How can I increase saw rpm (thus HP) through engine mods?

[bikesandcars]

I'm not sure how to reply to those last few side-tangents on which rifle is best... but now I got bigger problems....

I hooked up a ghetto type muffler mod, enlarged the muffler opening slightly to match the exhaust port, removed an interior baffle and spark arrestor, then drilled some larger holes in the exhaust and bolted it back together.

I took the air cleaner off to adjust the carb (need to pull the air cleaner) and the saw is spraying fuel/air mix back through the carb like crazy under high power. For how well it starts / runs I'm really suprised... seems to me the reed valve needs attention. Is that it? How could it run spitting gas back like that?

max RPM seemed to be around 12K but I didn't get an exact reading because I was afraid of exploding.

 

[cmarti]

........ But I agree with most here. It's not really worth putting a lot of effort into that saw. You could put a lot of time into it AND be doing all the right things, but still not see much gains.

Is he messing for fun? For those of us who read the the threads and watch the video.....and can't keep our *%$# beaters off the saws, cause we want to try it. Small, cheap, old, junked, or factory refurbs are a way to play and learn. You start by building a saw out of box of old craftsman saws, then your grinding the port of a factory rebuild Poulan........Now I am pricing a lathe, ..... or will my drill press cut....I hate this site:msp_sad:

On the bright side when I am out in the barn, I am not in the house with my wife and daughter planning the wedding that is going to break me. It's a victory if it runs when I am done......let alone gains.

 

[cpr]

I'm not sure how to reply to those last few side-tangents on which rifle is best... but now I got bigger problems....

I hooked up a ghetto type muffler mod, enlarged the muffler opening slightly to match the exhaust port, removed an interior baffle and spark arrestor, then drilled some larger holes in the exhaust and bolted it back together.

I took the air cleaner off to adjust the carb (need to pull the air cleaner) and the saw is spraying fuel/air mix back through the carb like crazy under high power. For how well it starts / runs I'm really suprised... seems to me the reed valve needs attention. Is that it? How could it run spitting gas back like that?

max RPM seemed to be around 12K but I didn't get an exact reading because I was afraid of exploding.

Without seeing it, a little spit-back is perfectly normal on a reed saw. A lot, then the reeds are done.

 

[bikesandcars]

I dug in a little and improved the situation.

The plastic housing the reed valve seals against wasn't exactly flat (I don't think it ever was). I sanded it flatter and the seal was much better. I test-ran it afterwards and it felt a little crisper. It still fogs a little at WOT, but at idle there isn't any spit-back and overall it seems a bit better. I'm impressed by the power/weight ratio for such a basic-model chainsaw

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Videos:
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[TPA]

Yea, you should go out and get a $1000 saw and learn to port on that one instead of doing something stupid like making mistakes on a cheap saw. :jester:

 

[jropo]

I'm not sure how to reply to those last few side-tangents on which rifle is best... but now I got bigger problems....

I hooked up a ghetto type muffler mod, enlarged the muffler opening slightly to match the exhaust port, removed an interior baffle and spark arrestor, then drilled some larger holes in the exhaust and bolted it back together.

I took the air cleaner off to adjust the carb (need to pull the air cleaner) and the saw is spraying fuel/air mix back through the carb like crazy under high power. For how well it starts / runs I'm really suprised... seems to me the reed valve needs attention. Is that it? How could it run spitting gas back like that?

max RPM seemed to be around 12K but I didn't get an exact reading because I was afraid of exploding.

I believe we were referring to the size of the holes to put in your muffler, because thats pretty much all a muffler mod is. Take a muffler and drill holes in it, a firearm seems like it would be an efficient way of achieving this. Now that would be ghetto.

Yea, you should go out and get a $1000 saw and learn to port on that one instead of doing something stupid like making mistakes on a cheap saw. :jester:

I don't believe anyone said you should.

I personally like working on these saws for this reason, they are cheap!

 

[bikesandcars]

You could put a lot of time into it AND be doing all the right things, but still not see much gains.

Possibly, but so far I've made some good improvements without any porting / timing work, plus I got to spend 1/2 hour in the garage and smell like 2-stroke and a bonus of having a chainsaw ripping in my neighborhood after dark (though only 6:30)... all that enjoyment... who would pass it up!!??

Best way to speed it up is to keep the chain absolutely sharp, everything after that is icing on the cake.

.. :msp_w00t:

I believe we were referring to the size of the holes to put in your muffler, because thats pretty much all a muffler mod is. Take a muffler and drill holes in it, a firearm seems like it would be an efficient way of achieving this. Now that would be ghetto.

... lol.. I found those posts amusing, but they are definately off-topic ... shooting a muffler to make a hole would be "redneck" not "ghetto"... :msp_biggrin:

I personally like working on these saws for this reason, they are cheap!

YES! I think some folks here get it, this post exists to help me and others learn about tinkering, not to find the most cost-effective or time-effective chainsaw.

 

[sachsmo]

I have a craftsman 14 / Poulan 2000 I recently purchased.

I'm going to do a muffler mod and re-tune. Ran it last night and it starts and runs well.

It seems like it revs lower than my other saws, which got me thinking about how I could raise the RPM to make it a little zippier.

Since HP is torque x RPM, I was thinking if I could mod the engine to raise the torque curve higher and raise the RPM it would make more hp overall.

