pent roof 4 valve experiment

[howboycat]

I am developing a pent roof four valve head and have run into something unexpected. I want to steepen the valve angle in order to increase the clip clearance and improve the angle of atack on the back of the valve. My question is based on the relation of the cam and the bucket. I have already decided that the bucket bore will need to be welded up and re-cut to align it over the valve. How will this affect the centerline of the cam lobe with the center of the valve? I'm afraid that the cam may put an unacceptable side load on the valve.

Is this something that has already been done or am I ( as usual) out in left field?

 

[BrianPetersen]

*That* is not going to be much fun to do.

If it is a bucket/shim arrangement with no rocker arms, the camshaft has to be centered (darn close) on the centerline of the valves. An important criteria is that throughout the entire stroke of the valve, the place where the cam pushes against the bucket must not ever reach the edge of the bucket (otherwise the bucket will dig into the side of the cam and destroy everything) and in practice ought to stay a few millimeters on the "good" side just to make sure. It is a consequence of this, that the cam has to be darn close to centered on the centerline of the valves.

On all the bucket/shim arrangements that I've seen, side loading is taken up by the bucket riding inside its bore. The bucket is not fixed to the top of the valve, it just pushes against it.

 

[bigpaul]

you would be better advised to go to a shallow valve angle so,that you keep good combustion. Flater piston crowns should give much more compleate burn usless you have a bad short side radius which is giving you bad tumble you are better keeping the chamber flater relitive to the piston
and keep a balance flow curve, much more productive than
big flow numbers.if cam blanks are large it may be possible to grind with small offset to allow centreline changes or
use a steel billet to allow the mods, you will need a cam grinder that is CNC operated rather than from a Master.

 

[howboycat]

I had two ideas for centering the cam. One would be to weld up the cam journal and re-bore it over the new centerline.
The second one is probably better. As the goal here for me is to run a cam profile that does not exist yet, I think I would have them ground on a bigger journal allowing me to offset bore the housing. I feel this would be a double positive no welding to destroy the heat treatment in the head and a bigger base circle to increase the area under the curve on the lobe itself.

As a side note the reason for the cams is it's a dragrace application. I and more than a few other people who are much more educated than I think the available cams are weak. The import and motorcycle aftermarket have a long way to go before they reach the level of refinement that the pushrod engine builders have achieved in the cam department. As always looking for input positive or negative it all helps.

 

[MikeHalloran]

Given the duty cycle, cooling can be left to conduction and thermal inertia, and you can have a head of arbitrary geometry CNC cut from a billet.





Mike Halloran
Pembroke Pines, FL, USA

 

[patprimmer]

Like Mike said.

Design the had you want. Cut it from solid billet.



Regards

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