Flywheel... How light is to light.

I am fairly new to the 240 scene. I was also looking into WRX STi's and what parts I would buy for it. I found that if you put a flywheel on it as light or lighter that 11lbs that it put unnecessary stress on the engine. Is the same true about the KA24DE. I am looking to free up as much HP as possible without taking away reliability. I also Plan to go turbo with it.

Crank pully(not under drive)?
Flywheel?

light as humanly possible isnt a bad idea if you do autocross but on the road the lighter the flywheel the easier it is to stall the car and it makes launching alot harder.

as for the Stress... The Extra weight the stock flywheel has dampens out parts that arnt perfectly weighed from the factroy (or something to this nature) but as for added stress... im not to sure on that

a crank pully probably wont help that much unless its underdrive.

i haven't heard this anywhere, but I was thinking, wouldn't a lighter flywheel cause more stress on the engine when the clutch is engauged harshly because there is less weight to absorb the impact. if you think about it, it makes sense. or am i just an idiot?

Yes, with a lighter flywheel it is more likely to stall the car because there is less rotational mass, especially when using slicks.

Also, the likelyhood of valve float is also increased because of the increased acceleration of the engine.

Yes, with a lighter flywheel it is more likely to stall the car because there is less rotational mass, especially when using slicks.

Also, the likelyhood of valve float is also increased because of the increased acceleration of the engine.

thats why u invest in some cheap, but engine saving RAS's :)

I am not really worried about valve float because I'm puttin Ti Valves and springs in it. I am more worried about the crank... But if nobody has heard of it I just wont go extreme with it. I am planning on just drag racing it so I am going to try and find a happy medium. Thanks for everyones help.
I was just trying to find out because I am one of those people that likes to know about everything. :biggrin:

12lbs. is the lowest anyone should go. end of story

Thank you Sir. :biggrin:

12lbs. is the lowest anyone should go. end of story


why?

if you go lower than 12lbs. than their won't be enough rotating mass to spin the flywheel, thus messing up your tranny

Thats Bull. I've Seen 9lb Flywheels Working Perfectly Without Any Problems. You Can Go As Light As You Want As Long As You Have The Engine/tranny Mods To Back It Up. Another Thing To Consider Is That The Flywheel Is Similar In Weight To The Driveshaft And If You Want The Most Effective Output You Should Lighten Both Sides Of The Transmission (input And Output).

wont be enough rotating mass to spin the flywheel? what?... Im thinkin that was most likely badly phrased.

Explain...

turbos aren't good for the engine, they put a strain on the engine and reduces its reliability. Turbo also makes the car require more maintenance and such. Now they aren't that bad for the engine, but definetly does not make the engine more or have equal reliability.

I'm looking at a 17 lb flywheel for my rx-7, I'd say a street car, that is about perfect, not too light but drops some weight and frees things up, perfect medium!

a crank pully probably wont help that much unless its underdrive.

undriving a crank pulley is actually a dumb idea on a street car. it lowers the output of all accesories on the engine. also, you get minimal gains from underdriving compared to lightening the crank pulley. i wish more people made lightened pulleys instead of underdrive pulleys, i would definitely buy one. until then, i'm leaving the pulley stock.

Thats Why You Get Matching Overdrive Pullies For The Alternator (only One That Needs It). The Ps Pump And A/c Don't Need A Specific Amount Of Rotational Speed As Long As Its Not Faster Than Stock.

they don't always make those. i know they don't make them for the maxima, not sure about the 240. underdriving only accounts for 15% of power gains, the rest of the 85% is all from lightening the pulley. If you can get the overdrive pulleys for the rest of the stuff then i'd say an underdrive crank pulley is good but for those of us who don't get the overdrive pulleys i'd stay away from underdriving.

Yes, You Are Correct. I Wouldn't Worry About Overdriving Any Accessory Other Than The Alternator (it Needs A Specific Speed To Keep Amperage Stable). But They Don't Always Make Overdrive Pullies Which Is A Shame.

One of the main reasons I want to put a lightened flywheel on is i read somewhere that every lbs you loose on the flywheel is like taking 100lbs out of the car. Is this true?

Rotational Mass. Yes You Get A Big Difference In Drivetrain Loss But Its Not As High As 100lbs.

I got an Unorthodox Racing VG30e maxima crank pulley in silver here lol.... they make a lot of pullies for those cars.

What is this nonsense about a flywheel being too light? The McClaren F1 does not even have a flywheel, and it does not have any problems stalling. The only time that a heavy flywheel should be used is in drag racing, where its recprocating mass aids in launching the car. I have never heard of a flywheel being too light in a street car.

I have a 93 240sx
mods- hotshot header
apexi N1 dual exhaust
Fidanza 11lb flywheel

I couldnt tell you exactly how much the flywheel helped because it went on at the same time as the header, but together there was a really nice pickup, it isnt hard to drive on the streets, occasionally I stall it, but only when im not paying attention to life, Its really not all that easy to stall, I only have an OEM clutch tho, so I imagine it would be easy to stall with a better clutch, but I hardly ever stall, and my engine/transmission havent flown apart in the 2 months ive been driving with these on there

oh BTW im a newb what are these cheap/engine saving RAS you speak of? I might look into this magical device.

i have an unorthodox underdrive pulley. i have zero electrical problems.

the mclaren doesn't have a flywheel????? where does the clutch engauge?

it would also need some sort of large gear to start the engine and its only a bmw engine in there so i don't think there is anything very special like a no flywheel setup. now i believe f1 cars don't have flywheels. not sure how they do the clutch system but that's why they stick that starter thing in the back.

They Have Electric Clutch Systems That Actually Grab The Crank Output On Some. They Use Direct Start Systems Also. These Are Formula One Cars By The Way.