Detonation horror compilation

[Rust Bucket]

Hi guys,

any of you got stories of detonation in M30 or M10,please share.I'm trying to expand our knowledge of how,where they detonate,when they do.

Maybe we can identify a pattern.Maybe for example,they are prone to break the ring land behind the exhaust valve(not saying they do).

These M30's are no CFM flow wonders,but the most I learn about them,the most I fully understand how serious BMW was about mixture motion.
But lean on it enough,boost on it enough and it will go kaboom.

If I was a millionnaire I would have the thing wetflow tested.So far Joe Mondello have'nt returned my calls(joking).

Have you blown one of these?Dont be shy,please share.I promess we wont laugh

[Rust Bucket]

I kept reading about detonation,in general.By detonation I mean explosive igniting of a air fuel mixture pocket often at extremity of the chamber,that detonates when flame front reaches it.It happen when a pocket of air fuel mixture(not atomized,not well mixed,fuel droplets) react to pressure and heat of the coming combustion flame front.Instead of gently combust like the rest of the chamber,this pocket detonates.

It is surprising at first,but not so much as you keep thinking about it,the most common place detonation occurs in a combustion chamber is not near the exhaust valve.No,it more often is near the intake valve,particularily near the bore,at the opposite side of the valve relative to the spark plug.Reason is
simple enough,the heat from the exhaust valve actually helps keeping fuel hot and vaporized,but the "cool" intake valve does just the opposite.

[marc79euro645]

Interesting! I've popped a lot of headgaskets on my turbo m106 (basically an m30), mostly between cylinders, but, not all. I have a knocksesnse light on my a pillar that alerts me to knock. I've seen knock from mid to high rpm under load, and pull timing or, go richer. I suppose going too rich could cause knock. I have read too much oil in intake tract can also be a problem. I was surprised to see how much was in mine during my recent h/g job. I've since added a catch can, so i'll see how that helps.

[demetk]

On my b35, detonation popped out the headgasket at cylinder 6.



Subsequently, exhaust gases pressurized the cooling system to such an extent that the radiator deformed.



It all happened 350 miles away from home. Loosened the rad cap and was able to drive the car back home with minimal coolant loss. The wideband didn't catch the lean mixture at cylinder 6 because it reads all cylinders. That's why it's important to have all of your injectors flow tested. Obviously I didn't.

[Rust Bucket]

Glad you could get home.

It appear to me the gasket popped right behing intake valve. The B35 head has less quench area.

I am curious about gasket popping between cylinders.
It might not be a localised problem but just the weakest point where pressure could exit,on that thin portion between cylinders.

I got myself a book about porting.I intent to move stuff around on a B34 head.Easily will I gain CFM's but am
concerned about mixture motion.

All of this is very helpful guys.For sure I will do my best to
have each cylinders fed properly and having a catch can.

[turbodan]

There are certainly portions of the combustion chamber that originate detonation before any others. If you have enough sustained det you'll begin to see erosion where it is occurring regularly, more often than not it is on the hot side of the chamber near the exhaust valve. The M30 is a different animal though, I feel the M20 chambers and pistons were more advanced with a more effective quench area.

What I've done in the past with the M20 is reshape the chambers to increase volume in the rear cylinders which run hotter and ping before the rest. Its been a while but I think I remember moving more volume to the intake side of the chamber, deepening the domed area of the chamber especially near the intake valve and spark plug.

[LeiseyJr]

Detonation will usually blow the headgasket if prolonged enough on 10:1 M30s. This is if it is light enough at high RPM to not hear it and for it to not completely kill engine power.
To blow a ringland N/A, which I have not done yet. It would have to be really bad enough to cut engine power a lot and happening for long periods of time.

[Rust Bucket]

The M20,in it's final form (885),is indeed a very well designed two valves head.It's quench area is really good
but not something I can reproduce on the M30.Well,not
while using stock pistons.

[Rust Bucket]

I entertain the idea of a N/A build.Not a screamer but for
sure having a higher compression ratio.Which present a
similar challenge of preventing detonation.Would be my
daily.Dont you know M30 are great on fuel haha(joking).

Pushing the enveloppe of a engine is not something new.
It demands multiple trials and errors,which take a lot of
time...and unlimited access to a flow bench and a dyno.

