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Jun Ultra-Lightweight Flywheel

 
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XS9909
Stage 9 - ported throttle bodies


Joined: 12 Jan 2006
Posts: 954
Location: Hawkes Bay

1989 Nissan 300ZX NA

PostPosted: Wed Oct 03, 2007 6:14 pm    Post subject: Jun Ultra-Lightweight Flywheel Reply with quote

http://www.fortyone.co.nz/parts/view/5474.html

What are peoples thoughts on this? Can anyone tell me what the weight is of a factory flywheel? Isnt it around the 10 - 11kg mark?
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erichns
Stage 8 - twin pod filters


Joined: 05 Sep 2003
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PostPosted: Wed Oct 03, 2007 6:41 pm    Post subject: Reply with quote

http://www.ttzed.com/products/products_detail.cfm?CFID=38307883&CFTOKEN=54145107&cat=102&grouping=1&grouptitle=Performance%20Parts&PartID=34&page=1&title=Flywheel%20%2F%20Flexplate&do=detail
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XS9909
Stage 9 - ported throttle bodies


Joined: 12 Jan 2006
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Location: Hawkes Bay

1989 Nissan 300ZX NA

PostPosted: Wed Oct 03, 2007 6:55 pm    Post subject: Reply with quote

apart from this product being Stillen, is there a reason you recommend this one erichns?
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erichns
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PostPosted: Wed Oct 03, 2007 7:07 pm    Post subject: Reply with quote

No, I was merely pointing out the weight of the stock unit which it said to be 21lbs. I'd actually prefer a JUN item myself

Here's a JUN flywheel for S15 review (not 300zx but it's a JUN flywheel nevertheless)

Simon C wrote:
Reviewer's car details:

Model: S15 Aero

Year of Manufacture: 1999

Engine: SR20DET

Transmission: 6MT

Modifications: Nismo exhaust, ST front pipe, Cusco strut bars, C's Short Stroke Shifter kit

Product Description: Jun Superlight flywheel

Purchase Price/Place: $700 2nd hand (almost new), $300 + 3 hours installation at M's Racing

Review Period: 2 days

Review:

I've suspected for some time now that my clutch was on its way out. It's been making clanky noises for the last few months. I've also been nutting out how to get more low end response out of my car. As we all know, the S15 turbo doesn't really start coming on boost until at least 2500 RPM, and before this it's a bit sluggish off the mark. Given that my clutch needed replacing, a natural option was to consider a lightweight flywheel.

After doing a lot of reading up on the net and asking around, I've concluded that there's a lot of misinformation regarding lightened flywheels out there. As such, I think that before I write my review, a quick summary of my readings in the form of a flywheel FAQ is in order.

-- BEGIN FAQ --

Your flywheel is the culmination of your engine's internal mechanisms. Power is transmitted from your engine to your gearbox via a friction interface with your clutch, which clamps against the flywheel when you let your foot off the clutch pedal. Flywheels also have a couple of secondary functions due to their rotational inertia once the clutch is disengaged: specifically, they smooth out the firing pulses of the cylinders at idle, and they retain revs during gear changes for smoother driving. These are characteristics of a heavy flywheel, with a large rotational mass.

The problem with heavy flywheels is that they're, well heavy. So your engine has more work to do to make them spin up to a given RPM. The end result is that your car accelerates slower, particularly at low RPM when the flywheel doesn't have much momentum. At higher RPM, this is less of an issue.

This is where a lighter flywheel becomes advantageous. Mathematically, because your flywheel is a rotating component (and rotates at high speed), 1kg off your flywheel's edge is worth the same as up to 40kg off your car's non-drivetrain mass in terms of acceleration (source: http://www.pumaracing.co.uk/flywheel.htm). A significantly lighter flywheel will make your car accelerate much more quickly, making it easier to get the car on boost and turn it into a rocketship once the boost comes on. Of note is that the flywheel is NOT an energy generating device - it CANNOT give you more torque or power, but likewise it will not reduce these either. In fact, it will make bugger all difference to your dyno charts, but the car will still be faster in the real world. A person on the NZ Hondas (*cough*) has performed a semi-scientific analysis of the benefits of his lightened flywheel, and this can be found at http://nzhondas.com/phpBB2/viewtopic.php?t=7296#93907.

Like all things in a high performance road car, the factory engineers made the stock flywheel heavier than the theoretical minimum in order to retain good idle and driveability properties. A lightened flywheel has some drawbacks:

- Lumpier idle (lighter flywheel can't smooth out the firing pulses from the cylinders)
- Poor momentum when coasting or during gear changes (so you have to rev higher before shifting)
- Noisier startup due to interfacing with the starter motor.

