Exhaust Manifold

[Frank Lee]

Originally Posted by Christ

Can you answer your own question?

I wasn't involved with cylinder heads when worked in an Eng. Dept., but I have some guesses:

It would make the whole assembly less compact. Pushing the guides "out" also pushes springs, rockers, or cams, out.

Valves would have to be longer. If they are longer would they also need larger diameter stems? Then the valves get heavier too.

It could compromise guide life. Yes, even if the guide ultimately was the same length as "baseline". Greater unsupported span of valve stem. Shorter guides likely lead to faster wear via less bearing surface, greater leverage for the nonlinear forces acting on it.

Heat transfer to the guides is a major conduit for valve cooling. Maybe there is some detrimental effect involved with that?

[theunchosen]

Ok I included 2 sketchup images that show what I am thinking the perpendicular pipes are the intake and the angled(its 20 degrees to avoid cams) are the exhaust.

If you want the file send me your email via pm and I'll send it

[Christ]

You raise some interesting points, but given the images I've provided, some of the answers to them are already present.

To being "less compact": That would be the primary reason for shortening the flow tract. Compare the sizes of parts from one drawing to another, they're nearly identical. This means that the valve and guide are the same length, or at least nearly the same length.

Springs could be seated in depth of the red shaded area, which would require them to be wider, but not taller in any way. Obviously, the "package" has grown headwise, but the runner has shrunk to compensate. The rockers might be pushed higher compared to the initial placement, but the head is shorter, so a taller rocker cover would only take up space that was gained by shrinking the head casting.

I'm not saying I have all the answers here, nor do I have real-world data or experience to back up what I'm saying, but the ideas seem to work on paper. (or MSPaint, rather.)

[Frank Lee]

Shorten the flow tract? Your image is gone. You are saying shortening the flow tract is better for flow than having a guide intrusion? Smokey Yunick says turning the air prior to it getting to the seat is advantageous. Seems most everyone agrees with him. I'd suggest some quality time with his book. Or a Vizard book.

[Frank Lee]

Originally Posted by theunchosen

Ok I included 2 sketchup images that show what I am thinking the perpendicular pipes are the intake and the angled(its 20 degrees to avoid cams) are the exhaust.

If you want the file send me your email via pm and I'll send it

If you ruin the intake flow capacity, you don't need extra exhaust flow capacity!

[Christ]

Originally Posted by Frank Lee

Shorten the flow tract? Your image is gone. You are saying shortening the flow tract is better for flow than having a guide intrusion? Smokey Yunick says turning the air prior to it getting to the seat is advantageous. Seems most everyone agrees with him. I'd suggest some quality time with his book. Or a Vizard book.

I'll have to read into that, because according to fluid dynamics, straighter is less resistance, and less resistance is faster (as a general rule, given that "less resistance" is still enough to keep linear flow)

I can say for sure that the radius in the flow tract actually decreases flow, rather than increasing it, per a given velocity. (Faster air tends to travel straighter, thus creating a shear point which acts as a wall to flow, attempting to keep it linear, and possibly aiding reversion. This can be desirable in some cases, but the only cases I've seen where it was advantageous were in limiting total intake charge (dynamic compression ratios relevant) to prevent detonation under boost and high static compression. (Larry Widmer, Honda engine - The Old One - Energy Dynamics it's in the archives somewhere, in one of the couple engine builds.)

I believe that 'Ole Smokey intended a less broad application of his wisdom in saying that a radius was better for the intake charge as a whole, wherein the intake charge contains the fuel mixture as well. Perhaps it helps to create the turbulence necessary to aide the atomization of fuel and air mixtures and create a more homogenous mix? I can't say for sure, but speculation is not beyond me.

With a Direct injection type engine, this would become historical engineering, and no longer a necessity in the flow tract. The idea would truly be to get in as much air as fast as possible with as little energy required to do so, then compress it, spray the fuel at a given timing, and bang. Once again, exhaust the fumes as quickly as possible, with as little resistance to flow as possible.

