Mufflers on engines with SPI? T

[frank mccune]

     My friend andI have “older”engines that we would like to use but they all have sub port induction that do not work well with mufflers!  There is large power loss of about 57%  using a muffler!  These are older ST engines that are a joy to use.

      Is there a way that we can meet the muffler requirement without having the huge power loss that a muffler would produce?

     Tia,

     Frank

[EddyR]

 Frank I am going to tell you a story that will answer your problem. Back in late 1970,s  I started to build ST /51 motors in 46 cases.  I had one in my first two Juno's and the one I flew at the 1988 Nats.  Big Art told me they were the most powerful ST46's he had ever seen. I did not tell him it was a .51 as I kept it a secret for many years.  One day I removed the tube muffler I had been using. It was a gutted Fox 35 Muffler and installed the stub I had been using on stock ST/46 motors. All the power went away. plane was hard to fly. The 51 in the 46 case had subport problems as the piston becomes uncovered on the left corner of the exhaust port at tdc. I fixed it in later 51,s .
  I sold a SV11 with ST/56 and tube muffler to friend. He had problems for two months and sold it to Eric V.  Eric and I put the original tube muffler on it and Eric flew that model for several years. The ST 51 and 56 share the same piston on early models and had subport problems.
   Frank Most older motors with this problem will run OK with tube mufflers. My 51 was critical to tube volume so you may need to try different ones to find the  correct one  for your motors.
Let us know how this works out for you.
 Here are my USA/1 showing the Fox 35 muffler I used on the 51 in the 46 case.  Also my first Juno with a 51 last flown by Jene Martine. Last my 1988 Nats 46case 51 powered Juno style plane went over 1500 flights on the 51. Still have motor.
Ed

[Doug Moisuk]

What specific engine are you wanting to use? Some super tigers work ok with mufflers.

[frank mccune]

     Hi Doug et al:

     Thanks for the replies.

      The engines in question are ST G 20-.23.  My friend has used the original ST muffler that was designed for that engine.  His engine was so weak, that it would not fly a Flite Streak ARF. My ST G20 .15D will fly the same Streak with ease the .23 has a bit more power than the Diesel.  Of course noise is not a problem with the Diesel.

     For some reason, the old ST engines have a bit of charm for their owners. 

     Be well,

     Frank

[EddyR]

 Frank     I use to use th .23 for class B FF and it was a screamer with 8/4 prop and a lot of nitro. Never tries one with muffler in CL.  The ST15 was also a hot FF motor back in the day.  ST/40,s had Subport and people would not use them for stunt. There were workarounds for that. Bill Werwage used them for a few years. Tigre made sleeves that were shaped to cover the skirt of the piston that was coming open for the .40 ,.51,.56 .   I asked them to make me  one for a .51 and they sent me some as it was already in stock. I have seen some late .56's with the newer liner. The problem with the overasquare ST motors is the piston skirt had to be relieved for clearance. They moved the wrist pin location to give the piston clearance at the bottom of the stroke to solve that problem. I am amazed at how these threads break loose the old brain cells and this all comes back to me.
Ed

[M Spencer]

Therees early & late 20/23s . Series II have ' crescent ' lower sleeve edge to exhaust . and NO SPI .

Intresting the 21-51s ! Eddie . take it that you dropped a V - 51 Piston in them . & gudgeon ? .

[EddyR]

  AIR.  I did build .51 in .46 cases. The only way to do it is to get cases that are not drilled and taped for the head. First ones I built I had to remove materiel from sleeve top to clear bolts.  That made the gasket area very small. Later I got cases that were not drilled.. I have seen a few of the conversions that the case has weld material around the head. Then redrilled and taped,rather crude.  One of the hardest parts was to get the 51 rod to fit. The 46 case has no room for a larger rod. 46 rod did not work.  It was more work than it was worth but it was a”I can do it thing” the last ones had to have custom heads. There is so much more to than just dropping 51 parts in bored out 46.
Ed

[M Spencer]

Cheers ! Glad to know that .

Just as well ive got a Como 51 or two . 
Sort of a slightly smaller P.D.P. ' V-60 ' ,
Bit heavier than a 21/46 tho . 


Seem to need 4 inch pitch , plenty of balls .