MyE28.com

a friend of mine build a 700Hp S38B36 turbo for a guy who dirfts with an E36. This went all fine until the guy spunn a bearing because he did a bad job on fabricating the sump (to fit the E36)
Now my friend had to rebuild it again but the S38 block was damaged so he took an M30B35 from an E34. He could swap everything over, made a oil return for the S38 head and torqued the head to the same specs as he did on the S38 block.

After the owner put it in the car again he ran it a couple of minutes and checked everything again. He noticed oil in the coolant so he contacted my friend and told him he didn't want to start it anymore so he brought the car to my friend. They took the engine out again and took the head of. After they checked the block they found the problem:

The headbolts are pulled from the block! It has cracks around 11 of the 14 headbolt holes.
Bolt where torqued to a higher spec because of pyramid rings.

Is this a common thing with M30's? The S38 looks to have more meat around the holes. Would studs be a better choice here?

I had an identical situation happen a number of years ago. I had torqued an s38 head onto an m30b34 block and had similar cracks in the block. I spoke with Frank Fahey who has built these motors for several decades, and my mistake was using a thread compound on the stock bolts which raise the torque by 20-30%. Also, I made the mistake of not having my block magnafluxed beforehand. He said a number of blocks he has received over the years had been improperly torqued and cracked at the threads, and a magnflux would reveal such damage. The m30b35 block itself is sufficiently strong to use with an s38 head. And yes, properly sized studs are a better option.

I spoke to some Scandinavian turbo guys and they told me the B35 is weaker and not suitable for high boost because the bolts or studs will be pulled from the block due to less meat compared to the B34 and S38 blocks.

So a lesson is learned!

I have a good S38B36 engine block from an e34 M5 that I can sell it to him for $200.00 plus shipping .

The M30(yes including the b35) blocks have more material between the cylinder and coolant channels even if you bore them to the same size as a B38. It is a pretty usual problem that there is cracks between the studs and oil/coolant channels. I know some people who have driven with the cracks and some who have had engines that mix coolant and oil. I've been lucky to only have crackfree blocks

The B34 block is stronger than the later B35 block. The early B35 block is the one to use if you must use a B35 block. I have 3 of them sitting on a shelf

mooseheadm5 wrote:The B34 block is stronger than the later B35 block. The early B35 block is the one to use if you must use a B35 block. I have 3 of them sitting on a shelf

Actually people here in sweden say that the newer B35 blocks are more beefier around the main bearings, haven't had the chance to compare.. Have an M102 block sitting around and a newer B35 also.. then I've got a B35 block sitting in the car also but unsure about the year of that one. Going to use it for inspections from now on anyway so.

That may be, but the point of failure seems to be the deck of the block. I have never heard of a main bearing issue or a block failure below the deck. The B34 does have more meat in the deck area where the B35 likes to crack.

turbodan wrote:That may be, but the point of failure seems to be the deck of the block. I have never heard of a main bearing issue or a block failure below the deck. The B34 does have more meat in the deck area where the B35 likes to crack.

Do you have any available photos? Would be interesting to see! Going to compare the M102 block to the B35 when I get some spare time but that might have a different cast.

Ventonz wrote:The M30(yes including the b35) blocks have more material between the cylinder and coolant channels even if you bore them to the same size as a B38. It is a pretty usual problem that there is cracks between the studs and oil/coolant channels. I know some people who have driven with the cracks and some who have had engines that mix coolant and oil. I've been lucky to only have crackfree blocks

The first block was a B36, no B38's where used here.
Strange thing is, a very well knowns Swedish turbo build campany suggested the E32/34 M30B35 because they where the strongest! Well, thanks for that but they are crap!

Jelmer538i wrote: The first block was a B36, no B38's where used here.
Strange thing is, a very well knowns Swedish turbo build campany suggested the E32/34 M30B35 because they where the strongest! Well, thanks for that but they are crap!

Read a bit too fast sorry Yes, even most of the companys in sweden recommend to use the B35 blocks because they think they are the strongest. That's why I'd like to see a B34 block to compare, just because I think it's interesting to see and learn about new things

Although there is a M30 with 1140whp here in sweden and I believe it had a B35 block in it. Not 100% sure, gonna check if I find any specs
Found a clip of it though.
https://www.youtube.com/watch?v=NUJLdeXlM5A
I know I've seen the specs of it somewhere but can't remember on which forum it was..

Funny because I've read acouple guys posting that b34 blocks are the strongest.
I guess it's whatever they have is what's going to be the strongest.
Unless I see a racing shop that sees blown up m30s all day posting what they see everything is bullshit.

I'm going to start posting about specifically 89 b35s are the strongest because bmw beefed them up that year
to fix the known cracking problem, then they went back because of cost and fazing out of that engine.
Sounds good right? Everyone find an 89 b35 block, I hear they're the beefiest block.

Ther´s quite a few cracked turbo m30 blocks on a Finnish bmw forum, it´s been speculated that most of them due to the torque spec of 115nm on the APR bolts, leaving them to ~80nm in wich the normal head bolts are tightened has helped with the problem

Allu wrote:Ther´s quite a few cracked turbo m30 blocks on a Finnish bmw forum, it´s been speculated that most of them due to the torque spec of 115nm on the APR bolts, leaving them to ~80nm in wich the normal head bolts are tightened has helped with the problem

So on an B35 block, I even have an early one (1988 635csi) haha, I should torque the ARP's to the factory recommended spec of 80nm instead of ARP's recommended 115nm?

Dunno about S38 but Paul Burke was adamant with me that the B34 block is less prone to cracking up top than the B35.

Is a properly built M30B34 as strong as a S38 B36? Assuming both engine make 1500 hp.

Both engines have the same high quality internals.

The thicker wall thickness of M30B34 should make it stronger compared to S38 B36. What are your opinions?