Spuds Porting and Tuning Thread

[spudulike]

Steve, Bit like my exhaust mod!

 

It is truly amazing what you can do with a wood chisel:lol:

[wyk]

Someone described porting as a slapping a thong on a Granny today:lol:

 

Slapping a thong on a MILF works well, I find.

[Daniël Bos]

Perhaps not strictly porting or tuning, but.... If I take the existing exhaust of my 880 and replace it with a motor bike one of similar cc-age will that be ok?

 

To elaborate: The 880 would only be used like this on the mill, with the exhaust fixed to the mill and attached to the saw with a flexi piece. This to quieten the operation a bit and direct the exhaust gasses away from me rather than in my face with the current set up.

I thought perhaps I could tune the exhaust to match the saw by making sure it was oversized to begin with, then squeezing the end until it runs just right.

[wyk]

Perhaps not strictly porting or tuning, but.... If I take the existing exhaust of my 880 and replace it with a motor bike one of similar cc-age will that be ok?

 

To elaborate: The 880 would only be used like this on the mill, with the exhaust fixed to the mill and attached to the saw with a flexi piece. This to quieten the operation a bit and direct the exhaust gasses away from me rather than in my face with the current set up.

I thought perhaps I could tune the exhaust to match the saw by making sure it was oversized to begin with, then squeezing the end until it runs just right.

 

It's a bit more complicated than that. Here's a place to start:

 

Expansion chamber - Wikipedia, the free encyclopedia

 

Motorbikes have a huge advantage over chainsaws in that they can place a large tuned expansion chamber(which some mistake for a muffler). A well-tuned exhaust can produce nearly twice the power the same engine would in a chainsaw because it frees up the design to run far more aggressive port tuning, and other port options. Boost ports become particularly effective then. In other words, a 120cc sport bike will have completely different port design and timing than your MS880 would.

 

 

Notice the absolutely huge ports on this KTM 125 VS an MS880. It simply flows more fuel and exhaust, partly due to having a tuned exhaust, and partly due to weight not being a factor.

[ame]

[/ame] Edited February 8, 2014 by wyk

[wyk]

Took me a while to find this:

 

 

I think that's a ported Honda MT-5. 50cc. That look anything like a 346xp? It produces about 4-5X the power of a 346xp and has no less than 15 ports.

[wyk]

I've been considering building a 125 piped saw since I do find these engines about for cheap:

 

[peatff]

Bikes need a different set up because they have to operate over a wider rev range and different load parameters where a saw is expected to tick over or run flat out with no middle ground.

[Graham]

Bikes need a different set up because they have to operate over a wider rev range and different load parameters where a saw is expected to tick over or run flat out with no middle ground.

 

All this is thanks to the defection of MZ rider Ernst Degner and Nazi rocket science technology. In 1961 the MZ 125 was producing 200bhp per litre. A phenomenal amount with a powerband of 400rpm! Suzuki stole it and the rest is history.

[spudulike]

I've been considering building a 125 piped saw since I do find these engines about for cheap:

 

 

Funny that expansions are coming up - just picked up a race pipe for a KX85 - similar stroke and cc to my 066:001_rolleyes: There is an option to try it on the saw once I get it going - just need to "create" a manifold connection and supporting brackets etc.

[wyk]

Funny that expansions are coming up - just picked up a race pipe for a KX85 - similar stroke and cc to my 066:001_rolleyes: There is an option to try it on the saw once I get it going - just need to "create" a manifold connection and supporting brackets etc.

 

And don't forget to up the compression to 220psi, set your transfers to 16*, add finger boost ports, and set your exhaust to 185*. And the stock Stihl carb won't feed that beast at that point.