Only good thing is this platform(M10/M30) is 60 yrs old
so I guess some things can be observed.

So here I am,hoarding pics and stories of M30's going
BOOM

[RobertRO]

I entertain the idea of a N/A build.Not a screamer but for sure having a higher compression ratio.Which present a similar challenge of preventing detonation.

During the past two decades I experimented quite a few M30 engine configurations, on two distinct platforms: E28 and E32.
I had a M30B34 8:1 compression, a M30B34 10:1, a M30B30 9:1, a M30B35 9:1, a hybrid M30 with B35 bottom and B30 head & intake manifold, a M30B35 9:1 with a dbilas 276 camshaft. I also played with several Motronic chips, and even with a Megasquirt.
Looking back, the best setups for spirited daily driving were the Euro M30B34 10:1 with a chip, and the hybrid M30 B35/B30 also with a chip.

Now, if you want to build a daily driver N/A M30 and detonation is one of your concerns, consider that your best "friends" are: flat top pistons (the combustion flame really hates hills on top of the piston), large squish area, and narrow piston to cylinder head gap.
Assuming you have a M30B34 block with 86mm stroke crankshaft, the correct solution for flat top pistons is to order custom ones.
To maximize squish area, use the B34 cylinder head. Bonus, you benefit of its smaller combustion chamber, which helps reaching a higher compression ratio. My experience showed that, for a daily driver, the B34 head (casting# 1277358) is better than the B35 head (casting# 1708843). Not to mention that it is sturdier as well. The larger B35 intake ports, valves and manifold bring in value if you want a high(er) rpm screamer. But screaming is done at the expense of low to mid rpm torque.
The piston to cylinder head clearance should be as close as possible to 1mm, but not lower.

Assuming the parameters listed below:
- M30 block deck height: 217.50mm;
- bore: 92.50mm (stock is 92mm, but you may want freshly machined bores);
- M30B34 1277358 cylinder head combustion chamber volume: 58ccm;
- M30B34 cylinder head skim: 0.2mm (I guess your old cylinder head would use a fresh seating surface);
- M30 rod length: 135mm;
- custom flat top pistons compression height: 40.20mm;
- piston dome volume: -1ccm (= estimated volume for valve cuts, only as much as needed, M30B35 piston style);
- stock M30B34 cylinder head gasket height: 1.72mm;
- stock M30B34 cylinder head gasket ring ID: 93.50mm;
you will end up with about 9.85:1 compression, 1mm piston to head clearance, and the least concern about detonation for a high compression M30. Great for a strong daily driver.
Talk to Conny / Coneus in Germany to provide you with a custom chip. His chips are great value for the money.
Note: all other parameters unchanged, if you keep the 92mm stock bore, then the compression ratio is about 9.75:1.

For the camshaft, I'd recommend the stock Euro M30B34 / M30B35 one, or one with a tiny bit longer duration. Be greedy, and again you kiss low /mid range torque good bye.

[Rust Bucket]

Good stuff my friend.

It's in line with pretty much everything I learned so far,still you got me thinking.

About making the N/A M30 to be used in the winter car.I dont need it to have any sort of top end power.It main tasks are to spin tires in the snow
and cruise on the highway.Being as fuel efficient as possible,which pretty much means higher compression and small camshaft.

I have some euro B32 pistons,with piano tops.I believe them to be 9.3:1 compression.I've been relatively unsuccessful trying to sell them.On photo
they appear to have bad scuffing but they're not that bad and I can have the skirts coated if I want to.So this project is mostly composed of things
I cant sell,with a E23 some other guy cant sell either

I also have B35 pistons in the shed.I can easily mill off the small bumps on the crown,effectively making em trully flat.So here I am,torn between
a smaller 3210cc M30,with significantly smaller bores which shall make for a more efficient engine or...a big daddy 3430cc B34 with flat tops.

Here a Euro B32 piston



Before Robert post I was leaning towards the 3.2 build but now am more into the 3.4 build.I think I can live with feeding those extra 220cc and
the bigger bore is accompanied by a much more effective squish band.

Last thing is,why not being more agressive on the quench height.I was more onto .030" but you suggest 1mm which is .040"

Good stuff guys.Thread almost getting sideway about my DD build but none the less still on the topic of M10/M30 combustion chambers,so all is well.