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    A good sports boat is a quiet boat - so fit an effective silencer. The aero  type silencer is not good enough! A second silencer needs to be fitted or  the  aero  silencer swapped for a manifold and a long straight  silencer.  I've found  'P&R' or  'Peace  Plus Power' and SoMoSo silencers to be very  effective (are they still around?).  Steel,  copper  or  brass  manifold are  much  stronger  than  aluminium  ones  and you can make your own without too  much  difficulty.  Silencers and manifolds should be joined together with large bore silicon  tubing  and the manifold to engine joint sealed with a small dab of clear  silicon  sealant or caulk.   (Silicon  sealant is sold in DIY shops as  bath  edge  sealant).  Clean all surfaces thoroughly with wet-&-dry sandpaper then  a  solvent  before  using the silicon.  Be careful not to over  tighten  the  manifold  screws  as  it is very difficult to remove a  snapped  bolt  or  repair a striped thread. Silencers need to be drained of "gunk" from time  to  time  by  standing  the boat on its transom overnight  with  a  small  container under the exhaust pipe outlet.

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    A tuned pipe can be used instead of a silencer, and it can  significantly  improve  an  engines performance.  Tuned pipes are funny things but  have  been  covered in a couple of model engine books but the best  information  I've  read  on them dates back to the January 79 edition of  MODEL  BOATS  written by John Goodyear, (below are a few links to other web sites on tuned pipes)

    There  are a few different types of tuned pipes silenced,    un-silenced,   water cooled,  mini pipes,  etc.   Some pipes are quieter than others and  the  MPBA  have a strict noise limit for any boat of 80db,  so make  sure  you're  boat within the law.  Tuned pipes will give a power boost over  a  range of revs depending on the size and shape of the pipe, each pipe fits  a  certain size engine.  A pipe with a sharp centre section give a  large  boost  over a small range of revs  compared to a pipe which bulges  providing a slightly lower boost but over a wider range of revs.
Pipe (1)  might  be  used  to provide a very high top speed and referred  to  as  a  'peaky' pipe.
Pipe (2) may have a wider power band & may give better acceleration but less top end.

Pipe 1 - "Peaky"


Pipe 2 - Wider power band


    The  important  factor to setting up a tuned pipe is the length from  the  widest centre section of the pipe to the centre of the engine. There is a  long  winded  scientific  calculation that can be made to  work  out  the  correct length but most boaters use a second method.  Start with the pipe  and  manifold at it's longest length and cut bits off until a  noticeable  increase in speed can be seen and the pipe comes "on song".     'On song'  means "it sounds right!" It's a little hard to explain but an experienced  boater  will  tell you what to listen for and what the changing pitch  reveals. The sound of a tuned pipe 'on song' reminds me of the  exhaust  "pinging"  of those  Lambretta scooters  that used to be around in  the  sixties....  if  that's  any help!! A pipe "on song" does sound good though.....  

If  possible make the  pipe  to  manifold  joint telescopic as in the drawing above.  The pipe can be adjusted a  couple of millimetres at a time,  in and out and this  will  prevent burnt  out silicon tube and cutting the tuned pipe too  short.

    A  good  test to check your tuned pipe is to run the boat flat out  in  a   straight   line  then turn it sharply at 90o to the right and see if  the  boat  looses  speed. If "on song" it should lose very little speed and pick  up  very quickly.  Adjust the needle setting,  pipe and prop  combination  until sharp turns can be taken with minimal loss of speed.

     I  personally don't like to see tuned pipes sticking out of sports  boats  as they are not very "scale".  If you boat is quite large then a pipe may  be  hidden  inside  the hull,  some boaters accept it  sticking  out  the  transom  just a little.  The Americans have a number of specialist  pipes  for outboard engines that are made into a 'U' shape which can wrap around  the engine so making it easier to hide below decks.  The Europeans have a  number  of  short tuned pipes for 3.5cc cars which should fit in all  but  the  smallest boats.  Also worth investigating are "Magic Mufflers"  from  Australia and the British Irvine mini power pipes. The Irvine power pipes  need  no  setting  up at all as they come in  one  piece,  complete  with  manifold.  Great  care  needs  to be taken when mounting these  pipes  as  resonant  vibrations tend to fracture the manifold section if the pipe if  it  is  not  secured  down in at least two  places.  Some  boat  modellers  pre-empt  this  by cutting the manifold in two and joining the  two  with  silicon tubing,  this seems to work quite happily.  The Irvine pipe works  extremely  well  and I highly recommend them for use on any side  exhaust  glow  engine but do use a secondary silencer as well as the exhaust  note  is quite piercing.

Full length tuned pipe as fitted to my heavily modified Robbe Unlimited


Ugly  fitting ( old fashioned ) of a full length tuned pipe ( with internal silencer) on my  first  'multi boat',  a SHG Laser.
I bought it like this - honest guv!

Mini tuned pip + after silencer fitted in a "over modified" ABC CESA 1882


For more info on Tuned pipe, have a look at...

HorsePower Lab

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Glow engine  fuel is a mixture of methanol and oil.  As the engine has  no  separate  lubrication,  the oil is mixed in with the fuel and  lubricates  the  moving  parts  as  it circulates around the engine  with  the  fuel.  Unfortunately  most  of the oil comes out of the exhaust pipe as a  smoky  gunge which seems to get everywhere. The oil in the fuel is either castor  or synthetic based. Some people swear by caster fuels and others swear at  it  and use synthetics oil based fuel,  e.g.,  Dynaglow.  Castor is said to  protect  the  engine better than synthetics but is more  oily.  Synthetic  fuel  although  more expensive puts less drag on the engine so it  should  allow  it  produce  higher  speeds.  Synthetics seem  to  be  gaining  in  popularity  as  it's an easy way of getting more speed out of  your  boat  without  doing any work to it.  Racers favour synthetics but I'm not into  racing so  I usually stick to castor oil based fuels e.g., GN.

     Most   boaters use fuel with nitro methane added.  Nitro methane when burnt  produces oxygen thus causing a better burn of the fuel in the engine. The  better  the  fuel  burns the more power it develops and the  faster  your  engine  will run.   Over here in Britain we tend to use small amounts  of  'nitro'  in  our fuel say 5 or 10% but our American friends regularly use  40,  50  and 60% when racing.  I like 5% as it gives just that extra kick  but  still as safe as straight.  For a new engine always use a "straight"  fuel i.e.  a fuel that contains no nitro methane,  it will put less stress  on the engine. Always filter the fuel before putting it in your boat.

More info on carbs & setting up engines...



    A  steady  flow  of fuel to the engine is a basic requirement to  all  IC  boats.  'Klunk'  type  fuel tanks are ideally suited to sports boats.  The  klunk weight on the end of the take-up tube follows the fuel as  it sloshes from side to side.  All model shops sell klunk type tanks, try  the  SLEC  square tanks as they don't require the manipulation  of  small  brass  pipes  into strange shapes.


  The fuel flow in some boats  needs  a  little  help  so the fuel supply can be slightly pressurized by  using  a  pick-up  from the exhaust system.  With a pressurized  set-up  the  flow  to the carb can  remain relatively constant regardless of  the  attitude  of  the  fuel tank or fuel level.  The needle valve  will  need  screwing  in a little more for pressurized systems to prevent the  engine  flooding. Use thick silicon tubing for the fuel pipe as it is less likely  to kink and give problems. Constantly check your fuel pipe for wear, damage & hole - it can save hours of time when trying to fault-find a problematic engine!!!

Well  all of this is just my opinion,  but what do I know! 

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