Extreme Speed Prop Planes Discuss the need for speed with fast prop planes (Screamin Demon, Diamond Dust, Shrikes or any REAL sound breakin'''' plane)

OS46AX w/ Macs pretuned pipe?

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Old 01-12-2007, 09:42 PM
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rideon67
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Default OS46AX w/ Macs pretuned pipe?

I bought Macs pretuned pipe for the 46AX on a Dominator. Can anyone give me some insight as to where I need to be on the prop, plug, length changes (if needed), expected RPM, and approx. speed? Plan on running 15% and starting with APC 9/7 unless somebody gives a heads-up. Running the 10/7 with Tower muffler seems kinda lame, but judging speed is not a strong suit.

thanks,
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Old 01-13-2007, 01:56 AM
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daven
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Default RE: OS46AX w/ Macs pretuned pipe?

Running the 10x7 with the tower muffler should be getting you close to 130 mph, not lame for most people.

I really can't tell you where you will get with the Macs pipe, but I doubt it is more than an additional 10 mph.

If you want to go faster than that, you will need to step up to a Jett or Nelson. 160+ is attainable with that airplane and one of those motors.
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Old 01-13-2007, 03:42 AM
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nitro junky
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Default RE: OS46AX w/ Macs pretuned pipe?

If you use an Apc 8.75x9.0w you can run the engine right to the max rpm on the ground.
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Old 01-13-2007, 10:49 AM
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Default RE: OS46AX w/ Macs pretuned pipe?

Marketing a pipe as being "pretuned" is an insult to anyone who has gone through the process. The tuning process is specific, there is no one size fits all set up. Last time I checked, they sell a performance enhancing muffler and they sell uncut headers and pipes. I wasn't aware of any "pretuned" systems. If they are, then there should also be a narrow range of reccomended props and nitro % provided..
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Old 01-13-2007, 11:47 AM
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Default RE: OS46AX w/ Macs pretuned pipe?

Back in early '03 I bought the "pre-tuned" set-up for the .46FX/TT .46...I was eager to try it out, and put it on my TT .46 that I had in my Model Tech Magic Extra.
This was before I learned (right here ) about the Tower muffler...

This was my first pipe, and not knowing much about them I just slapped it on and went for it...

My TT .46 went from about 12,500 with the stock muffler and APC 12.25 X 3.75 to about 14,100-14,200 (10% Powermaster and O.S. #8 )
It worked great on the top end but throttlability was horrible...
It would idle o.k. and once it got wide open, but anywhere in between was lousy.
Knowing what I know now, it wasn't the right airframe/engine combination for a pipe of course, but I wanted to give it a try.

The Tower muffler was about half way between the stock muffler and the pre-tuned pipe in r.p.m. boost.

I have that pre-tuned pipe ready for a Magnum .52XLS now, that I'm thinking of putting on my Sonic 500...and I think that will be a much better "situation"...and chosing a prop will be easier.
I'm still wondering about what plug to use though?

Hypothetically speaking, would the transition have been better on the TT .46 if I would have used a hotter plug? Colder plug and leaned the idle mixtire some more???
Maybe it was just too much prop...(that was also before I "discovered" the 12 X 4...or it actually might have been before the re-designed 12 X 4 was even available? )
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Old 01-13-2007, 12:55 PM
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Default RE: OS46AX w/ Macs pretuned pipe?

My experience with the small black Mac's muffler is that it is not a "tuned pipe" at all but just a lighter muffler. It actually reduced the rpm on an FX and AX that I tried it on. A factory muffler without the baffle was better and the tower was much better but a little louder. No comparison with a full length tuned pipe that is properly "tuned" or a Jett or Performance specialities tuned muffler. The Mac's muffler is good for what it is - a light weight muffler.
Fred
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Old 01-13-2007, 03:36 PM
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Default RE: OS46AX w/ Macs pretuned pipe?

