M90 options

[eriknetherlands]

So in my quest to get my car running again, I've acquired an M90 from Forum member @richard_csi who kindly offered it to me.
Block is now with renowned e9 Restorer Miklos in Hungary.
Engine # is 7400272

I'm open to opinions on what to do with the block - just throw in your experience, wisdom, and anecdotes if you'd like too.
I've read about almost all on the forum that has 'M90' in the text I think by now

I want the car to be able to cruise, and manage daily traffic. I'm not after a race car experience- I'd be better of taking driving classes instead of throwing (more) money into it. But i do grin when I'm first off at the traffic lights, and enjoy a spirited drive now and then through the twisties in the Belgian Ardennes hills and the Alpes (mountains). Still, 'Elegant Sport' is what an e9 is in my view, and I want my wife to be able to drive and enjoy it too. Helps also with allocating funds .

I'm desiring (i think..) an engine that doesn't look out of place in an E9, so i'll likely go for the 'Csi-look'.
As the M90 blocks regularly need new pistons (acc @sfdon who's been very helpful with tips along the way), custom pistons are already in the budget. 3,5 L is plenty for me, no need to go bigger.
So considering 10:1 compression, or perhaps even 10,5: 1. Gas quality isn't an issue here in EU (acc google Ai). Perhaps the price of pistons will force me towards std spec stuff.

wrt to the cam: the 284 Schrick cam seem to be a standard choice, though I've read some members regrinding their original cam to the same specs. Any thoughts on that anyone; pro/con? Would a 284 cam still make it a streetable car so my wife will be able to drive it? I'm not after a car that stutters and judders at a traffic light.
wrt to head choice, I'm not knowledgeable as to what head the block currently has. That'll need to be established (I'll ask Miklos and post pics here)
wrt to intake system I'd like the original CSi Looks. So that's then L-jet I think? I'm always mixing up what's what, and what will work on the head. I *think* the block has an L-Jet setup, though I'm ready to be schooled here. (again; I'll ask Miklos and post pics here) Is Motronic a sensible upgrade from D or L-jet? as it's
wrt to ECU, megasquirt, 123 ignition and other such systems; what the benefit and consequence in terms of required parts & rough cost? I'm in the Netherlands, so i am wondering if some of these solutions are "regional"; I've come to think Megasquirt is system favoured in the US< but don't see it as much on this side of the pond.

I'm considering an approach that if money turns tight, i'll nibble on aspects that i can swap/add a year later. So spending the money with a priority on the inside of the engine, then as we progress through the budget, there will be less frills on the 'outside' so to say.
As such, I'm planning to use the std 3.0 exhaust i still have; it's not new but almost NOS. If that turns out to be restrictive for the engine I can easily swap that out a year later.

Any thoughts? Spot something stupid? Fire away!

M90, confrimed by SFDon:

white painted 'L'

engine #

 

[nosmonkey]

E21 intake runners with a csi manifold would look nice and stock with a bit more airflow for the schrick cam. Not sure i would bother upgrading to motronic, a good standalone system with d jet appearance i think would look great.

 

[ScottAndrews]

None of your photos seem to have posted.

As you know I recently bought a rebuilt M90 with a Schrick 284 cam from SF Don. I took this plunge for two reasons: 1) Don pointed out to me that the US spec 3.0 engine was pretty weak (which is why so many folks convert to M30B35 engines and such) and 2) I have an M90 powered 1980 Euro spec 635, and I love it. Best engine I have ever driven...

I am sure you have read my opinions and experiences with this engine (funny aside...I Googled it a while back and the AI summary included some of the statements I had made about it on this forum.. )

Anyway the M90 running standard old L-Jet is a great ride. I think it runs an 002 ECU (I can check on this for you if you want). You will want to either get the AFM rebuilt or at least check it, and maybe tune up the resistor strip inside.. I would avoid a Megasquirt or other aftermarket setup unless you want to do a lot of dyno testing. The guys in Munich did their homework on the original, and it gets an A in my book.

Years ago, I ditched the Bosch ignition unit, and installed an MSD 6A ignition control unit (I know, sacrilege!) . That, Bosch Silbur plugs, and fat MSD wires seem to give this car what it likes (it also likes Toluene in the gas.. but that's because 91 octane is pretty much all that is easily available here). The MSD gives it a very robust spark.

