms with the stock rods
M90 is a great engine. B35 is a better foundation if you don’t mind making one custom motor Mount, you can bore out the b35 much more than you can bore an m90 , m90 is basically already factory bored out with a shorter stroke like don said
 
bavarian said:
B35 has the best flowing head out of any m30 period. With custom pistons it’s a no brainer , unless your going for insane rpms aftermarket aftermarket rods are very expensive and not needed, I know turbo guys doing 585whp on stock bottom end m30s
Wanna be safe, get arp rod bolts if you wanna spin high rpms with the stock rods
M90 is a great engine. B35 is a better foundation if you don’t mind making one custom motor Mount, you can bore out the b35 much more than you can bore an m90 , m90 is basically already factory bored out with a shorter stroke like don said
Click to expand...

Right, I understand that, that's why I'm asking if there's anything different (performance-wise, like enhanced cooling, different webbing clearance, etc) differentiating a M90 short block and a bored-out B35 short block. I haven't heard anyone say the B35 head isn't the best, given the porting and +1 valves.
 
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