Hey,

First off, i would just like to say that there should be a forum just for discussing flywheels and clutches and other drivetrain issues.

I have been doing a lot of reading and researching about what clutch to buy and what flywheel to buy, if any at all. So i figure i would combine my findings and conclusions into a post so others wont have to search for hours through the forums. Also, there seems to be some confusion about the benefits of lightweight flywheels vs heavier vs the stock one. I am going to start by giving some basic information ( prices and weight and etc) about the different companys out there that offer clutches and flywheels for the G35 coupe.

Basic Information about stock G35 coupe:

1) The stock flywheel on a G35 coupe weighs 23 lbs

2) The combined weight of the stock flywheel and clutch is 46 lbs

3) Automatic G35's do not have flywheels

4) The G35 coupe has what is known as a dual mass flywheel. To better explain what this means I am including an article from Road and Track with good information about this topic:

"One of the issues in replacing it with a lighter aluminum flywheel is the lack of a spring damper in the clutch disc,(amonst other issues) which can lead to rattling of the gears in the transmission. Somehow the dual-mass flywheel prevents this without a spring damper in the clutch disc."

"That's because a dual-mass flywheel is assembled from two pieces — an inner and outer ring — with a spring action between them. The idea is to provide a harmonic-dampener effect so engine vibrations won't enter the transmission and cause a gear rattle at idle.

This also means the conventional marcel springs in the clutch disc are redundant with a dual-mass flywheel as the cushioning offered by the clutch-disc springs is already provided by the dual-mass flywheel's springs.

Therefore, when eliminating a dual-mass flywheel and clutch combination in favor of a conventional design, both the flywheel and clutch disc are replaced.

If you're still a bit mystified, realize that two goals are being met by springs. In a conventional clutch, the springs in the disc cushion clutch engagement, making it less abrupt, less on-off. Dual-mass flywheels use springs for a completely different purpose — to dampen harmonic vibrations at idle — but also have a side effect of cushioning clutch engagement. That allows eliminating the clutch's springs. But do away with the dual-mass flywheel such as with your one-piece aluminum flywheel, and you'll definitely want a sprung hub in the clutch disc."


Heavy vs Lightweight Flywheels - Benefits and Drawbacks

Note: This is all information that i have gathered from various other threads and posts from different members and is posted in an unbiased fashion.

Drawback # 1-
A lot of members with lightened flywheels were complaining about odd noises coming from their car under 2000 rpm's or at idle. I believe this has also been referred to as the "Cement Mixer" effect. Some people were heavily bothered by the noise and to others, the noise was negligible...go figure?

"The gearbox does indeed make noises now. At idle and accelerating hard below 2000rpm, you would think something was wrong if you didn't know better, but since you put the flywheel in, you understand the noises. Above 2000 rpm, the gearbox is silent. The noise shouldn't translate into accelerated wear, by the way, it just sounds like it does." - SCC magazine

 

I have seen many arguements about what exactly a lightweight flywheel does to improve the cars peformance and in what areas.

Originally Posted by McG35:

"Installing a lightened flywheel will in fact make your car faster at the drag strip. Engines have to accelerate the mass of the car, as well as the mass of all rotational items, such as wheels, gears in the tranny, crankshaft, and accessories. However, lightening rotational drivetrain components (like a flywheel) have a more pronouced effect on make a car faster than just reducing mass of the body of the car, because the engine doesn't have a mechanical advantage to drive a flywheel, it is a direct connection. The transmission of a car is like a lever helping the engine accelerate the mass of the car. So, a 5lb savings on a flywheel could be equivalent to taking 50lbs out of the trunk.

Driveablility will suffer. When shifting, a heavy flywheel will keep the engine reved up to make the engagments smoother. Some race cars with no flywheel will drop to idle during shifts, the driver has to tap the throttle to keep the engine up in revs for a clean engagement.

Golden rule .....Force = Mass x Acceleration, to increase acceleration you have to either increase force (more hp) or decrease mass. Same applies whether you are talking linear acceleration or rotational acceleration."


In rebuttle, DaveB wrote:

"If this was really true, drag cars wouldn't have flywheels. Drag racing is heavily dependant on your car's ability to get off of line with the most acceleration as possible. The first 100' of any drag race is the most crucial. Adding a lightweight flywheel will make it far harder to launch the car effectively because of the lack of stored energy. The car will be far more prone to bogging in first gear which is exactly what you do not want in a drag race and drivability will suffer. Lightweight flywheels require a lot rpms and clutch slippage to get off the line hard.

If road racing is your game, then the lightened flywheel is a great mod because the start of the race isn't as crucial. Road racers use this mod not because it makes fractionally better power, but instead it's because it's easier to execute rev match downshifts. If you've ever road raced, you'd know that perfect downshifts are key to keeping the car and chassis in balance."

