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bob27s -> RE: Jett muffler's Gold, Red, Black???? (2/19/2008 5:38:18 PM)
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Hi Mike...
Simple enough to answer....
Yes, each muffler is a different lenght - and that is indeed the important part. They are tuned for different applications.
Lets start with the 428 engine. Uses Nelson glow plug.
Black carb - airvalve only - shutoff only. No real throttle capability - no idle capability.
Black muffler - tuned for 19,000 rpm and higher.
The 428 engines require the black muffler, and do turn quite a bit more rpm.
Prop selection is 8.75x9, 8.8x8.5, 8.8x8.75, 8.8x9 all which will exceed 19,000 rpm easily. Back off 600-800 rpm for launch.
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Sport Q-500 engine, or SS-40 engine - offered both with and without the Nelson plug head. They run pretty much the same.
This is a regular SJ-40 engine, just provided in a configuration for sport pylon racing. (CAPS, SEMPRA ran this configuration)
Red SS carb - looks like an airvalve - this has no low end mixture adjustment.
However, this carb will allow for throttle, and the engine actually will idle (for a bit of time) with a racing prop on it.
Red SS muffler - this red muffler has an enlarged section in the middle.
(the standard jett muffler is straight cylinder on the outside - no raised mid section)
Red SS muffler is designed for over 17,000 up to about 20,000 rpm.
For best operation, prop selection should be such that peak ground rpm is around 18,000 - back off 600-800 rpm for launch.
Prop selection - std 9x7, 8.75x8W, 8.8x8, 8.8x8.5 sometimes
(Although we found it has another tune point with a 8.5x7 and 8.5x7.25 prop up a little over 20,000 rpm - runs well like that)
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SJ-60LX engine
Carb is the standard red jett carb - includes full throttle, idle and transition - has adjustable mid/low mixture needle (resist temptation to adjust it though).
Gold LX muffler - it is actually the SS muffler noted above. Same raised mid-section.
It is just supplied in Gold these days since it is primarily for the 60LX.
On the 60LX engine, prop the engine for no less than 17,500 peak ground rpm. High end rpm prop selection around 19,000 peak ground rpm.
Runs best of all with the 8.8x8.5, 8.75x9W, 8.8x8.75 props --- also std blade 9x8, 9x9 and 10x6 props.
Same as the others... find peak rpm briefly ..... than back off 600-800 rpm below that for launch.
And....
You can use the black racing muffler on the SS-40 or 60LX engine to turn a lighter prop at higher rpm.
But prop selection is based on the higher rpm design for the muffler.
Select a prop that turns no less than 19,000 peak ground rpm.
(for example, on a 60LX, black muffler, 8.8x9.25 clipped to 8" diameter works here)
I hope this is not tooooo much info :)
Bob
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