SPEC Clutch with billet aluminium pressure plate

[24OZ]

Guys,

 

I need to purchase a performance clutch for my 240Z.

 

Been looking at the ones SPEC has to offer, I was on their website tonight checking out the options and for an additional $199 they offer a billet aluminium pressure plate.

 

What are your opinions on this, I am already running a lightweight Fidanza Flywheel - my thoughts were that it's good to have some rotating mass and maybe this billet pressure plate along with my lightweight flywheel will make the car harder to drive? I like my car to be streetable (if that's the right word) i.e to feel fairly refined.

 

Thanks,

[Dave@SBClutch]

I personally am not a fan of aluminum anything on the drivetrain unless it's a dedicated autocross car. You're absolutely correct that eliminating all the rotating mass will make it more difficult to drive. Yes, your engine will rev faster. But it'll drop nearly as fast. Which is why most guys who run them end up turning up their idle so their car doesn't stall. Infact, we see better 1/4 mile times with heavier flywheels on cars because it keeps them in the power band. Especially on boosted cars.

[johnc]

Infact, we see better 1/4 mile times with heavier flywheels on cars because it keeps them in the power band. Especially on boosted cars.

 

As Ricky Ricardo would say, "'splain please."

 

How can spending more time in the 3,000 to 6,000 rpm band through 4 gears (as an example) lead to quicker 1/4 mile times? Let's say you spend a tenth more time on that rpm band each time, doesn't that mean its taken .4 longer overall to cover the 1/4 mile? Wouldn't this especially true for a manual transmisison car?

[mark]

I could see the heavier flywheel having an advantage at launch but that is it.

[JMortensen]

Dave have you driven a Z with an aluminum or otherwise lightweight flywheel? They're pretty easy to drive and get off the line. I had a bunch of people tell me "Don't go that big with the cam, you won't be able to drive it on the street" and "Don't go with a light flywheel, you won't be able to drive it on the street" and "Don't get triples, you won't be able to drive it on the street" and "Don't get a stronger pressure plate, you won't be able to drive it on the street" etc. I ignored them all and drove my Z daily for years in stop and go traffic, never had a problem. I think I had the idle set at 900. I probably stalled it once a year when I completely brain farted or my foot slipped off the clutch pedal. I will say that on a small 4 cylinder or an engine with no torque like a Rotary it can be hard(er) to drive around town with an aluminum flywheel, but when you get into L6's they already have a pretty good amount of rotating mass with that long crankshaft and a lot of low end torque, so I think it's a non-issue.

 

As to the OP's aluminum pressure plate, I think my main concern would be how the aluminum deals with the stress from the springs over years of use. I'm not a metallurgist or anything, but that could be a long term concern as I think aluminum work hardens easier than steel.

[Dave@SBClutch]

John, I think it's a simple as following the torque curve. Lets use this as an example.

 

If you're power band is aprox. 3-6000 rpm, and your peak torque is 5000. To shift from 5800 and drop down to 3800, you're further away from peak torque. If you could get a bit closer, lets say.. 4100rpm. You're staying closer to your peak torque and peak HP. More power to the ground = faster ET's. Again, it's RPM fall off.

 

If you'd like to know the reasons we don't like aluminum flywheels, we see issues with aluminum flywheels too often. We see guys stripping out pressure plate bolt holes partially when assembling the unit and not knowing it. We see clutches coming off the flywheels. We also see the trend of aluminum flywheels is going away. It's moving twords lightened steel. The other problem I see is the hardened steel insert in the aluminum flywheel is not machined after being bolted in. If you were to grind the insert, you see aprox .004 low spots around the bolts holding it in. Creating an uneven surface, not allowing full disk contact. Aluminum has different expansion and contraction rates then steel. The relationship of the insert to the pressure plate mounting bolts allows the thickness of where the disk rides to change with heat. Where it would be more gradual with a one piece steel flywheel. .010 of change in disk thickness makes about .070 of change where the bearing rides at the end of the diaphragm spring. Not to mention heat can cause the insert to curl (soup bowl) causing a non release issue.

 

Jon, I haven't driven a straight 6 with an aluminum flywheel. It may not be too bad, just as a 4 puck on a honda civic isn't terrible. Not all cars act the same with certain parts. I understand that and maybe I spoke out of turn. But general knowledge in my industry is that drag racing times are better with heavier flywheels. It's seen a lot in boosted cars with big turbos falling out of boost.

 

As far as durability is concerned. There are two fulcrum points inside of a pressure plate. One on the inside of the lid and one on the casting. The diaphragm spring does wear the cast iron with miles. Aluminim would wear faster with a piece of spring steel riding on it.

