M20 twin turbo cracking heads. Please help

Mon Aug 17, 2015 1:14 pm

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 (I posted a pic in the facebook group some time ago) 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. 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 in the next post.

Mon Aug 17, 2015 2:04 pm

Tue Aug 18, 2015 8:34 am

and a pic of the old head:

Tue Aug 18, 2015 9:17 am

I take it you didn't have the heads tested before fitting, in which case your just guessing how good they are.

But like you say, if your dumping coolant from the turbos into the side of the block/head then this is going to upset the temperature balance a lot and is more than likely the cause of your problem

Tue Aug 18, 2015 10:13 am

Both heads were tested and fully rebuilt and skimmed before they were fitted.
I know quite a few people running water cooled turbos that are connected the very same way. The only difference is that I have two of those

I am wondering if anyone knows the direction of the coolant in the back of the block, where the TB warming goes in. Since the coolant goes at the top of the block, if it than goes in the head its possible to heat up the head, however if it is going in the block it shouldn't cause a problem I guess

Tue Aug 18, 2015 12:54 pm

Coolant flows from front to back of the engine, you really ought to be dumping the hot coolant from the turbos at the back of the thermostat where it can go straight through to the radiator if needed

Tue Aug 18, 2015 1:50 pm

ZoomeR wrote:Both heads were tested and fully rebuilt and skimmed before they were fitted.

There was another thread last week, where someone had built up a M20B25 with a tested, skimmed and refurbished head, only to eventually find it had the same crack as yours.
It appears that this crack doesn't always show in cold testing.

Tue Aug 18, 2015 2:35 pm

The first head was a bit wrapped I think, because the installation of the rocker arm shafts was quite tough (I had to hammer them in, however the second head was perfect. Also I drove the car with the first head for about 2-3k km NA and it had no problems.
Also I cant figure out how can it crack the head in just 20km (or even less)