flybyjohn

My Feedback: (2)

double post again, not sure whats wrong.

flybyjohn

My Feedback: (2)

Doing a little research I found this claim on the Jett site. It is kind of a little disappointing that they are only getting 12500 peak with an os 91 and 12x8 prop when my .75 is at 12250 with the same prop. Maybe I should just stay with the header pipe and mousse can I have.


Bolt one on to your favorite engine, and enjoy the instant 25-50% increase in power
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[TD]
OS .91 with Jett-Stream Muffler
Great Planes F-14 - 12x8 prop
pulls hard at 12,500 ground peak RPM[/TD]
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1QwkSport2.5r

Are you using an MAS 12x8 or APC 12x8? You will see more rpm with the MAS than you will with the APC generally.

FWIW, my ST S90K pulls around 14,800rpm on a 12x6 APC on 5% nitro fuel and red Jettstream muffler (.61-.91 size). 12,500rpm on a 12x8 seems like a misprint. It's probably supposed to be 13,500rpm. That seems much more realistic.

flybyjohn

My Feedback: (2)

My numbers for the 12x8 are with the APC prop on a .75 engine using 15% nitro. I would imagine that if this is advertised on the Jett Web Page that they would make sure they corrected a misprint of 1000 rpm if it was a low side error. If I remember correctly, I think I get about 10,500 with the stock muffler and a 13x10 APC on my Magnum .91 XLS.

You can definently see the difference in the rpms from the APC to MA props with my numbers from the first page. With a 12x6 prop there was over a 400 rpm difference.

1QwkSport2.5r

There has been a lot of misprints on the new Jett website. They state 17,000rpm for the Jett .35 on a 10x6 and in fact it's less than 16,000. I'm not sure who does the website, but I'll guarantee the 12,500rpm figure for the 12x8 is low. That or they were running a worn out engine. My ST .90 would easily top that on just 5% nitro.

flybyjohn

My Feedback: (2)

I suppose I am willing to agree with you on that seeing that they advertise a 15-30% increase in power by bolting on a jet stream muffler on one page and 25-50% on another page.

flybyjohn

My Feedback: (2)

I suppose I have nothing to lose except a little time to try to build a Jet stream type muffler. The least that could happen is I could gain more experience and maybe even get something that works great.

1QwkSport2.5r

That's how I would look at it. If you want/need any measurements from an actual Jett muffler, let me know.

flybyjohn

My Feedback: (2)

Thanks 1Qwksport2.5r, In looking at the design of the jett stream mufflers, I noticed that the sport mufflers are a bit longer than the racing mufflers. So I figure if I start a bit longer than the sport size and slowly cut shorter, I should come up with a design that will give me the best RPM for the prop I plan to use. My can diameter is a bit larger than the jett mufflers so the dimensions might be just a bit different. I am going to make this first muffler for my ASP 91 and if it works well might make one for the 75. My biggest concern is if the welds and thin aluminum mousse can will hold up to the vibrations of the engine.

1QwkSport2.5r

The red mufflers are the largest with the gold ones shorter/smaller, and the black ones smaller and shorter yet. The red ones have the widest prop range, gold is narrower, and the black mufflers are pylon mufflers pretty much tuned for just a couple of props. For the red .91 Jett muffler, the tuned range is 12,000-15,000rpm which I believe is the ground peak rpm.