Performance Airmotive 3" exhaust

I just finished test flying my cub with the modified Atlee Dodge 3" exhaust, gained 40 RPM static and at least 90 RPM on climbout.Climbout phase needs more flight testing as it seems to me this is where it really picks up the power. My 41 pitch I beleive is now innefficient at that RPM (2600) EGTs are down 40-50 degrees and CHT comes down when EGT comes down that much.
I am running a 41 pitch borer which I now need to repitch to at least 43, and get my climbout RPM down around 2475 to 2500.
What was the rule of thumb on pitch, 25 RPM per degree on the 82" borer?

I removed a stock Atlee Dodge muffler that was in good condition.

The beauty of it is it does not weigh an ounce more than a stock muffler, use your stock pipes and away you go.

Atlee Dodge and Glacier Aircraft sells them , my yellow tag says F Atlee Dodge "Hot Rod Muffler" P/N 3241HR

Bearsnack,

Wow!

Bob Breeden


www.AlaskaAirpark.com

Bearsnack,

Amazing timing.

I was almost going to start a thread asking questions on this muffler. I've heard from a friend that he gained 50 rpm over the LES. How is the cabin heat output? Is it comparable to the stock muffler?

I'm running a cracked LES with all the heater hoses disconnected so my skin doesn't turn blue in flight. It's starting to get a bit cold in there.

Jerry

I'll second that notion of good timing!

The guys who put together my most recent engine kinda poo-pooed the big muffler, said it didn't create enough/any back presure and therefore would "reduce" ponies. However I know of at least 3 people using them and have made claims of some RPM gain. I'll be watching this one and interested to hear more reports....

Of course this muffler doesn't have ANY guts, more than anything its a collection point for the exhuast... nothing to fall out, get loose, and NO A.D. in the forseeable future.

So is this just a "legal" gutted muffler, or something more. Not that anyone has ever run a gutted muffler before.... Does this muffler have any sort of baffles or is it just a open can?

Its a regular size "muffler" (collection point/ open can) w/ a massive 3" tail pipe

"Legal" or "Experimental" ?????????????????????????????????

It is an STC item. And it is just an open can with a 3" outlet.
I have never run a "gutted out" muffler so I don't know what you guys have seen for performance gain with those.
My engine is 130 SMOH and running like a top, I knew this would help because I have everything else in top shape, it could only help to remove that restrictor of a stock exhaust muffler.
I beleive this will become the top exhaust choice for alot of cubs in the future.
Jerry,
Cabin heat output? I don't know, I have my front shroud off right now, so she is not generating as much as it could. Hard to say.
I will take the penalty if it is reduced.

How about noise output? I tend to "sneak around" some sensitive residential areas around here at reduced rpm.... 8)

Are there any drawings for experimental high performance exhaust systems for O-320's around? I've built quite a few Motorcycle exhaust systems and would like to try one for the cub when I get to that part of the build.
Thanks
Glenn

I thought the muffler was the same and it was just the tail pipe that was larger. I would of liked to have gone with that muffler but I would have had to purchase the extra big heat shroud and my budget was shot with the price of the atlee d. muffler. teeweed

performance airmotive 3'' exhaust

howdy all,
just unboxed the performance/dodge 3'' exhaust,workmanship is excellent as usual,from dodge.will try and start numbers on the heavy duty stock dodge set up,and then the 3'' exhaust as quickly as we can change out on as close the same conditions as possible.
first impression was,this is a good looking alternative to the exhaust question.the only drawback i can see right now,it will still have the possibility of joint leak's,the plus is no ad's to comply with,possible performance increase,and a good source of used part's.
talked to butch at performace before buying for a good bit,he sold me,had dodge heavy duty.ppi/sutton on my last cub,so it will be interesting to see if there is a noticable change!
also trying to get a handle on the thrustline mod on this cub
durn thing flies different,come's off the ground faster,cruise is faster,land's slower,so something not right,but better,right?


jr.

I sent my prop out to be repitched to a 43, should have another test flight here this next week. As far as noise output goes, they told me testing showed 2 decibals over stock system. It does seem louder in the cockpit.
That to me, is minor. For the performance gain, getting rid of the AD, gaining speed(repitching prop to optimize performance), I see this as a minor downfall.
My gut tells me this muffler will wear better because of less heat retention, less welding and material into the fabrication of it. Bottom line, I beleive it will last longer.

How much? And, will it fit my stock everything without trouble.

It will fit with your stock pipes. A little trimming around the bottom cowl for the larger outlet pipe and that should be it.

I've ran this muffler for a whole season now and I really like it. Increase in everything, noise included but to me that's no big deal. Only thing that wasn't too high was the price.
Steve really does good work.

RB

3" exhaust

Its a touch louder,,, seems to get the yodel dogs up and moving better
Dave

I just bought this muffler and have one quick installation question.

I have a rear seat heater set-up installed which requires I cut a hole in the shroud around the exhaust pipe. Is it legal to do this or does it require further approval. I had it installed on both my les and stock system and assume I am ok to cut a hole in the shroud of the Performance Airmotive Exhaust system.

