Penguinracer

Any one have experience of or an informed opinion as to the pros & cons of a lightweight aluminium flywheel v a lightweight steel item. I'm thinking specifically of the 5.75 pound aluminium wheel offered by LR compared to their billet steel offering which weighs 7.75 pounds but due to is scalloped design is claimed to act like a 4.75 pound wheel relative to the crank. I suppose the steel f/wheel would be stiffer - but has aluminium f/wheel rigidity been an issue with high power/torque 951s?

gt37vgt

never heard of any complaints from them what kind of triggering you run is a bit of a factor i have steel fly wheel but i have removed one trigger trace to get the weight down ..

RobE952

A cheaper option, and perhaps a good compromise, is to lighten your stock flywheel. This will decrease the rotating mass to mildly speed up your engine rev without getting so light that she'll bog down or stall when moving from a stop.

Be careful not to remove too much material though. I've heard flywheels with too much material removed will flex, reducing the contact patch for the clutch disc and causing strange wear patterns. When I had mine lightened I made sure to leave a significant amount of the mass-block to provide that "L" shaped profile and provide stiffness. (I hope that makes sense)


I'm not trying to flame, just thought I'd spew some fun facts. 2010 F1 cars actually spend most of their time in the 18,000rpm (!) range and they are fantastic drag racers, even limited by tire regulations. Here's some stats for a 2006 spec car:

Power-to-weight ratio: 1250 hp/t
0 to 100 km/h (62 mph): 1.7 seconds
0 to 200 km/h (124 mph): 3.8 seconds
0 to 300 km/h (186 mph): 8.6 seconds
0 to 160 km/h (100 mph) back to 0: less than 5 seconds

TonyG

First off... You can't get enough weight out of the 951 reciprocating mass to be bad on the street (crank, rods, flywheel, pressure plate).

Secondly, you consume horsepower accelerating a flywheel. The heavier the flywheel, the more horsepower it requires to accelerate it, which in turn reduces the net power at the wheels.

Personally, if you drag race, an aluminum flywheel is foolish unless you have a scatter shield. That said, a 951 is a horrible car to drag race and won't every be very good at it.

I just saw a before and after dyno of a Japanese car with a stock vs light weight flywheel installed. Don't quote me on this but the difference was like 10-15RWHP which increased as as the rpms increased. I think the dyno run was only to 6500 rpms or so. I'll see if I can find that dyno and scan it.

TonyG

xtaC

I use the LR steel flywheel, and have zero complaints.

I use an aftermarket trigger setup, so that is not a problem for me either.

George D

The alum flywheel I used with my build has a replaceable friction plate. When you change the disc, you just replace the friction plate at the same time.

I'm not sure if the SPEC flywheel has a replaceable friction plate, but I'm sure someone here knows. There is less abuse on the drivetrain with a lighter flywheel. Less weight = more HP to the wheels. L Racing's billett flywheel looks really nice.

I've had good luck with a stock lightened flywheel on the 2.5 cars, but that billett wheel looks like the better solution.

TonyG

Nah... you did the right thing by going with the aluminum flywheel.


TonyG

George D

I know, and I had no choice. My motor back to the wheels is all 968 parts. Notice the notches on my flywheel? I now have the pickup for the TEC at the flywheel using factory 968 pickup sensor. The 968 bellhousing allowed us to use factory 911TT sport PP and disc. I was tired of trying to get aftermarket discs and pressure plates to hold up. Last disc we got just over 3K on it before it was toast. This setup is used on the 600whp+ TT 911's and it's OE Porsche with some mods to hold better.

I now can change the clutch if a few hours vs a day + issues.

gt37vgt

yeh there has been heaps of threads on this and they always end up with you have to cut crank down and get alu flywheel and PP before its difficlut to drive

TonyG

Not even close...

I've run light rods, cut the crank way down, aluminum flywheel and pressure plate, no balance shafts, and it's no issue to take off on very steep hills (like where my house is).

Honestly, even with all that weight removed, and a big turbo, it's no more difficult to drive than a Toyota Corolla 5 speed.

I always wished I could have yanked another 10lbs out of the reciprocating mass.

I found that the car was easier to drive with all the weight removed because it didn't rev like a slug (which is what stock 951's rev like).

TonyG

David Floyd

Agreed, be doing all of the above for the last 80k miles (8-9 years)

Even with KEP stage 2 and 6 puck clutch

George D

I completely agree with Tony and David. My 3.0 build has Oliver rods "lightest/strongest you can get", light pistons, lightened crank that my builder bullnosed.

This time around we did add a S2 vibration dampner. We felt that this may help with the clutch longevity.

Prior to these additions, the motor used a stock lightened flywheel and custom clutchmasters clutch kit. The power from this motor ruined the clutch and flywheel within 3K miles. I never abused the clutch. I never had an issue starting off, shifting, or downshifting. Most, if not all my starts were rolling then WOT. We did feel that there may have been an imbalance in the flywheel, but you couldn't feel it when driving the car. The clutch held fine, it just didn't last.

I went with the 968 bellhousing because I knew 911TT cars with 30K miles on their factory sport clutches with 500+ whp. No issues, and these cars are much harder on their clutches as most are AWD and weigh about 500 lbs more than my car. The GT2 cars come in around 3100lbs, but are RWD. I also had the 968 six speed and 968 axles installed.

Lighter mass equates to less driveline abuse when downshifting, accelerating, and shifting as long as you match revs on the downshift. You may/will chatter on the downshift if you don't rev match. No clutch likes to act like a brake, it's not designed to be a brake pad. You have to have it completely engaged prior to using the motor as a braking force. The reverse of it's intent will create chatter, and short life span to it and other components in your driveline.

Power delivery is much better with less weight, and the motor feels crisp. It will accelerate/decelerate faster with less weight. Mass moving your car forward because of weight inertia is a silly argument when you are talking about a sports car that needs to be off power quickly, then back on with power quickly. The less mass to move the quicker you'll move in both directions with thrust, tq, hp or whatever you want to call power to the wheels. If mass increase inertia increases. Pretty simple. The lighter the components the easier it is to stop.

Tony has been around these cars as long as I have. He knows what he is talking about. I don't know David personally, but he has about 1000 more posts than me, and what I've read were helpful towards the original post and stranger asking for advise or help.

Why do lighter wheels and tires make a car quicker? Same theory, similar results if done properly.

Trust me, a lighter flywheel will help your car be faster. Just use a proven part from a good vendor that has experience with our cars.

Do not take a stock flywheel to a machine shop and tell them to take a few lbs off. Make sure that they know what they are doing, and make sure that it's balanced perfectly. Our inline 4 bangers like perfection. They are vibrators without unbalanced parts winding up front or in their rears. Unbalanced flywheels will damage your bearings over a short period of time.

Long post, but felt it necessary to help the original person that posted his question.

George D

Sorry David, I meant about 5000 more posts than me. My bad.

Regards,

George

V2Rocket

felt like i was going up a rollercoaster

CurtP

Is that a 58-2? Who's flywheel is that?