Expert: Dan Liddy - 10/24/2008

Question
on average how much pressure is exerted on the piston head in one cylinder by the explosion of the fuel mixture? To help I am currently interested in a 1.4 liter 4 cylinder engine but anything you can give me so long as you also supply the size of the engine would help a lot. many thanks!

Answer
Well, I tried using Google and saw that you had beaten me to it !

I have two suggestions for you from my background in racing. First call the Summit Racing tech line at 1-330-630-3030 and failing that, try contacting one of the racing piston manufacturers such as J&E in California, or BRC Performance in Longwood, Florida.  BRC's number is 1-800-522 7478 ,  Ask for Danny  ( there're a bunch of us aren't there !?)

I'd suggest that before you contact them you have in mind more specific information such as bore and stroke, fuel type (methanol, ethanol, gasoline, etc.), fuel quality, and compression ratio. Perhaps also a leak-down ratio. All these things control combustion pressure.

That last term is something racers know and others sometimes don't.  We measure the leakage (past the rings and valves) in an engine using a contraption called a leak down tester, which consists of two pressure guages with a check valve between them, and introduces air pressure into the cylinder while the piston is at top dead center on the compression stroke. A 95% leak down percentage is great news ! When it starts sliding down past about 85%, it's time to rebuild.

Good luck in your search, and I'd be interested in learning the results.

Thanks for a challenging question.

Dan Liddy
Sarasota, Florida