Anyone have port timing #'s for NWP Makita/Dolmar 84cc P&C ?

[AUSSIE1]

"It was all about in which direction the charge entered the cilinder and how the tranfer streams influenced upon each other!"

This brings up something that has concerned me ever since I started reading this forum. Where did the idea come from of 'angling the transfer port towards the intake'?

Has anybody done any emperical research on this fad, or has it simply been a 'monkey see, monkey do' approach to porting?

With all the research the factories do in order to get the port angles right, I'm constantly bemused that someone with inferior porting tools, and no objective evidence to support the decision, would butcher the exit angle of the transfer port.

Who says the angles are right? If everything was so right, how come come we can modify quite extensively and improve dramatically the saw even in a work saw environment?

Aiming the uppers toward the inlet is supposed to help reduce the mix between the incoming and exhaust and reduce the chance of sending new charge out with the exhaust.

Has this theory not been written?

Carn Terry, what you thinking?

 

[Terry Syd]

What I'd like to see sometime is someone port their saw without sweeping the transfers back, then test it. They could get some objective evidence about how fast the saw cuts and where the powerband is.

Then go back in and and 'sweep the transfers' - the universal mod for all saws, in all situations. Then test it again.

 

[parrisw]

What I'd like to see sometime is someone port their saw without sweeping the transfers back, then test it. They could get some objective evidence about how fast the saw cuts and where the powerband is.

Then go back in and and 'sweep the transfers' - the universal mod for all saws, in all situations. Then test it again.

Well, what are you waiting for then?

 

[tdi-rick]

Al, the rear transfers already perform that function IMO.

What I think happens when you sweep the rear edge back is that the discharge velocity is lower/slower (port area is increased relative to duct volume) and it 'softens' the powerband of the saw.

What I've seen written somewhere was that narrower, higher velocity ports give more top end power, the wider sweep a broader torque curve at the expense of absolute power but can't recall if it was just a forum like this or an actual tuning book ?

Anyway, it's a good question as everyone always does it but is it always the best thing to do ?

 

[Terry Syd]

Ha Ha, not my jug. When I opened the transfers up on my 450, I increased the area by 12.5%. I spent a lot of time making sure that the angle of discharge would be identical to the factory angle.

I got both sides balanced perfectly, the flow pattern on the piston crown comes together flat across the crown and the central impact area of the transfer flows extends to less than halfway across the piston to the exhaust port. No way do I want to stuff that flow pattern up.

One of you guys must have a jug you're willing to sacrifice to the God of Speed.

 

[AUSSIE1]

What I'd like to see sometime is someone port their saw without sweeping the transfers back, then test it. They could get some objective evidence about how fast the saw cuts and where the powerband is.

Then go back in and and 'sweep the transfers' - the universal mod for all saws, in all situations. Then test it again.

I'm not quite sure I know what your saying Terry.

The theory looks to have proven itself as this is how basically all cyl's are designed these days.

Chainsaw cyl's are quite crude compared to say those previous pics of Ricks, hence the ability to be able to extract some reasonable no's by making these type of mods.

What I did find interesting one day was when I was washing out a cyl and the water pressure out the uppers was pulling around toward the cyl where most would cut the uppers across. This is with a solid so if this would happen with a gas is another thing.

 

[parrisw]

Ha Ha, not my jug. When I opened the transfers up on my 450, I increased the area by 12.5%. I spent a lot of time making sure that the angle of discharge would be identical to the factory angle.

I got both sides balanced perfectly, the flow pattern on the piston crown comes together flat across the crown and the central impact area of the transfer flows extends to less than halfway across the piston to the exhaust port. No way do I want to stuff that flow pattern up.

One of you guys must have a jug you're willing to sacrifice to the God of Speed.

I do it but I don't go crazy like I've seen some do. But you must carry that angle all the way back to the rear of the port, otherwise I think there is a flow disruption. I see allot of people do it with just cutoff wheels, and I really don't agree with this, you must be able to get in there and work that whole wall so the angle is the same all the way back, otherwise you end up with a hump in the middle of the rear wall of the transfer port closest to the intake.

 

[AUSSIE1]

Al, the rear transfers already perform that function IMO.

What I think happens when you sweep the rear edge back is that the discharge velocity is lower/slower (port area is increased relative to duct volume) and it 'softens' the powerband of the saw.

What I've seen written somewhere was that narrower, higher velocity ports give more top end power, the wider sweep a broader torque curve at the expense of absolute power but can't recall if it was just a forum like this or an actual tuning book ?

Anyway, it's a good question as everyone always does it but is it always the best thing to do ?

