Author Topic: Fiesta RS Turbo?????  (Read 7607 times)

Offline Tommo

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Re: Fiesta RS Turbo?????
« Reply #15 on: July 08, 2009, 05:23:32 pm »
What you're saying is that you've got more volume in the combustion chamber (correct) but the same swept volume (incorrect) this is impossible with a fixed length con-rod/crankshaft, You cannot gain in one area and remain constant in another.

Swept volume always remains the same unless you alter either the stroke or the bore. By swept volume I mean the cubic capacity of the engine, ie the CSA of the bore multiplied by the stroke. So yes you surely can gain in one area and remain constant in the other?

You appear to have neglected the combustion chamber volume increase in your calculations, in your second calculation your combustion chamber volume remains at 50,000mm3. But how can it remain the same if your con rod has changed length?

Offline Tommo

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Re: Fiesta RS Turbo?????
« Reply #16 on: July 08, 2009, 06:28:17 pm »
Your total chamber volume at BDC also increases, but this figure is not as sensative as the figure for the volume at TDC, the two figures both increase by the same amount.

A 2mm shorter conrod has the exact same effect on CR as skimming 2mm off the top of the piston crown would (assuming a flat top piston). Thats why dished pistons reduce compression ratio.

Offline Yoof

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Re: Fiesta RS Turbo?????
« Reply #17 on: July 08, 2009, 07:07:49 pm »
Yeah, fully agree  :) have removed the crap I previously posted  ;)
« Last Edit: July 08, 2009, 07:12:25 pm by Yoof »

Offline Tommo

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Re: Fiesta RS Turbo?????
« Reply #18 on: July 08, 2009, 07:31:22 pm »
No worries.