I've read here you can increase torque by compression, and you can raise rpm by raising the exhaust port. The compression part I understand but not sure what port mods do.

Do you experienced guys have any other suggestions for improving RPM (both in cut and max) and usable HP?

Just get a bigger saw.

They are just tools, you don't use a 1-1/4" wrench with a two inch length, nor a 1/4" with a 2 foot length?

 

[sachsmo]

Best way to speed it up is to keep the chain absolutely sharp, everything after that is icing on the cake.

Mark

Best answer.

 

[Scooterbum]

This could be a really good thread if kept on topic. I for one have never seen this discussed on this site.
Older cheap saws is the best way to learn. Don't even ask about the homemade twin cylinder box store poulan LOL !!! ( yes i was bored )
I think it would be neat to take an old XL12 type and make a screamer out of it. Just because.
Loed knows they have plenty of torque to spare.

 

[jropo]

Possibly, but so far I've made some good improvements without any porting / timing work, plus I got to spend 1/2 hour in the garage and smell like 2-stroke and a bonus of having a chainsaw ripping in my neighborhood after dark (though only 6:30)... all that enjoyment... who would pass it up!!??

.. :msp_w00t:



... lol.. I found those posts amusing, but they are definately off-topic ... shooting a muffler to make a hole would be "redneck" not "ghetto"... :msp_biggrin:



YES! I think some folks here get it, this post exists to help me and others learn about tinkering, not to find the most cost-effective or time-effective chainsaw.

I hear ya, garage time is time well spent.

Off topic happens, but it can keep the thread alive(on the first page) for a little bit so it can gather some interest. As long as the guys don't start talking about food I think we're good.
But I have also dug through the 20-30 page threads the find the 2-3 pages of the good stuff.

I love tinkering and I have never built a split case saw (yet) I'm still messing with clam shell type saws.
But if you read the build threads on these high dollar saws it helps with the understanding on what does what and when. If you so happen to have one of these saws that is where the cheap after market kits come in handy. Some work has been done on them as what numbers work and such. It would help with the learning curve.
On these cheap saws not so much. Their is no AM kits to practice on, so if you mess it up your done.
Just a thought.
If you don't understand what your doing your just grinding on a cylinder and making all the holes bigger.

 

[jropo]

This could be a really good thread if kept on topic. I for one have never seen this discussed on this site.
Older cheap saws is the best way to learn. Don't even ask about the homemade twin cylinder box store poulan LOL !!! ( yes i was bored ) I think it would be neat to take an old XL12 type and make a screamer out of it. Just because.
Loed knows they have plenty of torque to spare.

:msp_ohmy: :msp_biggrin: opcorn:

When people are bored in the garage that when the cool stuff gets built!

 

[50blues]

:msp_ohmy: :msp_biggrin: opcorn:

When people are bored in the garage that when the cool stuff gets built!

Or good stuff gets destroyed!!

Either way its fun.

One thing though, if you opened up the muffler you should also richen up the carb. a little. It will be running lean if you dont.

 

[bikesandcars]

Ok ok...so how can i boost up that rpm fellas...raise rhe exhaust port? Intake port?

 

[jughead500]

You can get more RPM from Porting.Some From a Muffler Mod but alot of your RPM is Governed by the weight of the Crank weight.If you turn the diameter of the Crank down then that will lighten and raise your RPM.BUT if you do that it lowers your Primary Compression.Then you have to Install a Crank case stuffer to take up enough Volume to raise the Primary compression back up.
In your case I would just start with a Muffler mod.Since your saw is reed valve and not piston port you may be able to do some porting and go with some windows drilled in your Piston skirt.Becareful though.Read up on the subject before modifying.:msp_wink:

 

[bikesandcars]

Thanks for the advice.

Speaking of Reed Valves, the reed valve that is in there is a sizable piece of stainless that doesn't seem too flexible. I was thinking that the blowback I get at max rpm would be better served in the engine the first time around. I bet if the reed valve was more flexible it would close quicker and open quicker enhancing combustion... is there much improvement available by switching materials on the reed valve? (lighter / more flexible)? Like going to a plastic / carbon fiber piece? It would be easy to make a reed valve out of another material if I knew what material to use.

 

[Plan-b]

You wont see any real perfromace gains in changing reed materal, we use carbon, fiberglass, plastic.... ect. in boats engines. The benifit is when the engine injests the reed it does not distroy everyting as a metal reed would.

 

[sachsmo]

You wont see any real perfromace gains in changing reed materal, we use carbon, fiberglass, plastic.... ect. in boats engines. The benifit is when the engine injests the reed it does not distroy everyting as a metal reed would.

Dunno 'bout that,

a less rigid material allows the "valve" to open further and faster.

 

[jughead500]

May be able to go with copper.Fiberglass would have to be special made.just cutting into a small sheet of fiberglass would weakin it causing self destruction.With copper it could always be "tuned" by annealing it.if it gets soft it could always be re hardened by heating and quenching.

 

[bikesandcars]

You wont see any real perfromace gains in changing reed materal, we use carbon, fiberglass, plastic.... ect. in boats engines. The benifit is when the engine injests the reed it does not distroy everyting as a metal reed would.

Where do you get your material? what thickness?