Change of cranskshaft pulley to lightweight.

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Hi
I have a 2004 WRX Impreza, and I am considering changing the crank, A/C and PAS pulleys for one piece lightweight items from RCM, however, there seems to be some discussion that the Crankshaft pulley specifically acts as a harmonic balancer. The lightweight pulley is about 250 g versus stock pulley of 2.5 kg, gains are seen as being better throttle response and a claimed 10 - 15 bhp gain, with the very unlikely perk of it being a one piece item and not therefore prone to disassembling itself under load (very few recorded cases).

Now I'm not particularly techie, but this, along with a lightened and balanced flywheel is a relatively cheap route to power before entering the world of forged pistons, rods and divorce.

There is a wealth of qualified knowledge here, and there are also threads pertaining to this on scoobynet, but it ended up in a gentlemanly difference of opinion but no actual evidence to support or deny either way.

Can anyone here shed any light on whether this is a worthwhile idea or if it is a bad idea altogether.

TIA
Pete

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Hi HTG
Thanks for the reply, I'm also unsure why there are claims made of a power gain, I can only assume less rotational load on the engine, but would that give more power?.

I'm always sceptical when power gain figures are mentioned because they never translate in the real world and are often given in an "perfect" scenario.

However, there has not been a reported case of catastrophic failure (I choose my words carefully) on any on the forums, but this actually adds to my suspicion. I would ask why Subaru invest time and effort developing an engine to work reliably without making a mass production saving on a heavy crankshaft pulley.

That said, one only has to look at the massive cock up that was the EJ255 Engine to see that their credibility is not that great.

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CrutyRammers said:

10-15 bhp gain for swapping some pulleys? If only tuning was so easy.
As above, don't know this particular engine, but the crank pulley is certainly used as an external balance / damper on some engines.

LOL if only it was!.

Like me, you are probably wary when figures and percentages are mentioned with a seemingly simple fix.

That reminds me, I need to get some Slick 50

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HJG said:

No, it would only allow the engine to 'spin up' (and down) faster

So there would be a noticeable amount of a reduction in engine braking (if coupled to a lightened flywheel)as well then?.

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stevieturbo said:

I rather doubt the OP is at a level where he finally needs to fit a silly pulley to scrape that last fraction of performance to enable him to win races, having already carried out every worthwhile modification possible to get to this last ounce of desperation.

However...if he wants a shiny colourful pulley...go for it.

Ha ha, it's not about colourful pulleys stevie ( I'd have opted for black) and your are in fact correct, I'm way behind a level of such need. What I was actually trying to get the measure of were whether the spurious claims of 10-15 were true and if indeed the changing of a pulley would be detrimental to the harmonics and thus reliability of the engine. I was also interested in the possibility of getting a power gain via a relatively simple and easy route. It would seem that there are others here with some great insight and knowledge who have answered my question and saved me spunking cash on a bit of gucci engine bling.

There was no definitive answer that could be found elsewhere hence I asked here and I'm glad I did. Thanks to all those who replied.

Years ago when we were tuning and others were racing Starion and Lancer turbo's the trick was to get as much power running standard boost as possible, then we would look to increasing boost and fuel pressures etc , as increasing boost came with its own set of problems. In this case I was thinking along the same lines.