I am the proud new owner of a 1997 Subaru Impreza 2.0 GL AWD.

It is a standard British specification, I think. Therefore should be 113 bhp.

I see from looking at https://en.wikipedia.org/wiki/Subaru_EJ_engine#EJ20 that there is possibly another engine version with 133 bhp.

What is the difference between these engines? Is there a way to extract the extra 20 bhp from mine easily?

Thanks
Ben

I may well be wrong as I'm not up to spec on the n.a engine range , unfortunately but is the 133 hp version still single cam ? 

As I wouldn't have thought that you'd gain 20 hp on a n.a by just adding bits from another engine or doing breathing mods .

Saying that I think some of the later dohc 2ltr n.a engines have almost 160hp, so maybe a later 2ltr 16v na engine might be the answer for more power but keeping it n.a .

Most people will just say to improve performance on a na, concentrate on handling ,lightening and braking mods to get the most out of the boxer low center of gravity and the AWD system. 

Then save for a turbo version 

I was just going by what was shown on the wiki page I linked to.

Under SOHC NA for Impreza it shows:

1993-1999 135 PS (99 kW; 133 hp) GC - GF series

and:

1994-1999 115 PS (85 kW; 113 hp) GC, GF series

It also shows 1993-1999 135 PS (99 kW; 133 hp) BD - BG series( ECU code EURO ,D3 ; Asia 4H) under Legacy.

I'm trying to find out what the difference is.

Thanks

Ben