But not completely the way I see it. Chainsaws are crude. We are bumping up alot of flow in all area's and if there was a loss of velocity here, albeit minute, which does make sense, I tend to think it would be negligible.

Sure there will be sacrifices in some area's to some extent to gain hopefully more so in others.

 

[parrisw]

But not completely the way I see it. Chainsaws are crude. We are bumping up alot of flow in all area's and if there was a loss of velocity here, albeit minute, which does make sense, I tend to think it would be negligible.

Sure there will be sacrifices in some area's to some extent to gain hopefully more so in others.

Ya, I kinda agree here. I think if it didn't work, people wouldn't do it, even the most respected builders do it. Yes the transfers are already pointed to the intake side of the cylinder, I guess in reality we're just increasing the area a little.

 

[Terry Syd]

Al, has the theory proven itself?

All I've seen is people doing multiple things to a saw at the same time. They do a muffler mod, widen intake and exhaust, lower the jug, maybe raise the exhaust - oh, and sweep the transfers.

So in amongst all that work, how do they know that sweeping the transfers helped? What exactly was the effect they wanted from this mod (more broad range powerband, more top-end???)

I can imagine the response from an engineer at the factory after reading one of these threads and seeing the jug that he spent hours tweaking on a dyno - "I can't believe what that moron just did to that port!"

Some of the logic for the mod reminds me of High School - "well, everybody else was doing it". Enlighten me, what effect to the power do you KNOW that sweeping the transfers accomplishes?

 

[mtngun]

I can imagine the response from an engineer at the factory after reading one of these threads and seeing the jug that he spent hours tweaking on a dyno - "I can't believe what that moron just did to that port!"

I wonder if the factory spent hours tweaking this Efco 165 jug that has its eccentric chamber located on the EXHAUST side and makes less power than its 62cc little brother ?

Seriously, there are some good jugs out there that are hard to improve on, and then there are jugs that make you wonder "WTF were they thinking when they designed this ?"

Biggest problem I run into is a low compression ratio, i.e., 130 psi at the beginning of this thread despite not using a base gasket.

Gains through port work are tougher, sometimes you're not sure if you are making it better or worse. MOTA is not perfect, but it helps to shed light on what's happening with the porting.

 

[Terry Syd]

I had the same reaction when I saw that EFCO jug - WTF?

The only thing I can figure is that they designed the head to be offset, so that the majority of the squish was over the hot/exhaust side of the piston. Then the design drawings were given to some middle management wonk who handed them backwards to the production guys. It was a Friday afternoon and nobody could be bothered to check and they went into production. It was finally noticed after 500,000 units were made, so middle management then contacted the PR guys and asked them to 'spin' it as a environmental innovation.

 

[Andyshine77]

Al, has the theory proven itself?

All I've seen is people doing multiple things to a saw at the same time. They do a muffler mod, widen intake and exhaust, lower the jug, maybe raise the exhaust - oh, and sweep the transfers.

So in amongst all that work, how do they know that sweeping the transfers helped? What exactly was the effect they wanted from this mod (more broad range powerband, more top-end???)

I can imagine the response from an engineer at the factory after reading one of these threads and seeing the jug that he spent hours tweaking on a dyno - "I can't believe what that moron just did to that port!"

Some of the logic for the mod reminds me of High School - "well, everybody else was doing it". Enlighten me, what effect to the power do you KNOW that sweeping the transfers accomplishes?

For the most part I agree with you. I've seen muffler modded saws out gun ported saws. Now if the guy with the MM saw ported the saw at the same time he'd think the gains came from the port work. However like others have said chainsaws are quite crude and almost anything you do to them helps.

 

[AUSSIE1]

Al, has the theory proven itself?

All I've seen is people doing multiple things to a saw at the same time. They do a muffler mod, widen intake and exhaust, lower the jug, maybe raise the exhaust - oh, and sweep the transfers.

So in amongst all that work, how do they know that sweeping the transfers helped? What exactly was the effect they wanted from this mod (more broad range powerband, more top-end???)

I can imagine the response from an engineer at the factory after reading one of these threads and seeing the jug that he spent hours tweaking on a dyno - "I can't believe what that moron just did to that port!"

Some of the logic for the mod reminds me of High School - "well, everybody else was doing it". Enlighten me, what effect to the power do you KNOW that sweeping the transfers accomplishes?

I don't know for sure Terry, just like alot of other mods and never stated that I did. I try and look at how things may work and give it a shot. The theory sounds fair so I go with it. I don't have the mental matter that others may posses but I do have a steady hand and a good eye. There is alot of work others do that I don't because I think slightly different. There is work I do that others don't and have been criticized for it, but that doesn't matter as I give it shot. Mostly I don't follow the sheep mentality, not that I see a problem with this.

