Effects of "free port"

[Dixiepipes]

Working on a 084 for a guy last night. Pulled the muffler off and low and behold this ported saw has at least 3/16" of free port and a hand ground domed piston.
What I want to know is why the free port? Everything you can find about porting says it's a horrible thing. I understand the negative effects it has. But is their a positive to having a little bit? I only ask because this saw works awesome. Here's a pic

 

[srcarr52]

It looks like some hack ported that saw and thought the bigger he made the port the better, so they ground way too much off the bottom of the port opening.

 

[blsnelling]

+1!!!

 

[jrs_diesel]

That can't be good

 

[Chainsaw Jim]

Free porting can be necessary with certain recipes to help the incoming charge get where it needs to be in time. Sometimes the incoming charge will build case pressure and this can allow sort of a venting affect as the charge enters the case.
I don't need any rebuttal over this since I'm not an expert on it. I do have some experience with it though...And have studied quite a bit of feedback from local shops around here who have used freeporting in the past for good gains.

 

[Dixiepipes]

Jim I appreciate your response. This is the kind of information I'm looking for. So their is some good reasons for free port if it's used in the rite combination of things? I see it a lot in my area but it's usually only about .030. This saw however is huge. And the part that puzzles me is that it actually runs hard. Has a home made pop up in it too. Every port has been molested in one way or another.

 

[srcarr52]

Jim I appreciate your response. This is the kind of information I'm looking for. So their is some good reasons for free port if it's used in the rite combination of things? I see it a lot in my area but it's usually only about .030. This saw however is huge. And the part that puzzles me is that it actually runs hard. Has a home made pop up in it too. Every port has been molested in one way or another.

Free porting 0.030" isn't going to effect much and it's usually as a necessary evil to get the exhaust duration in check on later Stihl models. Still free porting the exhaust is less than ideal, it causes a lot of problems with lower RPM power and throttle response. As RPM's increase the time it's open decreases and its effects decrease.

Jim can get all the kicks he wants out of what he thinks is a "lack of port work knowledge" but there are many other things I can see in that port that suggest a hack job.
1. Upper right corner appears to have a dip in the curvature, anyone who takes any pride in their work would smooth that out knowing that it is a potential ring snag.
2. Obvious waves in port opening in other places. It's not going to kill the saw but it's obviously an unskilled hand at work.
3. Port entrance is very oval shaped, you want more of a rounded corner box with a slight curvature to the roof to maximize time area and get the same mass flow without sacrificing compression height.

 

[Chainsaw Jim]

Free porting 0.030" isn't going to effect much and it's usually as a necessary evil to get the exhaust duration in check on later Stihl models. Still free porting the exhaust is less than ideal, it causes a lot of problems with lower RPM power and throttle response. As RPM's increase the time it's open decreases and its effects decrease.

Jim can get all the kicks he wants out of what he thinks is a "lack of port work knowledge" but there are many other things I can see in that port that suggest a hack job.
1. Upper right corner appears to have a dip in the curvature, anyone who takes any pride in their work would smooth that out knowing that it is a potential ring snag.
2. Obvious waves in port opening in other places. It's not going to kill the saw but it's obviously an unskilled hand at work.
3. Port entrance is very oval shaped, you want more of a rounded corner box with a slight curvature to the roof to maximize time area and get the same mass flow without sacrificing compression height.

I came back to edit that part out because I figured someone might get offended. But I guess it's too late for that.
I don't have an opinion of what I think of the work or who did it since that would be even more insulting than what I said. For all we know that could be a saw done by a very reputable shop. I'm not saying it is, but it does have a pretty good sounding review.
My 372xpw build is freeported that far and it rips. No idling or throttling problems. It does have a larger carb than stock.
You think that looks like a hack job on the 084...check this garbage out that I did with the wrong bur bits before I found the right ones. Lol

 

[blsnelling]

Free porting can be necessary with certain recipes to help the incoming charge get where it needs to be in time. Sometimes the incoming charge will build case pressure and this can allow sort of a venting affect as the charge enters the case.
I don't need any rebuttal over this since I'm not an expert on it. I do have some experience with it though...And have studied quite a bit of feedback from local shops around here who have used freeporting in the past for good gains.

