Exhaust Manifold

[Christ]

Originally Posted by Frank Lee

You have knowledge of straight through systems and how much the gains are?

Not with exhaust, but with fluid dynamics, which I compare liberally.

Basically, straighter pipe yields a higher available velocity, which creates a higher pressure differential across the valve, creating less potential for flow reversion. Less flow reversion means increased overall velocity, and the cycle is complimentary.

[Frank Lee]

Originally Posted by Christ

Given the second image, several things become evidently "bad" about current valve design and flow restriction, which, if addressed, would create significant gains on their own. Unfortunately, with technology advances occurring the way they do, the oft-quoted phrase comes to mind: if it's not broke, don't fix it.

It would cost a variable fortune to redesign completely such a small aspect of a much larger picture. It would essentially be like recoloring the faded sun in a painting of a magnitude reminiscent of the Milky Way.

Here you say there are significant gains to be had. I'm wondering how big the potential gains are? And what the solutions might look like? And why in the last 100 years (plenty of time for a few cycles of clean sheet designs to come and go) they aren't here?

[Frank Lee]

Originally Posted by Christ

Not with exhaust, but with fluid dynamics, which I compare liberally.

Basically, straighter pipe yields a higher available velocity, which creates a higher pressure differential across the valve, creating less potential for flow reversion. Less flow reversion means increased overall velocity, and the cycle is complimentary.

A well designed engine can already have over 100% volumetric efficiency. I think, on engines like that, there are bends in the systems?

[Christ]

Check back in a few mins, I'll edit the image to show potential gains and increased flow/decreased restriction.

[Christ]

Here, you can see that with machining, the restriction that the valve guide and it's required bracing would normally cause is removed. The removed bracing and the valve guide itself are moved up, and the overall cross section of flow area is shortened by ~25%.

The image creates a notable issue with valve lift and spring/seat position, which could easily be solved with larger seats/springs that would still allow for the vertical bracing needed by the guides. The upper length (above the guide) could be lengthened as well, to extend valve lift capability and decrease the likelyhood of spring binding and flattening.

Keep in mind, this is a simple representation, and will likely still have issues. I'm not an engineer, I just think like one.

[theunchosen]

Alot of L4 engines have the exhaust come out the front of the block and then rotate underneath towards the rear.

I'm also talking not just about the pipes coming from the block itself, I'm including the block proper in the discussion. If the exhaust traveled at an angle 20 degrees below the cams(just enough to avoid them) and then merged the total number of degrees of rotation on all axes by the exhaust gases on the outside cylinders would at most be 20 down 20 up and then ~30 for 4-2-1. Before mine or yours even leaves the block its already been rotated 90 degrees, then mine gets rotated an additional 180 to get it going backwards and then a few degrees here and there to get 4-2-1.

Now Frank I don't know that it will provide any advantages thats why I am asking. What I do know is its harder to push anything through a bent tube over a straight one(assuming the bend does not take advantage of gravity.)

[Frank Lee]

Not having the guides intrude into the ports- that seems pretty easy and obvious. Now why wouldn't they just do that?

[Christ]

Mine has the exhaust starting in the rear.

The actual flow would appear something like this:

[Christ]

Originally Posted by Frank Lee

Not having the guides intrude into the ports- that seems pretty easy and obvious. Now why wouldn't they just do that?

Can you answer your own question?

[Frank Lee]

Originally Posted by Christ

Now see how they sit in a cross-sectional view:


The second image is representative of a typical valved cylinder head.

Given the design you're attempting to achieve, your valves would have to operate in a completely different manner, so as to prevent the loss of gasses back into the head/oil containing areas, and to prevent the presence of mechanical parts in the (very hot) exhaust stream.

Could do it for the intakes- no hot gasses- if the gains are worth it. Or... if it can be done.