Is this an M90?

From https://en.wikipedia.org/wiki/Octane_rating:

Anti-Knock Index (AKI) or (R+M)/2
In most countries, including Australia, New Zealand and all of those in Europe,[citation needed] the "headline" octane rating shown on the pump is the RON, but in Canada, the United States, Brazil, and some other countries, the headline number is the average of the RON and the MON, called the Anti-Knock Index (AKI), and often written on pumps as (R+M)/2. It may also sometimes be called the Posted Octane Number (PON).

Difference between RON, MON, and AKI
Because of the 8 to 12 octane number difference between RON and MON noted above, the AKI shown in Canada and the United States is 4 to 6 octane numbers lower than elsewhere in the world for the same fuel. This difference between RON and MON is known as the fuel's Sensitivity,[4] and is not typically published for those countries that use the Anti-Knock Index labelling system.

"Regular Gasoline" in Australia, New Zealand and the US: 91–92 RON = 87AKI
"Premium" or "Super unleaded" gasoline in US (10% ethanol blend) 97 RON = 92-93AKI
 
This is getting to be great information. I had wondered why the pumps show RON (R+M). That starts to make sense of things. Thanks for chiming in. I had looked at the wiki and online info before when I was wondering why the octane seemed so low here but had not made sense of it. What threw me is that the pumps still reference RON (R +M) rather than simply calling it AKI, which now is apparent to me that it is. Good to know that the gas is not so much worse here after all. So then I wonder why BMW didn't bring the S50/B32 motor here? That is a very high compression motor and I had started to convince myself it was because of octane availability. Maybe it is more to do with emissions then?
 
i would guess 2 reasons - one their market analysis and our low speed limits of the time ... and their fear of maintaining a car within the emissions laws
 
WISE9UY said:
So then I wonder why BMW didn't bring the S50/B32 motor here?
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I read it was partly due to cost cutting, as they would sell a very large number at relatively low prices in the US, plus we had the 55mph speed limit when they first came out.
 
Bert Poliakoff said:
My E24 with an M90 has a build date of May '81. It is a first year Motronic and according to Andreas Hartz of Mobil Traditions in Germany, original. '81 was also the last year of the M90. My engine does not have a raised water package, but verified as an M90 by the "L" stencilled on the block, and bore size when torn down for the rebuild as. The "81 also uses a 1 year only engine harness and a rare 002 ECU.
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Time to dust off an oldie but a goodie. I posted this back in 2016 and as the years have gone by recently acquired an E24 built May 1982... yes, the very end of the line for the E12 based cars. In this post I think we solidly established the details of the block that helps us identify and M90 and also established that the raise water jacket is a feature only of the pre-1981 cars based on Bert's post above. My car does not have a raised water jacket either and will soon check the engine number. The chassis starts with 55 so it is an M90 car as far as when it left the factory and has the CR Dogleg transmission. But this comment is to address the intake manifold.

I always thought that M90 cars had the older style intake which I have seen referred to as "banana" I believe and "bear claw". Looking at some BaT listings for Euro E24s, most cars have the "bear claw" style, however for one example where it was the later style, the following comment was made:

The early M90 engine with the “bear claw” intake had the L-Jet. The “late” M90 with Motronic has the later-style intake and also a different cam and distributor (in how they connect to each other).
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My car, with VIN suggesting M90 has the later style intake also. So the topic for discussion is whether anyone definitively knows what the correct intake was and if it did change from Bear Claw to the later style, when did this happen? Did it happen with the change to Motronic as referenced by Bert? @Bert Poliakoff which intake did your car have?

I look forward to the input and once done I really should write up the summary of the M90 specifics! That is a long time coming.

PS: To cross link threads, Rob Siegel referenced this thread in one of his four years after I opened this one and that also has some great pieces of information:
 
Sorry for tyhe repeat of an old post, but thought it would help figure this out.
My 635 also has a build date of may 81. It is indeed first year Motronic 1.0 and does have the later intake manifold as well as an 002 ECU of which I have several. It does not have the raised water passage. It is original to my car and matching number and on tear down for rebuilding we verified it as an M90.
 
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Real oem suggests the change from L-jet to Motronic was September 1980, and the M90 ended September 1982. My M90 is from a 6/82 euro 735i, engine no. 7427850.
 
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Here is an M90 from a 1980 Euro 635.

In the "dirty" pic you can see the painted "L". This has the "long" water jacket with 3.5 cast into it. And per one of the early posts, the "A" type plenum supports. It is an L-Jet system.

I had the head off this engine, and can verify that it is actually an M90 based on the bore.
 