I've had vary good luck with the Mac's pe-tuned pipes on 46's and 32's. It's a system that consists of a header, Quiet pipe, coupling, standoff and hardware (a package deal). It's usually in the ball park for most sport and some speed applications. For some speed planes I have had to shorten the header up to 1/2". This is not to be confused with the One piece muffler (black). This muffler I have used on several different engines and I saw no power gain over stock. The One piece is lighter, smaller and won't shake apart or rotate like some stock mufflers do and the smoke stream is tighter so there seems to be less oil to clean up on the plane, a good replacement for lost or damage stock muffler. For most cases, in my opinion I would rate exhaust systems for high rpm power output like this:
1# Tuned pipe, un-muffled
2# Tuned pipe, muffled (like quiet pipe)
3# Ultra thrust-standard or Jett muffler-red version (note, both of these manufactures have other than standard versions, high & low rpm)
4# Tuned pipe, Double Quiet
5# Tower muffler
6# stock, baffle removed.
7# stock
8# mac's one piece
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Old 01-13-2007, 06:11 PM
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combatpigg
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Default RE: OS46AX w/ Macs pretuned pipe?

FF, thanks for taking the time to clear this stuff up. I don't have any experience with the systems between factory and tune it yourself type. Interesting that the Macs mu8ffler underperformed factory in some cases, because it LOOKS like it should do somewhat better. If the MACs muffler is lighter, there will also be less mass trying to part company with the engine due to vibration. Pre tuned doesn't sound like such a bad deal after hearing about PropTops' testimony, especially if you aren't into spending a day out of your life looking for 5 extra mph.
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Old 01-13-2007, 07:05 PM
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Default RE: OS46AX w/ Macs pretuned pipe?

One of these pipes on a Webra 36 w/9/6 APC, 15%, Scat Cat made the package come alive. The transition is good and the RPM gain exceeded 3K. That was with just slapping the thing on -- no length changes/prop changes/ glow plug changes, etc. I expect a lot of luck was involved here, but results is results. What prop are U using on the OS46?
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Old 01-14-2007, 10:18 AM
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bob27s
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Default RE: OS46AX w/ Macs pretuned pipe?


ORIGINAL: rideon67

I bought Macs pretuned pipe for the 46AX on a Dominator. Can anyone give me some insight as to where I need to be on the prop, plug, length changes (if needed), expected RPM, and approx. speed? Plan on running 15% and starting with APC 9/7 unless somebody gives a heads-up. Running the 10/7 with Tower muffler seems kinda lame, but judging speed is not a strong suit.

thanks,
The 9x7 will get you to the right rpm with the pre-tuned system.

If I recall correctly, the pre-tuned 46 pipe is set for appx 16,000 rpm. So a standard 9x7, 9x8 or 10x6 is about right
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Old 01-23-2007, 08:17 PM
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Default RE: OS46AX w/ Macs pretuned pipe?

Thanks for the suggestions. Testing the plane today showed you were right on. The 9 X 8 APC sport felt just about right for sport flying and on ground spun approx 16K. This made a new plane out of the Dominator as it went from nothing special to DAMFAST --- expecially from a dive where the prop unloads.

I went thru a few APC props with this setup and without instrumentation speed observations are:

10x8 too much prop for level flying but goes like a banchee in dives 14.4K on ground
8 3/4 x 8 racing is slow off the ground but very fast in the air. 17K+ on ground
9x8 sport is much quicker off the ground but a little slower in the air. 16K on ground

This thing gets very thirsty now but 5 minutes are sufficient at these speeds.

I am curious about the needle setting tho. I was able to run the HS needle WAY rich without changing the speed. I assume this was due to restrictions in my system. Does surging in the air mean too lean?
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Old 01-23-2007, 09:22 PM
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Default RE: OS46AX w/ Macs pretuned pipe?

You may have a foaming problem and the fuel system may have a restriction as well (more power needs more fuel) . See that the tank is isolated with Hibbico foam rubber and not touching the fuselage.
Make sure the prop is balanced too. A good way to test for foaming is to fill the tank half full, restrain the tail with a rope for safety and start the engine. Run it up to full power while lifting the plane by the wing tips so the wheels are off the ground and look for bubbles in the fuel line just before the carb. This trick works most of the time. One last thing you can do short of going to a bubble-less tank is to add 5 drops of STP's "Son Of A Gun" cleaner/treatment to one gallon of fuel. This will shorten the life of the glow plug!

