Go Kart Performance
Engines Making More Power
Quick Talk By The Go Kart Guru...
Engines by their nature are pumps, glorified piston pumps and they inhale and exhale gas. In order to make a pump work better you need to increase its frictional capability (in other words decrease its amount of friction), decrease its rotating mass, and also increase its pumping efficiencies.
The pumping efficiencies basically are increased by making the valves bigger, and also increasing the stroke of the engine if you can do that.
Increasing the stroke is basically making the crank shaft have a longer a throw. Changing the throw of a crankshaft is radically changing the engine. You will have to decrease the height of the piston and change the connecting rod, and change the crank shaft to get that to happen. So it is not as economical.
The most economical thing would be to change the lift or the duration of the lift on the valves. And what that does is it increases the pumping efficiencies of the engine. What that means, is that lets them more air and left out the air quicker.
You can also increase the pumping efficiencies of the engine by putting a compressor on the outside called a super-charger, or turbo-charger which rams more air into the engine and allows the engine to breathe more air/fuel mixture. As result there is more power. Increasing the pumping efficiencies really, let's the engine have more air. Having more air means more air/fuel, and having more air/fuel means more power.
You can also increase the power of the engine by increasing the compression of the engine. Now it's more difficult to if you're using an overhead valve engine, because in an overhead valve engine the clearances of the valves and so forth and are situated around a spherical head or a wedge shaped combustion chamber. The clearances have been taken out and you can not start milling off material to increase compression very easily. Typically an overhead valve engine is more difficult to change, and the flat engines are easier to modify.
The things you can change in a flat had engine are the cam shaft ( to increase the lift, and duration of the valves) and the compression. You can increase the compression of the engine by milling off material off of the cylinder head. There is a limit of how much material you can mill off. I remember vaguely that it was fifteen thousands (.015 inches) or more. That was enough compression that you could feel. It would give you snappy combustion power.
Another way you can increase power is to increase the bore of the engine. Typically on a Briggs and Stratton and Tecumseh style motor, you will have to bring it into a machine shop to have the engine bored out.
Bolt on horsepower is his milling off the head or putting in a new cam shaft or mounting a super charger.
Other ways you can increase horsepower is too lighten things things up. You can put in a titanium connecting round which would help with the mass. This would reduce the mass, and you would also increase the strength of the rod so that you could get higher RPMS.
Now you have to be careful when you're dealing with higher RPMs because things will fly of part, and you can get hurt very badly if something blows apart.
What happens as one something stars whirring the amount of energy that the unit has is related to the square of the RPM. In fact the energy equation equals E=I*W^2. . So as the RPM increases, the energy increases by a parabolic relationship. In other words the energy stars to skyrocket as the RPM's increase. So you have to be careful when you're dealing with higher RPM's. Make sure that things are holding together. If it is not they can become a flying projectiles. That is why on racers they use Kevlar blankets to at least absorption the energy of the flying apart material.
So it would be a good idea if you are designing something that has potential of whirring parts in any manner that it has guards and that you are well protected from anything that would fly apart. Because it would penetrate through skin, and actually into your skull: it could kill you. Flying projectiles are nothing to play around with. That is a side note for safety on engines. Engines of our fun powerful and but they are dangerous.
I had mentioned super chargers. There are off the shelf super-chargers that you can buy. They're different styles. One style I had played with, is the centrifugal super charger, which basically is a fan (a glorified fan), and it develops about a .50 PS I. Which is enough to get to some good power band.
The roots style super charger, which basically is a special type compressor, actually has lobes which rub very close each other. They actually don't touch but they are at very close tolerances, and that is what makes them expensive They're like to two gears rubbing it in opposite directions. The way they work is that the gear that is enclosed by the housing traps air between the housing and the lobe (which looks like a gear) space. When the lobe rotates it moves the air out from the space and then meshes with the other lobe. The displacement by the other lobe force the air to be compressed into the engine.. You will get about 50% increase using a roots style super charger. For instance if you have a five horsepower motor you will get around to 2.5 horsepower increase a total of about 7.5 horsepower. Now say you had a 10 horsepower motor then you would get an increase to about fifteen horsepower. Depends on what size engine you are dealing with.
Horsepower really comes down to torque. What you are looking for is torque which translates into acceleration and how fast you are going to sprint to top speed. Torque is desirable to have, if you are trying to do sprints and you're trying to accelerate faster than normal. The other way to get more torque is to simply add a larger engine with more cubic inches.
The modifications I've been talking about actually consume more gas. The basic relation is the more horsepower power the more gas you're going to use. A bigger engine means more gas, and more horsepower.
Other modifications to your engine is to increase the velocity of the air going into the engine by the manifolds that go onto the engine. So the intake manifold could be increased in diameter, along with a larger carburetor that would allow the air to flow freerer, and in get more air/fuel into the engine. The other way to, obviously ,increase your horse power or flow of air out of the engine would be to decrease the amount of exhaust back pressure. So ideally you would have a larger free flowing exhaust coming out of the engine.
There actually is a system called resonance. What that means is, you can tune your engine so you can use sound waves to to suck air out of your engine. You can also use sound waves to compressed air into your engine as well. That is a science in and of itself, I do not all know all the ins and outs of it, but the bottom line there is a science behind it you can tune your engine so that the exhaust pipe itself actually sucks air out of your engine. It is kind of like an inverse super-charger. It sucks the air right out of the engine.
The way you can play around with resonance, if you are very interested in that, it is to put a tube on the engine. You can do some calculations, to start, and then you can increase and decrease the length of the pipe and play with the throttle and listen to the engine, actually start and noticed different resonance sounds at different pipe lengths, and you also noticed differences and horsepower. You basically will do an experimental analysis to get the correct length of pipe on your engine. Or you can buy and aftermarket resonance pipe from a go cart racing manufacture, for instance the Godzilla block. They sell different manifolds for intake and exhaust. They are blue printed and are quite expensive. And they also run alcohol.
The engines that I'm talking about you can run what you want to run in them, gasoline alcohol, not diesel because diesels burn too slow (but you can perhaps mix it, but that something that we can talk about in a different article, about mixing oil and the effects on combustion and power. You actually start to foul things out but actually get better combustion, because the oil burn slower and you get more torque at the lower our rpms).
To get more horsepower out of your engine racers actually use alcohol. Alcohol burns hotter. It has a higher thermal efficiency, but you also use more alcohol. If you are not careful you will melt parts in your engine.
Gasoline is the primary fuel that I'm talking about. It is most readily available and you can add anti knock additives to the the gas if you have a high compression head on the engine. You will notice as I have, the engine will start to smell detonation if you are running a high compression head or a supercharger. A good idea to get around detonation is to use premium gas, or an additive. Additives are catalysts that slow down the burning gas, so that it does not burned so fast, or knock during a high compression.
Other ways to make your engine have more power is to lighten up to fly wheel. Lightening up the flywheel increases the amount as response you get when you stomp on the gas. It also reduces the amount of wind-down time when you are lifting off the throttle.
Basically what we talked about are three different systems:
Stochiemetric or Chemical efficiencies,
And Mass efficiencies.
These really are the variables that you have to play with on an engine.
You can make your engine lighter, and that is really what we're talking about, for mass efficiency. So you can start lightening up the parts: you can have a lighter piston, alloy pistons, lighter connecting rods, and a streamlined crank shaft.
And finally on the crank shaft, you can streamline the lobes so that have knife edges so that one in slices through the oil, the velocity event is not so bad inside the engine, actually decreases the amount of rolling friction inside the engine.
There's other stuff you can do, but these are the main items.
So that is my rendition for introduction on increasing horsepower for your go cart engine.
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