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Bert Poliakoff said:
Sorry for tyhe repeat of an old post, but thought it would help figure this out.
My 635 also has a build date of may 81. It is indeed first year Motronic 1.0 and does have the later intake manifold as well as an 002 ECU of which I have several. It does not have the raised water passage. It is original to my car and matching number and on tear down for rebuilding we verified it as an M90.
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Hi Bert, thank you for confirming that the manifold is of the later style on your car as well. I do wonder when the changeover to the newer manifold was. Looking at the BAT cars, 1981 and 1982 have the modern intakes but for 1980 most are the Bear Claw with only a couple having the later style. That suggests a changeover some point in the 1980 production year. Maybe it was indeed September 1980 aligning with the date @Ian C shared.

Thank you also to @ScottAndrews for additional pics. Those really showcase the raised water jack of the early M90s well.

I will try to check the engine number on mine tomorrow if I can get to the car, which is in storage. I had some initial concerns about the lacking raised water jack and modern intake and thoughts that the car may have been engine swapped but then came back to all this information.
 
I was looking for other information and this thread has a great shot of the M90 block with raised water jacket too:

A

Thread 'Looking for engine number location'

I am trying to find the engine number on a 72 E9 motor can anyone help me out. Did they stamp the vin number on the block or does the motor have it own number.
Thanks
 
This thread raises an interesting question about the M90 water jacket. Wonder if anyone knows why they changed it...

The M90 has a much larger bore than the M30. This means that the cylinders are spaced very close together, IIRC about 6 mm apart. This close spacing makes it impossible to get coolant between the cylinders. I suspect that the long external water jacket was part of an alternate cooling strategy. But that then begs the question if how the later "short" water jacket M90s were cooled..

Anyone know anything about this?

Just for fun, I also posted a phot of the exhaust side of the M90. I do not have an M30 around, so I don't know if the structure is different on that side.

ANd for those who have not studied this in detail, the M90 is an M88 with a SOHC head. They built it originally as a test buck fr the M49 racing engine, and then decided to use it in production, but only for a couple of years. I have attached an interesting history of this.
Scott
 

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“The M90 has a much larger bore than the M30. This means that the cylinders are spaced very close together, IIRC about 6 mm apart. This close spacing makes it impossible to get coolant between the cylinders.”

Actually, the M90 is the only block that has TWO coolant passages between each cylinder for cooling.
 

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sfdon said:
“The M90 has a much larger bore than the M30. This means that the cylinders are spaced very close together, IIRC about 6 mm apart. This close spacing makes it impossible to get coolant between the cylinders.”

Actually, the M90 is the only block that has TWO coolant passages between each cylinder for cooling.
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I meant actually between the cylinders. Not sure if the M30's do that either
 
ScottAndrews said:
This thread raises an interesting question about the M90 water jacket. Wonder if anyone knows why they changed it...

The M90 has a much larger bore than the M30. This means that the cylinders are spaced very close together, IIRC about 6 mm apart. This close spacing makes it impossible to get coolant between the cylinders. I suspect that the long external water jacket was part of an alternate cooling strategy. But that then begs the question if how the later "short" water jacket M90s were cooled..

Anyone know anything about this?

Just for fun, I also posted a phot of the exhaust side of the M90. I do not have an M30 around, so I don't know if the structure is different on that side.

ANd for those who have not studied this in detail, the M90 is an M88 with a SOHC head. They built it originally as a test buck fr the M49 racing engine, and then decided to use it in production, but only for a couple of years. I have attached an interesting history of this.
Scott
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I was just under my Euro 635csi with dirty M30 B34 and it looks the same as that from memory in terms of welch plugs and the date markings in the center and of course engine mount.

As another update and to align with @Bert Poliakoff with no surprises, my January 1982 635csi does indeed have a motor number matching the last 7 of the VIN which all aligns with it being an M90. For those interested to look it up, the last seven of the VIN are 5592957. Like Bert's example, I have no extended raised water jacket and later style intake. When I get the car home from storage I will check on the ECU. Below the engine number is "35 6E C" which also aligns with M90 because the other 3.5L engines are marked "34" as these first two digits are for the displacement. The 6 is for 6 cylinders, the E for Einspritz (fuel injection) but I do not know what the C is for because that represents the "differentiation index". Regarding the "35" designation I guess back then the M90 was also recognized as a true 3.5L and had the alternate designation of M30B35LE.

While checking out my 1985 635csi, the engine number on that indeed no longer aligns with the chassis number... just for those interested and that its engine designation code is 34 6E B.

For my 1982 E24, I am most pleased with the outcome because the lack of raised water jacket raised concerns as did the later intake but the learnings here have been great. Thank you for everyone sharing information and hopefully this continues to serve others too.
 
WISE9UY said:
Below the engine number is "35 6E C" which also aligns with M90 because the other 3.5L engines are marked "34" as these first two digits are for the displacement. The 6 is for 6 cylinders, the E for Einspritz (fuel injection) but I do not know what the C is for because that represents the "differentiation index". Regarding the "35" designation I guess back then the M90 was also recognized as a true 3.5L and had the alternate designation of M30B35LE.
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This is interesting. I suspect the famed painted "L" on the M90 represents this LE designation.
 
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