PICTURES EVO Light weight Rocker Arms?

[pweizman]

Sorry those are not stamped steel.. There is no way to form the inside corner on the backside by the lifter bubble via stamping...

I don't know about that. I have seen some very interesting stampings lately. I know GM is stamping a very similar piece.

I wouldn't doubt that it is a stamped part. It could also be two pieces put together after stamping...

Later,
Patrick

 

[pneumo]

Suparata My turn, inlet seat pressure should always be higher and should be calculated on the amount of max boost you choose to run! If you multiply the area of the back side of the inlet valve say the sq inch area is 2sq in just to make it easy, and mutiply that by the psi of boost say 20 psi that equates to an extra 40 lbs the valve spring has to fight against to get back on its seat! EASY ISN'T IT. wot do i win!!

What do you win? Nothing! You forgot that the pressure on the underside of the valve is not anywhere near zero when under boost.

On the intake stroke the cylinder has just slightly less pressure than the intake, nothing a normal valvespring couldn't overcome. Intake cams are designed to hold the valve open as long as air is still flowing into the cylinder (more or less, it depends on rpm). If there was higher pressure in the intake manifold than the cylinder, then why would the cam be designed to close the valve? Leave it open and stuff more air/fuel into the cylinder! Of course this depends on cam design, and better cams tend to fill cylinder better, meaning there is even less pressure difference between the intake and the cylinder.

The end of the exhaust stroke still leaves plenty of pressure in the cylinder to hold the intake valve closed without much spring pressure. Typically pressure in the exhaust manifold is higher than boost pressure, that's why turbo cams usually have less overlap than NA cams- so exhaust pressure doesn't flow back out the intake when the intake valve first opens.

Come to think of it, blue 1 and Crawford might be onto something. During the brief period of intake/ exhaust cam overlap there might be high enough pressure in the exhaust manifold to keep the exhaust valve from closing completely, especially when you add in the other forces trying to float the valve. The only thing I'm not sure about is that at high rpms a set ammount of overlap tends to make less of a difference in pressure across the ex valve.

Conclusion? Umm...well, at least this was a interesting mental exercise.

 

[blue1]

pneumo, Thats where you get valve float. I am not brilliant by any stretch of the imagination, but when it comes to the cams and valve train i use the experts opinions (ask Don Garlits) , Crow cams in Australia are well recognised for their research and development i have dealt with these guys for nearly 27years with performance engines and what they say i will take as gospel, Put it like this, i had a small RWD compact with a 354ci chev running 11's at 119 mph, i spoke to them and they supplied a milder cam and springs and retainers they said would wake up my car or there was no charge!!! first run after install was a 9.89 @ 141 mph, and still my mum could drive the car to the shops! They added 40 psi to the inlet seat pressure making it 150psi which is the most i could run on a flat tappet cam and took 10 psi off the exh' psi making 90 on the seat.
Crappy story but all i'm saying is, their are people out there a lot smarter than what you think you are, so i come on to these forums to listen and learn and to pass on what i know is good info. On these forums there are winners and losers the fun part is finding the winners info and utilising it!
I have boken the 10sec barrier in a chev and these 4gXX things i think have more potential and have seen this with the sheps and magnuses, we have some quick ### stuff in australia but i want to do it again and to me Mitsu will get me there!
Take care
Paul

 

[pneumo]

Sorry if I hurt your feelings with my explaination. I didn't mean to make it personal. My intent was to focus on a turbo engines intake manifold, cylinder, and exhaust manifold pressures acting on the valves at various points in the 4 stroke cycle. If I missed something important I wouldn't mind if someone could shed some light on it. If you have any additional info to add about your 9 second Chevy I'd like to hear it, too. (turbo'd, nitrous, supercharged?)

BTW I was also giving you credit for pointing out that air pressure could be strong enough to act on a valve. It is a good idea, these forums are full of good ideas. Some just need to be organized, merged with other ideas, or developed farther. That's what Suparata is trying to encourage in this thread.

And if I was posting boatloads of steaming BS, there are plenty of smarter people on these boards to point it out. (crosses fingers!)