what it means.

Please forgive these very basic questions. I did search this forum and was unable to find answers.

What is the compression ratio on a stock MCS and what do the numbers mean? How does an increase or decrease in the ratios affect whp and to what extent? Does a 20% increase in the ratio numbers equat to a 20% increase in whp?

Thanks

Bob

 

http://www.csgnetwork.com/compcalc.html

http://e30m3performance.com/myths/mo...comp_ratio.htm

 

I believe the compression ratio on a stock MCS is 8.33 to 1. Basically what this is is a measurement of the change in volume from when the piston is at the bottom of the cylinder to when the piston is at the top of the cylinder - there is 8.33 times the volume when the piston is at the bottom than there is when it is at the top.

A 20% increase in compression ratio does not translate into a 20% increase in horsepower.

Compression ratio is one of the variables in engine design. A lot of variables go into deciding what the ratio will be. For instance, the higher the compression ratio the more prone to predetonation the engine will be - but also the higher the compression ratio the closer the engine will be to the theoretical limit of performance. A higher compression engine also requires a stronger engine block, pistons, rods, etc. than a lower compression engine.

In addition, higher compression ratio engines require premium fuel, though a to some extent that is also a matter of the engine control computer and whether the engine is tuned for maximum performance or not.

It's not terribly difficult from a mechanical perspective to change the compression ratio of an engine - it can be done with different pistons and/or connecting rods and/or by machining down the top of the engine block slightly. It's not something that one should take on casually, however.

Experienced engine tuners can increase the compression ratio when modifying the engine and achieve increased horsepower & torque without sacrificing reliability, but in general lower compression engines are more reliable in the long term. Lower compression engines are also generally lower powerered on a pound by pound basis - it's all part of the tradeoff in engine design.

/gary mc

 

Thank you both. I now have a lot more information and reading than I had.

Bob