crank case preasure #'s

[klickitatsacket]

This is a question for the guys in the know. What is the preasure #'s that are built up in the crank case for factory stihls, husqvarnas and others. I am setting up a flow bench right now and I was hoping some one here could save me a little time and a crank case. If I have to I will drill and tap a crank case and figure it out, but really do not want to ruin one if I do not have to. Thanks

 

[Lakeside53]

Just put a 1/8 barb T in the impulse line...

From memory you'll see about .4 bar plus and .2 to .3 minus. Depends on the saw though.

 

[bwalker]

Depending on what your doing meusuring the case volume might be a better bet.

 

[buck futter]

case volume

I have always wondered how crank case volume was accurately measured?

 

[klickitatsacket]

thanks Andy, I was not even thinking fo the impulse line. That will get me close. The reason I am needing to know is that the one side of the flow bench is built using gauges and the other will be with smoke. On the smoke side I need to have a pressure # to feed the smoke in through the transfer ports. I am finally getting the time to get this build this gritter. When it is complete I will post some pictures on here and show you guys what I am building.

 

[sugarbush]

thanks Andy, I was not even thinking fo the impulse line. That will get me close. The reason I am needing to know is that the one side of the flow bench is built using gauges and the other will be with smoke. On the smoke side I need to have a pressure # to feed the smoke in through the transfer ports. I am finally getting the time to get this build this gritter. When it is complete I will post some pictures on here and show you guys what I am building.

Never knew exact running pressure but was told by small engine instructors about 3 or 4 lb. will be interesting to know for sure. may be able to tap into pressure relief outlet and test several differant size saw's. will be watching for test results.

 

[timberwolf]

Your going to have a tough time measuring the pressure on a guage as it cycles from .7 atm to about 1.6 or -4 psi to +8 psi (stock) thousands of times a second. Stihl and Husk are are a bit different but roughly the same order of magnitude. Add a pipe and you may run from about -8 psi up to +12psi.

If your just flowing the air in a static condition I am not sure it will replicate the dynamic environment of 14k when you have a moving crank and all kinds of bouncing waves, temp and density variations ect.

For the case volume, take the head off piston down and fill it to the deck with 2 stroke oil measure the quantity as it is added, then you need to take into account space under the piston and in the transfers. All that space is used as base volume when the base is compressed on the down stroke.

 

[klickitatsacket]

timber, it may not be a perfect representation, but it will give a better diea of how things are moving off of the edges and in what directions. It's funny you mention "static". While I was researching this project; I did a lot of reading about Smokey Yunick and the machines he built. I have taken a few cues from him and one of the set up we are building is an engine turned by an electric motor for the bench. We will cut windows into the cylinder and crank case so that we can watch as the smoke is moving through the engine. We would also like to do this with the pressure side of the bench. However the problem is that the electronic gauges and software for doing this is so expensive that it is out of reach for a shop our size.

 

[Big Woody]

Your going to have a tough time measuring the pressure on a guage as it cycles from .7 atm to about 1.6 or -4 psi to +8 psi (stock) thousands of times a second. Stihl and Husk are are a bit different but roughly the same order of magnitude. Add a pipe and you may run from about -8 psi up to +12psi.

That was my initial thought but then I figured he had some way of using a pendulum to compensate for it.:rockn:

Maybe Dean has an ultra low inertia gauge in development.

 

[timberwolf]

If you run the engine with an electric motor, how are you keeping the bearings and contact surfaces lubricated? Might need some oil injection?

Going to use a syncronized stobe to capture the smoke movement?

Sounds like it might be a lot of work only to net data that may have little real world meaning.

 

[klickitatsacket]

If you run the engine with an electric motor, how are you keeping the bearings and contact surfaces lubricated? Might need some oil injection?

Going to use a syncronized stobe to capture the smoke movement?

Sounds like it might be a lot of work only to net data that may have little real world meaning.

