bob27s
Posts: 4637
Joined: 4/9/2002
From: Cleveland,
OH, USA
Status: offline
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Hi. Thanks for writing.......
First.... thanks for the positive feedback Roger.
One point he makes here is quite true ..... the Jett engines are indeed higher performance engines than most others out there, but the sport-jett engines are some of the most user friendly and reliable engines available today. Complete the break-in as per instructions, ensure you have a good fuel system in the aircraft, select props as recommended for the engine, use good quality fuel - and the engines will perform great for many years.
Second... You noted your Rossi 53 was a bit tempermental. That 12x6 you have on it could be the cause - that is way too big (unless you are running a full size pipe, and have it set a bit long to provide some needed torque boost). With that much load it is bound to get hot, idle and transition poorly. The stock engine/carb/exhaust system is set up to run best above 14,000 rpm - preferably well above that. At lower rpm the carb will have difficulty delivering the correct mixture - its a big bore carb. You want to select a prop for this engine that turns somewhere around 14,000 or better peak ground rpm. You may find much better performance simply switching to a 12x4 prop.
As for the Jett and OS comparison.......
The OS50SX is a real nice engine. Runs well, and is well designed. With the stock muffler it runs good, but the porting in this engine takes full advantage of a tuned exhaust system. Add a jett-stream tuned muffler, turbo-jett tuned muffler, a full length tuned pipe system, or an ultra-thrust muffler, and it can really perform to its full potential. Set up with the jett-stream, it performs just shy of the Jett 46 on a 10x6 prop.
So if you goal is ripping fast.... Jett offers the SJ-46, SJ-50, SJ-60LX. All of these engines are designed to turn up. The SJ-46 and SJ-50 are designed to be propped for a mininmum peak ground rpm of 15,500 rpm. The 60LX must turn over 16,500. Each will easily turn a 10x6 well beyond that number. The jett website specifies the minimum performance for each engine on a specified prop. For the SJ-50, any prop from one of the D1 APC racing props, up to about a 11x5 is fair game. The 60LX has a higher output exhast system, but can swing a 10x6 up at 18K rpm, or an 10x7 somewhere around 17K rpm. None of these engines are suitable for use with a 12" diameter prop.
The 55AX appeares to be a pretty nice engine from what I have seen. Runs well. However it is not a good choice if you are looking for speed, however it does respond nicely to a tuned exhaust system. This engine is a big prop/low rpm engine, and is much better suited to turning a 12x6 than the Rossi 53 is. If you add a jett-stream "60L torque muffler" to this, or a 10cc turbo-jett, it can gain some in rpm, but will see a big torque boost. You can run an entire prop size larger and pretty much hold the same rpm you saw with the stock muffler.
Jett's equivalent to the 55AX setup would be the SJ-60L, SJ-60L"H" (hover,3d) engine, or the BSE-76L. These are all "46" size engines just like those listed above - same footprint and appx weight of an OS46 or OS50. Specs for these are on the web site. These are all set up for lower rpm and larger props. The 60L"H" comes with an un-tuned, light weight muffler - special carb, and is very happy turning the crud out of a 11x5, 11x6, 12x4 or 12.25x3.75 somewhere around 14,000 rpm. The standard 60L with the torque jett-stream muffler is good for the same props, can push up a bit toward a 12x5 or 12x6 if desired, with the key to selecting a prop that runs between 13,000 and 16,000 peak ground rpm. Jett's BSE-76L is a true animal of all of the small-block engines. This engine is set up for prop selection to run below 12,000 peak ground rpm, but can turn a 14x6 upward of 10,500 rpm (yes, this is a .40 size engine). Attached are photos of my Aeroworks 40-60 size edge with the BSE-76L engine and turbo-jett muffler. This turns a 14x4W prop over 11,500 rpm.... plane has insain flight performance.
As for cost... we perfer to say it this way.....
The Value of an engine (or any product purchased) extends far beyond the cost of the product.
Value means different things to different people.
Jett's tech support is second to none. Few other engines you can buy, where if you have an issue or question you can speak with the guy who actually designed, built and tested your engine
The Jett engine construction includes REAL ABC/AAC construction ..... chrome on the sleeve. The aluminum alloys chosen are the same used in the world famous Jett racing engines. Bearings are sized and selected to withstand the performance and intended use.
The sport-jett engines come standard WITH the jett-stream tuned muffler, spinner nut. They also come standard with Jett's universal remote needle valve assembly. This needle assembly is leak free - and can either remain mounted to the engine, or can be removed from the engine and be airframe mounted.
And.. all of the engines are built, assembled, tested, serviced and shipped from Houston, Texas, USA. When you account for what the EPA, IRS, DHD, insurance and all that fun stuff necessary to be a manufacturer in the USA, that constitues some of the actual product cost.
So for a real comparison on raw cost - Figure what the 50SX or 55AX costs, add in a $75 tuned exhaust system of some kind. Perhaps account for $25 to replace the engine bearings in about 18 months.
As for the Value, again .....
If you take into account everything, from engine performance, service, support and so forth... it is something you have to determine for yourself. Same sorta goes for choosing between BSE or cast case versions - performance is basically the same, just comes down to which one you like (although the 76L is a BSE only available in BSE)
http://www.jettengineering.com/engines/sj40-new.html
Recommendation for your Extra 300 ........
1) stick with the rossi 53, and prop it more appropriately - drop to a 12x4 or 11x6 prop at MOST
(also ensure your fuel tank is 100% isolated from the airframe - wrapped in foam)
2) Jett SJ-60L engine. With your installation being similar to the Edge I showed here, consider using a turbo-jett muffler. The muffler will trade about 400-500 rpm on the top end from the jett-stream, but you will have no problem at all turning the crud out of a 11x6 or 12x4 prop (well over 14,000 rpm). And, if you want to really move out, drop to a 10x7 prop and you will find tons of level flight speed.
3) Jett BSE-76L engine. Use the lite-jett muffler (untuned). Select a 12x8, 12x9 or 13x6 prop... the fun part here is your vertical speed will probably be the same as your level flight speed 
I hope this is useful. Feel free to contact me, or Dub at any time with questions.
Bob Brassell
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Bob Brassell
Jett Engineering - Engine Mfg Support Forum Host
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os 50 sx vs. Jett comparable engine options - 
