Camshaft lobe centres

Here is some info that might be helpful for those who are interested in fine tuning their bikes camshafts.

The common range of lobe center values for SUZUKI engines is only about 10 degrees wide from about 102 to 112 degrees, a change of one degree can have considerable effect on the power delivery characteristics of a SUZUKI engine.

The effect of moving lobe centers is that by advancing the intake and retarding the exhaust, known as CLOSING UP THE CENTERS, it will increase the valve overlap and will move the power UP in the RPM range, although it will at the sacrifice LOW- RPM power. The result would be LOWER numerical values on both intake and exhaust lobe centers.

If you retard the intake and advance the exhaust, known as SPREADING THE CENTERS, valve overlap will decrease and will result in a WIDER power band while sacrificing HI – RPM power. This is indicated by HIGHER numerical values on both intake and exhaust lobe centers.If you move only one cam the results are not as predictable, traditionaly it is the INTAKE CAM that is moved to change power characteristics since small changes here seem to have a greater effect.

Benefits From Increasing the Compression Ratio

Increasing the compression ratio is one component of many that will increase a SUZUKI GS / EFE’s HP. An increase in an engine’s compression ratio will provide more power for less fuel and add some snap when the throttle is opened.

Raising the compression ratio gives the greatest benefits with initial increases. This means that more HP is produced by the first point increase of the compression ratio as compared to the next point of increasing the compression ratio. To illustrate this lets use a stock 1985 (USA model) GS1150 (EFE) as an example. The stock compression ratio is 9:7.1 if you increase the compression ratio to 10:7.1 there might be a 4 or 5 percent increase in HP. Further increasing the compression ratio to 11:7 might only provide a 2 or 2.5 percent increase.

The reason for the a smaller percentage in the increase in HP with a further increase in the compression ratio is due to the aspect of the GS / EFE cylinder being like an lung, increasing its volumetric effiecieny basically means the lung is filling with more air and is breathing out more through the exhaust. It is not enough to just increase intake or exhaust. Both must be made more efficient.

GS / EFE 1150 stock cams open and close the engine’s valves with little or no overlap. This prevents emissions from escaping, but it also limits an engine’s breathing efficiency.

In conclusion a moderate increase in compression will use less fuel to produce more power and the extra cylinder pressure and heat generated will increase the gasoline’s burning efficiency. But if you really want to maximize the advantage of increasing a engines compression ratio this use of a Hi-performance camshaft is required.

Air density, a secret tuning factor

Air density is a computation mainly dependent on the temperature, barometric pressure, and the humidity of a volume of air.

Temperature in the USA is generally measured in degrees Fahrenheit, barometric pressure in inches of Mercury (inHg), and humidity in percent of Relative Humidity.

You can relate to how these factors effect the density of the atmosphere by using a balloon to simulate the earth’s atmosphere. When a balloon is filled with air and placed into a refrigerator it begins to shrink, this is due to the drop in temperature of the air inside the balloon. As the air cools it releases energy and slows down,because the air molecules are not bouncing off each other as much, they remain closer together and more of them will now fit in a smaller area. The opposite will occur if the balloon is heated.

The effect of humidity is a little more complicated. A change of humidity in the atmosphere is caused by a change in the amount of water vapor mixed in with the common gases already present in the air. As more water vapor is put into the air is displaces these gases. The water vapor is also less dense (weights less) than the gases in the air. When we take air that is at a set temperature and pressure and start introducing increased amounts of humidity we begin to cause the overall density of the air to decrease. Therefore, the density of the air is the greatest when there is no humidity.

Changes in temperature, pressure, and humidity can have different amounts of effect on the associated change in air density. A change in temperature or pressure causes a proportional change in density. In other words, a 1% change in temperature causes a 1% change in density. Again, the effect of humidity is more complicated, because the effect of humidity on density is also dependent on the temperature. A 50% increase of humidity when the air temperature is 70f degrees may cause a 1% decrease in total air density, but a 50% increase of humidify when the air temperature is 90f degrees may cause a 2% decrease in total air density. This effect is due to the fact that it takes lot more water to cause 50% relative humidity at a 90 degree temperature than it does at 70f degrees. The humidity must also be considered in that it makes up some of the density of the air, but it has no value being there.

The air in the earth’s atmosphere is made of various gases and water vapor. Neglecting the effect of pollution there normally is 20.9% of oxygen, 75% of Nitrogen, Carbon and very small amounts of some other gases. Oxygen is the most important gas in the atmosphere as far as an internal combustion engine is concerned. This is due to the fact that the oxygen is used to burn the fuel placed in the chambers of the engine. When more oxygen can be placed in the chamber it allows one to also place more fuel along with it and therefore create more power. The air density relates to this because when the air density increases the amount of the combined gases and water now fit into a smaller area, this includes oxygen. If the air is denser than there is more of it therefore more amount of oxygen will be taken into the engine.

The term commonly heard among racers is “density altitude”. Density altitude is the density expressed if feet instead of grams per cubic centimeter. It’s a lot easier to relate a change of density in a couple hundred feet rather than a change of 2.534 g/cm^3. The use of density altitude is taken from the U.S. standard atmosphere table. This table relates the density of an average day at sea level (59 degrees, 29.92 inHg) and how it changes at different elevations in the atmosphere. As one climbs in altitude the density falls off at a predetermined exponential rate.

In conclusion I highly recommend either an Air Density Gauge or a Altimeter as tools to be used for adjusting your Fuel Curve and Ignition Timing. I firmly believe that these items are essential for tuning at the Race Track

All you wanted to know about GSX tuning but were afraid to ask

Speedy Steve Racer was one of the original sites GSX engine tuning gurus. Steve produced a complete guide to GSX engine tuning and we will republish it here through the vault.

Here is Steve’s original introduction.

Steve racer

HELLO RACE M8’s,The objective of this thread is to create a information baseline for all of the OSS members who are currently or who are planning to race ‘AIRCOOLED SUZUKI’S’ in Santioned Motorcycle Racing Events throughout the world.

Currently we have a number of OSS Members who in the past or present have won racing Championships competing with their ‘Old Skool Suzuki’s’. The wealth of knowledge and experience from these individuals can help other OSS Members who have desire not only to WIN Races but Championships also.

Presently OSS Members have won National & World Championships
in ‘Road Racing’, ‘Sprinting’ and ‘Drag Racing’, and with the help and informational input from these successful racers there is no reason that in the near future when a competitor see’s an bike with an ‘OSS STICKER’ they will consider that Sticker as a “SECRET WEAPON”.

I am looking forward to your feedback in order for this Hardcore Race Thread to begin. So DnD, AT_, LUKE, PETE 750ET, H_ippy, Gary 1371, BBK and the rest of my OSS RACE M8’s and Members, let’s get this thread going.

CHEERS

SSR

I Shut Them Down, Then Shut Them UP