Rev-Limiters!!!

[rahtreelimbs]

What do you think...............as I do............garbage????

 

[badcars2]

two way street

in their defense, i have had rev limiters save some very expensive motors of mine at the drag strip due to drive line failure or excessive wheelspin.. on a saw seems to me the carb will be the ultimate rev limiter, such as, this mixture, this maximum rpm. one thing i have noticed on larger motors. the stuttering type limiters , such as msd, are very hard on crank and valvetrain components. the action is very violent, killing every other cylinder, things slow down and must regain their speed several times a second. just my two bits.

 

[rupedoggy]

Ken Dunn and I, and some others also, checked several saws for maximum RPM while in the cut. These were race saws and good chain. Most were 9,500 to 11,000 while cutting. These saws would easily rev to 14k or more if leaned out, while unloaded. Rich I am not too good at math but if you will do the math to figure the energy available in a saw flywheel at 14k I think it would be a fairly large amount of foot pounds of energy. If that flywheel lets go, at that speed, someone will get hurt if a piece hits them. So having said all that, why not have a rev limiter that still lets the saw turn up in the wood, but limits it for free wheeling? I don't think 14,000 would be unreasonable. Check your saw while in the cut with a good load on it. You may be surprised. Mike

 

[rahtreelimbs]

Ken Dunn and I, and some others also, checked several saws for maximum RPM while in the cut. These were race saws and good chain. Most were 9,500 to 11,000 while cutting. These saws would easily rev to 14k or more if leaned out, while unloaded. Rich I am not too good at math but if you will do the math to figure the energy available in a saw flywheel at 14k I think it would be a fairly large amount of foot pounds of energy. If that flywheel lets go, at that speed, someone will get hurt if a piece hits them. So having said all that, why not have a rev limiter that still lets the saw turn up in the wood, but limits it for free wheeling? I don't think 14,000 would be unreasonable. Check your saw while in the cut with a good load on it. You may be surprised. Mike

Mike, good post!

While all the info that give has merit, I was basing all this on the fact that a rev-limiter makes proper adjustment of the saw more difficult.

 

[bwalker]

So having said all that, why not have a rev limiter that still lets the saw turn up in the wood, but limits it for free wheeling? I don't think 14,000 would be unreasonable.

A couple of points, Mike. First of all IMO the rev limited coil causes many saws to fail that other wise would not. It goes something like this. The saw comes from the factory on the lean side and is tagging the rev limiter. The ham fisted woodtick takes this as a lean condition and leans the saw out further to stop the "burbling". The saw then seizes due to being run too lean. The second scenario involves a model that achieves its best power at a no load rpm higher(leaner) than the coil will will allow(the 372 is like this). In effect you can not tune this engine via tach, which is the average joes best way to set a saw to the same point with any amount of repatition over variable operating conditions.

 

[Lawn Masters]

As has been said, rev limiters can cause problems, and prevent a saw from making peak power, which may be just above where the limiter kicks in at. and the tuning issue too.

Now, on a car, if it limits the max engine speed by mechanical means such as closing the throttle and slowing engine speed down, it can be a very good means to prevent an expensive repair.

 

[pinus]

They are not bad, but better was the construction where red LED or something like that will indicate the real application of speed limiting circuit.

 

[ross_scott]

I say stick em on gypo's tractor

 

[rmihalek]

Is the rev limiter a device on the coil that can be removed and/or bypassed with some additional wiring or does removing the rev limiter require a new coil?

If a way could be found to temporarily bypass the rev limiter to allow proper tuning, then once the tuning was done, the limiter could be switched back on.

 

[Lakeside53]

Is the rev limiter a device on the coil that can be removed and/or bypassed with some additional wiring or does removing the rev limiter require a new coil?

If a way could be found to temporarily bypass the rev limiter to allow proper tuning, then once the tuning was done, the limiter could be switched back on.

It's all built into the coil and not acccessible.

There is nothing wrong with a "rev limiter", so long as it's accurate and high enough to enable reasonable tuning. Tuning techniques such as peaking then turning back to a "burble" need to be changed as the result will be misleading at best, and just using a tach is wrong as the spark-skipping plays havoc with the readings. One big Stihl saw manual says "set with a tach to 11,500, (below the rev limit turn on) then turn the high screw 1/2 turn leaner (ignoring tach reading)". You still get the upper power, but won't run too lean.

 

[brent denny]

I agree with you 100% on this Rich. The rev limiter on my ps-5100s has me scared to death. From what everyone tells me, this saw has to be leaned out 1/4 to 1/2 turn after it hits the limiter. How do you know where the best position is? I keep checking power in the cut and plug color but not being able to use my tach or ear to tune it is a real PITA, IMO.