going to build a pipe for my 660

[gink595]

I don't know all the science in figuring out the size and lengths but I do know that you will need a slip roll and a plasma or bandsaw, dollys and hammers and a tig and a lot of patience getting it to fit nicley. But it could be done. I always thought it would be cool to build one too!!! I've built BIG duct work and it is cool to lay that stuff out, just a beach to get it to fit nicley.

 

[breymeyerfam]

I was hoping to have a saw to work with and put a pipe on for gtg's , but if the porting is that much different, and not much gains would be made from putting the pipe on and tuning the carb, then I will probably just cancel trying it.

 

[gink595]

I was hoping to have a saw to work with and put a pipe on for gtg's , but if the porting is that much different, and not much gains would be made from putting the pipe on and tuning the carb, then I will probably just cancel trying it.

Why don't you find a e-bay cylinder and try porting for a pipe. You should be able to swap a cylinder and pipe on pretty quick for GTG.

 

[edisto]

I was hoping to have a saw to work with and put a pipe on for gtg's , but if the porting is that much different, and not much gains would be made from putting the pipe on and tuning the carb, then I will probably just cancel trying it.

The gains can be huge, but only if it is done right...which ain't easy to do.

 

[Crofter]

It would be a real chore to do by trial and error unless you start out with sliding adjustments in both header and belly sections. I dont agree with the statement that the header and diffuser part is unimportant. The pipe can only stuff back in what it pulls out into the header. The stuffing action is more critical though.

Yes an engine designed for pipe might have 25 or 30 degrees more duration on both exhaust and intake as well as more transfer. A torqy saw with the exhaust opening 100 deg. or so ATDC will not have near as sharp a blast at opening and that signal reflected is what stuffs the intake charge back in to enhance dynamic compression and charge density. The stronger the engine is on muffler the less percentage gain you will see from the pipe. 10 - 15% likely and more like 50% if it is made for pipe. Without the pipe it will hardly get out of its own way.

If you see no gain when you try a pipe setup or say a 20% loss, (which is actually more likely than a gain), you really dont know which way to change what and you wind up having to both lengthen then shorten a number of times then go back and test lengthen and shorten the other part of the pipe. It must both push and pull to really work. If you have ever actually shortened or lengthened a tapered section you will know it is not easy.
The reflector length can be changed easier if you have a sliding section in a straight belly. I have built a couple with that provision and find a move 1/4 inch either way makes the power fall off noticeably. Cant find what folder that pic is in.

The heavier the pipe assembly is the quicker it will break off. it takes good supports in two different directions and even so I bet you dont get an hours total running time before you develop cracks. More than a few exhaust nozzles have been broken off cylinders. You have to be very carefull not to score a piston with too many back to back cuts. Any and all welding you do on a pipe has to be free of spatter or scale on the inside or you will damage your cylinder plating and piston. A lot of people laugh at the notion of suckback but if you start a saw on pipe, with crap in it, you will become a believer.

I have made a few by my own calculations and got out ok but it is a lot of work doing the layout and cut out. The welding part is fun but that is my trade. It is less fingernail biting when you know the dimensions will be right without puckering and stretching things. To do a multi piece closely tucked in pipe like TW that keeps the chain brake active and doesnt cost you 6 inches of usuable bar length is not going to happen by trial and error on the first one you make. I imagine TW has made a dud or two until he figured the rules for wave speed/ gas temperature on a given engine. To me that might be the most critical part.

You can see in the pic of the 365 that I made an afterthought joint to sweep the pipe back a bit. Later I made a smoother sweep to the header once I knew the dimensions were right.

 

[edisto]

I dont agree with the statement that the header and diffuser part is unimportant. The pipe can only stuff back in what it pulls out into the header. The stuffing action is more critical though.

Didn't mean to imply it was unimportant! What I meant was that if all you want is the drawing action of the negative wave, then it is easy to build a diffuser by trial and error. The timing of the negative pressure wave is equally critical, but, as you say, the big boost in power comes with the properly timed return of the positive wave.

Great pics...talk about a butt load of planning and welding! Excellent point about the necessary support too!

 

[breymeyerfam]

with money being tight I cannot buy another cylinder, so I will not be able to port for max power w/ a pipe. however If I was to try to build a pipe for my saw with its current port timing, what kind of gains are possible and is it worth doing????

 

[edisto]

with money being tight I cannot buy another cylinder, so I will not be able to port for max power w/ a pipe. however If I was to try to build a pipe for my saw with its current port timing, what kind of gains are possible and is it worth doing????

Are your ports "ported"?

And it depends on how you value "worth". If the joy is in the journey, then it would be worth playing with it...but it will be a long journey.

 

[timberwolf]

For a stock saw pipes won't give you much more than 10-15% over a fully open muffler.

Cut to the chase, unless you have some welding skill and the equipment a pipe will cost you more than an aftermarkets cylinder to port. Building a decent pipe is at minnimum a good days work if you know your way around fabbing sheet metal. Results from reworking existing pipes to work on a chainsaw are most times not good as the timing, RPM and powerband of most piped engines is far different than a chainsaw.

