Sport Jett 40, pipe, Diamond Dust Questions

Sport Jett 40, pipe, Diamond Dust Questions (Full Version)

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PHall -> Sport Jett 40, pipe, Diamond Dust Questions (7/3/2007 2:47:11 PM)
I have what I assume is a Sport Jett 40 since it is visibly identical to the one pictured on the Jett site. It was bought used but still has a very tight "squeaky" fit which so be good, right? I called Jett and told him what I was doing and he said I needed a "quickie" pipe. At least that is what I thought he said. Anyway the new pipe is black and apparently identical to the red pipe that was on the engine. I compared the two under the following conditions: 30% Wildcat fuel 8.8 X 9 APC prop Engine mounted to the plane with a bubbless tank to the side (not mounted in the plane but using the same fuel lines) The red pipe turns 18,000 rpm consistently The black pipe turned about 17,500 - 17,800 but with a much richer needle setting I do not run lean and I do not burn plugs. Questions 1) Why do I need the black pipe as opposed to the red? 2) Am I turning to many rpm and need a bigger prop? Or, should I use a smaller prop as recommended by Jett? I do not want to over rev so I thought I would ask before I tried. 3) Any idea how fast this will go on a Diamond Dust? Thank You, Preston

rmenke -> RE: Sport Jett 40, pipe, Diamond Dust Questions (7/3/2007 6:24:51 PM)
PHall; Your question makes me wonder when "Bob's 27" is going to be back from vacation. Anyway, the Jett Black pipe is indead a Quickie pipe designed to give the engine more rpm's, should be good for700 +. Your engine should still idle and transition reasonably, but not quite as good as the red sports pipe. It seams like you are running a lot of prop on this little 40, but 18k is good overall. Any indication of heating, drop back on the pitch. I don't have a 40, so can't give you a good prop size, Bob can. Please, please do not turn that baby over with the prop. I know several englne nuts that would slug or slap you if thay saw you do this. Go back to Jett's web site and read on how to start these engines, basically wide open. This is to get heat into the engine as quickly as possible and to normal operatilng temperature. Now, not every engilne nut is going to agree here, but thats what Jett wants, so do it. If it's "squeaky" on top, thats like a new engine, or close. I ran against a 10 year old 40 in a LR-1 last week and got lapped in a club race, something that just does not happen very often. Yea, my 60 LX is back for service so had to fly my 5 year old little "Yellow Jacket" with a 35, point here is these engines are quality, and tend to run well foreaver. Run Jett's recommended prop, don't think there is any such thing as "overreving" these tneines. On a diamond dust, you should be over 150 flat and level, may see close to 200 in a dive, may see small pieces in a dive also if you get flutter. Keep linkages tight, seal all hing gaps well, I do it on both sides. ENJOY

MJD -> RE: Sport Jett 40, pipe, Diamond Dust Questions (7/4/2007 5:42:30 PM)
quote: ORIGINAL: PHall I have what I assume is a Sport Jett 40 since it is visibly identical to the one pictured on the Jett site. It was bought used but still has a very tight "squeaky" fit which so be good, right? I called Jett and told him what I was doing and he said I needed a "quickie" pipe. At least that is what I thought he said. Anyway the new pipe is black and apparently identical to the red pipe that was on the engine. I compared the two under the following conditions: 30% Wildcat fuel 8.8 X 9 APC prop Engine mounted to the plane with a bubbless tank to the side (not mounted in the plane but using the same fuel lines) The red pipe turns 18,000 rpm consistently The black pipe turned about 17,500 - 17,800 but with a much richer needle setting I do not run lean and I do not burn plugs. Questions 1) Why do I need the black pipe as opposed to the red? 2) Am I turning to many rpm and need a bigger prop? Or, should I use a smaller prop as recommended by Jett? I do not want to over rev so I thought I would ask before I tried. 3) Any idea how fast this will go on a Diamond Dust? Thank You, Preston I'll bet 5 bucks Bob will tell you something like this: - read all the tech info you can find on it on the Jett website - mount it on a test stand to get a feel for the engine - run it a few times on a 9-6 prop or a pylon prop that lets it stage onto the pipe easily - the 8.8-9 is probably too much load for the .40 with the black pipe - the engine is nearly bulletproof and do not be scared of letting it turn up, it's made to do that But I might owe you or Bob 5 bucks when he's back.. [8\|] Here's what he posted some time back on a similar question - he's talking 60LX here but the idea of the red and black tuned mufflers is the same, you need to adjust the prop load to suit the engine displacement. You'll see that you are likely loading the engine too much to let it stage onto the muffler, actually since you showed lower rpm with it than the SS muffler that is almost a certainty IMHO. In his comments below he refers to the 8.8-9 as one of the higher load choices for the .60LX, so you can imagine it is a tall order for the .40 to get into the muffler's tuning range with that prop: "The SJ-60LX comes standard with the SS type muffler - red one, SS racing type, with the expanded volume center. This is tuned for running best between 17,000 and 20,000 rpm. Works well with the 60LX, especially with the 10x6 and 10x7 props... and heavier full blade 9x9 and 9x10 props. The D1 8.8x9.25 is a good choice too. Most folks buying the engine were looking to turn heavier props. You want the engine to set 500-600 rpm down from peak for launch, no lower than 16,500 - preferably up over 17,000 rpm. The black Q-500 muffler is shorter. That one is tuned for 18,500 to 22,000 rpm. You can use the black muffler. The 60LX engine will love it. You just have to run the D1 pylon props, and make sure it turns no less than 19,500 at peak, and launches 500-600 rpm down - no less than 18,500. The 8.8x8.5 will get their easily. The 8.75x9W, 8.8x8.75 and 8.8x9 will too. Most likely will turn the 8.8x9.25 as well ( I have not tried it yet, but it should). Do not use any prop other than a good wood prop, or an APC Q-500 prop with the black muffler."

