2004 subaru impreza rs 2.5l

[Tireman28]

what are some plug and play horsepower tuners for this car. 

[GeneralDisorder]

There are none. Get a turbo model. 

 

There isn't really any HP to be had. The engine already has very high volumetric efficiency. Consider that HP per liter is the equivalent of a 300 cubic inch V8 making 330 HP. That's already over the magic 1 HP per cubic inch. 

 

GD

Edited March 7, 2018 by GeneralDisorder

[Tireman28]

what about head work? ive had cams done at delta, 3000 race grind. will the stock bottem end handle them? or do I need to get forged bottom end?

[GeneralDisorder]

The bottom end will be fine. But since you can't change the firmware you may actually lose power since the fuel and ingition mapping cant be changed to take advantage of the cams.

 

You would have to do a full stand-alone management computer and then you do risk bottom end failure because you will forfeit the factory knock control. Detonation will kill the rod bearings almost instantly.

 

GD

[1 Lucky Texan]

over at nasioc, you find folks love the RS enough that they do WRX or STI full swaps into them.

[carfreak85]

While I agree with GD that you would be better off starting with a turbo engine, if you really want to make power, but I'd disagree about his condemnation of the N/A 4-cylinder.

 

The VE on the N/A 2.5L engines isn't all that great, probably somewhere around 80-85%, the thing only makes 70 hp/L.  The real kings of VE, Honda and Ferrari, have engines that make over 120 hp/L, for reference.  If that same 300 ci V8 that had good VE, it would make over 585 hp.  But I digress...

 

The point is that you will spend a lot more money on the N/A Subaru engine just to make stock "turbo-engine" power.  Spend that same amount of cash (~$3-4k) on the turbo engine and you could be making an easy 350 whp on the turbo engine.  A LOT more people have gone down the turbo path, so there is more aftermarket support for the turbo engines, by orders of magnitude.

[GeneralDisorder]

You only need to look at Subaru timing advance curves to know that ultra-high VE really isnt possible. Even turbocharged you see crazy numbers like 20+ degrees of timing advance under full boost. Timing advance is a crutch for poor combustion chamber design and port flow. Compare the 4G63 - 4 degrees of advance at full boost.

 

Subaru engines have terrible combustion chamber efficiency. Heads and manifold of a tractor.....

 

GD

Edited March 8, 2018 by GeneralDisorder