In addition, the S15 flywheel is a "dual mass" unit, meaning that it's two flywheels in one. This is designed as a harmonic dampener, to cancel out resonance vibrations in the driveline at certain RPM. Without this mechanism, one could expect drivetrain harmonic rattles. Furthermore, the S15 flywheel has a spring rather than a solid centre, and as a result the clutch disc is solid from the factory. Changing to a solid centre aftermarket flywheel will necessitate a new clutch disc with a sprung centre, and for this reason changing the flywheel becomes much more economical when your clutch needs to be replaced. In contrast, I understand that the S13 and S14 SR20 flywheels are simple solid units with sprung clutch plates. S15 flywheels hence are a specific design and are not backwards compatible.

There are two routes to go in terms of getting a lighter flywheel.

1) Take out the existing flywheel and shave weight off it. This can be done cheaply ($100-$200 depending on where you go), and I believe that the S15 flywheel can also be machined despite its complex nature. Ideally, weight would be shaved off the edge of the flywheel as this has more effect on rotational inertia. Learned persons consider this the rangi way of doing things. First of all, the flywheel will need to be rebalanced, as it's a high speed rotating component and having an off balance flywheel will severely inhibit your engine's ability to rev. Secondly, and most importantly, a shaving weakens the factory unit. The edge of the flywheel can hit speeds of 500kmH, and if the flywheel disintegrates, the shrapnel will not stop for anything. It'll go through your bell housing. It will go through the floor of your car. It'll go through your legs and testicles. Consider a lightened flywheel a roulette wheel with your scrotum wagered. That being said, a number of people shave their flywheel modestly and seem to get away with it. Your choice, Stumpy.

2) Buy a purpose designed lightened flywheel. These can be very pricey depending on who makes the flywheel - local manufacturer DVM Design charges $600-$700 each, while the Jun Superlight S15 flywheel on my car will set you back well over $1k. You can also get flywheels prepackaged with a clutch assembly. This is the land of megabucks. Money buys you build quality and R&D. The flywheels are light and strong because of better metallurgy coupled with computer designs, and you can be sure that they've been tested to withstand absurd RPM without exploding. One of these will be much lighter than a machined flywheel, so your car will be faster, yet your legs will be safe (albeit your wallet will be quite a bit lighter as well). Quite often these flywheels also have extra holes and things cut in them, for better clutch cooling properties.

Another point of interest is the concept of integrated ring gear. Basically, your flywheel can come with teeth on it (integrated) or not. In the latter case, the teeth are on a separate ring, which is then mounted to the toothless flywheel. In theory, if the two bits are made from different metals (with different thermal expansion coefficients), the ring gear can shatter off the flywheel and, again, whip your legs off. An example of this is a steel flywheel with aluminium ring gear, as the iron will expand faster than the aluminium.

-- END FAQ --

I bought my flywheel 2nd hand off Jerry, who drives the pink S15 drift machine. It was 4 months old, and came up for sale due to clutch replacement (his new HKS clutch package being installed came with its own flywheel). Build quality wise, well, it's a big circular lump of metal, albeit well machined and obviously of high quality manufacture. There are no cooling holes in it, and the ring gear is integrated. It weighs 7.6kg, apparently the minimum possible for an S15 design. In comparison, the stock is 12.22kg, and a Nismo S15 flywheel 7.66kg (source: www.japanparts.com). As it's a solid unit, it requires a centre sprung clutch disc (recall that the OEM S15 clutch plate is a solid centre design).

Installation was performed at M's Racing, and took a shade over 3 hours. I also had them install an ST front pipe at the same time, so this may confuse the butt dyno a bit (although I suspect the front pipe matters much more at moderate to high RPM). Since my S15 is a daily driver and I don't do much track work, I had an Exedy organic clutch plate installed ($295), which shifts just fine.

As in my FAQ, there are two aspects to a flywheel - performance and driveability. I'll discuss each in turn.

Performance wise, I can't really tell too much difference driving around town. Under 2000 RPM, the car isn't really noticeably faster. However, above 2000 RPM it's much easier to get onto boost, and when the boost comes on by the gods you can feel the difference up to the midrange. Above this I attribute any extra acceleration to the front pipe.

Driveability wise things look pretty good too. Idle? Smooth as. Can't notice any change, unlike what I was expecting. Gearshifting? Absolutely no different to before. Coasting? Haven't done much so far, but no significant difference as near as I can tell. Noise?