I woudl definitely try to find an M90 head. I'd start with Don. I know he has several. The cam has a different end, and there are some variations in the cooling passages. You also cannot use an M30B35 head without changing the pistons to retain the compression ratio.. So trying to use original parts avoids going down rabbit holes chasing compatibility issues.

My 635 runs with a Getrag 265/6 overdrive trans, and a 3.07 LSD diff. As I have posted before, that's a high geared setup, but the M90 torque can handle it. In my E9 build I am likely going to use a 3.45, or maybe a 3.25, since I have no business driving the car at 100+ mph. I have a spare 3.07 with the external oil tank, and I am hoping Korman or someone can re-gear it.

Like most EFI cars, the L-Jet is very sensitive to vacuum leaks, so be mindful of hoses and gaskets... You might also want to locate a new fuel rail and some flow tested and matched injectors. AND, be sure to use the right head gasket and new head bolts...

Also get in touch with @Bert Poliakoff here on the forum. He did a major rebuild of his M90 (It is a later Motronic version), and is a wealth of knowledge about performance upgrades on this engine.

Looking forward to your progress!!

 

[rblongboarder]

I believe there's a M90 / Getrag 265 / 3.07 LSD for sale in the forums:

B

Thread 'M90/dogleg/3.07lsd drop out.'

Nov 7, 2023

Due to my current circumstances life has gotten expensive. I’m getting married Early December and have a reconstruction surgery on my elbow soon after. So this e24 has been put on the back burner and might never get to it.

It’s a 79’ euro 635csi with m90, a dogleg 265/5 CR and a 3.07lsd. Offering the full drop out including driveshaft and shifter assembly. Full price will have intake parts vapor blasted. Compression test will be done soon for any serious buyer. The car is currently complete and will not be pulling anything until parts are paid for. If it doesn’t sell I’ll just keep it...

• Bejoe16
• Replies: 24
• Forum: Parts For Sale and Wanted

 

[sfdon]

The M90 Head is specific to the M 90 block.

If you don’t have an M90 Head, you can drill another head to duplicate the important coolant passages.

Failure to do so results in what are called steam holes, which is something to avoid.

 

[eriknetherlands]

When it arrives, I'll crack the block open to inspect what I've bought, and see what head is on. It's supposed to be block that hasn't ben messed with though the wring harness has mods in it.
I'm sure I'll bug you guys with some ignorant questions along the way.

 

[eriknetherlands]

I believe there's a M90 / Getrag 265 / 3.07 LSD for sale in the forums:

B

Thread 'M90/dogleg/3.07lsd drop out.'

Nov 7, 2023

Due to my current circumstances life has gotten expensive. I’m getting married Early December and have a reconstruction surgery on my elbow soon after. So this e24 has been put on the back burner and might never get to it.

It’s a 79’ euro 635csi with m90, a dogleg 265/5 CR and a 3.07lsd. Offering the full drop out including driveshaft and shifter assembly. Full price will have intake parts vapor blasted. Compression test will be done soon for any serious buyer. The car is currently complete and will not be pulling anything until parts are paid for. If it doesn’t sell I’ll just keep it...

• Bejoe16
• Replies: 24
• Forum: Parts For Sale and Wanted

yeah, but that block is in the US. I'm not. These things end to sink if you stick em in a dinghy en push it towards the Netherlands.

 

[rblongboarder]

My apologies... I jumped right into the conversation and forgot you're on the other side of the pond. It's right there in your profile name .. 'netherlands' - head slap. doh.

 

[ScottAndrews]

When it arrives, I'll crack the block open to inspect what I've bought, and see what head is on. It's supposed to be block that hasn't ben messed with though the wring harness has mods in it.
I'm sure I'll bug you guys with some ignorant questions along the way.

Curious, If you "crack the block open" won't that ruin the compression?

Anyway. I'd strongly suggest doing a leak-down test before you open it up. That will tell you a lot about what needs to get done to it. I did this on my 635 M90 years ago when I rebuilt it. Turned out the bottom end and rings were fine. So I just did a valve job. The usual issue with M90s is cylinder to cylinder leakage, and exhaust valves.

Here is a rather amateurish presentation I did with a friend for a group of 6er folks aback about 20 years ago.. Forgive me if this is too elementary. I think the results at the end, comparing three different engines, is informative.

 

[eriknetherlands]

Ok, just returned from the engine builder with the block from @richard_csi.