This is a new one to me.

 

[USMC615]

Interesting thread to read...I know zero about this free porting...I kinda understand it and can follow it in theory...keep posting fellas.

 

[blsnelling]

The only thing I've ever heard about free porting is that it should be avoided. I've never heard of it being a good thing. However, if free porting does happen, it's not necessarily a deal breaker.

 

[RedFir Down]

Free porting can be necessary with certain recipes to help the incoming charge get where it needs to be in time. Sometimes the incoming charge will build case pressure and this can allow sort of a venting affect as the charge enters the case.
I don't need any rebuttal over this since I'm not an expert on it. I do have some experience with it though...And have studied quite a bit of feedback from local shops around here who have used freeporting in the past for good gains.

I came back to edit that part out because I figured someone might get offended. But I guess it's too late for that.

I also noticed you edited your initial post.
Why are you only a d i c k here and not on O P E?
I'm personally not offended but I'm sure Shawn could teach you a thing or two about porting BTW.

 

[SquareFile]

Free porting saws are the best.

Brad, I'll send you a couple to free port. One more stipulation. Free shipping.

 

[Chris-PA]

I have one engine that is slightly free ported and it runs great, but it's not to that extent. It was a mistake, and given the way that port looks I expect this was a mistake too.

I think a small amount of free port can be acceptable, but I don't buy that there is any inherent advantage to it. The piston is near TDC and the intake port is wide open, so it has no effect on case compression pressure. However, if there is any residual pressure in the exhaust port it will pull exhaust gas into the case. Adding a volume of inert gas into the case is equivalent to reducing engine displacement.

 

[Dixiepipes]

This thread is getting good gentlemen. So here's some better specs I pulled off this thing. It's got a hand ground domed piston looks to be about .050 in height. .020 squish. 100• exhaust timing. A bored out HT carb. Timing has been advanced half the key width.

 

[blsnelling]

I'd love to see this piston.

 

[Dixiepipes]

I'd love to see this piston.

Here's the best I could get for pics Brad , as I have no need to pull the cyl off for this job.

Pic taken at BDC

 

[Chainsaw Jim]

I also noticed you edited your initial post.
Why are you only a d i c k here and not on O P E?
I'm personally not offended but I'm sure Shawn could teach you a thing or two about porting BTW.

I said I was going to didn't I? I had thoughts after the fact that someone might take it wrong and get offended....well you sure sound offended by the whole calling me names and insulting me. Did you ever give a thought that I was being a smart ass and didn't realize I was being offensive at the moment?
If I'm a d i c k here then I'm a d i c k there too. I've toned it way down and have been maintaining better awareness for how my thoughts don't translate to text as well as others. Plus you don't see as many negative or provocative comments attacking someone like you do around here including my 372xpw thread last year for example....where I got laughed at and was told how I successfully ruined the saw. I'll put my builds up against the best out there and be confident I won't get laughed at if I don't win.
I don't know who Shawn is but if he has something to teach that I haven't learned then I'll be all ears. Or is this the part where I'm supposed to start showing off a bunch of pictures of my most recent work? Lol

 

[Chainsaw Jim]

Here's the best I could get for pics Brad , as I have no need to pull the cyl off for this job. View attachment 504163View attachment 504164

Pic taken at BDC

Wow that's a lot taken down on that crown. You'd think if they were gonna hog the exhaust out like that they would just raise the exhaust roof instead.

 

[Chainsaw Jim]

This is a new one to me.

I'm trying my best to absorb the tidbits of info I get here and there about it and remember it well enough to re-explain it. I know my own experience with it doesn't give me any real knowledge about it, but it helps with studying it. The builders who have done it have volunteered bits here and there when I brought it up as something I did by mistake on my build. I'd like to ask them to explain it to me in a complete story so I can better understand but they start using words like "proprietary" when anyone ever asks them what they do. So I'm stuck at that.