Not when Time, money, and ability to perform the work are factors...

Thank you!

Why the hell would replacing the cheapest and easiest components be silly?

The guy is interested in a bolt up kit, this other guy is all like.....what you need to do is build engines from the ground up like me...yep....I got engines just laying around...take it from me cuz im an effin genius...you wont see hp gains from a pulley kit and i can prove it by manipulating some numbers i just pulled out of my ass

The noticeable feel from a pulley kit is reving up faster and more importantly reving down faster. This car has a tendency to hang when shifting at high rpms. The more weight you can remove from the pulleys, flywheel/clutch, and yes the internal components of the engine will help out with this.

Seems an engineering degree doesn't make a guy any less of an asshat. Personally I'm growing tired with daily heated discussion about leaching every last hp from this engine and proving it on a dyno. I would like to see more discussions about making the car drive the way individuals think it should. Smoother/faster shifts at high rpms does sound nice

Some engines are not internally balanced and depend on external weights/dampers To quell harmful vibrations that in time can damage bearings
And other parts of the engine. I don't know how the FA20 is balanced, but the crank pulley is part of the equation and is weighted and sized as part of a whole unit. Many aftermarket vendors don't know either... But that doesn't stop them from selling parts that could lead to problems down the road.
The above info is something to consider before changing parts that could cause
Problems.

At least some people understand

If I change the "front pulley" on one of my race engines, I have to disassemble the entire engine & take the rotating assembly BACK to the balancer. The parts are matched to an engine.

Then I will offer to sell you a lighter crank pulley BOLT that weighs 25 grams less than stock and only costs $25 because it WILL make a difference.
It will make a NEGLIGIBLE difference (like the pulley) but hey that's all that matters right?
OR how about I remove 2.5 lbs by drilling directly down the middle of the crankshaft = Almost ZERO CHANGE in rotational inertia

I am actually AGREEING with that statement. Will a lighter pulley make a difference - YES. Will you notice it? - NO UNLESS you can "feel" the difference of less than .001 in the engines rotational inertia.
Hell a LIGHTER BELT would make a BIGGER difference because the effect of the belt on the rotational inertia of the whole system.

And I guess people "like THIS Asshat" who assemble these types of engines should just STFU because no-one wants to hear about REAL-WORLD experience.

The point I am making (and everyone wants to argue with) is that shaving 2.5 lbs off of the pulley makes almost ZERO difference in the engine's total rotational inertia. If you removed the SAME 2.5 lbs from the outer edge of the flyweel IT WOULD MAKE A HUGE DIFFERENCE.
If you remove GRAMS from the large end of each rod IT WOULD MAKE A HUGE DIFFERENCE
Now I suppose someone will contest that statement.

Seems Physics & common sense should just be left out of these discussions.

any hardware and/or software stock piece is part of the equation and changing it could lead to problems. so what are you doing on this forum as it sounds like you should just enjoy the car in stock form and free dealership oil changes?
the question is what that equation solves - eg many people don't care much about air pollution and noise level and are willing to trade that off for a bit more hp/tq by replacing exhaust parts.
as for the pulleys, a lot of folks have run lightweight pulleys on wrxs and stis without any problems. the throttle response is definitely better, not by much but enough to make shifts easier. i'll take that vs some what-ever engineer theoretical insinuations.

"I would not mess with it UNLESS you are doing a dozen other things that would make a bigger difference."

I guess reading is not one of your strengths.

You could take all of the carpet out of your car and shed 2.5lbs of weight.
Why dont you do that too?

They superimposed two separate runs on one video.
You know that you can easily get 3-5 HP differences between dyno runs done back to back with no engine changes right.
How long did it take them to swap the pulley?

That might be a useful comparison if they showed the logs instead of a video. That way we could plot the rate of change of the throttle position vs the RPMs.

A tiny difference in how quickly you depress the throttle can make that difference.
Notice how both pulleys DROP in RPM at exactly the same rate.
That actually PROVES my point. Thanks for that

Pulleys for the most part seem to be visual eye candy for car shows more so than actual use. I installed an intake along with the Perrin crank pulley and probably mistakened that for throttle response. Regardless I'll probably get the Perrin set to match the crank ones as it does look pretty slick. The stock pulley is heavy.... weight reduction is kinda nice on that one at least.

Here is a perfect example of "snake oil" that falls apart when physics is applied:
The "Automotive Hydrogen Generator".
Simple, it uses the engine's electrical system to separate water into hydrogen & oxygen, then injects that back into the engine where it combusts giving more power!

Many people argue that this generates more power, but Physics (and the laws of thermodynamics) would say otherwise.
Do I need to try it to know it wont work? No

[ame="http://www.youtube.com/watch?v=RXJKdh1KZ0w"]Rockwell Retro Encabulator - YouTube[/ame]

stugray enough already with your crusade to prove you are the smartest person in this thread. The OP was asking if there are any downsides. You have provided no proof that there is an actual downside to upgrading the pulleys.

OP: Regardless of an quantifiable proof of whether the pulleys make a difference they are, in fact, lighter. Removing static weight from the car (especially the front) is not a bad thing. If you don't mind spending the money then do it and enjoy your mod. I bought an inexpensive lightweight pulley kit and shaved ~5lbs from the car. I also enjoy the mod and feel it was worth every penny.

No but I have told you that "Pros" would not mess with the dynamic balance of an engine by changing a part that is specifically designed to provide dynamic balance without rebalancing the engine. But clearly that doesnt matter.
Did I mention "VOIDS THE WARRANTY"?

here you go:

Put the pulley on! It will give you (Insert HP number here) _____ More horsepower and looks great!

That I can completely agree with

I think it would be better to have a heavier crank pulley. More mass means more inertia. E=mc2 right?

Umm you do realize that my "rant" started because of:

I didnt attack anyone, I was told I didnt know anything about the topic when I, in fact, build nearly identical engines for race purposes and know a little about balancing the rotating mass and making more power than stock.