The serfaces and bearings will be lubed ahead of time and the it will only run for short periods and far below full RPM. Yes an adjustable timed strobe is part of the design. It would not be practical with out it. As for a lot of work, yeah its a little but well worth it. Just using water to flow through the ports has been absolutely invaluable in the knowledge gained. I am sure that for most people this would be just over kill but for those who really want to understand what is going on in their engines this is well worth the time and effort.

 

[timberwolf]

True enough, if you realy want to understand how something works, your going to need to look at it very closely in its static and operational state.

Saws don't run water so running water trough them would be little help for moddeling air flow, maybe a more suited experiment for designing water pumps, there is no such thing as trial and error, just try and see.

Back in my classroom days I did try an experiment making a crude wind tunnel and testing some model airoplane wings. I found the smoke paterns very hard to see and nearly impossible to photograph, just too much turbulence and instability. However the simplistic air drag and lift measurments worked quite well and I got good marks on the project dispite the smoke thing being a bust. Just an example of how it can be tough to realy see what is going on with out a million dollar research lab, however the effects can still be measured with more simplistic methods.

Not sure how much difference there is between low RPM operation and High, I suspect the difference could be dramatic as wave action and resonation kicks in at full RPM.

Good luck with it, as always it will be interesting to see what you find.

 

[rmihalek]

dyno?

Hey Dean,

Have you considered building a dynomometer to measure engine output instead of a flowbench? Or, do you already have a dyno and just want to complement that with the flowbench?

 

[klickitatsacket]

I have had access to 2 differant water break kart dynos. So building my own has not been the biggest priority until recently. I am in the middle of building my own using hydraulics rather than a water break. I should have most of it put together in the next 2 weeks. There is a lot of information on the net when it comes to building a dyno or flow bench. Now, neither of these is going to be some 5 million dollar peice of equipment that will give the most accurate information. They will be very usefull though in seeing gains in percentages of HP and in flow. These 2 peices of equipment should help us to produce better designs. We are hoping to hit the racing hard next season and because of that we are really pushing hard. The hope is that what we learn racing will help us build more reliable and stronger saws.

 

[klickitatsacket]

Timber, I completely agree with what you are saying. I have been looking at this and studying it for almost a year now. the hope is to turn the motor at low RPM like say around the 200 RPM range (I won.t know until I try) to get an idea of how flow and turbulance is effected by the changing of port opening in motion. For the most part though we will be using the static bays for R&D. As mentioned before the one bay is gauged and the other is static smoke.

 

[Cut4fun]

Hey Dean,

Have you considered building a dynomometer to measure engine output instead of a flowbench? Or, do you already have a dyno and just want to complement that with the flowbench?

Not to derail your thread Dean, but thought rmihalek might like to see this dyno set up and what they charge.Madsens special tools, thought you might like to see this dyno, scroll down some to find.
http://www.madsens1.com/dyno.htm

 

[rmihalek]

Thanks Cut4Fun,

they have some nice tools at their shop.

 

[Dennis Cahoon]

The best and cheapest "dyno" around is the Oklahoma dyno....a block of wood! Try it.....you might learn more than you think. BTW....it can tell you what a chain is doing also. :monkey:

 

[ShoerFast]

The best and cheapest "dyno" around is the Oklahoma dyno....a block of wood! Try it.....you might learn more than you think. BTW....it can tell you what a chain is doing also. :monkey:

Dennis

Having read before that your not a huge fan of dyno's, most NHRA racers would also agree that ET's are the final test. And there is no argument for sucess.

But from a builder/ experimental stand-point, I would think that a good dyno would be of a lot of use making and documenting changes, as it would seem that for myself, it would take the chain and operator out of the picture.

There is a chance that throwing the word "good dyno" in there may be the catch.

 

[josgmctk]

presure vacume

the only way that I can think ok is to install a vac gauge and pres gauge is with a check valve to each guage. there is small check valves uesd in vac lines on car a c controls. after all a compression gauge would not work without a check valve. do not know how well they will work at 13,000 cycles per min.