Cylinder Heads
What Do They Do?
The primary functions of the cylinder heads are simple. They top off the cylinders, sealing them so that the pistons under them can build compression, and they house the valves and their associated parts-on overhead-valve engines, these would include the valve springs and rocker arms-that enable each cylinder to breathe. They also compose the very top of each combustion chamber, and instead of being perfectly flat, often incorporate shapes to aid efficient combustion. Modifications to cylinder heads or adding a new set of aftermarket heads can unleash horsepower.
How To Get More Power:
Modifications to cylinder heads mostly deal with getting more flow of the fuel/air mixture through them. One way to do this is to "port" the heads. This means that the passages in the heads are enlarged and reshaped to provide improved flow. Most aftermarket heads come with bigger ports and passages. It's important to match these with the ports on your intake manifold. The result is a big increase in the ability to flow more air and fuel into, and spent gases out of, the engine. This makes for big horsepower gains. One thing to be careful of here, though, is that larger ports and runners tend to slow down the speed at which the mixture travels through them. This can detract from throttle response. For the kind of good, crisp throttle response needed by most trail rigs, you don't want runners and ports that are too large.
Tips For The Trail:
The major consideration when modifying a set of heads, or getting a new set of aftermarket heads, is to determine the rpm range in which they make their power. That way, you can select a set of heads, or figure out modifications to your stockers, based on where you want your power. A 40hp gain might sound great, but if it comes at 5,000 rpm, it's fairly useless on the trail.
Camshafts
What Do They Do?
For the overhead-valve systems typically found in our rigs, lobes on the camshaft push on the pushrods, and through them, the rocker arms, to open and close the valves located in a cylinder head. In overhead-cam engines, the cam lobes can still push against rocker arms, or they can directly actuate the valves.
How To Get More Power:
The proper camshaft choice is critical. A camshaft can also add more horsepower, and it can determine where in the rpm range that horsepower appears. The basic way it does this is through altered shapes of the cam lobes. Those altered lobes can hold the valves open a little longer-this is referred to as duration. With the valves held open a little longer, more fuel and air can make their way into and out of the cylinder. Also, the lobes can provide more lift, so more air and fuel can enter and exit the cylinder. As always, increased flow equals more power.
Tips For The Trail:
While a cam with a lot of lift and duration might sound great, these detract from idle quality. This might not be a concern if you run at a dragstrip, but if you are trying to creep along trails in low range, having an engine that barely idles is not the way to go. Another concern is that if you have a radical cam and a brake booster that relies on vacuum, braking performance can suffer because radical cams tend to produce less vacuum than milder cams do, thanks to all that lift and overlap. So when you choose an aftermarket cam for your engine, it's critically important that you select one that will place the horsepower and torque in the rpm range where you most need it.
Pistons And Rings
What Do They Do?
Pistons and rings have torturous jobs. The piston slides upward in the cylinder, compressing air and fuel as it progresses toward the apex of its stroke. Just before it reaches that apex, the spark fires and explodes the mixture at temperatures between 400 and 600 degrees Fahrenheit, driving the piston downward with great force. The ring gets the fun job of constantly being dragged along the cylinder wall. Its purpose is to seal the piston against the cylinder wall so that the combustion force can't leak past it into the engine's bottom end, while being lubricated by just a thin film of oil.
How To Get More Power:
The main way to get more power from a piston and ring is to install pistons that boost the compression ratio. Pistons with slightly different-shaped tops can produce higher compression ratios. This is desirable because the more you compress the fuel/air mixture, the more powerful the explosion is when it is ignited.
Tips For The Trail:
A higher compression ratio might sound like the hot ticket, but higher compression can also make an engine run slightly hotter; so care will have to be taken to properly cool the engine. Also, higher-compression engines can also require high-octane gas, which can suck the money right out of your wallet if you put lots of highway miles on your rig.