Connecting Rods And Crank
What Do They Do?
The connecting rods are the link between the piston and the crankshaft. The top of the rod, known as the small end, is attached to the piston, and the bottom, known as the big end, is attached to a lever arm, or throw, on the crankshaft. The size of that throw determines the crankshaft's stroke, which is one of the factors involved in measuring a cylinder's capacity (the other is the diameter of the cylinder bore). The crankshaft spins around in its bearings at the bottom of the block as the pistons transfer the force from combustion to it through the connecting rods. The crank's rotation then channels power and torque to the transmission. Obviously, a great deal of load and force is put on the crank.
How To Get More Power:
Crankshafts and connecting rods really don't provide more power. What they do provide is strength. The strongest crank and connecting rods you can afford should always be used in an engine that is going to see hard use. And here's another crankshaft-related item: A term that you might have heard is four-bolt main or two-bolt main. This is a characteristic of the lower end of the engine block. An engine with four-bolt mains has four bolts holding down each main-bearing cap on the crankshaft, compared to two-bolt mains, where just two bolts-one on each side-hold down each bearing cap. The four-bolt setup is much stronger than the two-bolt setup.
Tips For The Trail:
If you are going to be putting your engine under lots of load and high rpm, such as you'd see when dune running and mud running, you'll want to think in terms of a forged crank and rods, instead of cast items. Also, set them up in a block that uses four-bolt main bearings.
Headers
What Do They Do?
The header, or exhaust manifold, helps to evacuate the spent gases from the cylinder and then sends those gases out through the rest of the exhaust system. While a manifold's job is basic in function, big gains of power can be realized when tossing the stock cast manifolds and switching to an aftermarket set of good tubular headers.
How To Get More Power:
As we've seen with other parts we've considered, factory exhaust manifolds are built with cost being the primary concern. Other factors, such as noise, are also taken into consideration. Luckily, the aftermarket doesn't really have to abide by the same rules, and can make headers where the primary concern is to increase performance. So how does a set of headers make more power? Through their design, which is a science in itself, they do a better job of evacuating the gases out of the cylinder and getting rid of them more quickly. This increase in flow boosts horsepower.
Tips For The Trail:
Life on the trail is rough on a set of headers. Most of us have all overheated our engines at one time or the other. That heat can take its toll on a set of headers. That is why it is important to get a quality set of headers with a thick mounting flange to avoid warpage. Also look at the thickness of the material used to build the tubes as a thin-wall header can crack more easily.
Another consideration when selecting a set of headers involves, again, asking where you want your power. A Tri-Y style of header tends to increase torque at the bottom of the rpm band while a standard equal-length 4-into-1 header puts the power up a little higher. Also remember that smaller tubes tend to produce increases in torque, while larger ones favor increases in horsepower.
Finally, remember that an engine needs to be thought of as a system. So be sure, when you're building yours, that you select components that are aimed at achieving similar goals. You wouldn't, for instance, match a high-rpm cam with headers designed to produce low-rpm horsepower and torque. Now if women were only that easy to understand!