While the general idea that a radius in the intake tract is better for something may be widely accepted, what would be the advantage of a restriction or turn in the exhaust tract? I see none.

[Frank Lee]

Looks to me like, in the bottom image, from what I've read, the charge won't make the turn on the short side effectively knocking some large percentage of the valve opening out of commission.

[Christ]

I can't say for sure without a flow bench and the necessary machining.

But, lets say the initial image does not cut flow, and the new configuration does.

Now, lets make it more realistic looking, and set the angle of the valve stem (using the valve's face as the axial epicenter) to about 15*. This effectively cancels the short side radius altogether, by making the flow pattern straighter. By doing so, we can effectively shrink the area of the flow tract, keeping length a constant, thus giving us an even smaller head package with nearly the same flow characteristics.

This will also set the head of the valve further out on the head's overall area, and the angle will defeat excess length making the package taller. The cams can then be spaced between the valve stems with no impact on package height, and rockers can utilize higher ratios to increase lift as necessary.

Now, we've taken a simple design, which had some problems, and by turning the valve 15* on one axis, we've effectively solved the packaging issues.

But, ok - Maybe there is a reason for the valves to be straight up, like less torsional loading on the valve stem and guide... sure, we want them straight up for a low-friction environment.

Now, we re-cut the actual flow tract so that the valve can stay perpendicular to the deckline, but the flow comes in at less of an angle to the valve stem/backside. Still removed the short side radius for the most part, opened up more area for flow across the surface of the valve, and effectively, you can still reduce tract volume, keeping length a constant, further increasing velocity, meaning that more air gets in with less work, or a net gain in VE.

[Christ]

Even without the above post, consider swirl induction. The idea is to get the mixture to move in a specific direction as it's being drawn into the cylinder, causing a secondary vacuum beyond that which the piston's movement would naturally cause. This means that only one side of the valve can be used to the greatest extent, anyway. (The area of the valve's backside that would cause flow to intersect the cylinder wall at a sharp tangent, as far from perpendicular as possible.)

This presents you with another option for increasing VE and flow at the same time, even given the apparent faults of my edited design.

[Frank Lee]

Smokey

-good refresher for me too!

For our purposes- the focus on the bend in the bowl area- I think this is the pertinent part:

We want to run water pressure through the port and valve and exit into the combustion chamber to see what happens at 0.050 to 0.600 of valve lift. Most water pressure is 30 to 60 PSI, so we need to have a pressure regulator and cut it back to 'bout 5 PSI so we can vary velocity to look for changes. Water will do exactly what air does. You are gonna notice the water comes around the valve from the bottom of intake port where guide ends, to some distance after the valve head in combustion chamber. The shorter the cone the better the flow; the higher the pressure, the more defined the cone is. A perfect 360-degree even cone is affected by shrouding. Anything closer than a 1/2 inch to the edge of the valve slows flow down. And it's possible in heavy shrouding to only flow about 300 degrees around the valve and the other 60 degrees just bubbles, rolls, and twists. You'll also notice, that not a drop of water hits the lower inner area around the valve stem, or for that matter, over a 1/4 inch (at worst) inward of the valve, and you'll notice on the bottom side of the valve combustion-chamber side that it isn't touched by water either.
So you see, swirl in the port and whatever has been done to the valve or valve exit in the combustion chamber is overridden by the huge pressure drop at the valve seat caused by the tremendous increase in velocity. Remember, before that valve cracks open, the air column's velocity was at zero and pressure was at the maximum. That tremendous flow acceleration, accompanied by the sudden steep pressure drop, overrules all other physics. As the valve opens farther, velocity starts to drop and pressure starts to rise, but the kinetic energy induced by the start of the event remains in total control.

I have his book and it has an even better description of of these phenomena, along with illustrations.

And there is this:

What's the best port angle? Shallow as you can get-the top of the port up against the valve spring seat. Take any port shape, straighten it out all that you can, and for every degree you straighten it out, with no other changes and for every degree you straighten it out, the more you flow. That's great for airflow, but the compression target has to be addressed.

I don't have access to my book right now and I've forgotten what he says specifically about guide bosses.