do the ultra thrst mufflers provide any rpm gain as they claim

Yes, ultra thrust mufflers perform as advertised. I have one on os 46, forgot the actual tach reading but it will make a very noticeable difference. You'll need to set fuel mixture richer,more fuel for more rpm. Just a reminder so you don't fry your engine if you go with the UT muffler.

I agree with Vertigo's post. You will see a substantial increase in RPMs. As with any tuned system, you will have to make sure you are using the correct propeller. Since the UltraThrust is a fixed length tuned muffler, you will not be able to tune it to your favorite prop. You will most likely have to experiment a little to determine which prop diameter and pitch combination gives the best performance. I do not know whether Performance Specialties provides prop recommendations. A good tachometer is essential in order to truly know which prop is best. An accurate radar gun is even better.

I have one on a .46 FX and the advertised RPM was close. The Jett Stream muffler from www.jettengineering.com will give the same increase for $10 less if the red color is not a problem. The Jett also has the tank pressure nipple in a better place.

I am running a os 46fx on 15% and a apc 10x6 prop and I am getting right at 14,000 rpm with the stock muffler.

thanks for the info

dwsc,

I see the figures you posted for that engine/prop/fuel setup but what I can't tell is whether you think that RPM level is good or bad. In my experience, that RPM level is very mediochre and not really near what the .46FX is truly capable of.

Mike Connor,

What were the rpm readings you got both before and after you bolted on the Ultrathrust?

I said earlier that 14,000 rpms was pretty mediochre. I base that on long years of experience racing SIG 4-Star .40s where everyone had to use the same engine fuel and prop. The engine was a stock SuperTigre GS .40. The fuel we had to use was 15% mostly Cool Power but that might be different from race to race. The prop was a Master Airscrew 10X6(the old, wider blade configuration). Since we were pretty heavy into racing, we were taching these engines all the time. The competitive engines turned that prop from 14,800 to 15,000 RPMs. I retired many an engine that would no longer turn at least 14,800. The average engines were in the 14,500 to 14,700 range. Only once did I see an engine that would not turn well over 14,000 and that was a reallly worn out basketcase. The mufflers used were entirely stock but they were the ones which could be rotated around a short header, not the smaller ones that came out later. When Master Airscrew changed their prop configuration to a narrower blade, these engines consistently gained another 700 RPMs over what they turned the old prop with.

I guess the bottom line is that I would find it very hard to be happy with any .40 or .46 engine that would only turn a 10X6 prop at 14,000. I know that, if the engine is in good condition, the O.S. .46FX has to be capable of so much more performance than that.

My 46fx just after breakin would turn a 10x6 14,400 with the stock muffler. I removed the baffle and drilled out the exit and got about 14,900 with the same prop. I then installed the Ultrathrust and got 15,900 with the same prop. I then dropped down to a 9x7 APC and got 16,400 rpm. My numbers are consistent with the Ultrathrust adds. It is not uncommon to have two identical engines that turn different rpm's.

I think that the rpms are good but i think the can be better, what are you drilling out?

I drilled out the exhaust exit hole in the back of the muffler. The 500 rpm increase came from a combination of the enlarged hole and the baffle being removed. This did not seem to effect back pressure for the fuel tank. O.S. replaced this engine with a brand new one after the liner peeled and I do not have any rpm figures on the new one yet.

I had heard that the Tower mufflers for their 46 will increase RPM about the same as an Ultra Thrust. The best part is they are $13.00 I bought a couple and was able to get 16,000 RPM with an APC 10x6 on an OS 46FX. Not bad for the price. Any one else have any experience with these mufflers.

A friend used to buy the Tower mufflers several at a time because they kept coming apart in flight. They did increase the rpm of his TT pro and 46fx engines but not what you are experiencing. He did finally buy two Ultrathrust mufflers that gave a performance edge over the Tower mufflers and they do not come apart. Jett makes the Jett Stream muffler that is equal to the Ultrathrust but is $10 cheaper.

How about an UT muffler for a os 46la? Do they exist? Or do I have to make a mousse can muffler?

I own a tower hobbies muffler and the ultra thrust.
The tower does give a boost, but not as significant as the Ultra thrust...ya get what you pay for...

I had similar results to Mike Conner

I doubt the Ultrathrust is made in a size that would fit the LA series engines...I don't believe they're designed to withstand the huge RPM boost.

Just a warning: your engine has to have been broken in appropriately or might not see the improvement. I have one that wasn't (I've concluded... but not 100% certain).

I concluded that if your 46fx will turn a 10x6 at 14k+ on 10 or 15% fuel using the stock baffled muffler, then you are probably okay and will see it running at 15K+ on the Ultra or Jett. (I have a Jett Stream). I have never been completely certain if the 14K+ reports were baffle in or out... but I see Mike Connor reports baffle in.. so there you go.

Mine will not turn more than about 13500 with the baffled stock muffler and a 10x6. With the Jett it won't hit more than 14400 - fully leaned out, not backed off. The engine just seems to struggle to run past 14K. The Jett Stream is tuned for 15K. You need to run up around that speed to see the full benefit. If you get it up near 15K static rpm, then you should see a nice boost from the tuned exhaust when it unloads in the air and pushes into the 15K tuning range.

Hi all, I've got a question for ya...How about those Macs one piece mufflers? You know, the black ones that look like a big header that "necks down" near the outlet? I've got one but haven't used it yet(it's like 10below wind chill right now) Anybody know how they compare to the above mentioned U T + Tower muffs?

Macs. They don't compare. They're no better/worse than a stock muffler (IMEX).

I've never gotten less than a 1000rpm boost out of an ultra thrust and never less than 6 db increase in noise.

I agree that the Mac one piece muffler offers no improvement in performance. I have Ultrathrust mufflers on both of my OS46SF's and both picked up over 1000 rpm's. Pete

The Mac's one peice mufflers work well over the stock units. I have one on a YS .45 and works well for the price. We have them on OS .46s, OS .61s, os la.46s, ST.60s & 90s. All have provided a 400-500 rpm increase. No they are not pipes or Ultrathrusts, but they were not designed to be. Is the Ultrathrust a good unit for the "Price"? Sure, but so is the Mac's ($25-$35). In most cases the Mac's is lighter than stock and provides a nice boost.

I would agree the Mac is lighter and will not fall apart in flight. On the same 46's with the same prop I had no increase in rpm's on either engine. If you want to really get a performance boost at a great price use a Mousse can muffler. Do a search on how to make one. There is a source for complete Mousse cans down in Fla. I cant find to paper. I have one on my webra32 and it screams. At $28 it was a deal. Pete

I know what it did for our engines. I have no interest in making something for what I can buy it for. We are very happy with our "Boost".