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Discussion Starter · #1 ·
ok, my dad and i have been going around about these two things for a while now. and i want to know what your guys' thought are.

#1- a tach reading rpm is how fast the crank is spinning, or the cam?

I say the crank is the rpm and the cam is spinning half as fast.
he says the cam is the rpm reading and the crank is spinning twice as fast. (his reasoning is that other wise how do i know that my 034 is getting the correct rpm reading off the cam)

#2- when a valve is depress by the lifter/rocker/cam/whatever, does it rotate the valve itself to essentially lapped the valve constantly?

my dad says yes, that on pushrod engines( he didn't have an answer for OHC engines), the rocker arm is offset a tiny amount to where, when it pushes on the valve through the arc of it's motion, it turns it a tiny bit. his reasoning is that with out that rotation, the valves will burn.
I say no, because what about roller rockers? they can't have enough friction to cause the valve to rotate with all the force of the retainers being jammed in there by the spring pressure. another part to my agrument is that say on our audi engines for example, there is no rotational force to turn the valve.

the whole reason the valve thing even came up, was, one day i was day dreaming about valve area and what not, and i wondered, why doesn't any manufacturer make a head with half moon shaped valves, and use either a square od triangular shaped stem to keep it in alignment? that' seems to me the way to get the most area opened to flow air.

so, whutcha guys got for me????
 

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Discussion Starter · #3 ·
:D I KNEW IT!!!!!!!!!!! :lol: :thanks: jim
 

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Sorry, Nate has me in one of those moods :bump:

Seriously though, the RPM is crank speed, look at all the piston speed calculations, nothing about multiplying by two to get crank speed. Plus, here's proof, when you run 034EFI in wasted spark and trigger every rotation and not every other, the speedo doubles everything. That might lead one to say that means RPM's really are taken from cam speed, but not when the stock speedo originally took the signal from a 5 window dist that was mounted on the cam, that went around once every other revolution. Get it?

For the valves, I'd say they definatly rotate, look at your lifters, if they are worn at all, you'll see tiny little circles on them. Plus when I was test fitting the new Ti retainers, i was suprised to see the valve rotates very freely when locked into both the Ti and stock retainer.
 
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