[NSRCA-discussion] Engine tuning info

[Dave]

Dug up some old notes
..

 

Engine                          Exhaust    Intake                       


OS140RX

154

124


KB150

147

107


ST2300

150

116


Bully145

150

106


Webra160

142

107


Mintor140

140

120


Mintor170

150

110

 

If anyone has access to volumes of engine data generated by Clarence Lee,
crankcase timing for many of the above engines could probably be found.

 

In general –

- high exhaust port timing increase power and raises RPM of peak torque.

- high exhaust timing allows bigger power increases from a pipe.

- longer overlap allows more effect from the pipe (power, pipe jump,
midrange mixture, etc).

- given constant RPM and no other changes (compression, glow plug, etc),
lowering the exhaust timing will “want” the pipe shortened.

- lengthening the pipe (within a range) will increase torque, and lean the
midrange mixture.

 

And there is so much more to get the “perfect” tune on a 2C.

 

Most pattern timed engines will have a “window” (blowdown?) in which
exhaust, intake, and crankcase ports are all open – during that window, the
pipe can be very powerful as a negative pressure pulse from the pipe will
not only scavenge exhaust gases from the combustion chamber, but pull fresh
fuel/air mixture the length of the intake path.  I never documented
blowdown, but I think it was typically around 10 degrees.

 

Regards,


Dave Lockhart

DaveL322 at comcast.net

 

 

  _____  

From: nsrca-discussion-bounces at lists.nsrca.org
[mailto:nsrca-discussion-bounces at lists.nsrca.org] On Behalf Of John Pavlick
Sent: Thursday, November 06, 2008 9:06 PM
To: General pattern discussion
Subject: Re: [NSRCA-discussion] Engine tuning info

 

Karl,

 Thanks for the info. I never put a degree wheel on a model engine so this
is interesting to say the least. I'm surprised that model 4-strokes have no
overlap. Hmm. You'd think that something like the YS 170 could benefit from
that. I don't have as much tuning experience with 2-strokes as I do with
4-strokes (motorcycles). I'd like to do some experiments with model engines
now...

 

John Pavlick
http://www.idseng.com

 

 

----- Original Message ----- 

From: Karl G. <mailto:kgamueller at rogers.com>  Mueller 

To: jpavlick at idseng.com ; General pattern discussion
<mailto:nsrca-discussion at lists.nsrca.org>  

Sent: Thursday, November 06, 2008 7:19 PM

Subject: Re: [NSRCA-discussion] Engine tuning info

 

John,

 

Most of the 2C sport engines to be used with a muffler are timed

at about 145-148º exhaust down time.

On most of the .60 to 1.60 size, to get the benefit of the supercharging

effect from the pipe, I increase the exhaust downtime to 155-158º, without

changing the intake timing, except for some directional porting for better 

scavenging effect. This all will not decrease a reliable idle.

I believe that the pylon engines are ported to 170º exhaust down time and 

on those you are not looking for a reliable low idle. 

Never tried any work on 4 strokes. To get any benefit from a pipe on those

you would have to have overlapping valve timing, which none of our model

4 stroke engines have.

 

Regards,

 

Karl G. Mueller
kgamueller at rogers.com

----- Original Message ----- 

From: John Pavlick <mailto:jpavlick at idseng.com>  

To: nsrca-discussion at lists.nsrca.org 

Sent: Thursday, November 06, 2008 5:02 PM

Subject: [NSRCA-discussion] Engine tuning info

 


Has anyone taken the time to measure the port timing of various model
airplane 2C engines? Specifically the OS140 and 160? Also, if anyone has cam
profiles + index info for the YS 160 and 170 4C motors I'd be interested in
that as well.

 

John Pavlick


  _____  


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