The Jett .60L is a smaller engine. The regular SJ-60L engine runs well with 10x6, 10x7, 11x5, 11x6 - perhaps 12x4 props. Definately nothing larger. Runs at lower rpm than the other jett small block engines, typically set up for peak rpm between 14,000 and 15,000 rpm - but it trades the rpm for torque needed for the 11" props. The RE version can do a little better with 11x6 and 11x7 props since the pipe can be tuned a bit longer.

(for reference and comparison, the Jett 60LX engine produces more power, but goes the other way gaining rpm but giving up some torque, set up to run in excess of 18,000 rpm, and is not suitable for any prop larger than a 10x6)

The engine SJ-60L is best suited for any design that was originally powered by engines like the ST blue head, webra blackhead, OS goldhead --- earlier non-schnurle light-weight, small case 10cc engines, basic mufflers ---- typically those early to mid 1970s pattern planes. Turns out the current small block (.46 size) engines are nearly the same size and weight as those older engines - so weight and balance works out nicely.

Do not get fixated on the prop size. This engine turning the 11x5 or 11x6 prop outperforms what a G-61, Veco .61 or OS goldhead was capable of with an 11x6, 11x7 or 11x7.5 on the shaft.

Also, the OS 55AX has been very impressive, so worth noting here too. Especially with the jett-stream muffler added. It performs nearly on par with the Jett 60L for most props, and has better top end torque -- it really likes the 11x6 prop.

Yes, as noted, when getting up into the 12" props, the Jett 90L (big block) is where to go. Typically we run 12x6 props.

Vince, unless you are going for "very quiet", the 12x8 is a bit too big for the OS61FX on a stock muffler. Yes it will run ok, but you can probably come up with a better performance balance on most aircraft with props sized 12x6 and smaller. Get the rpm up a little bit. (prop selection always has to be matched to the aircraft/application)

Bob

Bob, will any of the Jett mufflers work on the O.S. SF .61 Long Stroke? I was wondering if the 90-size Jett muffler would do. I intend to use props like 12x8 and 11x10. With the stock muffler I'm turning these props around 10,750.

Thanks,
David

Two muffler would work....

1) the 90 Torque muffler - aka JS-120 size jett-stream muffler. It is just a little longer than the regular 60-90 size jett-stream.

That is the one Jett offers for the new OS120AX, and what was used on the Jett 100L and 120L engines.
Lower tuning band ----- 10K to 12K rpm is where you want to prop for at full throttle.
If your desire is big props and the lower rpm band..... this would be the choice.

My notes show that the SF bolt spacing is the same as the OS91, so it would be an off-the-shelf item - no adapter.

2) the turbo-jett 20cc size. This is the in-cowl muffler. Again, same one used on the Jett 100L and OS120 engines. Same range, same sorta boost, different packaging... not always suited for the front end of a traditional pattern ship.

Just of comparitive note, the OS 91FX with the "regular" jett 60-90 size muffler turns a 12x8 around 12,500-13,000 ground peak rpm - really jumps on it in the air. About the same with the OS61fx and an 11x8.

Thanks, Bob. The 90 Torque muffler sounds like the one.

David