M50 Headgasket question (turbo)

[E34Dave]

I currently have an M50tuB25 with a .140" Cometic and ARP studs. I plan on running lowish boost (as much as my motor can take before I need forged internals), but from what I read, people say to get a cut ring gasket. Why is this, and should I have gotten one instead? Would it be a worthy investment in the future if I ever rebuild?

[someguy2800]

The mls .140" headgaskets for whatever reason are very unreliable in m50 motors. Lots of other applications use them with success but they never seam to last long in an m50. I wouldn't change it until it gives you trouble.

[E34Dave]

The mls .140" headgaskets for whatever reason are very unreliable in m50 motors. Lots of other applications use them with success but they never seam to last long in an m50. I wouldn't change it until it gives you trouble.

I appreciate the advice! Do you know how much boost I should be able to push into the engine without damaging it? I read 6-7psi somewhere, but I want to double check.

[someguy2800]

They failures don't seam to be directly related to boost. Some last a long time, others fail quickly. My own theory is that they are too thick and they can't transfer heat out of the middle layers fast enough. Anybody that claims they can tell you a specific boost pressure it will fail at is an idiot. I would not be afraid to work my way up to 15-20+ lbs assuming the setup as a whole is sorted out, which will take some time. Start at 7 and go from there.

[TheJuggernaut]

It's not just us, I've heard it from many others. It's not the mls concept that I think is the problem but Cometic. A top Supra shop told me they couldn't get their motors to seal on Cometics much past 1000whp. They switched to stock gaskets, which are also mls, they've never had problems north of 2000whp.

[Butters Stoch]

I think the failure rate may not be as accurate as the internet will portray. There are obviously many cases where this won't apply, but I think the bulk of the failure rates are due to installation and preparation. There are loads more of the DIY'ers out there today, especially now that the recipe's are documented. The bulk of the DIY'ers even tho feel they are doing their best, its just not good enough. Then tuning also comes into play. I also feel the "whole" story is never told. I would bet that if a good deal of these failures were fully data logged when failure occurs, then we would see a cause to the effect. Now, again this isn't always the case, but I bet a good amount.
I have personally seen a good amount of DIY turbo cars, and the quality of the work is sub par. Then when failure happens, there is ALWAYS something to blame. But, i guess you have to start somewhere, most internet build DIY'ers have much different day job. But there are some that can produce high quality work, just as good if not better than those that work in the field. For example, guys on here like Pbonsalb, Jugghead etc etc. Then there are guys that have no business picking up a wrench. But with the internet and quickly Google searching folks can become iconic keyboard warriors and heavily respected. Tho they are no more than a YouTube scholar.
I get people on a daily basis when dropping off a car stating "this shouldn't be that bad, I watched a video where someone did a head gasket is 35 minutes, I'd just do it myself but I don't have the time".
Yeah. That happens.

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[E34Dave]

Thank you everyone for your responses! I have some confidence that we did the install right, so hopefully I won't have any catastrophic failures. If and when I do rods/pistons, I'll make sure to buy a cut ring next time!

[Mklock]

Yeah I had a Youtube warrior bring me his car. Yeah, just a front wheel bearing should be 15 mintues. Okay...what about the part where I'm using a torch on a hydraulic press and it not budging for 3 hours.

[318iser]

This may be construed as derailing a thread but I have a similar question. Just did a fresh 325i camshaft swap into my m20 bottom mount turbo car. I have an .040 stainless O-ringing in the block but not the head and I have had moderate success with the stock head gasket holding pressure (16-20 psi) until lately where I've somehow pinched the head gasket in the attempt to throw the head onto the block studs with all the manifolds and turbo put together already as well as the most recent attempt to date where I even pulled the block out of the car to ensure that I had a good seal. Just dropped the oil tonight after about 25 miles and complete have a milkshake. I haven't had the head off yet but judging by how finely the mixed the milkshake is I want to guess head gasket failure.

I'm not sure if I need to get my machine shop to O-ring some reliefs in the head as well but this seems to be happening pretty regularly lately. After some research tonight I found some company SCE that makes copper head gaskets, any thoughts on this as to maybe getting the O-ringing done on the head and getting SCE to make a couple M20 head gaskets as a more permanent fix to this issue? This is making getting this car ready for the dyno a complete bear.

[jjjjjjj]

I do not deserve to touch a wrench, but my (used) .140 mls has lasted 30k+ dally driven miles on an S52 nonetheless and going quite strong at 12psi on a smaller turbo. (Had it as high as 20psi before fuel pump issues)

Prep is key, many/most of the mls horror stories seem to be from poor or no block prep, and not getting the head machined to the proper ra so it’s not smooth enough for the mls. Pretty sure 40 ra was the magic number.

Cooper spray can also be your friend with the mls... a Cut Ring is likely the better friend