This is my conclusion about this topic: (And my Conclusion only, feel free to draw your own)

1) With a lightweight flywheel installed, it will be harder to consistently launch the car in a successful manor.

2) Lightweight Flywheels require you to keep the engine reved at higher rpm's before you release the clutch and take off from the line.

3) Lightweight flywheels require more slippage of the clutch to get a successful launch and the car is more prone to bogging.

4) I would assume that this would equate to more wear and tear on the clutch if you are consistently practicing launching the car. But I am not sure exactly, thats just my assumption.

5) Lightweight flywheels are an excellent mod if you are not going to the track every weekend or you don't launch your car from a stop all the time.

6) Lightweight flywheels will make it easier for you to succesfully complete a rev-match downshift.

7) Lightweight flywheels are more track and auto x oriented than drag racing oriented.

8) For better launches off the line, a heavier flywheel would be better. (Which makes me wonder why nobody offers a heavier flywheel for the car??)

9) Launch aside, a lighter flywheel will be easier for the engine to accelerate, and easier to accelerate the rest of the car.

10) A lightweight flywheel will definitly reduce drivetrain power loss. However, it is more unforgiving to mistakes. Once moving, the OEM FW has more inertia to maintain engine revs when shifting. With the lighter FW, your RPM drops fairly fast while shifting. This can kill you in the 1/4 if you mistime your shifts.

11) This is not a mod for novice 6mt drivers

12) A lightweight flywheel will enable the engine to go through the gears faster because the rpms are shooting up faster. The car will feel less slugish and more zoomy and better throttle response.

13) All aftermarket lightened flys rattle. In gneral the lighter the fly the more the rattle, but the more the perfoemance benefit.
Raisng idel a little to say 850rpm reduces it some. Lightened flys actually reduce the crank loads and extend tranny synchro life since the speed matching is more acurate especially during agressive downshifts. Anyone thinkin that a lighened crank pulley or ligtened fly (that are properlydesigned) put greater strain on the crank are mis-informed. The VQ35 is fully "internally" balanced. The heavy dual mass OEM fly is desinged to reduce noise from the "trans" not the longblock.

 

Excellent summary. This is basically the same thing I came up with when I was researching whether or not I wanted to add a lightweight flywheel. I came to the conclusion that I'm more of a "novice 6MT'er" and I never autocross/track the car, so for me the idea of dropping the money for this mod didn't make sense.

I used the same argument to talk myself out of a set of expensive coilovers...

GOOD WRITE UP!

 

Yes! good summary.
Light flywheels are harder to drive in stop n go traffic. BUT...
if you have to replace your clutch and flywheel... I found that a ligher Nismo flywheel is cheaper online then buying a stock flywheel at the dealer. go figure.

so if that ever happens to you... an exedy hyper single carbon clutch ends up being just a little more then stock clutch and stock flywheel at the dealer... it's $$$ but ooooohhhh so nice.

 

Thanks guys...actually im not even close to done with this writeup...i have a lot more info to post about flywheels and clutches and where to buy them and etc so that other members wont have to do any searching. Although i have made my decision.....i am gonna get a lightweight flywheel...most likely the JWT combo. I wont be doin much drag racing anymore and a lightweight flywheel will make the car just more fun to drive and more fun shifting and etc. ....i will post all the other info i have very shortly....i am really busy with work....sorry about the wait.

Evan

 

Great write-up and being one who has had a lightened clutch and fw installed, I would agree with your assessments.

 

i get the whole flywheel thing.. the clutch area is where it gets groggy for me.. i am probably going to get the jwt combo also.. but would like to know more about the other clutches out there and what the pro's and cons are...

 

IMO if you are getting free labor or doing the work yourself, something like the NISMO or JWT flywheel/clutch would liven up the car nicely without losing much down low. These cars have EXTRA heavy flywheel/clutches mainly for noise supression, so there is some mass to shed without penalty if you are willing to sacrifice some stealth (noise).

I would definitely not do a Tilton or any of the other very low mass flywheel/clutches, which will certainly kill daily drivability.

This mod is not worth it if you are going to be shelling out $500+ for the install unless you have it to throw around

 

I agree 100% Being the g35 on the heavy side.
Drivablity is the key here.

 

this is a good post, so I'll bring it back from the dead.

I don't understand the noise comment. On my wrx I had a exedy flywheel on my wrx and I never noticed any difference in sound from the stock setup. NOW that might be because I was used to what ever noise was present, that I'm not sure. BUT I will agree that driveabilty was a little more difficult to get used to.

But that was also a small 4 with awd, to make things a little more tricky to get used to. But to me it was a great setup and it was the perfect weight, seemed that at least with the subie if you went too light the car would start to run like crap.

 

After 5,000 miles on the car after the JWT clutch and flywheel upgrade I have to say I love it. It took some getting use to, but when I road race the car, engine braking is easy and my car revs like a motorcycle. It DOES affect your launch from a stand-still.