Personally I see the uppers need alot more work than is mostly performed if redirected than most do. If you are going to redirect the uppers, they need to be worked back into the port. I try and do very little opening up of the uppers and lowers. More on unshrouding and case matching and leave the dividers mostly untouched. As I say, this is only my thoughts.

If Ricks statement is true, wouldn't a softer powerband be well suited to a saw with slightly increased durations?

In a recent pic of Timberwolf's he has done some upper trans work and does more testing than most of us, so maybe he could enlighten us.

The engineer can have his own "moron" statement back with some of what we have seen, especially considering he may use a dyno!

 

[Terry Syd]

I'm all for trying different ideas, some of which may even be contrary to the accepted norm. All you have to do is look at what I have done to the exhaust side of the piston on my saw. I have two little scallops cut on the edge of the piston crown so that the entire exhaust port opens at once.

My saw has very little blowdown. It started at 12 degrees and I moved it to 14 after some experimentation by cutting the original piston crown. Part of the experimentation stage was trying the scallops. When I put in the new piston without the scallops in the ported jug (the new 14 degrees exhaust duration), it didn't perform as well.

Those two little scallops increase the area of the port opening so that the blowdown time/area works like a 16 degree blowdown. Probably most people would disagree with that mod as they get focused on the 'squish' issue and trying to get as much of the mixture out from under the squish band, there is also a tiny loss of compression. However, I knew before I cut the piston that the increase in flow was well worth it.

Actually, the use of old pistons to find a preferred duration is not something I have seen on this forum. It is a very old trick, but seems to have been lost for some reason. Heck, I had one bike that I modded the piston to give me a 'staggered' port opening on the transfers. It did broaden the powerband the way I wanted and decided to use the timing. There was a race coming up that weekend, so I left the piston in until I had some significant down time to port the cylinder. Well, one weekend led to the next and when I finally sold the bike it still had the trimmed piston in it.

The 'swept back' transfers is a theory at this point. However, it would be very easy to test the theory - make it a seperate mod and see what happens.

 

[tdi-rick]

I do it but I don't go crazy like I've seen some do. But you must carry that angle all the way back to the rear of the port, otherwise I think there is a flow disruption. I see allot of people do it with just cutoff wheels, and I really don't agree with this, you must be able to get in there and work that whole wall so the angle is the same all the way back, otherwise you end up with a hump in the middle of the rear wall of the transfer port closest to the intake.

[snip]
If you are going to redirect the uppers, they need to be worked back into the port. I try and do very little opening up of the uppers and lowers. More on unshrouding and case matching and leave the dividers mostly untouched. As I say, this is only my thoughts.

[snip]

If you are going to open the rear transfer for more area, that's how you do it.
I'm thinking more the practice that Will described where people just open the face without angling the port wall all the way back to the rear wall of the duct to match.
It'd just bugger up the flow.



Terry, I'm surprised more people don't mod the piston crown to see if a timing change would help or hinder too.
Piston's are much, much cheaper than a cylinder and it's an easy way to test combinations.
Having said that it was common on here once to trim the skirt on the intake side to see if more duration would help.

 

[AUSSIE1]

If you are going to open the rear transfer for more area, that's how you do it.
I'm thinking more the practice that Will described where people just open the face without angling the port wall all the way back to the rear wall of the duct to match.
It'd just bugger up the flow.

Yep.

Sorry Will, I didn't see your post when I did mine mate.

 

[mtngun]

Terry, I'm surprised more people don't mod the piston crown to see if a timing change would help or hinder too.
Piston's are much, much cheaper than a cylinder and it's an easy way to test combinations.

That would lower the compression, and these saws (mine, anyway) need all the compression they can get.

Top land on the 84BB is only about 0.125", not a lot of meat there to work with.

 

[parrisw]

Yep.

Sorry Will, I didn't see your post when I did mine mate.

No prob. After all, it was you that helped me learn how to do uppers that way.

 

[tdi-rick]

That would lower the compression, and these saws (mine, anyway) need all the compression they can get.

Top land on the 84BB is only about 0.125", not a lot of meat there to work with.

I think you may be missing the point.
The piston mod trick can be applied to any saw, and I realise how thin the top land is, the OE and BB pistons are the same there, it doesn't leave much room for a pop up.

Notching the piston is only an indicator to see if running more exhaust timing or transfer timing would help (or not).
It's something that Bell suggested way back whenever too.

I haven't CC'd the chamber on the BB kit I have here (one of Matt's) yet either but I'm guessing it comes out of the same factory the NPW kits do ? or maybe not, I really don't know.