M20 twin turbo cracking heads. Please help

[zoomer]

I got tired of destroying 885 heads, so I installed m20b20 with 731 head and removed the water cooling from the turbos. And voila - no cracked heads so far (although I had several blown gaskets but thats another story)
By the end of the month I am planning to install the m20b28 engine again with a fresh head. Hopefully the issue was with the water cooling (my theory is that since there are 2 turbos the coolant gets too hot and when it goes in the back of the block it goes directly to the head, so the front of the head is nice and cool and the rear is very hot and it cracks)

[barbierij]

almost a year later...what did you find out!?

[mikebloco]

I would go bigger single and make life wayyyyy easier

[CorvallisBMW]

^ I would be tempted to agree on the sequential vs parallel routing. I would aim for parallel routing on coolant and oil if at all possible.

[Bubbles]

I think that the turbos will be OK even without the coolant lines as I used to have a m20b23 with TD04HL turbo and I used it without the water for about an year without an issue.

This does not mean that turbo cooling is not necessary. The oil does a lot of cooling for the bearings, but if the bearing housing is built with a water jacket, it SHOULD be used. Especially with a twin turbo setup, since you just have a T in the oil feed line, one turbo could potentially be starved of oil. You need to have separate coolant passages otherwise you're heating up the second turbo in line instead of cooling it. The turbine housings and bearing housings are meant to withstand that kind of temperature. A normally NA engine might not have been designed to withstand that temp. I'm not saying this is the root of the cause for a cracked head, but you will definitely destroy your bearings in your second turbo over time.

As to the actual head cracking, have you done a coolant flush and/or inspection of the coolant passages to look for blockages? Hot spots can cause more thermal expansion and cracking. just an idea.

good luck

[zoomer]

The when the first head was cracked, we were just tunning the engine. It was on the highway and the temp was stable 80-82 degrees.
I dont think tunning is the issue as the person doing it is one of the best here in Bulgaria and has alot of experience especially with M20 engines. The blown head gasked was a result of installing a very cheap head gasket and not resurfacing the last head (the m20b20) The 885 heads that were cracked, had perfect head gaskets.
The reason I am almost 100% sure its the turbo cooling is because the 3rd try I drove without the water cooling, with just oil and the head survived.
Also the fact that I drove the car NA for several thousand km before I installed the turbos and it had 0 issues during that period, points that the problem is with the turbo setup, and I really cannot think of any other reason.

[ak-]

I'm saying the cooling setup you have for the turbo's isn't going to crack your head - I didn't mention the cooling system as a whole. If you think you have cooling issues, log your temps.
I also didn't say your turbo's are burnt/bad :) I was saying that if you would destroy one, it isn't going to play a variable in your head cracking. You don't even have to run water through the, - oil is just fine.

Who tuned your MS? Are you sure that your tune is good enough not to be blowing out headgaskets and causing heads to crack?

[zoomer]

I'm going to say that your cooling option for the turbos have nothing to do with your cracked heads. If you burn out s turbo, you burn out a turbo..
I haven't seen any mention of the type of tuning you're supplementing this build with. How sure are you of it and being solid?

On another note, I would not use replica wastegates unless you have some sort of boost protection/ignition cut off. I've broken two of them and overboosted with an old engine before buying a genuine tial and then implementing over boost protection.

If the cooling is not the reason, how can you explain the cracks.
btw the second head is cracked in identical way (the crack is the same size on the same place)
I am not saying you are wrong, but I am really out of ideas.
Apart from that I never said anything about burnt turbo. Both turbos are running fine.
What do you mean by "what type of tunning"? The engine management is MS2 Extra

Regarding your note for the wastegates, I agree, this is why there is overboost protection set through the megasquirt.

[ak-]

I'm going to say that your cooling option for the turbos have nothing to do with your cracked heads. If you burn out s turbo, you burn out a turbo..
I haven't seen any mention of the type of tuning you're supplementing this build with. How sure are you of it and being solid?

On another note, I would not use replica wastegates unless you have some sort of boost protection/ignition cut off. I've broken two of them and overboosted with an old engine before buying a genuine tial and then implementing over boost protection.

[zoomer]

The oil is parallel and the coolant was sequential, the reason I did this was because I was afraid that since the coolant line is not identical for both turbos (having in mid that it goes to the front and than to the back), and water (coolant) is trying to go the shortest(easiest) way there might be the case that the water is circulating only through one of the turbos.

I think that the turbos will be OK even without the coolant lines as I used to have a m20b23 with TD04HL turbo and I used it without the water for about an year without an issue.

And yes, I am planning to get some blankets for the exhaust housings and get some ceramic coating for the exhaust manifolds. I just need to get the engine running stable first

[Bubbles]

Just inspected the pictures closer. you should DEFINITELY have a separate coolant line for each turbo. I would also put some blankets on your turbine housings. Good that you wrapped the comp inlet piping for the aft-most turbo, but more shielding of the turbine housings to other adjacent parts is very important. Don't want to start melting components with two little 900°C radiant heaters!

[Bubbles]

Did you say that you've got the coolant line running into one turbo, then the outlet of that coolant port is directed to the inlet coolant port of the second turbo? If you do have the coolant ports connected in series like that, I wouldn't be surprised at all if you're overheating the second turbo in line. Those coolant lines really should be in parallel. If you were overheating that second turbo, I hope you didn't coke up the internal journal and thrust bearings! Similarly, the oil inlets should also be in parallel since the oil does a considerable amount of cooling as well.

good luck!

[zoomer]

So here is a quick update.
I strongly believe the issue is the water cooling of the turbos.
I had a complete m20b20 engine lying around so I dropped it instead of the m20b28 and bolted on the turbos without the water cooling. I ran the engine for about 300km at full throttle at 0.7bar and the head survived (well the head gasket blew but it was kind of expected)

[TheTacoMan]

You should do a sequential turbo setup, would be so easy they way you have it setup.
einstein is right, I havent cracked a head yet. Been at 15+psi for about 2 years now.

[einstein57]

I know high hp guys weld that part of the head. Not uncommon to crack under high boost. What head gasket are you running now?