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Old 05-17-2013, 09:15 PM   #1
MainiaxMotorsports
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Compression Ratio Help

Hey team - i am the rally racer needs 2.3L / 2.5L swap help. Good news is we are almost built and the motor should go back in the buddy on Sunday / Monday. I broke a head bolt - yes, reused TTY bolts - paid the price, got new bolts - back to work on her tomorrow - but in my downtime was playing with Combustion Ratio this 2.5L Block/Piston/Crank motor will have with a 2.3L head.

Here is the thread

http://www.focusfanatics.com/forum/s...68#post4729168

Here is my Calculation - where did i mess up>? 11.03:1 seems possible




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Old 05-17-2013, 09:42 PM   #2
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Well, the decimal point is off for the displacement... If you move it over one digit that works out OK. (248 cc sounded a bit small)

That would give about a 56cc calc. chamber volume, sounds about right with the dished piston.

Real "Stroker" of an undersquare motor, with a 100mm stroke and only 89mm for the bore...

What was the volume of the 2.5 head??

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Old 05-17-2013, 10:00 PM   #3
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The problem at present is i have to use the 2.3L head - not the 2.5L from the donor - on account of the VCT. We are working on an VCT delete solution....but have a few races to run - so, put the 2.3L head on - which i actually think ups the compression - but at the cost of decreased flow - the head on the 2.5 is wide open vs. the 2.3L

Motor build should be done this weekend - so, shall see next week on a few shakedown roads we will take her out on.

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Old 05-17-2013, 10:32 PM   #4
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I was just wondering if you had a 2.5 chamber volume handy to compare compression ratio's - extra volume there would lower it a bit as you're guessing.

You might be surprised by the flow from the 2.3 head, folks who've tried to improve it from stock haven't found any gains there. Some have tried porting & polishing with no gain on the flow bench or dyno.

Good Luck on the shake down & rallies!
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