Chainsaw Dyno bring saws to there knees. Build from start to end with video

[chadihman]

How did you center the shafts on the box that the pump is in so it would run true?

Made one not good enough second one is the keeper. The sprocket shaft was made by a member on here that goes by bigwhiteash. A local machine shop helped me make the pivoting box that holds the pump. Lots of measuring and a mill was used. I'll try next time to make the shaft and housing by myself. I was thinking I could start with a 1 1/8" shaft and weld it in as good as possible. Then bolt the pump in and lock the 1 1/8" shaft in my four jaw lathe chuck. Adjust the jaws untill the pump shaft pointing toward the tail stock is nice and true then turn the 1 1/8" shaft down to 1" that should make it perfect.
It took me a good bit of time to get it all welded so everything is in alignment and square.

 

[wigglesworth]

Cool build man. 3.8hp seems really, really low for a 460....

 

[Moparmyway]

Made one not good enough second one is the keeper. The sprocket shaft was made by a member on here that goes by bigwhiteash. A local machine shop helped me make the pivoting box that holds the pump. Lots of measuring and a mill was used. I'll try next time to make the shaft and housing by myself. I was thinking I could start with a 1 1/8" shaft and weld it in as good as possible. Then bolt the pump in and lock the 1 1/8" shaft in my four jaw lathe chuck. Adjust the jaws untill the pump shaft pointing toward the tail stock is nice and true then turn the 1 1/8" shaft down to 1" that should make it perfect.
It took me a good bit of time to get it all welded so everything is in alignment and square.

Maybe next one, you use a single shaft, bolt it up and do all of the welding, then remove and cut the shaft and assemble it in pieces into the assembly.
Its easy to play Monday morning QB ..... your idea is brilliant and I might just try something like this in my downtime after the summer ....... stupid me will just be quiet now.
AWESOME setup !!

 

[chadihman]

Cool build man. 3.8hp seems really, really low for a 460....

Yeah I was not happy with 3.8 HP. I put my stock 461 on and it was right at 4 HP. I'm not sure why readings are so much lower than Stihls specs. Its very simple to see a change in HP with just removing the air filter so I think it will do well for testing mod gains. I just wish I could figure out why I'm reading low. Maybe the saws are tested without a bar and chain. I wish I could find other real world HP specs on saws.

 

[Rudolf73]

Yeah I was not happy with 3.8 HP. I put my stock 461 on and it was right at 4 HP. I'm not sure why readings are so much lower than Stihls specs. Its very simple to see a change in HP with just removing the air filter so I think it will do well for testing mod gains. I just wish I could figure out why I'm reading low. Maybe the saws are tested without a bar and chain. I wish I could find other real world HP specs on saws.

Have you had a look at this site Geprfte Motorsgen

For the 461 they got 4.4kW or 5.9hp @ 9750rpm and 5.0Nm @ 7500rpm


I assume the difference in your readings are due to pump inefficiencies, bearing friction, etc. The only sure fire way to measure these losses is to have your setup tested by a hydraulic specialist. They will measure the difference in pressure over the pump and measure flow, etc. And then you can calculate numbers on efficiency. Or you can guesstimate you efficiency by using the above information as a guide.

 

[ptjeep]

 

[ozflea]

Just maybe horsepower figures aint as important as everyboby thinks your dyno will show if regardless of the saw performance gains or loses at time of testing and give an indication of gains that can be achieved some mods will prove to be worthless if not detremental to the saws performance, then you can see which way to go stick with it and create your own graph or mod curve i would.

Bob.

 

[Hddnis]

I would guess that only 80% of the power the saw is making is getting to the scale, maybe even less, the rest being lost to friction in the whole setup.

This in no way negates the value of using it for testing modifications since those measurements are independant of the friction losses. The whole system could be tuned and tested to get actual hp measurements if needed.




Mr. HE

 

[parrisw]

Yeah I was not happy with 3.8 HP. I put my stock 461 on and it was right at 4 HP. I'm not sure why readings are so much lower than Stihls specs. Its very simple to see a change in HP with just removing the air filter so I think it will do well for testing mod gains. I just wish I could figure out why I'm reading low. Maybe the saws are tested without a bar and chain. I wish I could find other real world HP specs on saws.

You can account in at least at a minimum of 15% loss on your setup.

