velohead66

ok not quite the real question.


ok, we all know (roughly) how a four stroke horozontally opposed four cylinder engine works, right ??

em, how come say an STI develops 280PS, whereas a Jap WRX develops only 240PS. Talking classic scoobies here of course.

I know STI's have stronger parts, such as forged pistons, but surely these give extra strength, not extra power.

And being devil's advocate, a WRX Type R (like mine) is supposed to develop 280PS but as a non STI does not have STI parts.
How does that develop 280PS.

Any links or technical explanations greatly appreciated.

nigelward

Not sure whether there is a technical answer for this.

In Japan all the manufacturers have adhered to a gentlemen's agreement where by they will not produce a car with more the 276bhp (280PS) for the Japanese Domestic Market.

So although the STI has stronger components Subaru won't, at the moment, sell one with more than this amount of power.

However, theoretically speaking, the STI engine is ready to take more power if it is done properly.

Outside of the JDM this may start to change as the next Legacy is rumoured to have 350bhp and Japanese performance cars are starting to loose out to European manufacturers who do not have such a restriction.

Nigel

RT

Cams, boost, ign timing are all different on the STI vs JDM WRX, I would guess. These in themselves, can account for the 40hp difference.

Turbo_Steve

It's all in the software. And if you believe that manufacteres are sticking to the "gentlemens agreement" you are mistaken

For example, a Supra TT can be rolling roaded at 310bhp straight out of the box. As can a nice new STi.

Basically the STi engine is setup for "silly" amounts of power, and the software then set to run it for the maximum reliability / power compromise. As is the Impreza, to be honest.

Subaru spend a lot of time / effort engineering the engine-software combination to be as reliable as possible. Tuning the engine yourself is basically operating within their 'failure-tolerance', i.e. they have to allow for bad fuel, no servicing, no mechanical sympathy etc etc.
Once you have a few gauges, (boost, Knocklink, AFR, etc) and know how to read them, you can push the limits a little more, because you KNOW you have to have the best petrol, etc.

But you reach a point where you start to shorten the life of compnents. That's where the STi stuff comes in: the same "tolerances" are required when they make the car, but with more power output, so stronger components are required. If that makes sense?

Er. Yeah. Not the best description. Open to someone ripping this to pieces!!!

velohead66

ok, so on say an STI version 4 or 5, what are the main engine differences.

Forged pistons which are stronger. Are these lighter too ?

Any other specific differences ??

velohead66

No replies ....

...so if I put forged pistons into my WRX engine I don't get an STI engine, so what are the other diffs ??

sammyh

iTrader: (1)

The cams, some turbos, pistons and ecu are different, in addition to this some STI's have semi closed deck blocks and the RA (i think) sometimes had a fully closed deck block.

Also the STI only has one cat

StickyMicky

and to further confuse

my97 4 door onwards wrx`s come with 280ps
although im told the sti has a little more torque