Nissan 370Z Forum - View Single Post - Ok, another basic question (engine related)

kannibul · 08-10-2009, 09:23 PM

Compression...relating to piston types - this is something I've never understood...so bear with me...

If you have piston/head combination that produces, say 9:1 compression - and you swap the pistons with some that claim 11:1 - all things being equal, shouldn't the compression really be the same? By that, I mean, if you calculate the volume of the cylinder + combustion chamber at BDC and TDC for the 9:1 compression pistons, and, calculate the cylinder + combustion chamber volume at BDC and TDC for the 11:1 pistons - the ratio should be the same...

The only way I can figure on the compression ratio increasing is if you increase the stroke of the piston, so that it has a higher BDC volume compared to the TDC volume...

Or am I missing something?

Thanks...

08-10-2009, 09:23 PM	#1 (permalink)
kannibul A True Z Fanatic Join Date: Jun 2009 Location: Jenks, OK Posts: 2,281 Drives: 370z Touring/Sport Rep Power: 267	Ok, another basic question (engine related) Compression...relating to piston types - this is something I've never understood...so bear with me... If you have piston/head combination that produces, say 9:1 compression - and you swap the pistons with some that claim 11:1 - all things being equal, shouldn't the compression really be the same? By that, I mean, if you calculate the volume of the cylinder + combustion chamber at BDC and TDC for the 9:1 compression pistons, and, calculate the cylinder + combustion chamber volume at BDC and TDC for the 11:1 pistons - the ratio should be the same... The only way I can figure on the compression ratio increasing is if you increase the stroke of the piston, so that it has a higher BDC volume compared to the TDC volume... Or am I missing something? Thanks...