kwiksilverz

I just ordered in some GM MLS gaskets for an LS1 we're putting together and was sent 6.0 (LS2) gasket, part number 12589227 from LS1 Speed. Is that what people are running on LS1's now or were we sent the wrong gaskets?? I have had 5.7 GM MLS in the past, so I just wanted to verify before putting the larger bore gasket in there. Thanks.
Joe

kwiksilverz

Anybody? I want to get this thing buttoned up for him. I was told by a buddy of mine that the MLS will not seal properly on the 99 motor and that they should have sent us an actual 5.7 gasket, not a 6.0. Anybody have any answers one way or another?
Joe

kwiksilverz

OK, he called LS1 Speed and they told him that it will work just fine, but the machinist I use locally said not to use it. Due to this not being the easiest car in the world to do headgaskets on should there be a problem, I would like to know for sure... Thanks.
Joe

PREDATOR-Z

12589226(5.7 MLS) and 12589227(6.0L MLS)

kwiksilverz

Yup, I saw that and I know they make an LS1 MLS, I have *one* here, but LS1 Speed is telling my friend (the one who ordered them) that these will work fine on an LS1. I just wanted to see if this was true and if maybe it had become common practice since the last time I checked or something. Apparently not and they just sent the wrong gasket. Thanks.
Joe

GuitsBoy

iTrader: (4)

I was under the impression that the 5.7L MLS gasket was discontinued and the 6.0 was the replacement for it. In any case, the 6.0L gasket has been used for years on stock bored LS1 and LS6 motors without issue.

kwiksilverz

I thought I read something about that somewhere, but couldn't find it anywhere when searching. I just don't need any sealing issues since this thing isn't too fun to pull heads on .
Joe

Krab

iTrader: (28)

What heads are you installing? I was told to use a set of 6.0 gaskets with a set of heads that came off an '05 GTO (243 heads). My car has been running fine with those gaskets for almost a year now.

kwiksilverz

Stock LS1 heads. I actually started to put it back together today. I'm sure it will be fine, but I just wanted to double check in case there was something I was unaware of...
Joe

PREDATOR-Z

They are the same gasket basically but the 6.0 has a bigger bore (4.060)

kwiksilverz

Yup, I realize they are the same, I was just told that the larger gasket bore may not seal, will drop compression, etc. I was also told that the 99 block is not machined properly for an MLS and it may not seal properly, so I was a bit concerned. I doubt there will be any problems though.
Joe

PREDATOR-Z

There is no "special" machining for GM MLS, yes compression will drop a tiny bit, yes it will seal properly. What you'll have is like added quench area.
In general you want to choose a gasket only about .030 more than bore, but unless you're boosted I do not see any issues here.

kwiksilverz

Ok, gotcha. It is not FI, but it does have a 125 shot on it, I'm sure it will be ok though.

Now that you mention that about the quench area though- I have my boosted LS2 that I ordered the Fel Pro MLS gaskets for (heard a lot of good about them, so I'll give them a shot) and they are a 4.100 bore. Do you think I'll run into problems using them?? Those are the ones I was told to use and I don't believe Fel Pro makes any others too, but I believe they are under 4". Will this cause problems ?? Thanks for your help.
Joe

PREDATOR-Z

Depends how moch boost you throw at it. In boost applications quench is not a big issue like NA. I've run .060+ gaskets on boosted motors with no issues. But always no more than .03 overbore, and usualy solid MLS (no sealant compounds)
Head and block prep was meticulous.

kwiksilverz

My motor is 9.4:1 and I run ~17 psi with plans of 20-21. I am currently running stock MLS gaskets but am having some coolant pushing issues, nothing severe, but enough for me to be tearing it down sometime in the future and replacing the ARP bolts I used with studs and I was going to use these Fel Pros since I have heard good things about them.

It isn't too bad yet, I just crack the radiator cap before I take the car out for the day to make sure there is no residual pressure from the day before. It's not like it pushes a quart in one pass or anything, so I'm in no big rush to do it. Just wanted to make sure those Fel Pros will work. Let me know if you think I'll have a problem or not. Thanks!


Edit- I should add- the 20-21 psi thing is for race days and special occasions only, not daily.

Joe