AraTidwell

I do not have readings with the stock muffler w/ baffle in. All fuel 15% Wildcat

Stock muffler w/ baffle removed:
APC 12x4 13,900 rpm

Jett / Evolution performance exhaust
APC 12x4 14,200 rpm

300 rpm? I was expecting to break 15K easy. I am a bit dissapointed.

Good news is it seems to run really clean, I had to richen the needle about 1 turn so it might guzzle a bit more fuel. I have not flown it due to snow on the ground, tomorrow looks good though.

Eganwp

My Feedback: (1)

That pipe is tuned for 14,500 RPM+, that's why it's not performing as well as you expected. It's meant more as a high RPM pipe (great for pylon racing), not a 3D lugger.

Prop that with a baseline before the pipe to 14,500 and then try the pipe. Try an 11x5 or 10x7/8 and watch her get close or break 15's. As well, in my experience, removing the baffle has already netted you 400-500rpm over stock w/ baffle, so you can't expect much more than 800rpm more with the pipe over that reading.

BTW, here are my approximate RPM results on a pylon setup with this engine/pipe:
9x7 APC = 16,740rpm
9x8 APC = 16,350rpm

AraTidwell

Ok I went out to the field again and spent a little more time with it. I got 14,500 this time around. Not bad, but according to the Horizon Hobby Evolution manual most props in my baseline RPM range were getting 1500-1900RPM more however you did point out my baseline spec was already with the baffle out.

ThumbSkull

My Feedback: (57)

14,000 and a 12" prop is not well suited for 3D.

MetallicaJunkie

there are three sizes of jett muffler that will fit a 55 ax one is 8.5" in length the more common one is 7.5" and the balls out rpm one is 6.75 inches long

http://shop.vendio.com/rossienginesu...816/index.html
http://shop.vendio.com/rossienginesu...812/index.html
http://shop.vendio.com/rossienginesu...817/index.html

ThumbSkull

My Feedback: (57)

Macs also has three choices for the 55AX.
1. MACS Scotsman Muffler #6724 *will need to be ordered with a $3 extra tap for the muffler pressure.
2. MACS Regular Black Muffler #6720 *comes stock with a muffler pressure tap.

Either of those are going to lose you 2.1oz over the stock muffler and
give a substantial gain in power without sacrificing the midrange.
I get a tick over 13,000 RPM on a 13x4 APC or Xoar with either of these on my 55AX's

*The #6590 made for the 46AX was originally suggested by Macs for the 55AX
but it is too small in volume so they made one specifically for the 55.

MetallicaJunkie

does the scottsman give a boost in power over the black muffer

ThumbSkull

My Feedback: (57)

They seem about the same but I have not swapped which engine they are on for comparison.

Mine perform about the same but the Scotsman is about twice as loud (+6dB) over the regular
black which is slightly louder than the stock muffler with the baffle in.

1QwkSport2.5r

A little off the subject, sorta... Where is a good place to get a dB meter? I've got a few engines and a few exhaust choices and would like to check the noise level..

on the subject: I've heard from a few sources that the Macs black pipe doesnt boost performance much over a stock muffler (generalized statement, sorry). Someone recommended a tower muffler over the Macs.. any reason behind this?

proptop

My Feedback: (8)

A friend of mine got one of these...

http://www.radioshack.com/product/in...ductId=2103667

Don't know how accurate they are, but we figure that our measurements are all relative to one another anyway...one engine vs. another, not some "standard"...

The Macs one piece (black ) muffler is basically a large volume header with a restricted end. I have a few of them, and like them as a slightly lighter (and much cooler looking ) replacement for the stock muffler. I have seen an approx. 200 r.p.m. gain over stock on a TT .42 GP.

The Tower / Aquacraft muffler seems to act a bit like a mousse can...sort of a "poor mans pipe"...but they seem to be getting rather hard to find. (GMS makes Tower's engines, and production has slowed dramatically )
They typically sell for less than 20 bucks, so they are a great value, IMO. The Tower / AQ .46 muffler fits all the same basic size engines like the TT .46, and O.S. .46 FX, AX. .55AX, Magnum .46 and .52, Evolution .45, .46, .52 and .60

1QwkSport2.5r

Sweet... Thanks!

ThumbSkull

My Feedback: (57)

Macs one piece mufflers do help on performance.
After actual testing, the original 6590 (made for the 46AX but fit the 55AX) gave only a few hundred RPM over stock.
The new 6720 and 6724 both give a great performance boost of 1,000 RPM over stock with a 13x4 APC sport or Xoar.
The 6720 and 6724 is very comparable to the tower muffler performance-wise but is lighter.

Most SPL meters are uncalibrated and useless for reading actual SPL. The RS meter is OK for relative levels when comparing two setups.
A real calibratable meter and calibration device will be well over a grand.

The real problem with SPL meters is the way they are used in this hobby. Most of the guys using them have really no clue what they are doing.
Since the inverse square law is in play with sound, the distance from what you measure is critical as well as any boundaries or reflective surfaces.
High frequency is directional and low frequency is not directional.
Also with the meters there is something called weighting that limits what frequencies are being measured is very mis-understood.

lfinney

My Feedback: (44)

the macs mufflers are much better with fuel consumption versus the tower mufflers and more durable as well....