[JMortensen]

If you're power band is aprox. 3-6000 rpm, and your peak torque is 5000. To shift from 5800 and drop down to 3800, you're further away from peak torque. If you could get a bit closer, lets say.. 4100rpm. You're staying closer to your peak torque and peak HP. More power to the ground = faster ET's. Again, it's RPM fall off.

The speed of the engine after the shift is determined by the road speed, not the engine speed. The aluminum or light flywheel allows for a faster shift due to the speed of the input shaft of the transmission slowing more quickly and the synchro having to brake the mainshaft gears less, so given the faster shift the road speed should be higher after, and hence you'll be at a HIGHER rpm after the shift with a lighter flywheel than you will with a heavy one.

 

If you'd like to know the reasons we don't like aluminum flywheels, we see issues with aluminum flywheels too often. We see guys stripping out pressure plate bolt holes partially when assembling the unit and not knowing it. We see clutches coming off the flywheels. We also see the trend of aluminum flywheels is going away. It's moving twords lightened steel. The other problem I see is the hardened steel insert in the aluminum flywheel is not machined after being bolted in. If you were to grind the insert, you see aprox .004 low spots around the bolts holding it in. Creating an uneven surface, not allowing full disk contact. Aluminum has different expansion and contraction rates then steel. The relationship of the insert to the pressure plate mounting bolts allows the thickness of where the disk rides to change with heat. Where it would be more gradual with a one piece steel flywheel. .010 of change in disk thickness makes about .070 of change where the bearing rides at the end of the diaphragm spring. Not to mention heat can cause the insert to curl (soup bowl) causing a non release issue.

These all sound like poor machining issues or people overtightening bolts. I remember the spec on the pressure plate bolts on an older 911, because I was pretty shocked when I looked it up the first time. 13 ft/lbs. People tend to want to crank these things down, and I think that is the source of the problems. Poor machining of a part doesn't mean the idea behind the part is bad. I've got friends who have used the same Tilton aluminum flywheel on L series engines for 15 years. The fact that you saw one that wasn't machined well doesn't prove that they don't work.

 

Jon, I haven't driven a straight 6 with an aluminum flywheel. It may not be too bad, just as a 4 puck on a honda civic isn't terrible. Not all cars act the same with certain parts. I understand that and maybe I spoke out of turn. But general knowledge in my industry is that drag racing times are better with heavier flywheels. It's seen a lot in boosted cars with big turbos falling out of boost.

I can see where launching a turbo car with a lot of lag would be easier with a heavy flywheel, or maybe similarly a very heavy car with an underpowered engine. Barring the "not enough power to get off the line" scenario, I can't see the heavy flywheel being a benefit to overall speed.

 

As far as durability is concerned. There are two fulcrum points inside of a pressure plate. One on the inside of the lid and one on the casting. The diaphragm spring does wear the cast iron with miles. Aluminim would wear faster with a piece of spring steel riding on it.

I'd have to guess that they wouldn't have a spring resting directly on the aluminum. I would hope that is the case anyway. I was more concerned with the flex in the pp as the spring is compressed and whether that slight amount of "oil canning" would eventually lead to a brittle area in the pp.

[johnc]

John, I think it's a simple as following the torque curve. Lets use this as an example.

 

If you're power band is aprox. 3-6000 rpm, and your peak torque is 5000. To shift from 5800 and drop down to 3800, you're further away from peak torque. If you could get a bit closer, lets say.. 4100rpm. You're staying closer to your peak torque and peak HP. More power to the ground = faster ET's. Again, it's RPM fall off.

 

I agree but that has nothing to do with the flywheel and everything to do with gearing. When you go into the next gear, the rpm you start off at is determined by the drive tire OD, final drive gear, and transmission gear. The only way to pick up the extra 300 rpm in your example above is to spin the tires, slip the clutch, or shift at 6100 rpm.

[Spddracer]

Remember every tenth you save off the line will gain you 2 in the 1/4

 

With turbo cars esp the quicker you get off the line the quicker you get into boost.

 

I dropped a considerable amount off my 1/4 mile times by going 5lbs heavier on my flywheel. Almost a full second actually.

 

There are a lot of variables here but the "correct" weight flywheel for your car can make a huge difference in 1/4 mile times.

 

My 60fts with a 11..lb flywheel were in the 1.9-2.2 sec range dumping the clutch off the rev limiter, 17lb flywheel 1.5-1.7 60 foots, Times dropped from 12.8's-13.20's to 12.20's-12.30's

[johnc]

I agree 100% that flywheel weight is critical to a good launch. After that, you want to shed as much flywheel weight as possible, but that's not allowed for safety reasons.

[Dave@SBClutch]

safety?