Jerry

Rear seat heat

Jerry I think your Dodge rear seat heater STC allows you to cut the hole in the shroud same as the stock system.
Dave

Bearsnack, i'm not sure that I'm following the logic of your decision to repitch from 41 to 43 in order to reduce the rpm that you can turn during climb. Are you saying that you want to reduce your available excess power during takeoff and climb, reducing your rate of climb and increasing your ground roll so that you can cruise at a lower rpm and and extend your range for long trips? What does the prop map for the borer indicate re efficiency at the two rpms and speeds?
All the best,
JimC

Jimc-- I repitched because I was turning 2480 to 2500 static and on climbout 2600. That climbout number was with the stick held back to keep the RPMs down, airspeed was indicating around 55 to 60 MPH. I would rather be climbing out at 2500 to 2550 at 65 to 70 MPH.
I believe i would be producing more thrust with a 43? Rather than the 41 cavitating at high RPM.
Thats my theory, as I recall you have some in depth knowledge in this department, tell me what is optimum performance here.

The following is considerably oversimplified, so don't take it too much to heart.

Climb is directly proportional to excess horsepower. You are proposing two changes. The proposed reduction in rpm will reduce your excess horsepower, so will reduce your climb performance. You are presently climbing at close to optimum airspeed (for a given aircraft, optimum airspeed changes with weight), but if you are flying a cub type aircraft, you are proposing to increase your airspeed to considerably faster than optimum, which will further reduce your climb performance.
However, your engine will cool better at the higher airspeed. Its all a tradeoff, and I'd say whatever you want to do is best for you. Personally, I like to static about 2500-2600 and climb out at about 2640 at about 55 mph (2640 is never exceed rpm allowed by my particular engine 337).

In general, for a given prop diameter your climb performance will increase as you reduce the pitch and let engine turn faster (like climbing a hill in 2nd gear rather than 3rd). If you reduce the diameter, then you can increase the pitch. For example, on an O-200 J-3 at typical weights, a 74-41 and a 71-42 have almost identical climb performance, but a 74-41 will outclimb a 74-42 and substantially outclimb a 74-43. Note that the engine is developing more horsepower with the 71-42 than it is with the 74-41 and it is developing more horsepower with the 74-41 than it is with the 74-43. As a rule of thumb, for a given horsepower a large diameter, slow turning prop will be more efficient than a smaller diameter, faster turning prop. But the difference is usually only a couple of percent, and slowing the engine down usually means that you lose more in horsepower than you gain in efficiency. In other words, your thrust horsepower is reduced, so your climb is reduced.
JImC

P.S. About the only time a prop will cavitate is when the pressure on the front surface is low enough to boil the fluid the prop is submerged in, turning it from a liquid to a gas. I doubt that your prop is cavitating.
JimC

My prop guy is the one that introduced the term cavitating to my vocabulary. He is on the conservative side of the park when we are talking climb props, it is hard to get him to pitch a prop down towards the climb pitch.
I think you are correct in saying it depends on the mission, in the past my cub has been used primarily to commute to work, light and empty most of time. I do some hunting and fishing with it.
So I guess I have been waiting for any excuse to reduce my commute time. Flying a 41 pitch where I run now would be a waste in my book.

What produces more thrust, a 43 at 2500 RPM or a 41 at 2500 RPM?
My goal is to have the high RPMs and the 43 pitch prop, that is what the exhaust mod is for on my cub.

> What produces more thrust, a 43 at 2500 RPM or a 41 at 2500 RPM?<

That's not enough information to make a determination. It also depends upon the manifold pressure and the airspeed, plus a few other factors (though I assume you''re holding them costant for purposes of discussion). Normally, you use the flatter pitch to allow you to turn higher rpm for more power. Have you looked at a prop map for your prop?

> My goal is to have the high RPMs and the 43 pitch prop, that is what the exhaust mod is for on my cub<

I understand that
Keep in mind that higher pitches will somewhat choke down the potential for higher rpms (speed increases with the cube root of the horsepower ratio -- it takes a lot more power to go faster).

My off-the-cuff hunch is that you'll go 3-4 mph faster with the 43, and lose perhaps something on the loose order of 10-15% of the takeoff and climb potential that you'd have with a 41. Again, I think the choice is dependent upon your personal mission for the aircraft. I'd go flatter, but I'm not spending much time enroute and more pitch may well be the appropriate choice for you. Fly both pitches and see which one you like best. Keep in mind that too much pitch will both choke you down and slow you down -- but that would take a good bit more pitch than 43.

JimC said:

> Normally, you use the flatter pitch to allow you to turn higher rpm for more power. Have you looked at a prop map for your prop?

Click to expand...

Jim

Where do I get the prop map for my prop? I have an 82x42. Is this something that an end user can read and interpret? I wouldn't mind furthering my knowledge in this area.

I was also considering going to a 43 but may reconsider now since take-off power is more important to me at the moment.

Thanks for sharing your expertise.

Jerry

I was under the impression that engine torque had something to do with with this propeller business.

JimC you mentioned prop map in a post care to elaborate? Bill

Prop maps are usually available from the manufacturer (when the manufacturer has done one and makes them available). For a given prop, it is a map of thrust vs.diameter, vs. rpm vs. horsepower vs. density altitude vs. airspeed vs. prop efficiency, relating all the variables. As an example of one format, Hartzell provides them as computer data files, including the software that interpolates them.

Torque does have something to do with it, but the relationship between torque and horsepower is a function of rpm, so if you know horsepower and rpm, you know torque. If you know torque and horsepower, you know rpm and so on. Climb is a direct function of excess thrust horsepower.
JimC

So, bottom line, you guys running the AD Hot Rod muffler...are you happy with it? I'm now facing the same notion that I'm needing to replace my worn out stock muffler, so the question is, which one? Hot Rod, LEES, or PPI? Any others not mentioned here?

This thread was started a few years ago, so there should be a lot more thoughts out there. Anyone care to share?

Thanks.

Bob