We are sometimes asked about cylinder firing pressures in S.I. gasoline engines. In the 60's and 70-s it was pretty common to see peak firing pressures of 600/650 p.s.i. in naturally aspirated engines.

Since the 80's many changes have occurred in passenger car engines. Computer controlled engines, turbocharged, supercharged, and fuel injection to name a few. All of these changes have resulted in more efficient engines. The result of a more efficient engine is higher peak cylinder firing pressures and higher engine temperatures.

It is common in today's engines to encounter cylinder pressures of 900/1000 p.s.i.

The above figures and statements should be considered general. Many other factors affect cylinder pressures such as fuel injection position, piston top design, valve over lap, etc.

Norman W. Pugh
Manager-Piston Ring Engineering
Hastings Manufacturing Company
7/95

(P91)