I don't see a problem with that. I know a guy who swears by the hcw crank. he tells me of guys in P.R. revving to 10,000+ rpms , sure thats with 3TCs (73 mm stroke) thou. He said one benefit is the hcw crank is lighter. fully built (main studs , rod studs , race balance) 8,000 rpm all day!!

73mm =/= 96mm. Thats almost an inch difference. At stock bore size on a ka that would be 1.8 Liters. Your in a completely different situation with that short a stroke.

And sorry op, your thread got totally hijacked.

SX APPEAL wrote:Yeah but I'm not smart enough to do the calculation required for max piston speed lol. Took calc 1 for engineers once, didn't do too well

http://www.engineersedge.com/engine_for ... motive.htm

Cool site, but I still see no equation for max piston speed. I see mean piston speed and max piston acceleration, but no max speed. Good info to have though, thanks

Sorry, I saw the piston acceleration on this site and got distracted by the physics and didn't check for the velocity equation. Try looking up piston motion equations in wiki (I'd link it to you but we're apparently anti-wiki here still). They show the equations there. The x' value is what you want. However, you will need to know the crank angle the max occurs at which requires you to calculate the maximum based on a free body diagram. Or of course, you can seek out a chart where someone already did the math as they did at the bottom of the following site:

http://www.epi-eng.com/piston_engine_te ... basics.htm

You will need to know the rod length to calculate this.

Marahutay wrote:but im talking about shifting at 8000 WITH a (nearly) fully balanced factory crank shaft.
and how much does the average piston speed really matter if we do not know how much the weight difference is between the two pistons? and the rods for that matter.

i just want someone to tell me its alright to kick it to 8000 with a fully built KA once that corvette pulls up next to me on the way to work and thinks hes Mr.coolguy. i dont plan on revving it to 8000 on a daily basis. only when needed to spank those guys in their 60,000$ waste of their daddys 401K plan.

While the vibration in a KA is an issue at high RPM, that's not the only issue. The max acceleration the piston sees will determine how strong the rods need to be (though its likely a built KA will have pistons and rods beefy enough to handle this), I believe the air velocity has a limit. Basically you don't want air speeds in different parts of the motor reaching the speed of sound. This is where piston speeds are significant. But the calculation for it takes into consideration the bore diameter and port diameter in addition to piston speeds. This is why building a higher revving motor is much more difficult than adding or turning up the boost. Turning up the boost keeps the air velocities the same. The air is just denser.

340 m/s (speed of sound) vs the 25.6 m/s @ 8000rpms?
correct me if im wrong, but it doesnt seems possible for the motor to get anywhere near the speed of sound....

He's talking about the air velocity, not any part of the reciprocating assembly. Its conceivable that at the pistons' max speed, which is bound to be a lot higher than 25.6m/s, the volume of air needed to fill an 89mm bore moving through a 38mm intake port could potentially reach 340m/s (venturi effect) of course once again the equation for this escapes me. What I don't really understand is why the air velocity breaching the speed of sound is a problem? Does it have something to do with the sound waves in the intake tract piling up and forming a shock wave, like what happens in supersonic aircraft?

You'll get a "manifold danger" signal then your passenger side floorboard will fall off...

WDRacing wrote:You'll get a "manifold danger" signal then your passenger side floorboard will fall off...

i have seen that happen one time. its crazy, trust me you dont want that to happen. the pop rivets arent that strong. and lots of sparks go everywhere when the aluminum hits the ground.

LOL... and then some crazy gay guy will run in circles around the car ranting about how he's gotta replace fried piston rings right?

I like the tuna here...