I recall a couple mentions on this board of the race saw builders (EHP and perhaps one other guy) saying that they can build engines with variable compression. I understand this from the aspect of having more tuning variables, but then the other side of my brain says "why not just build in the maximum compression desired for the fuel the saw will run on and leave it at that?" Any thoughts?
Variable compression
- Thread starter rmihalek
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ehp
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I donot think we meant that will build a saw with a head that can change it's compression as the higher it rev's like some race cars do , but we put heads on them to raise or lower the compression to what we want, the reason you donot want max. compression on some wood is the hardness and size that you are cutting, if you build a 3120 nitro saw to cut nothing bigger than 12 inch round you can run more compression in that saw compared to a 3120 nitro saw that is going to cut 20 wood, reason there is only so much fuel that a carb can pump, now your cut times are going to be alot faster in 12 inch 3 cuts compared to 20 inch 3 cuts, so with faster cutting times you can raise your compression to because you will be done before you run your carb out of fuel , in 3 cuts in 12 inch the saw will only be running just over 3 seconds once you take the coldstart off your times, so compared to 3 cuts in 20 inch whitepine which should be cut in 8.5 seconds of saw running time once cold start is taken off your times so you will need alot more running time so you can do this by less compression and lower your rpm's on your pipe plus you can use a smaller degree header on your pipe as well, the smaller degree header uses less fuel because it doesnot draw as hard as a bigger degree header on the transfers ports
So what you're saying Ed is that in smaller wood, you can run a hotter saw ( higher compression) because the cut times are faster? That seems totally the opposite of what I would think: bigger wood would need more horsepower and therefore higher compression. Why can't you just put a bigger carb onto a high compression saw so that you can get the fuel flow that you need for the high compression engine? Or, like Jamie said in that thread about his bike saw, slap on a fuel pump...
ehp
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That would be great but the rules out here will not let you do that, you have to use a carb from a chainsaw, not a bike, snowmobile,kart.
that sure would make the job alot easier if you could put any carb you wanted on your saw. Another thing I have seen that would be great to use is putting a small fuel tank up on your handle bar so your fuel supply is above the carb , this way your pump does not have to lift it up to the carb , but again you could only use it in some shows, they are getting pretty strict now on stuff like having all your covers on and in some places in stock appearing you are allowed 1 small hole in your covers so you can squirt fuel into your carb to prime it
that sure would make the job alot easier if you could put any carb you wanted on your saw. Another thing I have seen that would be great to use is putting a small fuel tank up on your handle bar so your fuel supply is above the carb , this way your pump does not have to lift it up to the carb , but again you could only use it in some shows, they are getting pretty strict now on stuff like having all your covers on and in some places in stock appearing you are allowed 1 small hole in your covers so you can squirt fuel into your carb to prime it