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Old 01-24-2007, 08:16 AM
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Default RE: OS46AX w/ Macs pretuned pipe?

Do you have the pressure tap installed correctly on the pipe's large diameter just before the the taper? Is the fuel line, clunk, stopper tube, filter(if used)the right size and clear? Too long of a fuel line run?(a larger fuel line can help a little if you can't move the tank closer) Is there crud at the needle? Is there a pin hole in the fuel line? Did the clunk get stuck? Did the clunk line have a kink in it or did it fall off?(short flights?)

These are some of the things Iv'e come across. If all is working correctly, you should easly be able open the needle a turn or so that the engine goes in to "four stroke" and turn a little more it's so rich that it dies.

I hope this helps.
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Old 01-24-2007, 01:22 PM
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Default RE: OS46AX w/ Macs pretuned pipe?

As noted, if the needle becomes insentitive, or the engine surges in the air, it is likely a fuel foam problem. Make sure the fuel tank is surrounded by foam, and does not touch the airframe structure. When you get to that 17K+ rpm range, foam can and will happen easily. You may not even see it on the ground - but it happens in the air. Check things out.

That is why with some high output and speed engine installations, using a bubble-free fuel system like a Tetra tank or the bubble-jett tank is the best solution. They eliminate the possibility of fuel foam (fuel and air never meet)

A few drops ( note here, DROPS) of armor-all in the fuel can help the foam issue ... sometimes .... it only cure the symtoms, not the problem.

With a pipe, you usually want to needle off of peak rpm 500-700 rpm - when the engine unloads in the air, it will want the additional fuel.

Bob
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Old 01-26-2007, 09:22 PM
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Default RE: OS46AX w/ Macs pretuned pipe?

I'll check for foaming and bubbles -- I suspect it is happening since the tank is too big to isolate in this airframe. I took the plane apart to relocate the pipe, rotate the engine, etc and will do as much as possible to clean up the flow, but don't think it's the problem since the tank fills so quickly with my fueler, and the blow thru test seems clear. The pressure tap is in the thick part of the header where it meets the exhaust port. This seemed a lot simpler than putting it at a thin part of the rear of the pipe. It's working OK on a Macs pipe on a 36 webra there. How do you put a tap into the thin pipe material without being able to get to the inside to put a nut on the tap?

Prop balancing raises some questions. The method I use is to static balance so the blades are level, but often one side of the hub is heaver so the prop only balances with the blades horizontal and not vertical -- like the bore isn't centered on the mold tooling. I worry about removing material from the hub to correct this condition. Also, the dynamic forces on these props are extreme at speed and compensating for any dynamic imbalances is way past my pay level.

These motors are amazing to be able to hold together at these speeds and energy levels. Is seems like this becomes a completely different animal once it goes beyond 16K RPM.
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Old 01-27-2007, 01:01 PM
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Default RE: OS46AX w/ Macs pretuned pipe?

It is worth mentioning that the Macs pretuned pipe and the black Macs muffler are different products, the black muffler does indeed suck and the pretuned system is a winner.

Cheers!
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Old 01-27-2007, 01:01 PM
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Default RE: OS46AX w/ Macs pretuned pipe?

I found surging at full trottle is caused by being a LITTLE too rich You are close to where you want HS needle.
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Old 01-27-2007, 04:08 PM
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Default RE: OS46AX w/ Macs pretuned pipe?

I have to disagree about the Macs black mufflers. I think they are great and performance depends on which engine you are using. I have found on the OS FP series I was gaining 1,000 rpm over the stock muffler. I found on my .25 FX it was a wash with the baffle removed from the stock unit.
The major benefit of the Macs mufflers is they are one piece. I hate those 2 piece stock mufflers and see them lose thier back half all the time. They solve many problems but cannot be compared to a tuned system as they are 2 differant animals.
It seems many people get them confused with a tuned system when these mufflers really do not belong in the same conversation.
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Old 01-29-2007, 08:48 AM
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Default RE: OS46AX w/ Macs pretuned pipe?

Good point.

The black Macs work well... but they are only light-weight mufflers.

Many folks do confuse these with tuned exhausts (I guess since Mac sells them). So on occation they show up in these threads.
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