Mintor Review

[David Lockhart]

Jeff,

I think most of the guys involved with this thread probably agree with you.

I think it is worth noting that every exhaust system (save open stack) is
tuned to some degree at some RPM (actually multiple RPMs).  A good muffler
is one that is designed and constructed such that it does very little tuning
at any particular RPM.  Tuned pipes on the other hand are designed to
produce some amount of tuning at a particular RPM.

Traditionally, an engine that advertised having "pipe timed" porting had
very high exhaust port timing and the intended use of the pipe was to
increase maximum power (and the pipe design was oriented at maximum boost).
Increasing max power is only application of tuning the exhaust on a 2C - In
very general terms, 2C exhaust systems can be tuned to -
- increase scavenging of exhaust gases
- accelerate the incoming combustion mixture, and,
- "pack" a more dense charge in the combustion chamber just prior to
combustion (the more classical use).

The whole "art" of tuning a 2C exhaust system is a balance of muffler or
pipe design, tuning lengths, and the actual porting of the engine.

With regard to the modern large pattern 2C, I've extensively tested the
following engines - KB150, OS140 RX, OS 140 EFI, Bully/Webra 145, and Webra
160 on the following mufflers - Bolly 605N (essentially same as 590R), and
Graeber (sp?) muffler, and on the following pipes - Hatori 650 (60 size
pipe), Hatori 900 (same as OS140), Bolly EQ140R, MAC 1092, Webra 145, and
Asano 140.  And I've tested all of those exhaust systems at multiple lengths
on the ground and in the air and with a variety of props.  (yes, it is quite
a bit of data).

The Bolly 590R is an extremely good muffler that works well on a variety of
engines, at a variety of lengths, and with minimal effect on throttle
linearity and midrange mixture.   On some setups, it does make more power
when the header used is longer.  Compared to a well tuned pipe setup, it may
be down as much as 500 RPM on the ground at full throttle - qualifying how
much less power a given engine may make in the midrange is more difficult -
but that is noticeable too.  The apparent amount of torque in the midrange
in the air and the amount of unload are also different.  Practically, my
setups with the muffler turn the same RPM as a pipe, but with 1 or 2" less
pitch on the prop.

Dave

----- Original Message -----
From: jghughes
To: discussion at nsrca.org
Sent: Thursday, April 01, 2004 9:14 PM
Subject: Re: Mintor Review


I normally agree with you guys on 2 stroke tuning, but as we lengthen the
pipe to get a smoother transition, what is really happening is you are
bringing the "resonance" rpm down and giving up top end power. If you go to
Ed Hartley's two stroke page, You will see that there is not a lot of
difference in rpm between the muffled OS1.40's and the tuned pipe ones. I
agree that if you have an engine ported for a pipe and all's you care about
is top end, a pipe makes a huge difference. But we care more about
throttleability on these engines, so the HP is down. I'll loan one of you
guys my 590 and you can test back to back if you want.

----- Original Message -----
From: Dean Pappas
To: discussion at nsrca.org
Sent: Thursday, April 01, 2004 12:41 PM
Subject: RE: Mintor Review


Karl's right.
    Dean
-----Original Message-----
From: Karl G. Mueller [mailto:kgamueller at rogers.com]
Sent: Thursday, April 01, 2004 3:37 PM
To: discussion at nsrca.org
Subject: Re: Mintor Review


Steve,

With proper exhaust port timing and setup with a good pipe you will
loose that bet. My bet is that you will gain closer to 20% improvement
in power, of course with more power comes a higher fuel consumption
as well. Most engines are very conservatively ported in the exhaust
timing to run on a muffler as well as on a pipe. Just an other compromise
by the manufacturers.

Karl G. Mueller
kgamueller at rogers.com

----- Original Message -----
From: Patternrules at aol.com
To: discussion at nsrca.org
Sent: Thursday, April 01, 2004 9:49 AM
Subject: Re: Mintor Review


In a message dated 4/1/2004 9:28:50 AM US Eastern Standard Time,
d.pappas at kodeos.com writes:
Mintor 140 article, how does it run on a muffler as
opposed to a pipe. I would expect some loss in power
but also a loss in cost.
 I don't use pipes on any on mine engines Jeff Hughes and I have been using
the Bolly 590r which is a muffler, no tuning head aches, no midrange
problems, if you change props, fuel or anything else NON PROBLEMS, I have
been running the Mintor 140 with it and it runs super, don't know how much
less power you get from just running a muffler but I'd bet it's not over 5%,
I use Coolpower 15% fuel.


Steve Maxwell

=====================================
# To be removed from this list, go to http://www.nsrca.org/discussionA.htm
and follow the instructions.