3.0 pistons same as 2.5s?

Don't know for sure, but probably. It was my understanding, when they replaced the engine on my '97 OB, that the reason for slap is that they used short skirt pistons. Reasoning: less friction gives better gas mileage for advertising.

That probably was NOT an engineering decision!!! :-[ Username munged by FixNews

Questions: (Because I don't know)

Is piston slap necessarily a bad thing?

(I hear it referred to as bad, maybe I don't know what it is.)

Are we referring to the noise that all Subaru (boxer, horizontally opposed) engines make?

That dull clicking noise that varies with RPM and can be heard a mile away on Subaru's WRC car?

Or is it something more threatening than that?

Seems to me, decrease in rotational mass = faster RPM gain (performance) and less friction for higher gas mileage.

Someone let me know the downsides of the Short Skirt Pistons.

Thanks,

Ed

My H6 has a tendency to rattle a little bit when cold started below 45deg. It becomes most noticeable when the motor has only partially warmed up, and goes away completely when totally warm.

The pistons are physically different from the 2.5 since the bore/stroke are different, but they probably share the same short skirt design.

Piston slap is metal hitting against metal, which over time will cause damage. Why would Subaru have a "countermeasure piston replacement kit" in addition to a "short block replacement" fix, if there wasn't a problem? Subaru of America says that it will shorten the life of the engine by 10%, which is not an insignificant number if you plan on keeping the car a while.

I was wondering if they had modified the pistons to deal with the problem on the 2004 6 cylinder or 2005 engines?

You are correct!

I'd say that was a relative statement. It's insignificant if you DON'T plan to keep the car and it doesn't do damage while you have it; and Sub, like other manufacturers is after New Car Sales. And you know they are going to try to make it sound "not so bad". If they go to the short s kirts in the first place because of "better gas mileage" you know damn good and well they are going to defend that decision.

I got my "short skirt" information from the service manager at Subaru in Coeur d'Alene, ID and he seemed pretty knowledgeable and wasn't panning Subaru in general. Personally I can't see the gas mileage reason for going to a piston design that would cause failure down the road. After all Subaru has always been known for good warrantees (spelled $$$) and longevity.

I'm a Johnny Come Lately as far as owning a Sub is concerned, my first was a '97 in '99. But, I see more OLD Subs running around Coeur d'Alene than other cars from the 70's. I know of at least 10 old Brats that look and sound pretty good. Of course I don't know anything about their engine rebuild status.

Ed brings up some good points I'd not considered, the rotation mass, higher RPM (= more HP advertisments).

Don

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