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Guest Message by DevFuse
 

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I need some old-school engine building expertise...


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33 replies to this topic

#26 Kostamojen

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Posted 17 April 2010 - 06:19 PM

Alright, I went back to the machine shop to discuss the piston. He basically said he doensn't think it will be an issue considering he doesn't think the CR will go that high. I told him i'd go do some maths and get back to him on that...

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:

http://www.csgnetwor...m/compcalc.html

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.


#27 Don_Quixpunch

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Posted 17 April 2010 - 07:36 PM

I don't think 10.5:1 is too high for premium pump gas. Sounds like you have more knowledge there than I have.

#28 Kostamojen

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Posted 17 April 2010 - 07:52 PM

The machine shop did say they could "dish out" the piston of CR ends up being too high.

#29 Kostamojen

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Posted 17 April 2010 - 08:51 PM

I just double checked something, realized I made a couple errors.

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:

Posted Image

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)

Posted Image

So I'm going to run some calculations again to see what I come up with...

#30 Kostamojen

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Posted 17 April 2010 - 08:53 PM

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.

I was taking pics and realized I didn't have any showing the intake/exhaust port flow of this head, so here you go:

Posted Image

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 Image

#31 True2Blue

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Posted 20 April 2010 - 10:27 AM

CLICK THIS

they can do anything Subaru engine. and will have answers for your many questions:grin:

Edited by True2Blue, 20 April 2010 - 11:52 PM.


#32 Kostamojen

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Posted 20 April 2010 - 08:36 PM

RAM is quite expensive, more expensive than my local machine shop that can do basically the same things (minus the fancy pullies and what not)

#33 ShawnW

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Posted 20 April 2010 - 09:46 PM

Can't wait to see a post saying its running. :)

#34 Kostamojen

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Posted 20 April 2010 - 10:02 PM

Can't wait to see a post saying its running. :)

Hey shawn!

Its probably going to be awhile...




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