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Discussion Starter #1
First of all, I am NOT contacting you about your car's extended warranty!

I am, however, interested to see if anyone has or knows of articles on the 250x port theory.
I enjoy researching things, beforehand. I am not able to put my hands on the casting right now.
I assume this is a lower the floor situation? Lower the intake floor, transition the exhaust for the head pipe curve? Are the valves considered shrouded?
GOPR0041_1615316639627.JPG

Anyone know what areas are thin? I do not want to bandsaw a decent casting just to look.
What manifold size maintains velocity? Sorry, not a fan of big bores, belching raw gas. (Yawn) I am anxious about increasing carb size, factory can't be that far off in '87, right?. But, what effects on intake bore sizing take place, if it is moved off the mush box and over to a slide/pumper? It seems easy to go over bore with slides. Yes, it can be tuned, but that groaning growl makes me want to squeeze the intake tube. Lol, hopefully someone else understands!
Anyone remember an article? Or from experience?

Target is for a near stock bore. 12:1 compression 250x.
 

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Discussion Starter #3 (Edited)
Things I know... under vacuum, the velocity stream is greater on the inside of the turn. Under pressure, this stream moves more to the outside of any curve. Increasing bore can result in less velocity... and pay special attention to prevent or remove existing ballooning or bullfrogging of the port.

I understand carburation needs more of a rough finish to atomize the mixture, vs F.I. say 80 grit equivalent, on the intake should suffice.
I get that the transition from the port to bowl area is crucial. That's my interest in lowering the floor a little, and maybe widening it out to give a little more space in the intake runner. Hopefully without slowing it down, the same stream, just larger.
I am also intrested in how far the valves sit down in the combustion chamber. There may be material stacked there, around the valve. That causes shrouding of the valve. Like a air umbrella. Interesting note: G.M. tuned port theory. That doesn't apply, but it is interesting.
Unfortunately, piston options (outside of custom) limit any "cloverleafing" or relief to the piston top. See quench theories. (Other than mechanical reliefs) Both of these can dramatically affect compression ratios, especially together, when material is removed.

The exhaust side of the atv application is what I am most interested in. I naturally want to blend everything together and possibly raise the roof, if the port bore limit allows me to do so. BUT... the immediate curve in the header throws me off.
I am accustomed to automotive applications, not ATV/torque monsters.
I can't wrap my head around how to move the inside exhaust port, or transition it to meet the header curve without crowding the outer port. Or is that just how it is? Bahaha! Guess I could run a triangle header... Bahaha!

What is the best transition for torque in the exhaust port?
 

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Discussion Starter #4
I feel like I should widen the outer at the top, and widen the inner at the center. In an attempt to throw one high and one low, but under pressure.

Anybody know if this hurts the scavenging of one port to the other?
 

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Discussion Starter #8
Looking at this, I think I can make this happen. I would like to find more visuals of different designs before I guess which one will work. Bahaha!
 

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Discussion Starter #9
Keep in mind, that's most likely a vaccum visual. We are talking pressure so your imagination is required.
 

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Discussion Starter #11
Now throw harmonics and valve motion reverb in there...
I will take pics as I attempt to manipulate that which is invisible.
 

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You are miles ahead of me now - I don't study it, I use the trial and error method - I've thrown many good parts that were mangled beyond use and learned what not to do, but I never got into the theory and applied R&D. Me thinks you have too much time on your hands.
 

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Discussion Starter #13
No sir, I am not ahead of anyone. I travel for work, so I sit in hotel parking lots for hours on end, each day. No room for play tools, so it's all in my head! You are correct, I do have too much time. Bahaha!

I grew up racing, mororcross/cars in red clay. My uncle was one of the most talented mechanics/gunsmiths that I have ever met. I owe him my entire life... rip.
AND he was almost blind! Used to tell me stories about building "cog" wheeled carts behind the mills they worked, to race downhill. He would talk as he band sawed head casting to mic thicknesses for porting. He did the long framed, dirt drag bogging on 2.5 ton Rockwell's. Amazingly scary... it feels like the truck jiggles, and the earth moves under/by you. 🤘 The same man, shotgunning cigarettes in evap tubes to find leaks before we ever knew a machine existed. Crazy how he grew...

As the 250x goes. Nothing can be proven beyond a theory without a flow bench. I would pay someone's child support to have access to one. Bahaha! Messing it up and tossing it is exactly how you know what too big is! But not very nice with these hard to find parts.

Essentially all it is... is hoping to keep the velocity the same or faster, while opening the area it sits in, to allow for more. Certain types of bowl shapes, around the valve guide and angle of the valve in relation to the ports angle can change, flip or spin the air.
I just want the intake larger, and the exhaust to merge better and spin clockwise into the header. Northern hemisphere, everything naturally spins clockwise. Example: flush the toilet... watch.
I will take pics of my attempts next week.

On a different note: People are tempted to cut off their valve stem guides. Do not. It does not gain more than it compromises the valve train. Some intake manifolds intentionally do this before air enters the port for better atomization. The guide may actually ruffle it to aid in movement through the valve opening. I will pick it up, in a few days.
 

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Discussion Starter #14
Anyone runs across a good article or port design, I would love to see it. Or just drop your opinions, thoughts.
 

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Discussion Starter #16
Tumble is gold, excellent for filling chambers and creating turbulent eddies in gasoline engines regardless of fixed valve or motion. (2 or 4 stroke).
Blue is swirl, not worth a dime on gasoline, diesel engines love it. Blue causes gasoline particles to de-atomize and stick to cylinder walls. Poor ring seal is a good indicator, after modification.
1-s2.0-S0142727X18302625-gr1.jpg
 

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Discussion Starter #17
This doesnt help our application, but it's a good visual on why you may want a bias bowl.
Other uses are to direct the stream away from direct impact of the cylinder wall.
Hot/cold spots, ring wash, all that stuff.

When all is right, less advance in ignition timing is the reward. Which brings it's own perks. 🤘
images.jpeg-10.jpg
 

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Discussion Starter #19
Anything can be taken too far. Bahaha! Fact is your engine castings are made on large production runs, almost always benefitting from attention. They don't have the time. Thanks to Honda, the castings put out are satisfactory to anyone, including me. (Honda beats Oreo in my blind taste tests) Example: Yam-er-haw, kam-er-saki, suki, just don't fit with my southern accent. Bahaha!

Just showing where my head is, before I start posting pixel packages. Niiiiice!
 
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