thebluemax

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Hello Bob,

Iam seeing some sites sellingbridge adapters to put the Jett-stream muffler for a .40-.50 engine on an OS-61.I don't understand why you would want to put the smaller muffler on thebigger engine.The only thing I can see is saving some moneyspending $15-$20 for the bridge adapterversus $85 for the right muffler.

Will the Jett-stream .40-.50work on the OS-61? Wouldn't there besome performance issues as well as maybe overheating? Or noise or back pressure issues? Or will itwork with a specific plug/prop combination?

I have a couple ofthe .40-.50 Jett-stream mufflers and I do have an OS-61. I have an adapter to put one ofthese mufflers on a Rossi-40 which you need to fit but I don't see putting the smaller muffler on thie OS-61. Unless I am missing something here?

thanks for your time,
Bill

bob27s

My Feedback: (19)

Hi Bill..

Thanks for writing ...

If you have a link to share, let me see where these places are.

You are not missing anything ... It is NOT a good application to adapt the .46 size muffler to a larger .61 size engine. We know well from experience this leads to big problems. It may run, but it will drive you nuts with over-heating and backpressure balancing issues. Not having the proper expansion volume is the main issue.

Just for clarity... since others may search here too.

The Jett muffler sold by Horizon for use on their Evolution .60 engine was configured specifically for that application. It will work with other "small block" engines from .46 - .55, and of course the Evo .60. But it is not intended for real "Big block" 10cc engines like a Rossi .60 or OS .61. That blue muffler is set up to run around 14,000 - 16,000 peak ground rpm and will pull down toward 14,000 as a lower limit for prop selection.

The standard Jett 40-50 size Jett Stream muffler is tuned for rpm target around 15,000-17,000 ground peak. Engine needs to turn up. Its porting and volume balance suits this displacement range. The Jett Stream provided with SJ-60L is similar, but tuned for slightly lower rpm. The SJ-56LX muffler is tuned for 17,000+ rpm. Neither well suited for large displacement big block engines. The Jett-Stream mufflers are available with either Jett/ST/Webra spacing, or OS .46/55 type spacing. Adapters are available for other types and older bolt-on muffler engines like YS .45 and Rossi .40.

The Jett SJ-90 muffler is what we recommend for big block .61-.90 size applications.

This has the proper expansion volume and tuning rpm target that suit these engines. Works outstanding on the OS .61, OS 75AX, OS 90FX, and other similar size engines. Has integral bolt pattern that matches both Jett/ST and OS spacing. Also a great choice for older engines like the OS .61FSR, YS.60 and Rossi .60 pattern engines - and Dub does have bolt-on adapters for these engines.

I hope this is helpful!

Bob

thebluemax

My Feedback: (151)

Hi Bob,
Thanks for the quick reply and explaination. It didn't make sense to me to use it for that.

Just thinking, the only thing I could see as a possibility for using thatadapter and muffler combination would be fora 40-45 size engine that has a 42mm bolt pattern. For example, the Enya 40CX and 45CX engines have a bolt pattern of 42mm which is the same as the OS-61.Sincethe 40CX and 45CX would be in the same.40-.50 power band as the mufler,this adapter and jettstream muffler could be an option. Am I correct in that assumption? Those two Enyas are powerful engines.

Here is the place where I saw it. http://shop.vendio.com/rossienginesu...012/index.html

if you google "muffler bridge adapter, rossi/OS 61 to JETT 45 muffler" a bunch of others come up.

Also on Ebay if you search for "61 muffler bridge adapter, JETT 45 muffler" some show up but I think it maybe the same place as the link I gave you.


thanks again....