Engine Displacement

This one is for all of you younger Hot Rodders out there who have been looking for a simple article explaining Displacement, Bore and Stroke but only found Wikipedia and a bunch of forum threads. Some of these forum threads may actually be helpful but you're not sure if you should trust these forums, so you want a real article and not a wiki. So I decided to write this and help people like you out.

First thing is first lets, go over what engine displacement is, if you are into hot rodding you already know the names of several engines such as the Chevy 350, Ford 302, Chrysler 440, etc. Well the numbers are the cubic inches of engine displacement. What displacement is, it is the measure of how much fuel and air you can fit in your cylinders.

Now how you figure out engine displacement is by a simple calculation (oh no, not math!) Now how you figure out displacement is (3.14)/4 X bore (squared) X stroke X number of cylinders.

An example the Chrysler 3.18 LA

3.14/4 X 3.91^2 X 3.31X 8= 317.79ci (aka 318ci)

Now some of you maybe be wondering why use PI? Well because Cylinders are round and we are figuring out a volume, PI is used in volume so it is used to figure out engine displacement which is volume. As for those wondering why the 318 LA in the example, well because the SBC 350 is to common.

Now for those of you who are too lazy to use paper, there are plenty of online displacement calculators for your convince. The best one I have found is here at the csgnetwork, not only does it calculate displacement it shows you all of the bore, and stroke for all of the stock hot rod engines. That way when you bore it out, or do a custom stroker job, you can calculate it right there.

Now getting on to bore (yes your calculator will come in handy for this), watching or attending drag races you may have heard people say they something like this "I've got a 350 SBC, 30 over..." which is the most common. What the 30 over means (its actually written out.030) is that he bored out his cylinders by thirty thousands of an inch increasing his displacement which if he didn't stroke the engine it would bring it too 355.

Now you have probably heard of stroker motors, such as the 383, the 331, the 496, etc. What is a Stroker motor you may ask? Well first lets go over stroke.

What Stroke is the measurement of how far down a piston is from the Top Dead Center of the Cylinder to the bottom dead center of the Cylinder. As mentioned early the 3.18 has 3.31ci of stroke, that is 3.31 cubic inches from the Top Dead Center of the Cylinder to the Bottom dead Center of the Cylinder.

A Stroker motor is when you increase the engines stroke so the piston distance can increase and more fuel and air can get in the cylinder. To do this you will need to bigger crankshaft and longer connecting rods for your pistons.

Now I hope that helps you guys out. If you are planning one doing a bore or a stroke job please research it before you do it! Most engines have kits available for both so look into that as well. If there is any engine that you want me to do a tech article on I will do that.

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Electric Scooter Parts - Replacing a CDI Module

One of the most common of electric scooter parts in need of replacement, the CDI module is as essential to the scooter ignition system as the spark plug. Thought to be an invention of the brilliant Nikola Tesla, the Capacitor Discharge Ignition (CDI) is the standard system used on most of today's gas-powered motor scooters, as well as on many motorcycles, marine outboards and other small engines. A complete CDI module is made up of a transformer, the charging circuit, the rectifier, a capacitor, and the trigger circuit.

How the CDI Module Works
The transformer first raises the voltage to 400 to 600 volts. Moving along the charging circuit, the electric current charges the capacitor, with the rectifier preventing the capacitor from discharging before the ignition point. Receiving the triggering signal, the trigger circuit stops charging and allows the capacitor to discharge to the low inductance ignition coil. This increases the original 400-600 Volt capacitor discharge to as much as 40 kV at the secondary winding, jumping the spark plug gap, and igniting the gas/air mixture in the cylinder. The charging circuit is then reconnected and resumes charging the capacitor all over again.

AC or DC?
Most current scooters us an alternating current (AC) system; however the popular KYMCO scooter brand uses direct current (DC). As a result, electric scooter parts for KYMCO machines, including the CDI module, can sometimes be difficult to find.

Engine Size
It is always best to match the engine size to the CDI specifications. A CDI module made for a 50cc engine might work on a 100cc, 125cc, or 150cc engine, and some are designed to function over a range of engine sizes. Others however, will only work for a particular engine displacement. Always check the specifications to be sure of getting the correct scooter ignition parts.

2-stroke and 4-stroke Scooter Ignition
The 2-stroke and 4-stroke engines are completely different, and as a result, their engines' ignition timing is totally different as well. You cannot use a CDI made for a 2-stroker on a 4-stroke scooter. Conversely, you cannot use a 4-stroke scooter's CDI on a 2-stroke scooter.

Connectors
On many current CDIs, the connectors are integral to the unit's case, forming a plug that snaps directly on to the scooter's wiring harness. On other models, the connectors may be located on wires, allowing some leeway on exactly where the module is mounted. The skillful mechanic may shorten or lengthen these wires as necessary. The most common CDI connector style uses two plugs side by side; one 4-pin plug, and a 2-pin plug. These connectors may be square, rectangular, or simple spades.

Note: Photo illustrations of many CDI connectors can be seen at the website listed at the bottom of this article.

Unrestricted or Restricted?
An unrestricted (or racing) CDI provides the current no matter how high the engine RPMs go. As the CDI controls the spark plug, the plug will continue to fire at high RPM. For reasons that should be obvious, these CDI units are made for racing use, and are not very suitable for regular highway use. A restricted CDI module however, will stop firing once a pre-set engine RPM is attained. Without current reaching the spark plug, the engine RPMs slow to below the pre-set limit and only then will the CDI resume providing current to the plug.

When replacing a CDI module, or any other scooter ignition or electric scooter parts, it is always a good idea to reference your owner's manual. If the manual is lost or otherwise missing, many manufacturers and brands have downloadable manuals available on their websites.

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