Peter Harris <peterjfharris@...>


I have added some pics in the photos section section heading OSKAR JABIRU
3300 (posted by Noosa Flying Club). The pics show some details of the Jab
3300 installation including the straight out exhaust tail pipes with NACA
mod. outlets as well as a modified intake plenum with a twin injector
throttle body for EFI (TBI) , an electronic ignition module and the tubular
fiberglass tail spring.

The access hatch for the oil filler is held by a magnetic latch.



From: Q-LIST@... [mailto:Q-LIST@...] On Behalf Of
Sent: Tuesday, 21 October 2008 7:56 AM
To: Q-LIST@...
Subject: RE: [SPAM]RE: [Q-LIST] Exhaust primary length-outlet tips

Could you send some pictures of your set-up?


From: Q-LIST@yahoogroups. <mailto:Q-LIST%40yahoogroups.com> com
[mailto:Q-LIST@yahoogroups. <mailto:Q-LIST%40yahoogroups.com> com] On Behalf
Peter Harris
Sent: Monday, October 20, 2008 4:37 PM
To: Q-LIST@yahoogroups. <mailto:Q-LIST%40yahoogroups.com> com
Subject: [SPAM]RE: [Q-LIST] Exhaust primary length-outlet tips


Thanks also for the clear insight in header design.

I have modified the two X 3 into1 header outlets on my Jab 3300 at the tips
by cutting NACA shaped outlets. I think this is reducing back pressure
because the shape causes an escalating progressive escape for the hot high
pressure gases inside the pipes and the effect is to soften the exhaust note
so it is deep but soft and no longer barking.

I am very happy with the sound effect but have no way to prove the benefit
in reduced back pressure.



From: Q-LIST@yahoogroups. <mailto:Q-LIST%40yahoogroups.com> com
[mailto:Q-LIST@yahoogroups. <mailto:Q-LIST%40yahoogroups.com> com
<mailto:Q-LIST%40yahoogroups.com> ] On Behalf
Sent: Tuesday, 21 October 2008 5:04 AM
To: Q-LIST@yahoogroups. <mailto:Q-LIST%40yahoogroups.com> com
Subject: [Q-LIST] Exhaust primary length

Hi Lynn,
I hope I can help you with your quest for understanding exhaust tuning
here, I don't know how much you have learned about it already but
hopefully I can add something to it.
Exhaust tuning is a function of controlling pressure back waves and
works in conjunction with value timing to augment exhaust travel and
maintain inertia, and additional power is gained from the extra
scavenging of the cylinder before refilling it. It is extremely
important on 2 strokes more than 4 strokes because of the way the
valving works, but the reasoning and functions are the same, it's all
about augmentation and scavenging. Tuning is a function also of
frequency (RPM) and pressure and or inertia, and for airplanes it
makes it much more easy to tune because we run a constant RPM most the
time and tuning can be done predictably because of it.

First the old aircraft engines we use are very rudimentary in design
(no fancy valve timing and over laps) just a low power reliable power
plant, most are in the .50 HP per C.I. area.
Second what have we changed in the design already (no muffler) less
back pressure.
Generally longer primary lengths give more torque and lower end power
which is what we want but in airplane weight is a cost and return
thing. In short this is a function of friction of how fast an engine
can breathe (VE). In all honesty the amount to be gained from tuning
on our engines is minimal and I think more is to be gained from
reduction of drag of the cooling and exiting air, then by adding more
weight from joining collectors. If one could afford to build titanium
exhaust to take the weight thing out of the picture along with the
additional heat in the cowl from the long runner lengths, it might be
more worth it. The 0-200's running at Reno races are tuning 4,500 rpm
and would benefit more from it then us putters. Also if someone would
start grinding great cams for these engines it would become much more
worth it, but we don't have that either... Retaining heat in the
exhaust is good to help augment and develop and maintain inertia.

OK so all that being said
Here's what my calculation say... Our 0-200 use 1.5" OD
Which would be 58" for header length using 2900 RPM, or 62" if using
2700 RPM
or 1.6" OD tube
Which would be 51" for header length using 2900 RPM, or 54" if using
2700 RPM. And this would give a little broader torque curve which
would be good for us and the 30" less total tube length is a good
thing If you want to just shorten the primary length than it's done
with the diameter, but this doesn't account for changes in HP it's
just not that easy because this throws off the inertia and
augmentation. I think torque would suffer to much if OD went over
1.75" If you can make it out of 321, 304, or similar SS to protect
from rust than wrap the pipes to keep the heat inside the pipe.

David Hiatt
Q-200 in

LJ French <LJFrench@...> wrote:

I am contemplating building a new set of exhaust pipes for my O-200
and thought I would try to build them as "tuned" as possible.
However, I don't know what it takes to do that. There is some brief
mention of tuned exhaust in the archives, but I can't find any
formulas or information that tells me how long each runner should be
or how long the collector should be.
Does anyone know where this kind of information can be had?

I plan to stay with the two into one configuration.

LJ French