M20 twin turbo cracking heads. Please help

[zoomer]

I've been struggling with a very strange issue.
Let me begin a little bit further:
M20B25, stroked to B28 fully rebuilt, with stock internals and Catcams turbo camshaft. I've been driving it for 3-4k km NA without any problems.
Than we built a twin turbo setup and than the issues started:
During the initial tune up of the car (running at arround 0.6-7bar) on the highway the head cracked (I saw that there was water in the oil). The car was running stable 80 degrees.
Initially I thought that I pulled the short straw with the current head and it was defective, so I got a replacement head, and installed some upgrades (catcams valve springs, vac motorsport valve retainers, custom made stainless steel cam followers). I also poured some Motul racing coolant to avoid the normal coolant boiling at low temp. Also installed ARP Head studs.
To my surprise 20km after the car was read - there was coolant in the oil once again. Both heads were pressure checked, skimmed and fully rebuilt before they were installed.
Since I checked the first head and it turned out that it was cracked, I am fairly certain that this one is cracked as well (havent removed it yet as its quite a pain in the ass to remove the turbos)
I really dont believe that I got a defective head twice in a row. And I am really lost why this is happening.
There is one theory I have - the turbos have water cooling as well, and I am using the line for the Throttle Body warming, from the thermostat the water goes into one of the turbos, than to the other one and than to the engine block. The only thing I can think of is that the water/coolant is very hot when it goes into the engine. As a result one end of the engine/head is getting much hotter that the other and than the head wraps and it cracks.
If anyone has any other ideas/advises I would appreciate it greatly.
Some pics:









And the old(cracked) head

[gath]

Wow! I don't have an answer, but it looks very impressive. ;D

[zoomer]

Thanks, it drives awesome as well (for the short distance I drove it), but I dont want to install another head before I figure this out

[zoomer]

Some specs as well:
M20B28 Fully rebuilt (m52b28 crank, 130mm rods, m20b25 low comp pistons skimmed)
M21 Oil Pump
M52 Oil spray nozzles installed on the engine block.
Head is (was) stock with CatCams Springs, Vac Motorsport spring retainers, custom stainless steel rockers and CatCams Turbo camshaft (270/249)
Nuke Performance adjustable cam pulley
Turbos are 2xTD05-16G off RB26DETT
Custom Exhaust manifolds with individual external wastegates (Chineese Tial replicas)
Mitsubishi Evo intercooler and 63/76mm turbo piping.
76mm stainless steel exhaust
660cc fuel injectors Siemens Deka
Individual coils from M50 with custom ignition leads
MS2 Extra with wideband 02 sensor for real time corrections.
6 plate ceramic clutch with hevy duty pressure plate

[TobyB]

Have you checked the basics- fuel pressure, injectors all flowing correctly, coolant bled, etc?

I know it's frustrating, but something as simple as a bit of junk in one of the injectors will make that cylinder
run lean, and at boost, >pop<

t

[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?

[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.

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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)

[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!

[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!

[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

[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]

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 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]

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.