Part Three: The Transfer Ports

[Darryll]

Longer intake duration sucks more fuel because the intake signal lasts longer. Same thing a bigger bore or longer stroke does.

Your exhaust seems low for even a work saw. Are you milling with it?

Just experimenting. After cutting the combustion chamber I thought I'd run it just see what it's like. I've never run a saw that low either. I'll take it up bit by bit and make some notes. I've never built a 372 @ 100 ex that I have been entirely happy with so going to try a minimalist approach and see if that's any better. That way I can at least open it up if I need to. I'm really surprised how that 87 ex saw cuts. I used it today and bloody liked it. Tomorrow it will be in bigger wood so that will be interesting, well if the wind lets me that is.

 

[Nutball]

I've had good results running an Echo 590 with an intake of 90. It's all about the variables. Some saws will be strong runners around 70. Just experiment to tune the ports to whatever works best.

Does a long intake duration use waste more fuel or what? Sucking more fuel is good if you can burn it, so is there too much intake charge over-filling the cylinder and leaking out the exhaust? I wouldn't think blow back would be the cause of waste because those vapors will get sucked back in, and the carb may need adjusting to compensate for the extra fuel in the air filter from blowback, or that's what makes sense to me.

 

[Wonkydonkey]

The spit back, when it’s sucked back in (the stuff that’s not soaking your air filter and clogging it up) will be saturated, and make an even richer mix.
I'm not sure that it’s constantly even across the rpm , so I don’t believe the carb can be tuned for it.

 

[Ketchup]

The saws that I have that waste the most fuel have an overly large exhaust port or muffler with too big an outlet. Transfer uppers that are aimed towards the exhaust side also waste fuel. If you added intake duration to those problems I’m sure it would waste even more.

 

[Nutball]

Why would the transfers be aimed towards the exhaust? One of those where they point straight out on the exhaust side? I think the FT 660 cylinders are that way. Seems like Stihl are natural gas guzzlers, but maybe they just have small tanks. They tend to have a lot of blowdown too, maybe that only becomes an issue when the muffler is modified.

I find a bigger sprocket and aggressive chain go a long way toward improving efficiency of wood cut per tank.

 

[Darryll]

I think all of the points you two have made here are valid. So by lowering the Intake we must be increasing transfer velocity enough to lose some of the fresh charge straight out the exhaust. As lightning said a high exhaust also contributes as would a high transfer. My goal is to build saws that hold in the cut at around that 10-11k. To some extent I have got that. Now I'm trying to get greedy and have a saw cut strong at those revs but also handle a tight spot or a bit of a heave on the bars without snagging. As yet I wouldn't claim to have found the perfect compromise.
It seems just as I get to a point where I think I have it all worked out something left field like the 87ex port 372 comes along and causes me to rethink everything. It seems many of you here hold the same beliefs/theories as myself and this bloody high port 372 is defying all of them. To think I gave up on it a few years back and I was so close to having it run as it now does just highlights how fine a line we are walking here.
I almost never look in here but it's been great to read these various threads Randy started and it's nice to bounce ideas around with others who are suffering the same self inflected obsession as myself.

 

[huskyboy]

A 066/660 is definitely the worst saw on fuel that I’ve used. Maybe we can learn why by studying it. I think it has to do with the intake duration and the long duration of dwell time it stays open from the longer stroke maybe? My smaller bore 064 isn’t as much of a pig and still has very good power.

 

[drf256]

I think all of the points you two have made here are valid. So by lowering the Intake we must be increasing transfer velocity enough to lose some of the fresh charge straight out the exhaust. As lightning said a high exhaust also contributes as would a high transfer. My goal is to build saws that hold in the cut at around that 10-11k. To some extent I have got that. Now I'm trying to get greedy and have a saw cut strong at those revs but also handle a tight spot or a bit of a heave on the bars without snagging. As yet I wouldn't claim to have found the perfect compromise.
It seems just as I get to a point where I think I have it all worked out something left field like the 87ex port 372 comes along and causes me to rethink everything. It seems many of you here hold the same beliefs/theories as myself and this bloody high port 372 is defying all of them. To think I gave up on it a few years back and I was so close to having it run as it now does just highlights how fine a line we are walking here.
I almost never look in here but it's been great to read these various threads Randy started and it's nice to bounce ideas around with others who are suffering the same self inflected obsession as myself.

Lowering an intake reduces transfer velocity. Case compression is derived from the intake closing and pressure building before the uppers open. It’s what makes saws peppy and what makes a saw recover rpm when it’s suddenly loaded up. Generally I like 40* +.

Physically lower intake floors allow for more spitback which doesn’t always mix back into the intake flow. It’s worse in a worksaw when rpm is less.

An exhaust roof that opens too early will not allow an engine to utilize all of the pressure that is created by the burning charge. You want it open at the point where parasitic loss just begins to exceed power production.

The heights are like valve openings in a 4 stroke engine. More duration means more peak power but at a higher rpm. Generally less forgiving and causes loss of lower curve torque.

Your 372 ran better with more intake because you “balanced it”. Usually piston ported 2T engines will run the best when the degree # of the intake floor plus the intake floor equal 180* give or take. So a 90* ex roof wants a 90* intake floor give or take. This doesn’t include piped saws.

