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I need some old-school engine building expertise...
Posted 17 April 2010 - 06:19 PM
So, I just did a "ghetto" CC measurement of the combustion chamber (using a syringe, some gatorade, a straight edge level and a toothpick).
The results were:
The combustion chamber is approx 30-33cc
Removing 2mm from the combustion chamber makes it approx 21-24cc
Using this compression calculator:
And the associated required information -
Bore x stroke - 85mm x 60mm
Gasket bore - 85mm (measured it)
Compressed headgasket thickness - 2mm
Piston dome volume... Zero I presume, but there is a little space around the edge of the piston, possibly worth a couple cc
Piston deck clearance - 0 (its flush with the deck)
The worst possible scenario i've come up with is a CR of 11.5:1
The best possible scenario i've come up with is a CR of under 10.0:1
An average of the two puts it in the mid-high 10's, 10.5:1 or so.
Posted 17 April 2010 - 07:36 PM
Posted 17 April 2010 - 07:52 PM
Posted 17 April 2010 - 08:51 PM
1) The EA63 1400 2-port head has a slightly LARGER compression chamber. That was the head I was using for CC measurements because its still assembled:
What that means is that the CR is probably higher than I calculated. Probably about 5% less CC is my guess.
2) The piston isn't completely flush with the deck, its about .5mm lower (checked with a straight edge and feeler gauge... not perfect but worked)
So I'm going to run some calculations again to see what I come up with...
Posted 17 April 2010 - 08:53 PM
I was taking pics and realized I didn't have any showing the intake/exhaust port flow of this head, so here you go:
The uneven port overlap will indeed hurt overall airflow, but just look at the flow path once it gets past there. IIRC, the EA81 head has 12 turns from intake gasket to exhaust gasket. Ideally, there would be less than five.
That makes for a total of THREE turns for the intake from the carb to the combustion chamber. The exhaust port is one turn, basically straight out the side.
Plus, I took pics of the gaskets for your amusement... The exhaust gasket could actually be matched a little better:
Posted 20 April 2010 - 08:36 PM
Posted 20 April 2010 - 10:02 PM
Can't wait to see a post saying its running.
Its probably going to be awhile...
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