What head gasket for boost? MLS leaking oil

[nm9stheham]

OK, cool; thanks.

On the CR and such, I ran some numbers on this, working with 9.1 static CR and a 62* intake closing for your cam, and 11 psi boost, and I am pretty positive that you are on the ragged edge. I have a 2.6L Starion turbo running around 8.2 true static CR that I limit at around 14-15 psi, controlled with a waste gate, and if I push to 16-17 psi, bam-o the knock sensor starts going off, so I have that as a data point for the ragged edge. (Running 93 octane fuel, per US methods which gives a lower number than the Euro octane methods.... I dunno what you guys do for octane numbers there.)

Your engine at 9.1 SCR/11 psi/62* closing angle is running at the same level of estimated compressed DCR as my Starion with 8.2 SCR/14-15 psi/59* closing angle, with a set-up that is less optimum than the Starion engine. Chamber shape is less optimum, your pistons are down in the hole a bit, exposing the upper cylinder walls which tends to detonate more easily, and you have an iron head rather than aluminum, and you don't have piston oilers for piston cooling. Throw in a dry, cool day in April down under, and it all invites some detonation. (Plus we know nothing of your ignition timing or fuel...) You can back off ignition timing all day long, but if the detonation is off of hot piston edge or something like that, the retarded ignition timing won't prevent it. Soooo..... Lower boost? Better fuel?

It is not as bad as I thought, but you are on the edge, IMHO. I don't see the point on the cam LSA .... with a wider LSA, the intake closing will be later, and that will lower cylinder pressures a bit....But, heck, I may be associating the Comp cam with the wrong engine LOL

Not sure if this helps you or not.....

 

[maca]

Thanks for the info nm9stheham
I understand where your coming from with cylinder pressures now. Is there a program or a way to calculate what max boot can be run with different comp rates? I have another magnum I am running a turbo on and would like to run numbers to chek on that as the turbo is very tempting to up the boost
However this supercharger engine I am doing will now have
engine quest heads out of the box 62cc
mls head gaskets .040 thick
11 cc factory pistons and factory 4" bore
pistons .055 down the bore
our fuel is 98 octane but I am not running an intercooler but can ad one if needed.

 

[MiradaMegaCab]

What's the total timing, on both engines?
You're running colder spark plugs?
What's the AFR's?
W/M might help......

 

[nm9stheham]

You can use the Wallace Dynamic compression calculator: Wallace Racing: Dynamic Compression Ratio Calculator

You'll need to first separately compute the static CR with either the Wallace CR calculator or the Pat Kelley calculator (my preference).

I ran it on my estimates of your engine parameters and got 12.9, and get 13.0 for my Starion turbo engine. I was not sure which cam to use for which of your engines, so used the 62 intake closing angle for the Comp cam listed earlier. Somewhere around 13 is the upper end of the recommended range for pressurized engines; but differences in engines will modify that limit. There is an assumed fill efficiency in the engine intake, valves, cam, etc., that goes with that 13 limit number, and one other thing that occurs to me is that with the big lift cam that you have, the fill efficiency in your setup may be higher than for most turbo cams which don't have such big lifts. Ditto for the heads that you have; they flow well and will increase the fill .So that may effectively push your real number past 13.

And you mention intercooler; my Starion does run one; my pressure numbers are after the intercooler. That engine has all the advantages that I mentioned before. Of course, an intercooler is going to INCREASE the air density to the intake along with the reduced temps, so that tends to increase the cylinder pressures.

BTW, I looked it up; your 98 octane is the equivalent of our 93 octane. As an FYI, some research back in the 80's indicated that the atmospheric humidity on a humid day can be worth the equivalent of up to 3-4 points extra in octane; that is the point of mentioning a dry cool day as a possible contributor for your situation.

 

[MopaR&D]

I think this has more to do with the clamping loads than the cylinder pressure. ARP fasteners require their own spec'd torque and lube to work right, end of story... Buddy of mine is a high-performance/diesel (kinda the same around here lol) mechanic, a practice where he works is to hand-sand the block decks with a flat stone in stages from ~350 grit up to like 2500 (I think?) whenever an engine is getting replacement head gaskets. And that's mostly on heavily boosted gas and diesel engines. I'd sand the decks by hand, get some Cometics and install them clean with ARP-spec'd torque on those studs.