 

[breymeyerfam]

For a stock saw pipes won't give you much more than 10-15% over a fully open muffler.

Cut to the chase, unless you have some welding skill and the equipment a pipe will cost you more than an aftermarkets cylinder to port. Building a decent pipe is at minnimum a good days work if you know your way around fabbing sheet metal. Results from reworking existing pipes to work on a chainsaw are most times not good as the timing, RPM and powerband of most piped engines is far different than a chainsaw.

I can weld(enough to get by), can and like to fab things from metal, and if there is 15% to be gained, I might give it a shot. only investment should be the sheet steel and my time, which I have much more than money.

 

[Crofter]

Found the pic of the pipe with the fine tuning belly section. You would want to take it out once dimensions finalized. Sections were very tight fit but still, three sheet metal screw loosened almost immediately even with the stainless clamp; here you see it also tack welded. You would not believe how much the pipe throbs from the internal pulses and engine vibration is greatly magnified at the end of something over two feet long bolted to its ex. flange.

Here are two pipes for differently ported saws. Notice the colour difference. The larger pipe was for a saw of about 165 deg exhaust duration, the other for about 195 degrees. Greatly different wave velocity and rpm. Occasionally like this they can come out to similar lengths when far different tuned rpms coincidently affects dimensions dictated by degrees of duration and exhaust gas temperatures.

Takes me two full days from start to finish to lay out, cut, weld, mount and support a pipe. I know it can be done quicker with power cutters and roll formers. That is for a pipe of about 15 separate pieces. Looks like some of TW,s are thirty or so sections! The first few sections have to transition from basically square at the flange to round. The people who will tell you there is nothing to it wont be the ones who have made ten! More likely that will come from someone who has made none.

 

[demographic]

I don't know about saws but the only thing I would say about someone wanting to just bolt up a different expansion chamber onto a motocrosser and expect it to work properly is "Oh dear". A little knowledge is a dangerous thing.

Theres a lot of working out to be done and its no mean feat, no wonder the first bloke who made good expansion chambers on motor bikes was WALTER KAADEN and he really was a rocket scientist who had worked on the German V2 rocket programme at Peenemunde for Verner Von Braun.

Little basic primer about expansion chambers HERE as well although its nothing like as involved as the Jennings book.

 

[timberwolf]

Here is a 361 pipe I am just finnishing up, Steel is not the big part of cost, it's welding gas. Possible to mig a pipe up and it is quicker and less gas but pretty ugly. Torch or TIG would be best, if you got the old school type skills torch welding is likely the best as it does a good job of stress relieving everything.

To start though I'd port a saw before puting a pipe on one, easier and bigger gains to be had on a stock 066 with port work.

 

[gink595]

Here is a 361 pipe I am just finnishing up, Steel is not the big part of cost, it's welding gas. Possible to mig a pipe up and it is quicker and less gas but pretty ugly. Torch or TIG would be best, if you got the old school type skills torch welding is likely the best as it does a good job of stress relieving everything.

To start though I'd port a saw before puting a pipe on one, easier and bigger gains to be had on a stock 066 with port work.

Thats looks really good. I think I would avoid mig welding it to many berries(splatter) Mig welding just doesn't cut it for small percision welds. Oxy-Acetylene or Tig for sure. I would rather tig it if it were me.

Have you had a problem with tig welds cracking where stress relieving is neccessary ?

 

[blsnelling]

Here is a 361 pipe I am just finnishing up, Steel is not the big part of cost, it's welding gas. Possible to mig a pipe up and it is quicker and less gas but pretty ugly. Torch or TIG would be best, if you got the old school type skills torch welding is likely the best as it does a good job of stress relieving everything.

To start though I'd port a saw before puting a pipe on one, easier and bigger gains to be had on a stock 066 with port work.

I like that pipe a lot. That's much better than sticking way out and up to one side, IMHO. I wouldn't think it'd get in the way as much. Maybe this is whay I should do with my 460 now that I have the 440 with the 460 topend. Hmmm?:yourock:

 

[blsnelling]

Hey Brian, your PMs are full.

 

[Nitroman]

Best place to start will be to read both Gordon and Jennings, then decide if it would be worth your time. Also, consider the additional cost of a dynamometer to test your builds.

 

[timberwolf]

It's real tricky to hold two pieces of sheet together tight enough to TIG them. Find it easiest to tack them with Mig then finish with TIG. Pipes do sometimes crack over time, but have not found any one way of welding them that is better or worse. Though the ones crofter did with torch seem maybe better, but they have seen less abuse too.

Here is a vedio, keep in mind it's still a work saw on pump gas, original carb, no cut off head, boost ports or funky fuel.

Good old wood dyno and stop watch works for me, though I imagine I could find use for a dyno.

http://www.youtube.com/watch?v=PyNt-E6VxHM

 

[troutfisher]

I use a oxy acetalene torch and filler rod to weld pipes. I tried MIG, but I had cracking problems. Like TW said, how well you cut and fit the pieces will make the welding easier. Filling gaps is tuff to do and ugly.

 

[timberwolf]

WIth torch you have to watch the mill scale that comes off on the inside of the pipes. Would be easy for this to flake off and get injested by the engine.