Wednesday, May 25, 2011

Modification Ducati

Modification Ducati
The basic theory of engine performance is this: AIR + FUEL = POWER. To gain power, you need to ram more air into the engine, and also suck more air from the engine. This means you need to play with the stock air intake/filter and the exhaust. But, just increasing air flow won't increase power. In fact, it may actually
decrease power. This is because an engine needs to have a certain air-fuel ratio. The more air you throw into the engine, the LEANER the engine will run. A lean running engine is an inefficient engine. Well, it may be efficient on gas but it is not making its max power potential. It will run hotter, it will detonate, and it will not extract the max amount of power out of the fuel. This means that you need to increase the fuel flow if you increase the air flow. To increase the fuel flow, a jet kit can be installed (for carbureted engines) or a new "power chip" can be installed to re-map the fuel delivery settings (for fuel injected engines). But, this can only be done to a certain extent as well, because if you throw more fuel than air into the engine, it will run RICHER.
A rich running engine fouls the spark plugs, causes misfiring, and burns the mixture inefficiently. So, the key to any performance modification is to keep the air-fuel mixture balanced. BUT- there is one thing to keep in mind before starting any of this, and that is the fact that stock engines come from the factory very lean. This is done to meet emissions standards. The reason they are running lean is because the air-fuel ratio has been leaned out- either the computer fuel map is telling the engine to burn only a small amount of fuel, or the jets in the carburetors have a smaller orifice, thus limiting the fuel flow mechanically.

In order to start on an even playing field, it may be necessary to increase fuel flow just a bit. For example, on
carbureted engines, it is easy to simply back out the fuel mixture screws slightly and maybe change the needle
position. On computer controlled engines, it's not that easy. You will need to wait until you upgrade to some kind of exhaust before messing with the fuel, because I am not aware of any power chips that simply bump the fuel mixture up only slightly. They all bump it up a lot, because they assume that you are upgrading the exhaust and intake as well.

Slip-ons are probably the most widely considered performance mods for motorcycles. They are basically mufflers that are less restrictive than stock, and sound better to boot. They retain the stock exhaust pipe, so flow isn't greatly increased. When I say that, I don't mean that they flow the same as stock, it's just that the exhaust pipe is kept stock and thus is still a bottle neck in the flow equation. Just adding a slip-on won't necessarily increase power. You need to also increase air intake and fuel flow to maximize the efficiency of the slip on. In combination with a jet kit and filter, you may be looking at about 5-8 HP. Just a slip on may net 1-2 HP, but will also make the bike run leaner.

Full Systems
Full systems replace the entire stock exhaust with wider diameter pipe and mufflers for more flow. For example, going with 50mm pipes from the heads instead of 45mm pipes. Full systems, however, are very expensive. There is also another drawback to full systems, and that has to do with torque. Even if the fuel flow is tailored accordingly, the full system will increase HP, but will decrease torque (noticeable torque anyway). Why? Well, it has to do with backpressure- if an engine doesn't have enough backpressure, the torque curve is moved up in the RPM range. This means that you may still have 60lb.-ft. of torque, but instead of seeing it at 4,000 RPM, you won't see it until 6,000 RPM. Mainly for track bikes, full systems work marginally well on the street.


The term "coring" applies to the removal of baffles inside a muffler for increased flow. The increased flow leads to increased horsepower. Coring a muffler (IF DONE SCIENTIFICALLY) will yield better results than most, if not all, slip-ons because it is basically a slip-on with even more baffles removed. Coring is popular because it is cheap, and you can tailor the flow to your needs. Again, I point out that there is an art to coring, and to get the most flow and most horsepower it needs to be done by a pro. However, if you're a shade tree mechanic like myself interested in coring, peruse this article for more information. My mufflers are cored about halfway down (it is extremely hard to get inside a Monster muffler), and it sounds awesome. Performance (torque) may have dipped slightly, but high RPM pull seems very healthy. I have no dyno tests to prove it, but it feels awesome to me, and that's all that counts.

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