In a message dated 6/26/2005 7:00:56 PM Eastern Daylight Time,
lendich@optusnet.com.au writes:
Kelly,
Ah so! I wasn't aware of that one and was hoping
Lynn would make some comment.
Everything affects everything. Unless there is a need to
operate the engine well above 9,000 RPM, there is no need to modify the exhaust
port to any great extent.
Later closing the exhaust port (Port cut taller) extends the
open time and increases overlap with the intake ports. This is quite helpfull at
very high RPM. The same for early opening of the port. (Cuting it lower) there
is little to be lost here at high RPM. The available work left in the charge has
been reduced to near zero, and the late opening is to help sound by allowing
more complete expansion before the charge is released. Radiusing the opening lip
of the port gets flow started along a smooth curve where much of the flow stays
along the bottom of the runner. There is some interest in removing the exhaust
flow completely before uncovering the intakes. Adding the radius along the
opening line and up the sides of the port does that.
Other than removing tooling marks and smoothing the top of the
port there is not much to do. You don't want flow from the top of the port in
either direction. So leave the top as per factory. I would reduce the
chrome and iron around the port in all directions just s few thousandths
to avoid any possibility of snagging an apex seal. Just a 16th of an inch or so
is fine.
If a chunk of anything goes through the port you can stand a
burr being stood up or a scratch along the edge of the port. In the stock
situation this would be seen by the next apex seal. If the surface next to
the "hole" has been reduced slightly you may survive that gremlin without any
drama at all.
If you want more exhaust flow, you can go wider and not change
port timing at all.
The engine suffers from exhaust dilution of the intake charge
well into the RPM range. Adding a big radius to the top of the port opening
would raise the RPM where dilution more or less stops. So I see no point in
changing it much.
Lynn E. Hanover
Yes your right the top edge of the exhaust port
is correct.
I had spoken to Lynn in the past on the bottom
edge ( leading edge) but not the top edge - I didn't know he suggested to
slightly radius that edge - if he did I can't remember.
If we are singing from the same sheet of music -
radiusing the top edge, does increase exhaust flow
characteristics. See attached drawing.
Jump inhere if you wish Lynn!
George ( down under)
George and All,
I do not follow
!! I am familar with Lynn's suggestion to add slightly more
radius to what I call the top edge of the exhaust port.........Are you
suggesting
additional work to this edge ?? Perhaps a
simple drawing would help my simple
mind visualize what you are suggesting !!
--
Kelly Troyer
Dyke
Delta/13B/RD1C/EC2