Re: Compression Ratio's Yet Again

[Craig Overend]

David,         increasing the piston pin height (the distance from the piston pin centre to the top of the piston) will bring the piston closer to the cylinder head and therefore increase the compression ratio by reducing the area available for combustion. What you may be encountering is the way in which the program interprets "below deck". If a piston is below the block deck a negative measurement may need be input. for example a standard L18 piston sits 0.5mm below deck so you may need to enter -0.5. If you didn't get my last post get  http://www.ozdat.com/members/uploads/datsun_engine_calculator_v1.0.xls it includes block deck height, piston pin height with automatic calculation of piston to deck clearance or the option to manually set the piston to deck clearance if you don't know the block deck height rod length or stroke. Hope that helps, Craig. David Costello wrote: Guys I'm having trouble getting my brain around something to do with calculating compression ratio's. I know the formula I'm using is correct, I've tried using figures for motors I allready know the compression ratio of and it's been spot on every time. the thing that's got me stumped is if you increase the piston height value, the final compression ratio decreases.  I'm having trouble understanding how that works, shouldn't it increase compression since it's bringing the piston closer to deck? I've tried using 2 compression ratio calculators as well, and exactly the same thing happens. The compression ratio calculator doesn't have a "piston height" option, but it does have "piston below deck" field, and if you bring the piston closer to the deck then exactly the same thing happens....compression ratio DECREASES this has got me stumped :(maybe I should stop trying using mathematical formulae at ungodly hours of the morning :) hehe Dave --membersozdat------------------------------------------------------- OZDAT Mailing List Please Note:- Send (un)subscribe requests to [EMAIL PROTECTED] Send submissions to [EMAIL PROTECTED] No unauthorised redistribution of this email http://www.ozdat.com/ozdatonline/index.htm http://www.ozdat.com/ozdatonline/listindex.html http://www.mail-archive.com/membersozdat@datascribe.com.au/ --------------------------------------------------------------------- --membersozdat------------------------------------------------------- OZDAT Mailing List Please Note:- Send (un)subscribe requests to [EMAIL PROTECTED] Send submissions to [EMAIL PROTECTED] No unauthorised redistribution of this email http://www.ozdat.com/ozdatonline/index.htm http://www.ozdat.com/ozdatonline/listindex.html http://www.mail-archive.com/membersozdat@datascribe.com.au/ ---------------------------------------------------------------------