Let's talk MLS(low-comp) vs. O-Rings(high-comp)

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Let's talk MLS(low-comp) vs. O-Rings(high-comp)

Postby blasphemy101 » Wed Jul 08, 2015 11:40 pm

We all know turbos and high compression are difficult to make play well together. Right now I'm debating between two routes to take my 24v build.

Option 1) Take the 'tried-and-sort-of-true' approach M5x route of dropping compression with a thick MLS head gasket and running a large amount (15-18psi) of boost.

Option 2) Retain stock compression and maintain headgasket seal by o-ringing the block with copper rings. I imagine boost will be more limited with this setup because of the danger of detonation.

The trade-off is likely peak power from Option 1 vs. a broader torque curve and better off-boost response with Option 2.

I like the sound of Option 2, but it doesn't appear to be a well-tested route. If the O-Rings are as good as people say they are, I also run the risk of doing mechanical damage if I run into an unhealthy amount of detonation.

Option 1 is more proven, but I'm not impressed with the reviews I've seen of the M5x MLS gaskets. Nearly every review I read contains some complaints of sealing problems, so I'm not sure it's the way to go. It seems like everyone who runs the MLS winds up blowing it and replacing it like a maintenance item.
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Re: Let's talk MLS(low-comp) vs. O-Rings(high-comp)

Postby Yoshi » Thu Jul 09, 2015 1:31 am

What are you doing for a tune? My suggestion is to go to rk tunes and get something off the shelf. Talk with Jordan and figure out what he would suggest. Let other factors guide your build.

If you're going full stand alone and have a tuner in mind, I'd go with just an O ring and cap at like 12psi. Though, I think it could hold 15 on a decent sized turbo. But all of that also does depend on your over all goals. IMO KISS.
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Re: Let's talk MLS(low-comp) vs. O-Rings(high-comp)

Postby M20_fever » Thu Jul 09, 2015 10:43 am

O-ring is only going to matter if you A) have a failure in the system causing detonation B) have an poor tune causing detonation. Point being, with a good tune either option should work fine. Option two will make way more drivable on the street, though peak power will suffer, option one will take more "acceptance" of the pitfalls of low CR engine off boost. I opted for O-ring and stock CR, but on an m20 thats 8.8:1 which it pretty low to begin with, not sure what the CR is on the 24v engines?
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Re: Let's talk MLS(low-comp) vs. O-Rings(high-comp)

Postby Yoshi » Thu Jul 09, 2015 11:13 am

I've driven both MLS and non MLS motors. You kill quench area and lose some power but I wouldn't be able to tell you just from driving a car which one was the MLS or not. It won't make enough of a difference anyway. I just feel like MLS gaskets leak more often than not. Ask me how I know. I've installed 4 or 5 at this point. Copper spray, no copper spray. Separate all layers THEN copper spray. Torque to 100+ft/lbs, blah blah. Even stripped a stud in the block I torqued the bitch down so hard once.

O rings will seal. But they also won't blow when they should. I'd rather a HG blow than put a hole in a piston. But, if you're popping engines like molly to a raver, fuck it. I've seen success with a stock HG.
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Re: Let's talk MLS(low-comp) vs. O-Rings(high-comp)

Postby blasphemy101 » Fri Jul 10, 2015 5:54 pm

M20_fever wrote:I opted for O-ring and stock CR, but on an m20 thats 8.8:1 which it pretty low to begin with, not sure what the CR is on the 24v engines?


The stock CR is 10.5 on my M50TU, so there is obviously less room for error with respect to detonation. I just don't know by how much. I'm going to go through the math to get an estimate of how much the change in CR actually changes cylinder pressures. I'd also like to talk to some of my professors - many of them have worked on engines in the past, and I'd like their input.

I believe, in theory, the M50TU combustion chamber should be less prone to detonation than the M20, not taking CR into account. With flat-top pistons and the spark plug in the middle, there should be more even distribution of the heat and pressure from ignition. That's beyond my knowledge base, though. I have no idea of knowing if it really is better, and if so, how much it actually helps.

Yoshi wrote:I've driven both MLS and non MLS motors. You kill quench area and lose some power but I wouldn't be able to tell you just from driving a car which one was the MLS or not. It won't make enough of a difference anyway. I just feel like MLS gaskets leak more often than not. Ask me how I know. I've installed 4 or 5 at this point. Copper spray, no copper spray. Separate all layers THEN copper spray. Torque to 100+ft/lbs, blah blah. Even stripped a stud in the block I torqued the bitch down so hard once.


This echoes what I've seen in my research. My thoughts are if I run the MLS, I'm just accepting the fact that I WILL have to redo it at some point.

Yoshi wrote:O rings will seal. But they also won't blow when they should. I'd rather a HG blow than put a hole in a piston. But, if you're popping engines like molly to a raver, fuck it. I've seen success with a stock HG.


This is the biggest concern with the O-Rings. If they're really that good, there's the potential of doing some serious harm on a bad tune, instead of just having to replace the gasket. In your experience, do they really seal things that well?
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Re: Let's talk MLS(low-comp) vs. O-Rings(high-comp)

Postby blasphemy101 » Fri Jul 10, 2015 6:06 pm

Hmm...Have you guys heard of putting M42 pistons in an M50?
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Re: Let's talk MLS(low-comp) vs. O-Rings(high-comp)

Postby Yoshi » Sat Jul 11, 2015 12:29 am

Some crappy O ring jobs will still blow like regular head gaskets. But if done right, you will grenade the motor before the HG blows. So don't do it if you don't trust your tune/tuner

M42 pistons are poo. Don't use them. They aren't made for the motor and they break easier than the factory M50s.

IMO man, Get a good tune, use a stock HG. Don't go MLS OR O ring. Trust the tune and have fail safes to make sure you don't detonate.

M50s are so cheap, if you blow it up, you can easily have another motor ready. Maybe build a second one while you run on the first one and learn.
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Re: Let's talk MLS(low-comp) vs. O-Rings(high-comp)

Postby blasphemy101 » Mon Jul 13, 2015 6:27 pm

Yoshi wrote:M42 pistons are poo. Don't use them. They aren't made for the motor and they break easier than the factory M50s.


I noted the other stuff, just so you don't think I ignored it ;)

Just curious what kind of failures you've seen with M42 pistons? On paper, the pistons appear almost identical to M50tu pistons, except the M42 piston faces are dished.
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Re: Let's talk MLS(low-comp) vs. O-Rings(high-comp)

Postby Yoshi » Tue Jul 14, 2015 11:00 am

I've only seen like 2 people run them. I believe one had cracked ring lands. Regardless, the pistons aren't made for that cylinder head so you're mixing and matching geometry. Which means shittier combustion.
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