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Blowing chunks....
I, like Bob, are an Engine-nerd. I understand that the stresses seen by a clutch assembly and flywheel are directly affected by engine speed through the velocity component being squared. I understand that this simple fact is why stresses are amplified with increasing engine speed. What I don't understand is why the OEM components are understood to be unsafe. Why do we need specially approved bell housings and flywheel/clutch components? I've heard the near death experiences, but why is it that if an OEM set-up is engineered for a 6000 or so red-line, and I build a 289cid for the street that will occasionally hot-dog it to 6750 or 7000 to scare the piss out of a local boy racer, do I need to buy all this special stuff? I suppose that when it's all done and dusted, a lakewood bellhousing and some approve internal bits are cheap insurance compared with prosthetic legs. Is this everyone's thinking???
Thanks! |
I guess it's like insurance, hope you never need it. On a percentage basis it's pretty rare for a clutch to "explode" and come through the bell housing/trans tunnel. Of course on a Cobra it's likely your trans tunnel is "glass" so that won't offer ANY protection over and above your bell housing.
I lost the one in an old Mercury years ago. The trans tunnel stopped the parts, after the flywheel absorbed most of the energy. So what kind of cars would this be MOST likely to happen to? High perfomance cars of course! High revs are the most likely "trigger", along with aggressive clutch engagement on a down shift, up-shift, or the "killer",,,,standing start engagement at high rpm launch! Ernie |
Thanks, Ernie.
I suppose my scenario doesn't really include aggressive down-shifting and 5000 rpm clutch dumps. I was mostly speaking of spirited driving/acceleration. Is there still a risk in using stock components in such an event? Like I said, it would be irresponsible street/back road driving or the occational hill climb where I would expect to achieve such engine speeds. Thanks,:confused: |
More than likely you will be fine with stock components considering your "street" use approach and common sense application.
By the way,,,,,I was doing about 115 mph on the freeway when the Mercury blew. Not "excessive" rpm, not "jerking" it's chain, just an old clutch who's number was up! Stuff happens. Ernie |
Give me protection
I witnessed an exploding clutch assembly last summer.
FFR 302 w/ stock aluminum bell housing. the gentleman was unhurt but the car suffered a shattered windsheild a hole punched through the body at the base of the windsheild and a bunch of FI wires sliced. At the time I was 10 car lenghts behind him and it freaked me out! Needless to say I have the lakewood scattersheild in my car! Seeings as we build our own cars why not put the best parts and safety equipment available? halatron extingusher, 5 point harness and scattersheilds to name a few of the cool safety bits! Just something to think about. %/ |
Ty,
Good story, thanks! Al, I put mine in because I wanted to be eligible to run at any track. Some tracks require it. Same reason I have less than 12" of rubber fuel line in my whole fuel system. Paul |
Al .
I think your first notion is the best one ........A blow proof bell housing and high rpm clutch are at least what you should do . My step dad had his right leg taken clean off just below the knee by a big chunk of shattered flywheel. The engine was maybe turning 3000.........he went to the hospital in a helicopter or he probably would be dead.....and no.......they couldnt get it back on. Now think about the relative location of your flywheel to yourself when seated in your car...!! These are thinly disguised race cars and most of us are running vintage hardware that is a bit more prone to snap than it once was. I dont mean to sound preachy , but I've seen the aftermath and I wouldn't want to be "the one" good luck ;) |
I have seen a 409 impala nearly cut in half by a flywheel that let go. Tranny tunnel didn't stop the parts, dashboard didn't slow them, windshield was gone, brake pedal arm severed cleanly. On a cobra, that flywheel is moved back quite a bit. $300 to save me and my car, just in case that one in a million chance, you betcha.
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Another thing to consider: %/
While I'm sure that we humans get better with age, **) the poor flywheel gets a bit fatigued after 30 years. A little Depends around it can't hurt. |
Can a shattered flywheel go through the scatter shield? Say the Lakewood?
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If you ask the flywheel mfrs, they will tell you it isn't just the rpm but also the amount of torque applied to the flywheel assembly. That's why they can come apart at seemingly low rpms.
I don't know anyone that had an assembly come apart with a scattershield or blowproof houseing, but I know two very lucky people that have had pieces fly out of/through the car. Remember, that's a lot of weight moving at a high rate of speed when they let loose. |
I saw a television program which showed the testing procedure that Lakewood uses. They build a saw blade into the test housing whch cuts through the clutch or flywheel while it's spinning at maximum velocity. The explosion is pretty loud but only causes dents in the 1/4 inch steel plate of the scattershield.
Paul |
If I recall my physics right, the energy stored in a spinning disc is proportional to the square of it angular velocity (RPM). So a flywheel/clutch assembly spinning at 7,000 RPM has about twice as much energy as that same assembly spinning at 5,000 RPM. It has more than 12 times as much energy as when it's cruising along at a leisurely 2,000 RPM. It's all that energy that the scattershield/bell housing must absorb if any of the parts fail. I'm glad I've got a scattershield.
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There are additional nefarious forces at work too, including thermal fatigue, microscopic fractures and resonances. A blow proof bellhousing is cheap insurance.
Jim |
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