[Shotimes] Re: Gasket Matching on the Intake

[David P]

Kurt,

    In port matching, while some values will hold true for any situation,
there are a lot that don't. It's extremely hard to weigh the factors, in
this case remove air restrictions vs. decreasing velocity. To really be able
to make an informed decision, you need to determine the exact effects of the
last 3" and calculate that against the increase in I.D. Runner shape and
direction also play a part. This can get really complicated, and sometimes
after making changes, a tuner finds no improvement, little improvement, or a
decrease in performance.

    This problem is worst when dealing with porting the head since the
intake turn-in and shape has a large effect on the final velocity and mixing
properties. This is less of a problem when dealing with matching the runner
to the head port. I know some use a formula that weighs the area of offset
vs. the increase in total area to determine whether or not porting will be
worthwhile, but I do not know it. If it's possible, a much better idea would
be to find someone that has performed this exact operation and dyno'd before
and after.

    If this is not possible, I can tell you that you can round the offset
edges with no ill effects. Rounding the edges no more than 1/2" into the
runner will decrease turbulence while affecting the volume for only a small
section. You don't want to make a circle off the edge. You actually want to
create a shape that is almost an "s". It should look like a hill that would
be good for sledding. One that you could slide down, that flattens out at
the bottom so that you can come to a stop by slowing down rather than by
hitting a wall. Same thing on the head port, except I'd limit my grinding of
the head port to 1/4" unless the ports were really long.




David P

95MTX



~
----- Original Message -----
From: "Kurt Metros" <kmetros@elkhart.net>
To: <TechSHO@topica.com>; "'shotimes'" <shotimes@autox.team.net>
Sent: Monday, February 10, 2003 06:15
Subject: Gasket Matching on the Intake


>
> A couple of years ago when I had my SHO apart for it's second 60K I
> ported out the leading end of the intake runners to match the gaskets
> between them and the butterflies.  When I was done, the opening was as
> large as the gasket and was tapered about 1.5" into the snakes, after
> which the went to their normal size.  I also opened the holes in the
> surge tanks to match the gaskets.
>
> At that time I didn't mess with the openings between the snakes and the
> heads.  This year, while it's apart, I am considering using a dremel to
> port out the intake runners to match them to the size of the intake to
> head gasket.  I am also willing to port out the heads to match these
> gaskets.  Until yesterday, I wasn't willing to do this, but now that I
> have the intake off and have looked at it more closely, I have a better
> idea of how people are doing this with the heads still on the car and am
> willing to try it out.
>
> In reading about porting on the web, a couple of things came up that
> cause me to question  whether or not this would be a good or bad thing
> to do to my intake and heads.  My main concern seems to be that of
> velocity.  Let's say the intake opening throughout the snake is 'x'
> (where x is some volume of air, or some unit of measurement with regards
> to the size of the opening) until 3" before the air hits the valves,
> then for the last 3" (the area I port out on the snakes and head) the
> volume becomes 'y' (some measurement slightly larger than x), will there
> be enough loss of air velocity in the last 3" due to the larger chamber
> size to cause a negative effect?
>
> I'm wondering if this mod shouldn't only be done on an extrude honed
> intake, where the size of the intake snakes are the same from the surge
> tanks all the way through to the heads, where the size isn't going from
> smaller to larger?
>
> Am I on the right track?  BTW, here's an excellent article I found on
> porting....
>
> http://www.sa-motorsports.com/portdiy/diyport.pdf
>
> Input appreciated.....
>
> Kurt
>
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