srcarr52
We can't stop here, this is bat country.
It's peak HP is probably higher than 9100 RPM.
Chainsaw Dyno rework finally complete and ready for some mod testing.
- Thread starter chadihman
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It's peak HP is probably higher than 9100 RPM.
chadihman
Addicted to ArboristSite
I need a good reference on two stroke dyno tuning. Anybody have a good link? I'm impressed how well this o2 sensor picks up the smallest fuel change.
chadihman
Addicted to ArboristSite
I thought the same. At 9600 Rpms I lost a little HP. Its cool to watch the torque increase as the ROMs go down. HP is lost after going lower than 9000 because of the loss of rpms for the equation
srcarr52
We can't stop here, this is bat country.
Well that is uncorrected HP as well. So transpose that to sea level with standard temperature and humidity and it could be a lot different.
What is your gear ratio? You may be over spinning the pump and getting a lot of internal loss that is not accounted for.
bikesandcars
ArboristSite Operative
I'm not sure either of those matter too much unless you are tuning on a cold dry day then a summer day 6 months later (but in the same room). if you tune in the matter of a few minutes it doesn't matter because you are just after improvements.
Gear ratio shouldn't matter, it's the force on the torque-arm giving HP (not a back-calc from fluid flow/rpm). You increase drag until the saw reaches a desired rpm and record the torque off the arm. The internal loss only matters on how much you have to adjust the machine to give resistance (which isn't part of the equation).
chadihman
Addicted to ArboristSite
My ratio is 3.428:1 The ratio doesn't matter because my rpm sensor is at the pump shaft. Any drag on the pump is put into my torque reading. The only drag not accounted for comes from the bar, chain, oiler and the bearings on the 24 tooth sprocket shaft. The bearings are minimal. If the lower power comes from chain, bar and oiler I'm good cause that's real HP like the saw is run cutting wood.
bikesandcars
ArboristSite Operative
Are you able to get a torque / hp curve from this approach?
A descending torque curve after peak torque will give a flat HP curve as rpm rises, a steady torque curve will give a predictable rising HP curve.
The way to make an engine "flat" is to give it high torque at low rpm and then as rpm climbs (and torque decreases) the hp curve turns flat.
I guess what I"m saying is torque is the lead indicator, it doesn't increase because rpm goes down, it increases because that is the tune of the saw. If torque is flat and rpm are decreasing then hp goes down right?
chadihman
Addicted to ArboristSite
I think I get what your saying. My 460 has max HP around 9000 rpms. The torque continues to rise if I crank the flow valve tighter but the rpms are falling faster than the torque is increasing. Torque x rpm/ 5252 . Can't get HP without rpms or torque. I'll have to test the max torque its probably max at around 7 or 8 k
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bikesandcars
ArboristSite Operative
That's probably a whole study in itself for tuning a saw, not just the peak torque / rpm numbers, but what does the powerband look like? What does an ideal power band look like? how many rpm between peak torque and rpm? How do those old "torque monster" saws that people love look compared to a new high rpm pro-saw.
I've never seen a mnfr publish any torque / hp curves for comparison.
I generally consider the powerband of something to be between peak torque and peak hp....
I'd assume a saw with a wide power band (i.e. low peak torque rpm) would bog less, but have lower peak HP. After you're done with compression, breathing, and obvious mods, you can really only move the peak torque number around to increase HP... a saw with peak torque closer to peak rpm and a high rpm will naturally make great numbers, but not necessarilly be great in the wood... the minute you drop the rpm in a stiff cut it will fall below the torque curve and stall out.
I think this whole 2-stroke thing complicates it, you have a mechanical max rpm, a "breathing" max rpm (defined by ports and nature), wear and tear of higher rpm, and many factors to consider when tuning I guess. funny how 2-strokes are easier to manufacturer and maintain than 4-strokes but are so much harder to model!
srcarr52
We can't stop here, this is bat country.
It matters because the manufacturer is going to advertise corrected HP and what you measure is not corrected. So there is a large source of difference.
Gear ratio does matter because there are internal losses within the pump which do not show up in the reaction torque in the arm. For instance since it's a spur gear pump the reaction of the drag of the driven gear to the pump housing counteracts part of the drag of the drive gear. Also you have losses due to the compression on the fluid which just results in heat. If you push a hydraulic pump past it's recommended speed these internal losses start to go through the roof because of cavitation of the fluid.
chadihman
Addicted to ArboristSite
I'd be lying if I said it doesn't bother me that my #'s are off from manufactures spec
I'm happy that this dyno allows me to see the change in torque and HP at any rpm with mods made to the saw. This was a relatively cheap way to test saw gains. My torque curve now is my chicken scratch on a notepad. I run the saw at 500 rpm increments and record the #'s. I can even draw a fancy shmancy curve with those #'s if I really wanted to. I could have had a Cadillac but I settled for a Chevy and I'm OK with that.
I'm happy that this dyno allows me to see the change in torque and HP at any rpm with mods made to the saw. This was a relatively cheap way to test saw gains. My torque curve now is my chicken scratch on a notepad. I run the saw at 500 rpm increments and record the #'s. I can even draw a fancy shmancy curve with those #'s if I really wanted to. I could have had a Cadillac but I settled for a Chevy and I'm OK with that.
bikesandcars
ArboristSite Operative
It doesn't bother me, you're doing great work here, your methods are sound and manufacturers are always optimistic!
SkippyKtm
The Lorax, my FIL rip...
Great job on the dyno!
This piece of equipment should be mandatory for any saw builder. I know it would be expensive especially if you couldn't build one yourself, but its the best way to consistently check for gains after mods and be able to quantify a value on it.
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What numbers are you getting for AFR at the richest and leanest points you're comfortable setting it? Chances are the accuracy with a 2-stroke is going to be off, but if it's repeatable it will be a good tuning tool.
Dont worry about the manufacturer's numbers. Most are advertising pipe dreams or calculated hypothetical s.
chadihman
Addicted to ArboristSite
The # was holding pretty stable as the saw got hot. I noticed it jumped to 14.5 witch is to lean then the saw sputtered cause it was out of gas.
How rich will it go? You should see 10 or lower before it starts 4-stroking.
chadihman
Addicted to ArboristSite
I'm doing more testing tonight so I'll get to play with the o2 sensor more. I tuned the saw with a bar and chain and had it four stroking. I put it on the dyno and it ran smooth under loaf and I could hear it four stroking when it wasn't under load. I had a reading around 13.1. I then was reading that a two stoke is tuned best between 12.5 and 13.5 on cycles.
I was talking about richening it up until it 4-strokes under load, that would happen the 10:1 AFR range. A saw will be happy at 12.5 but 13.5 is too lean. My earlier point is to not assume the AFR numbers from the meter are accurate as it's not designed for the high O2 and high HC concentrations in 2-stroke exhaust.
