2 things that might help-
do your pistons come up flush to the deck? Even if they sit 0.5mm below at
tdc, that makes a huge difference in final combustion chamber volume.
use vaseline to seal the plate to the head. And you can use water- its lower
viscosity makes it easier and more accurate to measure.
hth,
Toby
-------------- Original message ----------------------
From: "Daniel Neuman" <neuman@radonc17.ucsf.edu>
> So remember like a month+ ago when I was asking about CC'ing my U-20 head
> and figuring out the compression ratio?
>
> Well I finally got to it this weekend. Seems like I had to replumb and redo
> our master bath first????
>
> I made the measurements and well. could someone please check if my numbers
> are at least in the ballpark.
>
> Here are the measurements needed for calculating CR.
>
>
>
> Combustion Chamber volume = 35.5 cc
>
> Bore = 3.460 "
>
> Stroke = 3.235"
>
> Deck Height = .025"
>
> Compressed Head Gasket Thickness = .04"
>
>
>
> If I plug these #'s into one of the many online CR calculators I get a CR of
> 11.95!!!
>
> That's a little high I think. Working the math I need a gasket of .175"
> compressed thickness to get a CR of 8.51.
>
> I know my head is probably thinner than it should be ~4.450" (I think that
> was not as easy of a measurement to make as I thought..)
>
>
>
> Do these numbers seem way wacky to y'all. I only have one decent digital
> caliper to try and get these measurements and I have to admit that my
> technique is not as repeatable as it should be.
>
> I got a big syringe and used it to fill the combustion chamber with veggie
> oil. I had a super hard time with the plastic over the dang head technique.
> I kept getting air trapped under it or the oil would leak out the sides so I
> gave up on it. I managed to get the head pretty darn level and fill it with
> the veggie oil all the way up till it was just about to spill out. That's
> how I got the 35.5cc number up above. Is that any kind of a reasonable way
> to do it?
|