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Home > Technical Articles
Polaris RMK 800 Twin Running Compression Data

SLP pipes improve flow and efficiency of combustion, therefore running compression is increased. The ideal performance combination is a balance of the pipe and head design for maximum effective horsepower.

Bar "A" shows the increase in pipe efficiency (the air flow dilivery ratio* and trapping efficiency**) of high performance SLP twin and singles compared to stock. The stock pipe is the least efficient, while the SLP twin pipes are the most efficient.

Bar "B" shows the sea level cranking compression as shown on a compression gauge. You will notice that the SLP head is 125 pounds of cranking compression while the stock head (2001 model only) is 150 pounds. Cranking compression will be the same with any ehaust system even though the running compression is higher with a more efficient pipe system.

Bar "C" shows the horsepower achieved in the different combinations. The horsepower is slightly better with the SLP head used in comination with the SLP single and twin pipes even though it is lower cranking compression than the stock head. This is because the SLP head was designed to burn the fuel/air mixture more efficiently which is preferred to relying on an increase in compression only to make more power.

Bar "D" shows the running compression of the various combinations. This graph also shows the acceptable fuel requirements. You will notice that even though the stock head does not make the highest horsepower in graph C, when used in conjunction with the SLP twin pipes it is out of the safe zone for use with pump fuel. This means that a race/premium fuel blend will have to be used wiht this combination at sea level. At higher elevations, air density is less and in turn compression is less. Therefore, the twin pipes work fine in conjunction with the stock high compression head on pump fuel above 6000 feet. The better combination would be the SLP head with the SLP twin pipes. Race fuel would not be required at low elevation and the combination produces slightly better horsepower.

SLP pipe are efficiently supercharging the exhaust which increases the running compression. Only so much pressure can be pumped into the engine for a given fuel octane*** before it goes into a detonation stage. An engine that has an efficient pipe does not need high compression ratio to run well either on the bottom end or the top end. SLP head designs are very efficient allowing maximum horsepower that will withstand today's variety of unleaded premium fuel. SLP heads and pipes have been designed ot oprimize horsepower without sacrificing reliability. If you have any further questions regarding this or any other technical subject, feel free to contact our technical service representative Jim Fairchild at slptech@slp.cc or at (208)524-3397

*Air Flow Delivery Ratio: This is the mass of fresh air actually delivered to the cylinder divided by the mass of fresh air that the cylinder could actually hold (higher number= more efficient cylinder filling).

**Trapping Efficiency: This is the amount of fresh air/fuel charge that remains inside the cylinder after the exhaust port is closed (higher number= higher horsepower and higher percentage of fresh air/fuel charge in the cylinder).

***Fuel Octane: This is the measure of a given fuel's resistance to detonation (higher number=higher resistance to detonation).
"Setting the World's Performance Standards"