It'll need some love, but it going to live again. Acc to my engine builder:
Block needs a bore due to the piston rings forming edges on the outer two cilinder walls. You could actually feel them with your fingers. The other 4 bores looked good with some cross hatch still left in them.
So custom pistons are a must.
Cam is worn (see pic), so regrind or choose a 282 or 284 Schrick cam
Oil drain plug was hard to get out: it shaved some asphalt and was missing 2 sides of the hexagon!
We didn't remove the pistons, as the need for a bore was already evident.

Next up are choices to be made
Here's where i am now:
(Happy to learn, so if you spot something stupid/wastefull/senseless, let me know)
1. Go for a compression of 10, 10.5 or even 11: 1 ?- fuel is not an issue here as is can be in the US. Is 11:1 too much?
2. Overbore: just slightly, perhaps go from std 93,4 to +0,3, staying clear of the 94.0 max limit that I find via google
2. I tend to think i'll keep the M90 head, but use new valves, valve guides and seals
3. Inconel valves vs std valves: higher compression makes for hotter gases: is the extra money for Inconel valves really necessary?
4. I wonder about using a B35 crank to raise the stroke from 84mm to 86mm. I'll loose the rev happy engine feel, bit will get a tad more Hp's and a bit more Touring feel.
5. the M90 block seems to have a water heater installed on the side of the block in the location of one of the freeze plugs - ditch, as it's not likely running often at freezing temperatures?

Wrt parts:
Anyone have a lead on custom m90 pistons?
Recommendation for the head gasket? I remember "Cometic" as being referred to as 'good', but doesn't the m90 use a specific headgasket?,

 

[ScottAndrews]

Ok, just returned from the engine builder with the block from @richard_csi.

It'll need some love, but it going to live again. Acc to my engine builder:
Block needs a bore due to rings forming on the outer two cilinder walls.
So custom pistons are a must.
Cam is worn, so regrind or choose a 282 or 284 Schrick cam

Next up are choices to be made
Here's where i am now:
(Happy to learn, so if you spot something stupid/wastefull/senseless, let me know)
1. Go for a compression of 10, 10.5 or even 11: 1 ?- fuel is not an issue here as is can be in the US. Is 11:1 too much?
2. Overbore: just slightly, perhaps go from std to +0,5
2. I tend to think i'll keep the M90 head, but use new valves, valve guides and seals
3. Inconel valves vs std valves: higher compression makes for hotter gases: is the extra money for Inconel valves really necessary?
4. I wonder about using a B35 crank to raise the stroke from 84mm to 86mm. I'll loose the rev happy engine feel, bit will get a tad more Hp's and a bit more Touring feel.
5. the M90 block seems to have a water heater installed on the side of the block in the location of one of the freeze plugs - ditch, as it's not likely running often at freezing temperatures?

Wrt parts:
Anyone have a lead on custom m90 pistons?
Recommendation for the head gasket? I remember "Cometic" as being referred to as 'good', but doesn't the m90 use a specific headgasket?,

Calling @Bert Poliakoff

Bert did a major rebuild on his M90 about 10-15 years back, and he did many upgrades.

I'd definitely ditch the "heater"

Don says: "I don't like regrinds" so go with Schrick.

Not sure what additional evils may lurk in using a longer stroke. @paul cain did it in his 3.8 coupe many years back.

M90 head has special water passages that the others don't have. Also need to be careful of the combustion chamber volume. Using a B35 head on an M90 will LOWER the CR. Yes, the gasket is different. IIRC you can get them from Maximillian, and Walloth. I keep a set of spare gaskets, just in case they become NLA.

 

[eriknetherlands]

Spare gasket - good one, didn't think of that. Thanks for the other pointers

 

[Clubsport_CSi]

So many options, so much money to spend...
For custom pistons, I would select Wössner or JE. Going custom, you could also adopt compression for the different combustion chamber of the B35 head. And benefit from the 47mm inlet valves. Or even go HEMISPHERIC
Would not go beyond 10.5 CR unless heavy sport engine, the renowned tuners did not do so.
As long as not charged, I would not see a need for Inconel. But shape optimized, maybe - like VAC.
It really depends on budget, also regarding use of 86mm crank with S38B36 rods...

 

[sfdon]

Never use anything besides a BMW head gasket.
The ones from Wallothnesch leak horribly. I believe they are manufactured in England.
Carl Nelson helped me on that after 3 in a row were bad. The fire ring is proud of the composite even after final torque.

Race engine builders here that I use can make a 10:1 b34 block with a b35 head.
Custom pistons are whatever you want!


