REFLECTOR:Re: Reflector digest, Vol 1 #708 - 6 msgs

[dalexan48]

Hi all,

Long, long ago in my mis-spent youth, I built a set of Tri-Y headers for a
big block 396 Chevy that I shoe horned into a 63 truck. The Tri-Y were best
for midspeed torque that I wanted at 2800 rpm. The formula asked for cam
timing, port size, cylinder displacement, number of cylinders yada-yada...

The primary pipes, or the ones directly flanged to the exhaust port were 38"
of 1 3/4" pipe in pairs to a Y connector and then another 12" or so into the
4-into-one collector and onto the exhaust pipe. When finished, header was
over 50" long and the outlets to the exhaust pipe were located near the rear
transmission mount!

A 4 or 6 cylinder aircraft engine would more than likely be tuned for best
performance in its highest 25% of the rpm band and as such would more than
likely use a four-into-one or 6-into-2 arrangement. I'm only guessing here
as I haven't done the math, but I would think that a properly designed
system would be 36-40" of 2 to 2 1/4" pipe (takes a BIG pipe to exhaust 90
c.i.) into a collector and then onto some sort of muffler. If not a muffler
then another 3 feet or better of exhaust outlet would be needed. That's a
lot of pipe to stick into the engine compartment. Add your slip joints, make
out of a least stainless and you have the trappings of a grand work of art!
Stick in any MOMA and reap the benefits.

An old truism from racing days when I used to build expansion chambers for
two-strokes: A properly tuned exhaust system will either 1). force the
relocation of at least one major frame component, 2). drag on the ground, or
3). burn the rider. As one can see, there are a lot of conflicting
parameters that have to be dealt with in order to get a proper exhaust
system in a plane. Brien Seeley of CAFE has done a great deal of work in
this area, but I doubt that you could call his system anything other than
"optimized" (or compromised) to all existing variables.

http://www.cafefoundation.org/aprs/EPG%20PART%20IV.pdf

This is NOT to say that nothing can be done to improve a stock set of pipes,
but Brian and I have shown at least a little bit of what is needed for a
"tuned" exhaust.

Yours in blue skies,

Dale Alexander
173 RG Stealth Gullwing

> Message: 1
> From: "Brian Michalk" <michalk@awpi.com>
> To: <reflector@tvbf.org>
> Subject: RE: REFLECTOR:TUNE, STRAIGHT EXHAUST PIPES
> Date: Thu, 5 Feb 2004 10:22:26 -0600
> Reply-To: reflector@tvbf.org
>
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>
> Hmmm, 12 inch tuned pipes?
> From your description of a flange, I'm assuming they bolt directly to the
> cylinders?  I wouldn't attach them to anything either.  Safety cable is a
> good idea.
>
> Tuned to what?  High RPM engines are much better suited to exhaust tuning,
> and what it does is change the torque peak (mostly).  There are scavenging
> benefits involved, but a per-cylinder tube would have to be a bit longer
to
> take advantage of scavenging.  It's quite a science and art to make a well
> constructed scavenging exhaust system.  Something I wish I understood
> better, because (from what I've read) the theory doesn't always apply in
> practice.  You do your math to get in the ballpark, but the real world
> engine doesn't match your mathematical model.
>
> For us in the GA world where there are many combinations of compression
> ratios, camshaft timings, intake manifolds/carb/injectors and cylinder
> geometry even within the same engine line such as an IO360, a one size
fits
> all tuned exhaust system doesn't perform very well.  It's a lot easier to
do
> on a stock 350 Chevy (or whatever) because they are all alike, so it pays
> for someone to research the tuned system for that particular engine.
>
> Generally, a shorter tube gives more torque at a higher RPM.
> A longer tube give more torque at a lower RPM.
>
> After having gone through my own engineering mating a turbo to a Franklin
> (which still may not work), I might do it differently given a different
set
> of assumptions that running high power ops is only for takeoff and
> emergencies.  Everything else is below 85% power or some number.  If this
> were the case, I'd install high compression pistons with a good scavenging
> cam, electronic fuel injection/ignition with a reliable knock detector
> (ionic sensing).  I would have either a spare tank of toluene, or water.
In
> the presence of knock, either inject water or toluene -- both increasing
the
> octane rating of the fuel.
>
> The cool thing is that most of this is well within the normal homebuilders
> grasp.  The MSAVR is an open source/hardware engine control system, soon
to
> have ionic sensing.  By the way, ionic sensing is a method of measuring
> cylinder pressures using the spark plug as the sensor.  Lot's of patents
on
> ionic sensing, and most of it is being developed from that technology.
You
> have to build it yourself, but the soldering is not difficult.
>   -----Original Message-----
>   From: reflector-admin@tvbf.org [mailto:reflector-admin@tvbf.org]On
Behalf
> Of Tom Martino
>   Sent: Thursday, February 05, 2004 9:33 AM
>   To: reflector@www.tvbf.org
>   Subject: REFLECTOR:TUNE, STRAIGHT EXHAUST PIPES
>
>
>   I ordered and received six straight, 12-inch, tuned exhaust pipes -
> stainless, with a generous flange and a reinforced collar.  I have talked
to
> a few structural welders for ideas of brackets to tie them to the engine.
> Each one of them examined the installation and told me they wouldn't do
> anything.  They said I should just let them hang (with the exception of a
> safety cable on each, in case they broke away.
>
>
>
>   Their reasoning is this:  The exhaust tubes become part of the engine.
> They will move and vibrate with the engine and a 12" extension does not
hang
> down far enough to create a mechanical "disadvantage".  They say if I tie
> them to the engine, I could actually create a weak spot, causing it to
> stress at that point.
>
>
>
>   I am not a welder, nor have I had personal experience with straight
pipes
> hanging 12 inches off of an engine.  Can I get some feedback?
>
>
>
>   I plan on using a safety cable but should I go further?
>
>