differences in the legacy 2.5 engines from 96 to 97

[00]

The 96 legacy with the 2.5 has to have premium fuel while the 97 2.5 can use regular fuel, subaru even recommends it. What is the difference in the engine that causes it. Is it from the changes they made to the piston's design. Or is it from other parts and if so, what are those parts, also are the heads the same from 96 to 97. I'm getting a engine for my car and it has a 97 2.5 block and pistions but has 96 2.5 heads. All other parts are 97. I just want to make sure It's the pistons that make it able to run regular, so I can run regular without messing up the engine.

Thanks in advance

[decke48]

96 was recommended 91 octane.
96 has different heads then 97-99 and has a different piston. i cant tell you why they ran recommended premuim in 96 maybe because the 2.5 was a new engine for subaru and it was play safe. theres a lot of factors to determine the correct octane rating. so i cant tell you why.

[Huffer]

I know some 96 GT owners have run 89 octane and been fine...

[liquidracing]

i have a '96 2.5 and i run mid-grade 87 octane....i have found this to be the best trade-off between the slower burning, less pinging, extra-expensive premium, and the faster burning, more pinging, quicker detonating, lower priced mississippi mud we call regular! no problems yet! however, i do recommend putting in a can of bg44k every time you change your oil(3000mi) that ej25d loves to gunk up around the valves and lifters i think partially due to undersized(imho) valves that were oem installed in the '96. btw oversized valves is one of the things i plan on doing to my heads once i have sourced the right set.....or maybe a set of custom rotary valves? anyone, anyone? ROTARY VALVES! ever thought of it? a 12,000rpm ej25d? hmmmmm......the costs!

[impreza_GC8]

The '96 2.5 had Hydraulic Valve Lash Adjustment heads. They also flowed very very well, I have been told they flow the equivalent of JDM STI heads at the time of production. I have '96 HLA heads coupled with a newer 2.5 block on my hybrid turbo Outback build.

[liquidracing]

gc8...really?, i'll have to look into that farther as i'm looking into some new heads and port/polish work this winter. i'm thinking the basics....port/polish, decked, valve oversize, new guts, higher comp ratio maybe 10.5:1, bigger cam(not too much)etc. some old school sleeper tricks!

[liquidracing]

btw, now that i have photobucketed my pics....here's what i'm doing the valve job and head work on. also, i have 119,000mi clocked with ZERO leaks! oem head gasket, although i know the inevitable is on the way [/img]