 

[Darryll]

A 066/660 is definitely the worst saw on fuel that I’ve used. Maybe we can learn why by studying it. I think it has to do with the intake duration and the long duration of dwell time it stays open from the longer stroke maybe? My smaller bore 064 isn’t as much of a pig and still has very good power.

Well stock they are 95ex 125 tr and 85 intake. These are pretty hot numbers.

 

[huskihl]

Well stock they are 95ex 125 tr and 85 intake. These are pretty hot numbers.

I’ve seen them range from 94-100 on the exhaust. 118-127 on transfers and 78-85 on intake. They’re about the least consistent timed cylinder I’m aware of. Probably something to do with being manufactured over a 20 year span

 

[Darryll]

Lowering an intake reduces transfer velocity. Case compression is derived from the intake closing and pressure building before the uppers open. It’s what makes saws peppy and what makes a saw recover rpm when it’s suddenly loaded up. Generally I like 40* +.

Physically lower intake floors allow for more spitback which doesn’t always mix back into the intake flow. It’s worse in a worksaw when rpm is less.

An exhaust roof that opens too early will not allow an engine to utilize all of the pressure that is created by the burning charge. You want it open at the point where parasitic loss just begins to exceed power production.

The heights are like valve openings in a 4 stroke engine. More duration means more peak power but at a higher rpm. Generally less forgiving and causes loss of lower curve torque.

Your 372 ran better with more intake because you “balanced it”. Usually piston ported 2T engines will run the best when the degree # of the intake floor plus the intake floor equal 180* give or take. So a 90* ex roof wants a 90* intake floor give or take. This doesn’t include piped saws.

I need to put a tacho on my 372 to see when the spit back cleans up but Id say its somewhere around 4-5k. For the record it idles and runs down low sweet as and even has very decent throttle response. Its about to get a real work out today I'll let you know how it goes latter.

Mine are pretty much between 38-40* I'm not so worried about fuel economy. My goal is to get a saw to hold 10-11k in the cut with a decent load. I have had no luck at around 100*ex I find they pull well and easily free rev to 13k+ but as soon as you put them in the wood they load down to 9k. Nice saw to use and very forgiving and certainly a step up from stock but not what I'm after. There are a few guys who have cracked this. You can hear it and see it in there videos. So it can be done. I'm close but not there yet. OR I am actually there and it's my chain setup holding me back. Watching John Riley's videos sure does not help LOL.

What I do know is it's a fair bit of fun working it all out.

 

[Agent Smith]

I’ve seen them range from 94-100 on the exhaust. 118-127 on transfers and 78-85 on intake. They’re about the least timed cylinder I’m aware of. Probably something to do with being manufactured over a 20 year span

So is a little jb on the intake floor after machining n such standard procedure on these?

 

[Darryll]

I’ve seen them range from 94-100 on the exhaust. 118-127 on transfers and 78-85 on intake. They’re about the least consistent timed cylinder I’m aware of. Probably something to do with being manufactured over a 20 year span

Wow! I've not had much to do with them but that's terrible. I traded this saw and was pretty impressed how well it went. Its the odd ball in the fleet of Huskys. I never use it because my ported 372 is faster cutting and lighter and the 395 does all the heavy lifting.

 

[huskihl]

Wow! I've not had much to do with them but that's terrible. I traded this saw and was pretty impressed how well it went. Its the odd ball in the fleet of Huskys. I never use it because my ported 372 is faster cutting and lighter and the 395 does all the heavy lifting.

I guess I was thinking about 066’s or something. Lol.

372’s are all pretty consistent that I’ve seen.

 

[huskihl]

So is a little jb on the intake floor after machining n such standard procedure on these?

Some aren’t bad after machine work but it’s pretty rare. I think the epoxy helps the really low intakes. The ones that land at 85 gain some zip when raised back up

 

[Agent Smith]

Some aren’t bad after machine work but it’s pretty rare. I think the epoxy helps the really low intakes. The ones that land at 85 gain some zip when raised back up

Good to know thank you.

 

[Darryll]

I guess I was thinking about 066’s or something. Lol.

372’s are all pretty consistent that I’ve seen.

It was the 660 I have that I was referring too.

 

[MustangMike]

Most 660s and 460s benefit a lot from porting, and #s for both are all over the place.

 

[Wonkydonkey]

I’ve gleaned some numbers for the 660 and the boss says more than 80 ain't good. I’ve ran mine and I get green fuel in my air filter I use green 2mix it’s 80* atm ... so I shall fill it a bit to bring it to 75ish then grind away and keep checking till I get what # I want
I can’t do lathe work so the exhaust stays put @96*
I can tickle the transfers a bit, was 125 but I raised them to 118..

I’ve put a few tanks through it so at some point I will fill the intake soon

 

[huskyboy]

Exhaust numbers aren’t really a guaranteed indicator of performance sometimes. I guess that’s why giving numbers out freely is commonplace? A curved less wide exhaust at 96 probably has more “torque” than a wider/flatter/more “square” one that opens more port area at 98.... I guess the same can be said for the intake number. Flatter floor vs more curved. Shape can mean as much as the numbers sometimes.