To replace or not to replace Head gasket

[R4/CR]

Hi, this is my first post so bear with me. Im building a rally car out of my 1990 325is.

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Got the roll cage installed last winter, drove it around all summer feeling pretty BA, and this winter I set to preparing it for racing this summer at the Ojibwe Forests Rally.

I pulled the engine out last saturday, for two reasons. One: To clean and fix rust spots in the engine bay, rerun fuel brake lines, and remove subframes. Two: To make preparing the engine for the turbo I plan on adding easier.

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I have done a lot of research on these forums and on the internets on how to get the engine ready to handle boost. And I feel pretty confident in my ability to do so. But what I am struggling with currently is what to do about the head gasket?

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The motor has about 180 thousand miles on it and ran pretty good before I pulled it. I have read that some people just replace the studs one by one with APR's and rock the stock head gasket. While others pull the head get it resurfaced and replace the head gasket with a MLS and APR's.

What should I do? I am planning on running 10-15 psi with the turbo; so nothing crazy. I really don't want to blow a head gasket and could use your sage advice.

[CrazyPrime]

If I was in your position I would pull the head clean the surfaces and check to see if they are flat and true. for 10-15psi a stock gasket and studs is doable. If you want you could o-ring the block and have more reliability.

[e30davie]

You are ~20 bolts away from having the head off. I'd do it and have the head checked for your own piece of mind.

I was in the same position as you (admitedly no boost...yet) and had a good runner of an engine on my garage floor. I bit the bullet, pulled the head, head overhaul (not cheap...) and all new gaskets. But now i know they are all done and everything is good. 30,000km later and not an issue.

I think if you don't do it it will always be in the back of your mind how the head, valves and gasket are. Especially if you are going to be adding horsepower.

[R4/CR]

I am not against O-ringing the block but don't have the access to the tool, unless you now something I don't. My local engine shop really wants nothing to do with this motor, they build V8's for stock and drag cars, and are only begrudgingly willing to resurface the head and thats it. I know valve guides are not something I can replace, but is it likely they need to be? Valve seals I think I can do right?

What do you suggest for cleaning the block surface? I have read about using sharpening stones, is that the best thing to do? and I have read to use a MLS head gasket it has to be super clean and flat, is it as finicky as I think?

[ForcedFirebird]

Stock gasket and replacing the bolts one at a time will hold about 300whp. Different turbos will act differently as far as power, but a small t3 will be safe for ~13psi (I've used this combo a lot, avg is about 275whp/290wtq).

[Paul-Z]

If I was in your position I would pull the head clean the surfaces and check to see if they are flat and true. for 10-15psi a stock gasket and studs is doable. If you want you could o-ring the block and have more reliability.

+1

You already have the engine out so why not. I’ve been running 15psi for a few years with a .120 MLS head gasket and ARP’s. Aside from that, engine management is key...

[e30davie]

My local engine shop really wants nothing to do with this motor, they build V8's for stock and drag cars, and are only begrudgingly willing to resurface the head and thats it.

First step...find a new shop :/

[ForcedFirebird]

+1

You already have the engine out so why not. I’ve been running 15psi for a few years with a .120 MLS head gasket and ARP’s. Aside from that, engine management is key...

You could have done that with a stock gasket. Although, with .070" you have .040" piston quench instead of .120".

You would make more power, the boost would come on earlier, and you would make more power prior to boost if you had a .070" on am otherwise stock b25. If you have and eta rotating assembly and b25 head, it's even worse.

An m20 with .140" gasket is rediculously low compression. The stock engine is only 8.8:1 to begin with. If anything, compression should go up on an m20 ... in any/all conditions to increase performance IMPO.

[Paul-Z]

You could have done that with a stock gasket. Although, with .070" you have .040" piston quench instead of .120".

You would make more power, the boost would come on earlier, and you would make more power prior to boost if you had a .070" on am otherwise stock b25. If you have and eta rotating assembly and b25 head, it's even worse.

An m20 with .140" gasket is rediculously low compression. The stock engine is only 8.8:1 to begin with. If anything, compression should go up on an m20 ... in any/all conditions to increase performance IMPO.

I run a smaller turbo so maybe that’s compensating? I see full boost pretty early. Top end suffers a bit, but i was looking for an overall fun driving experience. If this head gasket goes I’d prob skip the MLS and o-ring the block with a stock gasket. Hopefully I don’t have to cross that bridge anytime soon.

[R4/CR]

Alright, I definetly live in the land of American v8's, it took some searching but I finally found a shop that will work on my engine. I got some quotes on things and think he is a little high, but what do I know. I was surprised to see that having the shop O-ring the block was around the same price if i were to get a MLS head gasket.

So the questions is, MLS head gasket or O-ring the block?

and if it's MLS do I have the shop resurface the block too, or tackle that myself?