After 10 to one compression timing becomes a serious issue and intake air temperature changes (high) also cause a problem.

A head from a B35 has to be drilled to match the block of an M 90 or you will have a steam hole on one side of the head/block

A 292 cam with a high idle not a problem- you start going into the 300 degree high lift Csl duration Cams and they’re not much fun on every day driving.

 

[eriknetherlands]

@sfdon , thanks for the info.
I'll make sure to get the bmw head gasket. A second one for spares as well likely. I'm guessing based on the engine number they should be able to get me the correct ones?

Re compression and timing: I'm currently planning to use the std L-jetronic setup: does that system limit my compression to 10:1 max? Meaning if i want to go 11:1 i need megasquirt or a similar system?
Wrt to the temperatures, do the Inconel valves not cope with those higher temps?

I have the m90 head with the correct holes, so that should work just fine I think.

 

[ScottAndrews]

Looks like some typical M90 cylinder to cylinder leakage between 1 and 2, and 5 and 6. L-Jet should support higher compression, but Don is right, even with good gas, things can get finicky at very high Cars. Motronic or others that control ignition timing can prob handle high CR better. What specifically are you hoping to achieve?

 

[Clubsport_CSi]

Wrt to the temperatures, do the Inconel valves not cope with those higher temps?

I assume Don is referring to uncontrolled self ignition of the mixture when very high CR and relatively high intake air temperature come together. Not the exhaust valve temperature is the problem; as mentioned, I know the latter problem rather from forced induction M30s.
Not sure if the Dutch summer will actually limit CR on your engine Alpina went up to 10.6 in the B9 engine AFAIK. But for sure, Don has a lot more experience and valid reason to suggest not to go higher with the CR.

Edit: OK, I see - it is related to the L-Jet...

 

[eriknetherlands]

Looks like some typical M90 cylinder to cylinder leakage between 1 and 2, and 5 and 6....... What specifically are you hoping to achieve?

Interesting note on the leakage - I didn't spot that.
It Doesn't help that it's my second head ever to lay eyes on.
What i am hoping to achive? Good question. I am not they guy wanting to be first away at the traffic lights. I still look like 20, but not quite in reality (48).
I do fancy a spirited drive through the twisties of the Belgian Ardennes, the German Bavaria region and the Swiss alps. But I want my wife to be able to drive it as well. And have something that lasts a 100.000 km or 100.000 miles. I came from dual carbs, nadly adjusted, so likely running under a 100 Hp in reality.
So if i end up with a smooth reliable engine with 200 rwhp, I'd be grinning all day long.
So 10:1 compresion combined with the other mods seems to work just fine if I condense all of your above inputs.

 

[ScottAndrews]

Interesting note on the leakage - I didn't spot that.
It Doesn't help that it's my second head ever to lay eyes on.
What i am hoping to achive? Good question. I am not they guy wanting to be first away at the traffic lights. I still look like 20, but not quite in reality (48).
I do fancy a spirited drive through the twisties of the Belgian Ardennes, the German Bavaria region and the Swiss alps. But I want my wife to be able to drive it as well. And have something that lasts a 100.000 km or 100.000 miles. I came from dual carbs, nadly adjusted, so likely running under a 100 Hp in reality.
So if i end up with a smooth reliable engine with 200 rwhp, I'd be grinning all day long.
So 10:1 compresion combined with the other mods seems to work just fine if I condense all of your above inputs.

A bone stock M90 will generate 218 hp. Add in a warmed up cam and 10:1 compression, and you will end up above that. As I have said several times, the real joy of the M90 is the flat torque curve. That provides a lot of forgiveness in gear selection on twisty roads because it pulls from the low end all the way to redline, so the car is just not so fussy and demanding.

 

[Jimmi]

A bone stock M90 will generate 218 hp. Add in a warmed up cam and 10:1 compression, and you will end up above that. As I have said several times, the real joy of the M90 is the flat torque curve. That provides a lot of forgiveness in gear selection on twisty roads because it pulls from the low end all the way to redline, so the car is just not so fussy and demanding.

Scott/Erik - I totally agree with this assessment. My car has an M90 with a mild cam, headers, and a DME. You can see on the dyno it peaks a little above 220 HP at 5800 RPM (you don't need to wind it to redline), with a very flat torque curve. This translates to exactly what Scott describes: a torquey and tractable car that pulls well from lower RPM in every gear. and is particularly enjoyable on the twistiness. Based on your criteria Erik, I think this approach is a great solution for you.