PHall -> RE: Sport Jett 40, pipe, Diamond Dust Questions (7/4/2007 7:09:51 PM)
MJD, Now that you mention it, I agree that I am probably over loading the engine with the black pipe. This explains the richer setting. I will try some of the suggested smaller props by Jett. I would have done so before but as I said I did not want to over rev the engine. Over loading is just as bad but I did not run the engine long in either case. Thank you.

MJD -> RE: Sport Jett 40, pipe, Diamond Dust Questions (7/4/2007 7:48:03 PM)
quote: ORIGINAL: PHall MJD, Now that you mention it, I agree that I am probably over loading the engine with the black pipe. This explains the richer setting. I will try some of the suggested smaller props by Jett. I would have done so before but as I said I did not want to over rev the engine. Over loading is just as bad but I did not run the engine long in either case. Thank you. In truth I would say overloading is way worse unless you're running ridiculous revs. These engines are robust. I think the most important advice I would give is if Jett says to do something, do it. You can probably run the 9" pitch prop if you clip it down to 8-8.25" or so. That is a bit of a guess on diameter, but the key point is to clip it until the revs come up to the right range. Whether it iworks well for your DD would be answered by flight tests. Or.. stick with the 8.8 diameter series and go down in pitch to hit the rev range. Probably that is the wise move for initial flights, then experiment from there. In any case, get that engine staged and happy and your DD will go like snot.

bob27s -> RE: Sport Jett 40, pipe, Diamond Dust Questions (7/6/2007 2:39:14 PM)
Hey.... I appreciate you guys covering for me..... :) Information is good, thanks ! PHall, the engine will have a number engraved on the crankcase mounting lug. If you do indeed have a .40, it is likely an SS.40 sport racing engine (Jett only makes .40 engines for racing, per rules SS40, 428, 422 .... all of the sport engines are .46, .50, 60L). Red (or gold) SS muffler, use a 8.75x7.75W or 8W, or a 8.5x7.25 prop. A standard 9x7 works well too. If you are getting a clean 18K with the full blade 8.8x9 on the red muffler..... FLY IT !! Back off 500-600 rpm for launch. That is a very good number for a sport .40 or .46 with that prop. Black 'race' muffler..... same props, maybe add the 8.8x8.5 You can use the 8.8x9, just clip it to about 8.3" diameter and balance it. Bob

rmenke -> RE: Sport Jett 40, pipe, Diamond Dust Questions (7/9/2007 6:02:27 AM)
Bob: Great to have you back, you were sorely missed. Hope you had a great vacation. Strange your first pop back said Jett does not made sports 40's. One just kicked my old buttox at a club race this last Sunday. It was indeed a 40 with black muffler, but red jett carb. Very suspect when it cranked up, sound like it was turning around 21500-22k, unwound nicely in a LR-1. Yep, he finally lapped me, just cause my 60 LX is in the shop for minor repair. Gonna let him run it again at our next race, then require the old idle test after the 60lX kicks tail. Its in my latest "user friendly" yellow jacket. Can sit her down on the ranp, taxie out for takeoff and then watch the guys run for the fence. With the full 52" quickie CF wing and total weight of 3.75 lbs, it lands like a sport model. Wonderful combo!! Don't laugh at the guys, bet you would hide also with a now 73 year old geeser flying something around that fast. Really scary! ENJOY

bob27s -> RE: Sport Jett 40, pipe, Diamond Dust Questions (7/9/2007 2:17:08 PM)
Ya have a fun bunch of guys out there :) Jett no longer produces a "true" SJ-40 engine. Dub sells the SJ-46 instead. The SS-40 has a sorta-carb on it (will idle and transition, but not very well). And the 428 Q-500 racing .40 engine (with the black racing muffler) is available with the regular red carb (full throttle) as an option. Dub sells a number of those each year. Perhaps that is what your club member is flying. That engine has to launch over 19K rpm, and will unload to 20,500 in the air easily ----- so hearing 20K or so sounds about right.

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