so was at the roadcourse the other day and was talking to some l motor racing guys, they both have 240z cars, with the l28. and both have broken their cranks between #5 and #6 cylinders. they are both non turbo, with carbs, non stroker. one is 10.5:1 cr the other 13:1 cr. they say its from regular abuse, but im really wondering. i havent read much about the problem. some guys have 500hp and boost them and still dont break stuff. they both say the problem is from the aluminum flywheel and centerforce clutch being too heavy at anything above 6500 rpm. has anyone heard of this as common in the performance world. im wondering if its a balance issue, maybe they are using non balanced cranks and flywheels or they arent balanced good enough. just a thought as i now have the motor portion of the car going together soon.

 

From what I've read, I think it's the harmonics. Were those guys running aftermarket harmonic dampeners? I believe the stock crank can't be revved much beyond 7K before it will start to cause damage. There's a huge thread on HBZ regarding the issue. Most turbo guys don't run past 6500 rpm due to the stock cam's powerband.

 

hmm couldnt find the thread there, gonna have to look more, typed in broken crankshaft, got lots of good info, but not much on breakage. one guy reved too much without balancing the lower end, after he re-did it and balanced it, no probs. these guys say to use the quartermaster system

 

http://forums.hybridz.org/showthread...rank+harmonics

That's the thread I believe that might have the info you're looking for. I don't plan on revving my Z much past 6K, so I haven't gone as extreme as some of the guys there have.

 

good reading, man 5 pages, still no real word on the 3 pulley setup for the damper. im gonna do more reading, and next time at a track day see what kind of damper those guys have, betcha its solid! they say a well inspected stock will work, but needs to be replaced often (max 2 years) or buy the aftermarket one, only 2 pulleys, need the power steering on the outer pulley? or is that the center one, i cant remeber, i gotta look.

 

kind of a bummer.... if i went Z power again next year i was planning on stand alone and rev'in the motor out to 7k for a longer pull. ill have to read more about this to cause what if i go super awesome extreme and go like GT42 turbo and let the engine run out to 9k like all the supra's out there i wanna be just like them!

 

My brother's L28 is reved to 7000-7500RPM's! Non turbo 11.25to 1 Comp Ratio stage 3 cam. Holley 450CFM Carb. He is on his second crank, first one warped/bent. The F54 block is still fine. He is running a Fidanza Alum flywheel and a custom Alum front pulley.

 

Yeah it seems as though for long term safety and reliablility, the aftermarket dampeners are better, but for a street car (like mine), the stock one is fine. Since your Z is going to be race oriented, I'd look for the 2 pulley if you need p/s.

I don't think I'd ever need one until I go crazy and get a ported head and an aftermarket intake manifold with a larger turbo, etc, etc. But that'll probably never happen since this Z is a DD and nothing more.

 

yeah im prolly gonna have to get the 2 pulley damper and keep inspecting it every year at least. ez, read about having the solid front pulley in that link lifegrddude has put up, i would get that thing off there fast. stock would be better they say. it seems to be a limited problem, but with very limited solutions. good thing i can change it out later when required

 

On a road course race car, the crank is being subjected to whatever redline the driver wants a bizzillion times in one season.....

Many road course race cars experience redline or near extended redline blasts more often in one race than many street cars see in a 3 months worth of driving.

Not only that, the engine is also being shoved to very high rpms by drivers who harness that little extra bit of engine braking you get by being more agressive concerning rpms at which you drop to a gear. (very important in S30s in I.T. trim)

 

very true, but you havent seen me drive on the street when im in a hurry!!! yeah i even heel toe

 

well duh! i heel toe all the time... ok not really but when i feel like in a track driving mood or in a hurry. its much more fun on the crotch rocket though.... yummy!

 

i heal toe everywhere, but if i need to get somewhere, ill increase speed when safe to, im not gonna race thru traffic, its just not wise. i got a aluminum flywheel yesterday and it only cost me 150 bux. its from an scca car. this guy bought a lot of stuff and had it shipped to him in the crate, he doesnt use flywheels on his midget cars, so he graciously sold it to me!!!