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

[Nitroman]

I'd definitely work things out on the flow bench before I looked for gains on the dyno. Unfortunately, I don't even know of anyone who has access to either, so I thought I'd give a practical answer.

There will be a lot of variability between cuts just due to the wood itself before you even factor in human error, but like everything else, you deal with the variability by doing replicates and quantifying the error before you make a comparison.

Build'em. I have two sets of plans for the flowbench, but believe the dyno would work better overall. I had been thinking of a smoke machine to watch the flow on the bench, but that would be messy after awhile. Still.......

 

[timberwolf]

Stihl has been doing this for a long time, just look at the intake boots. It does not seem to do anything at full RPM, but when sitting at low speed it seems to keep the fuel from building up droplets on the floor of the intake that cause stumbles on acceleration or if the saw is suddenly moved about.

Dimples inside a duct won't make it flow more, why they put dimples on a golf ball does not apply to flow that is already turbulent inside a duct.

As for the dyno, the log does not lie, make a bunch of cuts in a consistent log, toss out the worst times that were affect by opperator error and average the rest, small differences can be measured, just takes time and effort.

Built this flow bench up last winter, but found it takes a lot of time to look at some pretty small changes. Lets just say, I won't be getting too concerned about surface finnish texture until a lot of other aspects of engine performance have been addressed.

 

[edisto]

Build'em. I have two sets of plans for the flowbench, but believe the dyno would work better overall. I had been thinking of a smoke machine to watch the flow on the bench, but that would be messy after awhile. Still.......

I have read for 2 strokes of people using acrylic cylinder heads and flowing water with bubbles.

It has crossed my mind to look at what it would take to build a dyno, but I have so little time to work on things as it is (60-70 hour work weeks and an 17 month old boy), I'd rather spend it working on my saws.

Built this flow bench up last winter, but found it takes a lot of time to look at some pretty small changes. Lets just say, I won't be getting too concerned about surface finnish texture until a lot of other aspects of engine performance have been addressed.

That's an excellent point...little stuff like this won't help if the fundamentals are not there.

 

[smokinj]

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?

yes it would work if you can pull it off! not sure how it could be done without taking to much off

 

[jonsereds49sp]

smokinj, you have anything to back that up? Cause everyone else seems to think otherwise...

 

[smokinj]

smokinj, you have anything to back that up? Cause everyone else seems to think otherwise...

"yes it would work if you can pull it off! not sure how it could be done without taking to much off"


not much need to back that statement up! But the vortex would make better air fuel mix! can it be done, that would be a better question for the hot saw guys. I wouldnt try it!!!

 

[edisto]

"yes it would work if you can pull it off! not sure how it could be done without taking to much off"


not much need to back that statement up! But the vortex would make better air fuel mix! can it be done, that would be a better question for the hot saw guys. I wouldnt try it!!!

So...you're saying that if it would work, it would work?

 

[timberwolf]

Spinning the charge and making vortex patterns is going to cause more disruptions in the intake hurting flow more than any potential gain by mixing fuel and air up better. Keep in mind the charge gets pushed and pulled through the venturi a couple times, chopped up by the piston, wrapped around the crank, jammed up the transfers and run through a scavenging cycle before it gets near a spark.

Full RPM air flow in the intake is 100% turbulant so nothing to be gained in atempting to mix it up more. I think this is another 4 stroke hangover idea, where the only thing between the carb/TB and the cylinder is a runner and valve.

 

[smokinj]

So...you're saying that if it would work, it would work?

"will not work":greenchainsaw: but I like hes thinking!

 

[edisto]

Spinning the charge and making vortex patterns is going to cause more disruptions in the intake hurting flow more than any potential gain by mixing fuel and air up better.

It could really hurt flow if the system were initially set up for proper resonance in the intake...or does that not translate well to chainsaw engines?

 

[smokinj]

to bad billy mays is gone it does sound like a grate late night info comercial!

 

[jonsereds49sp]

I guess maybe I'll try the dimpling idea, sounds like it would produce better results, and it would be a whole lot easier to do...

 

[romeo]

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?

I have tried it, I don't think it either helped or hurt the build. I think the charge experiences enough turbulence when traveling through the crank case to aid in fuel atomization.

 

[jonsereds49sp]

romeo, you don't have pictures, do you?

 

[serial killer]

Stihl has been doing this for a long time, just look at the intake boots.

I'm surprised that it took someone so long to point this out. I don't know if all of the newer saws are like this, but I know that the 361 has a pattern of what I would call raised diamonds on the inside of the boots.

 

[jonsereds49sp]

from what I understand the point of dimpling the intake is to break up the mixture into a more homogeneous mixture. So, why do it at the intake, before is has to go around the crank shaft and through the transfers, why not dimple the transfers themselves?

 

[edisto]

from what I understand the point of dimpling the intake is to break up the mixture into a more homogeneous mixture. So, why do it at the intake, before is has to go around the crank shaft and through the transfers, why not dimple the transfers themselves?

One of the advantages of having a homogeneous mixture of small droplets is that the larger droplets don't drop out of suspension. There's a lot going on in the crankcase, but that is where the potential for dropping out would occur.

Don't forget that the mix also is the lubricant, so there are obvious lubricating advantages to having atomization occur at the intake.

 

[jonsereds49sp]

What if you were to dimple both the intake and the transfers, would it create to much turbulence, or would it ensure a totally atomized and homogeneous mixture?

 

[timberwolf]

why not dimple the transfers themselves?

Think edisto hit it pretty good there.

Dimples and bumps only help out on low speed where charge wants to drop out. When the engine is cranking out the RPM transfers are flowing well up over 200 fps and fully turbulent, little to gain and what a PITA from a casting prespective.

Adding a few bumps on a rubber boot is easy at the factory, transfers not so much.

Anyway at the transfers the cylinder and ducts them selves are hot and to preserve maximum charge density you want the incoming charge to stay as cool as possible. Think intercooler on a turbo car. So keep the transfers smooth and clean with minimal surface area is the way to go IMHO.