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

[bikesandcars]

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?

 

[pioneerguy600]

Just add a few mothballs to each tank of fuel, that will get the job done without and grinding..LOL

 

[bootboy]

Port it. That's going to be the only reliable way. It basically allows everything to happen faster as I understand it. There's a lot of guys on here way more qualified to advise you on this subject. Honestly though, with that saw you get what you pay for and it's probably not worth the time/money/effort to port it unless you know what you're doing and do it yourself. You should have just bought a bigger saw.

 

[bikesandcars]

Port it. That's going to be the only reliable way. It basically allows everything to happen faster as I understand it. There's a lot of guys on here way more qualified to advise you on this subject. Honestly though, with that saw you get what you pay for and it's probably not worth the time/money/effort to port it unless you know what you're doing and do it yourself. You should have just bought a bigger saw.

Thanks I'm happy with the saw, it's in good shape, ruggedly built, really light, starts well, and perfect for what I want to do with it... Would I like something newer / nicer... of course..

But..

..since being on here has given me a case of CAD I'm just trying to learn a little about how to raise the rpm.. I tried searching this forum but couldn't find (at least through a title search) a link about how to raise the RPM of a saw... most of the threads relate to carb tuning, which isn't what I'm curious about.

I have all the porting tools like carbide burrs from auto work, so I figured someone who has more 2-smoke experience than me could help with a little guidance

 

[mountainlake]

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?

Raising the exhaust will give you more RPM at the expence of lower RPM torque, you'll end up with a narrow powerband like some smaller Husky saws. Steve

 

[z71mike]

You have to realize this is not an easy question to answer. 'Raising RPMs' isn't just 'apply grinder'. Everything from proper port work, to timing advance, to lightening the piston, cutting squish ring, milling a pop-up........

And I'm not sure about the cylinder on your saw, but on alot of saws, the transfer ports are too tight to fit a normal size Dremel head into. Most of the time, you really need the right micro-grinder to get the job done (which is expensive). I've spent countless hours following the porting guys on this forum, and it's not as easy as you'd think. And that's just the porting. Then you need to degree the flywheel, measure blowdown, duration, etc etc.

Not trying to talk you out of doing the job. I'm all for custom work in the home garage. Just pointing out that it's alot more involved than you'd think. Spend about 10-12 hours reading through porting and timing threads. Don't search 'increasing RPM', as that's not the main goal of a custom port job. No one will have titled their porting thread with that specific nomenclature.

 

[514mach1]

^ that's even if the carb is big enough that it's not the choke point. I have a Johnson 9.9hp outboard. The ONLY difference between it and the 15hp is the carb. Bigger carb lets it rev higher and make more power. So just porting may not gain you anything if the carb is undersized also.

 

[mt.stalker]

That's a small reed valve engine . It'll be very hard to pull more rpm's out of it . Not saying it can't be done though . If you raise the ex. , you'll lose compression and power . You might be able to widen the ports a tad , but you may not see any gains, unless you install better reed valves , or modify the reed block in such a way as to help them flow more air/fuel . It's easier to see rpm gains modding a piston port engine .
This poulan 2000 could still be a fun , learning experiance , if you mod it . WTF ? give it a try !!! Do a lot of research on here before you start . Maybe some of the wonderful engine guru's on here will help you out with their experiances/advice

 

[jropo]

You have to realize this is not an easy question to answer. 'Raising RPMs' isn't just 'apply grinder'. Everything from proper port work, to timing advance, to lightening the piston, cutting squish ring, milling a pop-up........

And I'm not sure about the cylinder on your saw, but on alot of saws, the transfer ports are too tight to fit a normal size Dremel head into. Most of the time, you really need the right micro-grinder to get the job done (which is expensive). I've spent countless hours following the porting guys on this forum, and it's not as easy as you'd think. And that's just the porting. Then you need to degree the flywheel, measure blowdown, duration, etc etc.

Not trying to talk you out of doing the job. I'm all for custom work in the home garage. Just pointing out that it's alot more involved than you'd think. Spend about 10-12 hours reading through porting and timing threads. Don't search 'increasing RPM', as that's not the main goal of a custom port job. No one will have titled their porting thread with that specific nomenclature.

You must read fast!

 

[z71mike]

You must read fast!

haha no, my eyes just start burning after looking at a computer screen for more than 20 minutes at a clip :msp_tongue:

 

[jropo]

haha no, my eyes just start burning after looking at a computer screen for more than 20 minutes at a clip :msp_tongue:

Yup, and scroll sickness.
Then when I'm done reading its all just jumbled numbers and stuff.

What is most important is what numbers works best for the saw. What them are.....:msp_confused:

It would be almost easier to start out on a 372 or a another popular saw. There is more info on them.

 

[struggle]

Did you put a carb kit in the saw? i have a DOlamr 5100 that would not respond well but would still run OK and after I put a carb kit in it would rev and respond like it should.

 

[blsnelling]

Add an extra exhaust port, size .357 Magnum

 

[jropo]

Add an extra exhaust port, size .357 Magnum

What he said...

 

[Freakingstang]

Add an extra exhaust port, size .357 Magnum

lmfao i much prefer a quality sized mod like a .45

 

[jropo]

lmfao i much prefer a quality sized mod like a .45

You guys are being conservative, most gains are to be had when you holster the hand guns, and break out the slug gun.

 

[514mach1]

I'm a fan of my 458 winnie. For shortish distances, it gets the job done nicely on just about anything, living or not. 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.

 

[heimannm]

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

Mark

 

[z71mike]

You guys are being conservative, most gains are to be had when you holster the hand guns, and break out the slug gun.

...with one of those old Brenneke's. ow, the pain.

 

[jropo]

...with one of those old Brenneke's. ow, the pain.

Yup, them be the one's that I use for muffler mods. 3in. Rottweilers. Nasty lil buggers.