[Shotimes] Gasket Matching on the Intake

[Bruce Malachuk]

I'm just about to undertake my gasket matching and cleanup of the runners
and head. I'm just getting the final parts I need for my dremel to do what I
want to do. I only plan to gasket match the heads and the ends of the
runners, and if I can get up inside the long runners I will clean up any
casting flash that I can get to with my dremel and/or sandpapers of varying
degrees. From everything I've been reading on the subject there is truth in
that porting without a flowbench or without having enough experience can
lead to a los of power specifically because of lost velocity. other than the
gasket matching I don't believe I will do any enlarging to the upper part of
the heads or valves area. I would think that Yamaha designed this area the
way it is based on gettin air supplied from intake matching the heads. I
don't believe that tapering out the long runners and not being able to get
to the middle would have much if any effect of losing HP or velocity. As the
air passes each of the bends the air on the inner radius of the bend moved
faster than on the outer because of the extra distance it has to travel.
Thats kinda why I think the long runners start straight from the tanks, then
go up, then curve down to make the straight shot into the heads where it
then looks like the air is directed towards the injector. It's kinda like
the long runners bends are "tuned" so that the air should be moving about
the same speed as it makes it's last shot into the heads. By gasket matching
and tapering it out a little on the straight shot all we are doing is
reducing the resistance in the airflow path. Making the engine breath
easier, but not giving it more to breath in reality. Thats what the short
runners are for.

Now on the short runners I do plan to open them up to the size of the gasket
the whole way that I can. But again I won't be porting the head to increase
volume of air in the chamber before the cylinder. Just smoothing out the
airflow restrictions. I won't even polish the upper parts of teh heads cause
the slight roughness induces a bit of turbulence to help mix the fuel and
air more so than just an injector would do if spraying into a smooth channel
of air. I've already talked to a machine shop here locally about boring out
my secondaries to a specific size, and the price with new plates
(butterflies) is very very reasonable. Just from staring at my spare intake
I have here, I'm sure that I can very easily duplicate what EH would do on
the short runners. And if I really wanted to spend a long time with
sandpaper on a stick, and possibly a mushroom shaped small polishing bonnet
with some aggressive grit material I could prolly come close to the EH
results on my long runners as well. I also think that a posible change to
the horns on the secondaries might help bump up the velocity that is lost
via the enlarging the runners.

All it seems that gasket matching, polishing and some porting takes, is a
basic understanding of how air flows under a vaccum. And how to not interfer
with how it flows, just remove the restrictions. Once you start to increase
volume and what not then you run into tuning issues. I just can't wait till
I can get a little JB weld and a spare set of heads to try velocity porting
the final run past the valves into the combustion chamber. Mmmm that and
some higher lift cams might be interesting.

If anyone finds any good places for bits that can be used in a dremel for
decent prices, cause I have 2 intakes to do, so I figure I'm gonna uese a
few bits up.

Bruce
94 Opal Frost MTX
----- Original Message -----
From: "Kurt M" <kmetros@elkhart.net>
To: <TechSHO@topica.com>; "'shotimes'" <shotimes@autox.team.net>
Sent: Monday, February 10, 2003 6:15 AM
Subject: [Shotimes] 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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