Well, this is where things get muddy. As I said, the Jun unit is a solid centrre flywheel, and lacks the dual mass mechanism of the factory unit. Nissan's engineers put it there for a reason. There is a very brief grind on startup, but nowhere near as bad as the infamous SR20DET VVT rattle which plagues my engine and most others out there. 1st and 2nd gear are just as quiet as stock. However, in third gear, there is a very faint chatter from the gearbox at 2000-2500RPM, and it's definately noticeable in 4th, and even louder in 5th and 6th. It sounds a bit like, but not as harsh as, the aforementioned VVT rattle. My first thought was my legs, so I took the car back to M's Racing the next day to make sure nothing was loose or wrong with the new flywheel/clutch. I was reassured that this was a resonance rattle from installing the new flywheel, and there wasn't anything that could be done about it.

I'm quite a conservative driver around town. I hate NVH, I hate the S15 gearbox whine, and boosting around town wastes pricey petrol (I open up a bit on the motorway and open road). The S15 SR20DET has enough torque and the gears ratios are sufficient for me to shift at 2500 RPM, keeping the cabin quiet and making the trees smile at me as I cruise along. So obviously, the resonance noise was driving me mad, as every time I shifted up a gear, the car kept making louder and louder noises. I have a Nismo exhaust system which is barely louder than stock, so it can't mask the noise. Jerry told me that he didn't have a problem with this, as he habitually upshifts at 3000 RPM and never gets the noise. So I tried this, and sure enough, no rattle! But at 3000 RPM, I'm getting more engine noise, more exhaust noise, and more gearbox whine. Also, it means I can't really use 5th gear around town, and I can't use 6th gear for 80kmH zones, otherwise I'll get rattling. 3000 RPM also puts you into boost, which means that I find myself racing from traffic light to traffic light a lot more than before, whereas I'm used to just coasting along quietly and happily between (as the cars in front are usually of course a heck of a lot slower off the mark than an S15 Spec R). This is only going to happen more as I put more mods into my car - pod filter, actuator kit and Power FC are all due before the end of the year.

So all up?

If I was a more aggressive driver than I am, if performance mattered most to me, then the flywheel is a great thing. Really, the car feels quite a bit quicker. However, because I'm a sedate driver around town, and because I can't stand rattles and NVH, the flywheel represents a bit of a compromise situation and necessitates a change in my driving habits. I've always intended for my car to be a quick street cruiser and GT car rather than a track beast or drifter, so this differs somewhat from my build plan. I plan on trialing it for a few more weeks, then making a decision whether or not to switch back to the old dual mass and sell it off. I'm slightly tending towards the latter at the moment, but I may get used to it.

So, if anyone is interested in buying a Jun flywheel, please let me know.

Rating:

8/10 if you race your car, it's already noisy, or you habitually shift at 3000+ RPM. To rate higher, it'd have to be cheaper. Something worthwhile doing when your clutch is on its way out. If you're a sedate driver or a NVH Nazi like myself, 6/10 so stick with the dual mass unit.

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XS9909
Stage 9 - ported throttle bodies


Joined: 12 Jan 2006
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Location: Hawkes Bay

1989 Nissan 300ZX NA

PostPosted: Wed Oct 03, 2007 7:59 pm    Post subject: Reply with quote

good read that, I did pick up on the weight btw, I just thought you were recommending the Stillen one lol. Its interesting to see that the guy didnt notice much difference on the dyno, but on the road he did.
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Mungyz
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Joined: 25 Dec 2005
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1990 Nissan 300ZX TT

PostPosted: Thu Oct 04, 2007 4:35 pm    Post subject: Reply with quote

MMMMMMMMMMMM light fly wheel mmmmmm gooooood Very Happy


Mine is an ally one at around 5kgs much faster car does go
plenty of bang for buck to be had there man Cool
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Kratos
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PostPosted: Thu Oct 04, 2007 7:34 pm    Post subject: Reply with quote

thats good to know thanks mungyz, and with those turbos on it, it would fly off the mark....mmmmmmm it's gonna be great to see what you do at the old taupo track...08
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Mungyz
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Joined: 25 Dec 2005
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Location: The Mighty Waikato

1990 Nissan 300ZX TT

PostPosted: Fri Oct 05, 2007 3:47 pm    Post subject: Reply with quote

It's had the ally flywheel in for ages, hell I was in Te Awamutu when I got that from his royal madness Laughing Done many many big launches etc and never had a problem with it but I guess flywheels don't normally give trouble.
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