Re: Compression ratio .
Posted: Thu Dec 18, 2014 6:26 pm
I ALWAYS use water...
A mop out with some paper and a blast with the air-line
soon sorts out the wet. For the paranoid amongst us,
a quick squirt of WD40 would keep any rust at bay.
I also use a burette - I can't tell from the photos, but my
1/4" thick perspex sheet has TWO holes in it.
One to feed the water in, and the other to let the air out.
I normally chock the heads slightly to make the air rise
and escape from the vent hole, which I position right at
the edge of the chamber.
The benefit of water here is that the increased surface
tension prevents it from leaking out of the feed hole.
(And when you are doing this on your kitchen sink
draining-board, like I do, you don't make your house smell...)
The burette I use was bought in about 1979 and is
"Terry Clipped" to a backboard with a piece of 2"x1"
prepared timber up each side to protect it. It also
has a silicone hose, so it should last for ever.
DON'T FORGET TO FLICK THE AIR BUBBLES OUT OF THE
HOSE/TUBE BEFORE TAKING ANY MEASUREMENTS.
My 1480cc was originally put together with a 16cc head.
I needed the Omega "short deck height" pistons, which
I further shortened by another 60thou purely to reduce
the CR. Even with a largish capacity in the block, I ended
up with about 13:1.
With a 649, this would probably be acceptable, but with
an MD276 it was way too high. I now have about 11:1
and it runs so much better...
Conclusion:
The final deck height will be dependent on the CR that you
want and what the rest of the "unswept volume" adds up to.
A sensible CR will be determined by the cam that is used.
Ian
A mop out with some paper and a blast with the air-line
soon sorts out the wet. For the paranoid amongst us,
a quick squirt of WD40 would keep any rust at bay.
I also use a burette - I can't tell from the photos, but my
1/4" thick perspex sheet has TWO holes in it.
One to feed the water in, and the other to let the air out.
I normally chock the heads slightly to make the air rise
and escape from the vent hole, which I position right at
the edge of the chamber.
The benefit of water here is that the increased surface
tension prevents it from leaking out of the feed hole.
(And when you are doing this on your kitchen sink
draining-board, like I do, you don't make your house smell...)
The burette I use was bought in about 1979 and is
"Terry Clipped" to a backboard with a piece of 2"x1"
prepared timber up each side to protect it. It also
has a silicone hose, so it should last for ever.
DON'T FORGET TO FLICK THE AIR BUBBLES OUT OF THE
HOSE/TUBE BEFORE TAKING ANY MEASUREMENTS.
My 1480cc was originally put together with a 16cc head.
I needed the Omega "short deck height" pistons, which
I further shortened by another 60thou purely to reduce
the CR. Even with a largish capacity in the block, I ended
up with about 13:1.
With a 649, this would probably be acceptable, but with
an MD276 it was way too high. I now have about 11:1
and it runs so much better...
Conclusion:
The final deck height will be dependent on the CR that you
want and what the rest of the "unswept volume" adds up to.
A sensible CR will be determined by the cam that is used.
Ian