crazy porting idea, don't laugh....

[jonsereds49sp]

Ok, me and a buddy were talking about porting a saw and this came up. We were talking about how you are supposed to leave the intake rough, presumably because you want to "swirl" the fuel/ air mixture. Why not file the intake in such a way as to create a "screw like" surface, spinning the air/ fuel and, possible even creating positive manifold pressure. I doubt if you could get more then a psi, but it would certainly help. Anyway this would possibly work, or are we crazy?

 

[Deadwood Kid]

try it and tell us about it.

 

[jonsereds49sp]

problem is I've never done any serious engine work, so I have to find a saw I don't mind possibly hurting...

 

[Deadwood Kid]

im sure you can find a wildthing somewhere.

or i have a 1983 61 husky for sale lol. $120 x.x

 

[pioneerguy600]

Its been done!
Pioneerguy600

 

[Metals406]

Its been done!
Pioneerguy600

And?..

 

[edisto]

Seems like that would just create extra drag with the increase in surface area and slow flow. It also would effectively increase the length of the manifold, which could cause resonance issues that would reduce flow beyond the additional surface area.

The rough finish is not to create a large "swirl" but rather to generate "micro" pockets of turbulence to better break up the fuel droplets in suspension (thereby creating a more homogeneous droplet size). It's a tradeoff because any turbulence will reduce flow, but if the droplets are small and evenly sized, the gains due to more efficient combustion can outweigh the loss of flow.

There used to be a company that would port 4-stroke heads, and add strategically placed "dimples" in the combustion chamber to create this effect.

 

[Nitroman]

This is not a new idea.

The GMC 71 series engines' cylinder liners have slots cut into them so the supercharged air enters, and swirls violently upwards pushing out the bad gas. They are all 2-stroke Diesels.

Many Diesels have swirl chambers built into the top of the piston, and some old Caterpillar engines even squirted the fuel into a cup chamber across the combustion chamber to encourage mixing.

Obviously, Diesels are much slower compared to our little engines. Not to mention they are Diesels and not spark fired.

Everything I have ever read about high-performance gas engines is the air coming in should be as smooth and turbulence free as possible.
The other consideration is the gasmix in entering so quickly due to the short time duration any device would have to be fashioned in such a way as to not allow stalling of the mix as it passes the device.

 

[HimWill]

Well, do you think adding dimples to the intake port walls(with a spring-loaded center punch) would make a difference?

 

[pioneerguy600]

And?..

Has not caught on and is an old idea.Check out some of the 1945-1950`s chainsaw intakes and pistons.
Pioneerguy600

 

[edisto]

This is not a new idea.

The GMC 71 series engines' cylinder liners have slots cut into them so the supercharged air enters, and swirls violently upwards pushing out the bad gas. They are all 2-stroke Diesels.

Many Diesels have swirl chambers built into the top of the piston, and some old Caterpillar engines even squirted the fuel into a cup chamber across the combustion chamber to encourage mixing.

Seems like the analogy to what you are describing would be a transfer mod for saw 2-strokes...nothing you do to the intake on conventional saws would affect scavenging (your first example). Is the second example supercharged as well?

 

[edisto]

Well, do you think adding dimples to the intake port walls(with a spring-loaded center punch) would make a difference?

I don't think so...the dimples (probably a poor word choice on my part) were raised to generate the turbulence.

Divots might actually improve flow if the mix were moving fast enough because of a decrease in surface area...isn't that why golf balls have the surface they do? I'm guessing the size of the divots would have to be engineered for the amount of flow.

Or maybe that only works on a spherical surface.

 

[Nitroman]

I used these examples to show the idea of getting the intake air moving (other than just into the cylinder), to better mix the mix is not new.

The Cat was naturally aspirated.

 

[Tzed250]

.




If any of this worked you would see it on a MotoGP 250 roadracer.






It isn't there.....




.

 

[Metals406]

Has not caught on and is an old idea.Check out some of the 1945-1950`s chainsaw intakes and pistons.
Pioneerguy600

 

[husky455rancher]

its been a while.back in my 4 wheeler days there was a company that was doing something similar to the head for a yamaha blasters and possibly banshees.

 

[gmcman]

I remember a short while ago looking up cylinder heads for BMW's and a few aftermarket companies had valves that were designated "ST" for Surface Turbulence.

They had about 6 or 7 rings on the top of the intake valves to give a more turbulent effect to the intake charge to further atomize the charge.

 

[edisto]

I used these examples to show the idea of getting the intake air moving (other than just into the cylinder), to better mix the mix is not new.

Indeed not. I was just pointing out that the costs if creating turbulence go up pulling air into the crankcase. I'd love to see the examples you mentioned.

 

[chowdozer]

Well, do you think adding dimples to the intake port walls(with a spring-loaded center punch) would make a difference?

dimples like a golf ball, yes. dimples with a centerpunch, no.

It's been awhile since I've studied fluid dynamics and it's not my field of expertise, but I'll try to explain the general idea.

At the point where flow meets the wall, there is what is called a boundary layer. The molecules right next to the wall can be considered to be "anchored" to the wall, meaning the friction is high. They will be moving, but not near as fast as molecules in the center of the port. Molecules adjacent to the "anchored" molecule will be moving a little faster and so on as you get further from the wall.

Think of it like a freeway with multiple lanes where the slowest lane is next to the intake wall. As you move away from the wall, the "lanes" travel faster because the friction with the previous "lane" is less. Those slower traveling "lanes" are the boundary layer.

Adding dimples or small craters on the wall creates small pockets of turbulence. These little pockets of turbulence isolate the faster moving molecules from the wall which makes the boundary layer thinner.

It would be difficult to put those dimples in an intake and whether they would make a difference I don't know. You would have to run a computation fluid dynamics model run to get an idea. Sorry I'm not up on CFD software.

edit: I should also note one of the major benefits of the dimples on a golf ball to airflow is actually at the rear of the ball. The dimples decrease the "wake" in the rearward path of the ball. This greatly reduces drag on the ball.

another edit: Skunk sells a dimpled composite intake for the fart cars. http://specs.jazzproparts.com/wiki/INTAKE_MANIFOLDS

 

[Nitroman]

Indeed not. I was just pointing out that the costs if creating turbulence go up pulling air into the crankcase. I'd love to see the examples you mentioned.

That's easy, just call a local heavy equipment shop and ask them to let you know when they tear down a 71 series Jimmy. Also, put out feelers for old Caterpillar bulldozers. Find one that is naturally aspirated from the '50's.