Mechanics, the head on the MY96 2.5 were different than previous or post years. I'll see if I can find out what it was...

 

in the interum, anyone else know the difference?

 

EDIT:

 

so far on cars101 for the MY 96:

 

2.5 Liter 155 hp, dual overhead cam, sequential multi-port fuel injected engine (new for 1996)

 

and the MY97:

New: 2.5 L now has 165 hp on regular unleaded gas instead of 1996's 155 hp on premium fuel.

 

 

I know the '96 2.5 still had hydraulic lifters(HLAs to be techical), and the later 2.5s had solid shim type valve adjusters, so there must be significant differences in the heads. Compression ratio, I do not know.

 

Nathan

I dont know if this adds anything new to the discussion, but the original question did involve a 96 2.5, so I thought I'd throw this in. My 96 Legacy OB with the 2.5....the owners manual states: 'Use premium unleaded fuel with an octane rating of 91 AKI or higher. Regular unleaded may be used if necessary. For optimum engine performance and driveability, it is recomended that you use premium grade unleaded fuel.' I have the owners manual for a 97 Legacy Outback that I borrowed some parts from, and in that book, there is no separate fuel recommended for the 2.5., both engines require 87 octane. I know I have the HLAs, I wasnt sure which years used them or if that coincides with the premium requirement...from the owners manuals, 96 2.5 has a compression ratio of 9.5:1 and the 97's is 9.7:1 (both years 2.2 have 9.7:1) Interesting that they gained 10 HP without the premium for 97... ok, Im confused now....LOL!

 

Ive put about 4,000 miles on my Outback since getting her back together and I have kept track of my mileage from the start. Ive used mid-grade most of the time with a few tanks of premium. I see no difference in performance or mileage between the 2 grades. The only thing that seems to affect my mileage is running the A/C, which is no surprise. Im about 75% highway miles and Im averaging around 24 mpg.

 

As far as piston slap, yeah my 96 has it, John....in fact the reason I was on the board this morning was to research that some more....it seems to be getting worse and Im a bit worried...but thats a topic for another post

Wasn't MY96 and maybe 97 the only years the 2.5 had DOHCs? I thought one of the main reasons for gaining more HP in the following years, the Phase II SOHC was going to a single cam.

 

On the piston slap, remember that *sometimes* it could be from a noisy tension belt idler.

As far as piston slap, yeah my 96 has it, John....in fact the reason I was on the board this morning was to research that some more....it seems to be getting worse and Im a bit worried...but thats a topic for another post

 

here's a great link for 'engine noise diagnosis'.

 

http://remanufactured-engines.com/page4.htm

 

there's a 'test' similar to a wet compression test but with the plugs in, that if it silences the noise, then it's piston slap.

 

here's a print out from subaru canada about piston slap.

 

http://www.ultimatesubaru.org/forum/showpost.php?p=503185&postcount=4

I'll throw this on the table. Not for anything other than a reference. The ea81 owner's manual recommends an octane rationg of 90 of high. And darn near everybody runs 87 in them. So I don't personally believe it will hurt anything to just get the cheap stuff and go.