Pressure plate question - cast iron vs aluminum

[widebody911]

My clutch was giving me issues, needed to replace it. I had a Sachs "Power Kit" and looked at my options: Anothr SPK, Centerforce, or Kennedy (or stock, I guess...)

The consensus (from what I read on various threads) seemed to be that the Centerforce was way overpriced for what you get, which was a modified Sachs PP and a stock disk.

So I went out on a limb and ordered a Kennedy "Stage 1" clutch kit for my 911. It arrived today, and it turns out it is a Sachs cast iron pressure plate. Is it just me; I don't see how any sort of 'performance' clutch can be cast iron. This cast iron PP weighs a bunch more than the aluminum one, and for a 95% track car I don't want to give up any performance I don't have to. Between the chip and AFM tuning, I didn't have too much of an idling issue with the aluminum PP.

I'm tempted to put in the new disk with the old aluminum PP and call it a day.

Thoughts?

[Plavan]

You have a 915 right? I have a tried and true kit for the 901.

[carrera]

One would think that with the alu pp the car should be quicker. If your pp is not scored then it would seem to be a good idea to use it.

[widebody911]

Yes, I have a 915.

[Tyson Schmidt]

They don't make aluminum PP's anymore. The difference is 4#. I don't think I'd lose sleep over the difference. Especially if it means less likelihood of a slipping clutch.

You're still about 30# lighter than what that motor originally came with.

[jhora]

Chad,

What do you use for the 901?

John

[Plavan]

Look here:

What do you guys think of this? I am testing it next weekend.

[Shaun @ Tru6]

2 weeks ago I put a Sachs Power Clutch in my car with the Al pressure plate. it was significantly lighter than the stock Sachs PP in the car.

Performance gain? tough to tell with the Steve W chip, test pipe, MB911 muffler, weight loss program... I can say that engagement is buttery smooth, couldn't be happier with it.

[Zeke]

It is my belief that the less rotating mass the better, AFA shifting goes. But, you have to be one hell of a good driver with excellent shifting technique, and have a super tranny that works perfectly and quickly to utilize the low mass principle. Drag racers really love light flywheels and light PPs. I wouldn't know the difference myself on a 911.

[Tyson Schmidt]

Originally posted by Shaun 84 Targa
2 weeks ago I put a Sachs Power Clutch in my car with the Al pressure plate. it was significantly lighter than the stock Sachs PP in the car.

Performance gain? tough to tell with the Steve W chip, test pipe, MB911 muffler, weight loss program... I can say that engagement is buttery smooth, couldn't be happier with it.

Where'd you get an aluminum PP? Last time I checked they weren't making AL. anymore.

Most people can't tell the difference that the 4 pounds makes between an Al and steel PP.

If the Aluminum is still available in Sport form, then by all means trade it, Thom. But I wouldn't run a weaker stock pressure plate behind a 3.6 just to save 4 pounds. Bad trade.

[widebody911]

Originally posted by Plavan
Look here:
What do you guys think of this? I am testing it next weekend.

Neat, but I don't think it would work with a 3.6L

[911pcars]

I thought the difference between the two Sach's units was that the "aluminum" version has an aluminum housing around a cast iron pressure plate. The steel PP uses the same cast iron PP.

If the "aluminum" PP was entirely aluminum (save for the diaphragm spring), the weight difference would be considerably more than 4 lbs. Please correct me if I'm wrong.

Sherwood

[widebody911]

I've been running an Al pressure plate since I did the conversion - I got it with the kit from Timmins.

In comparing the Kennedy pressure plate to the old one, there is one extra leaf spring between the two parts of the pressure plate.

[RoninLB]

Originally posted by widebody911

, there is one extra leaf spring between the two parts of the pressure plate.

thx on that one. I'd probably have to be concerned with stall on the streets.

[Tyson Schmidt]

Originally posted by 911pcars
I thought the difference between the two Sach's units was that the "aluminum" version has an aluminum housing around a cast iron pressure plate. The steel PP uses the same cast iron PP.

If the "aluminum" PP was entirely aluminum (save for the diaphragm spring), the weight difference would be considerably more than 4 lbs. Please correct me if I'm wrong.

Sherwood

The only difference is the outer housing. So only 4 pounds difference.

[Steve@Rennsport]

Hi Tyson:

Its not just the 4 lbs,....its where its located on the PP.

Its all about Moment of Interia as thats real benefit here most folks can feel the difference,....

Just like the real estate biz; weight issues are not simply the involved poundage, its location-location-location.

My opinion only, of course.

[Shaun @ Tru6]

Originally posted by Tyson Schmidt
Where'd you get an aluminum PP? Last time I checked they weren't making AL. anymore.

Most people can't tell the difference that the 4 pounds makes between an Al and steel PP.

If the Aluminum is still available in Sport form, then by all means trade it, Thom. But I wouldn't run a weaker stock pressure plate behind a 3.6 just to save 4 pounds. Bad trade.

My shop, Rensport, got it for me, owed me a favor. It was definitely Al, or at least a magnet said it wasn't iron.

is everyone sure about the 4# difference? I didn't weigh the two, but the Al was MUCH lighter than the stock PP.

Steve is correct about Inertia, but have to add that my MB911 provided a very noticeably, quicker "spool-up" over the stock muffler. With that, I'm not sure I could feel the quicker revs just due to the PP since the muffler already was doing so much.

I really like the clutch engagement and smoothness, which *could* *might* be attributed to a lighter PP with less rotating mass.

Final thought: Chris Bennet just rebuilt my 915, we used some good used parts to save a few $. That coupled with brass bushings in the coupler, new bushings in the shifter a year ago with factory SS kit, new sport mounts on the motor AND trans and hte new clutch provided one result:

my old 84 shifts like a new 89. Just my $.02.

[SC-targa]

I installed an aluminum pressure plate a couple of years back when I rebuilt my tranny. I was expecting to notice a real difference when I drove the car.

Realistically, I couldn't really feel any diference. I was afraid the motor would stall easier or that I would need to slip the clutch more to get off the line, but the car seemed to drive just the same.

Jerry Kroeger

[randywebb]

"My opinion only, of course."

(To quote someone... LOL!) It's a mathematical truism as Steve well knows.

BTW - no one has mentioned ceramic - C-GT is a rolling test bed for some things we may eventually see on more affordable Porsches...

[widebody911]

I just talked to Kennedy a few minutes ago. My findings:

They've been selling Fe/Fe pressure plates because they can't get Al/Fe versions any more.

For $600, you can get an Al/Al pressure plate.

For $200, they'll rebuild my Al/Fe pressure plate and beef up the holding capacity.

All of these use the stock disk.