 

[PogoInTheWoods]

Have you had a look at this site Geprfte Motorsgen

For the 461 they got 4.4kW or 5.9hp @ 9750rpm and 5.0Nm @ 7500rpm


I assume the difference in your readings are due to pump inefficiencies, bearing friction, etc. The only sure fire way to measure these losses is to have your setup tested by a hydraulic specialist. They will measure the difference in pressure over the pump and measure flow, etc. And then you can calculate numbers on efficiency. Or you can guesstimate you efficiency by using the above information as a guide.

Great observation and supports the need for a baseline to establish more accurate absolute measurements. Until a calibration method is applied to the system, a simple "correction factor" based upon known saw specs could possibly be introduced into the system efficiency math for more realistic measurement results in the meantime.

Relative +/- modification gains can obviously still be determined since they are, well, relative on a percentage basis.

 

[Naked Arborist]

Losses here losses there who cares. The numbers can be adjusted if you like to see big HP# readings. This high pressure juice box is the ****. I like it a lot. I think some junk could be used and the price could be knocked down to two three hundred. That's a sweet deal anyway you slice it. 1,500 done or back yard bits for 250

Nice work!

 

[chadihman]

Its really hard to believe that I'm loosing 20% but maybe thats it. The bearings on the unit spin free and the chain feels as if it pushes just as easy as when pushed on a real bar. The pump drag should have no effect at all on the the loss because the pump rotates. The extra pump drag should be put to the scales.
Does anyone know how the saws are tested for hp. With or without a bar and chain. The bar and chain would make a big change.
Well if its 20% off so be it. I could care less if it has 1 or 100 hp. It looks like so far the air filter removal made a jump in power that was easily picked up. I'm happy that I can get a % in power gain or loss with mods. This dyno is all about before and after.

 

[parrisw]

Its really hard to believe that I'm loosing 20% but maybe thats it. The bearings on the unit spin free and the chain feels as if it pushes just as easy as when pushed on a real bar. The pump drag should have no effect at all on the the loss because the pump rotates. The extra pump drag should be put to the scales.
Does anyone know how the saws are tested for hp. With or without a bar and chain. The bar and chain would make a big change.
Well if its 20% off so be it. I could care less if it has 1 or 100 hp. It looks like so far the air filter removal made a jump in power that was easily picked up. I'm happy that I can get a % in power gain or loss with mods. This dyno is all about before and after.

Sounds good, in the end that's all that matters, is in knowing what kind of difference you made. You could just calibrate it to stock HP numbers and call it good.

 

[wigglesworth]

Put a known HP electric motor on it so you can compare the known to the readout. Should get you alot closer to the correct percentage of loss.

Just my .02....

 

[Big_Wood]

repped

 

[ttyR2]

Dyno's are only good for relative measurements. That's why quality high perf shops don't like to quote HP/torque figures because the same engine wouldn't read that on a different dyno.

 

[young]

Dyno's are only good for relative measurements. That's why quality high perf shops don't like to quote HP/torque figures because the same engine wouldn't read that on a different dyno.

right on, one dnyo jet to the next on cars have different figures. not to mention mustang dyno numbers.

baseline compared to end result and the percentage gain on the same dyno is all that matters.

 

[Yukon Stihl]

I know that the saw was not to lean because it had the four strokin still going on with no load. It probably made it a little more lean but not enough to hurt anything as I tend to tune em a little on the fat side now anyway. I'll get a video tommorow of the saw running with the air filtr on and off.

I was just stunned to see the results in front of me when the air filter was pulled off while the saw was held at 9000 rpms. I found that the highest readings for the 460 were at 9000 rpms. It seemed like the saw was still pulling hard at 8000 rpms but the gain on torque was not great enough to raise the Hp because the rpm went down. The torque will continue to rise as the saw is pulled down harder but torque and rpm make hp not torque alone.

Try a quick test and hook up some shop air from the compressor to the carb,like a mock turbo.Set a regulator for a few pounds,and increase i gradually and see what happens.
Thomas

 

[mad murdock]

Mega cool dyno rep sent. You could come up with some custom K&N filter adapters for different saws, and have booked numbers on %increase in performance. Chads performance customs! Nice work professor!!

 

[Justsaws]

Well done, well done indeed.