540 Lycoming 300 hp exhaust size 2.5 or 3"?

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twister69z
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540 Lycoming 300 hp exhaust size 2.5 or 3"?

Postby twister69z » Sat Dec 18, 2010 2:13 pm

Pros and cons to running 2.5 inch exhaust headers with mufflers or should I go 3"? Engine is a 300 hp O-540. Anyone tried both? Thanks in advance.
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Re: 540 Lycoming 300 hp exhaust size 2.5 or 3"?

Postby billybob » Sat Dec 18, 2010 2:31 pm

Either works fine! 3" sounds more throaty.
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Re: 540 Lycoming 300 hp exhaust size 2.5 or 3"?

Postby Bubba » Sat Dec 18, 2010 5:10 pm

2.5 without mufflers, 3 with mufflers.
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Re: 540 Lycoming 300 hp exhaust size 2.5 or 3"?

Postby chuckitt@earthlink.net » Sat Dec 18, 2010 5:28 pm

2.25 with Tuned headers will make you about 25 more HP, even with 2.25 mufflers. Makes more torque too.
Thanks, Chuck

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Re: 540 Lycoming 300 hp exhaust size 2.5 or 3"?

Postby jre1226 » Sat Dec 18, 2010 6:50 pm

Thanks, Chuck[/quote]
chuckitt@earthlink.net wrote:2.25 with Tuned headers will make you about 25 more HP, even with 2.25 mufflers. Makes more torque too.
Thanks, Chuck


thats interesting when my motor was built i was recommended to use 3'' how did you come up with those numbers

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Re: 540 Lycoming 300 hp exhaust size 2.5 or 3"?

Postby swamp runner » Sun Dec 19, 2010 11:35 am

now this is a topic ive not herd before,COOL, i personally wound like to know about exhaust size and performance!
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Re: 540 Lycoming 300 hp exhaust size 2.5 or 3"?

Postby pirate » Sun Dec 19, 2010 11:47 am

If I'm not mistaken "tuned" six into one and four into one exhaust systems are the same diameter as the exhaust of the cylinder until they are joined. In the case of the O-360/O-540 this would be 1 3/4 inches. This is also the case for the 2 "tuned" two into ones on the O-360. See link below.

http://www.aircraftexhaust.net/projects ... ojects.php
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Re: 540 Lycoming 300 hp exhaust size 2.5 or 3"?

Postby Big Casino » Sun Dec 19, 2010 4:28 pm

I'd like more real facts also. I'm in the process of building an exhaust system for a new O-520.

I,m gonna try a criss-cross pattern, but without tying them together thru an x-pipe or anything. I'll run the left bank down, under/across, then up and out the right side; and vice versa. Stack a pair of DynaFlow's just above the stringers and inline with the fuel tank, since that air space is already disturbed.

The increased length of flex from the muffler back should reduce engine noise. I figure 2.5" between the header and muffler, then 3" out, to compensate for the increased length.

I want quite but WITHOUT sacrificing performance .....
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Re: 540 Lycoming 300 hp exhaust size 2.5 or 3"?

Postby cntry141iq » Sun Dec 19, 2010 11:26 pm

I run big truck muflers .. carquest part # 5571 I beleive .. my left side exits the boat on the right side .. etc. engine is very quiet .. but after 2200 or so prop noise takes over .. but for froggin it is cool .. I cranked it up today out in the shop and people in the house never knew I hd started it and I ran it up to about 2000 rpms several times ... two engine pipes into a 3" collector then flex to a 3" muffler but it is a quiet truck muffler .. I gained 200 rpms over the noisy shorty straight thru mufflers most a/c run .. same prop setting guaranteed becaus eit is a whirlwind and take it off and put it on no pitch changing .. I had to add pitch
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Re: 540 Lycoming 300 hp exhaust size 2.5 or 3"?

Postby twister69z » Mon Dec 20, 2010 9:31 pm

Thanks for all the responses , I am going to do some test cell time with both sizes and mufflers with more and less back pressure.Checking Manifold pressure and RPM output with varying degrees of pitch on a ground adjustable propeller.
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Re: 540 Lycoming 300 hp exhaust size 2.5 or 3"?

Postby Southern Style » Wed May 06, 2015 6:15 pm

Those are some really nice custom exhaust set ups! Looking at the pvc mock up's, it could get harry if you are just a little off on your markings. But it seems like they know what they are doing. Great to hear that some are actually gaining RPM's or HP from doing their homework...... and getting some really rank looking exhaust set up's to boot!!!.... Great thread, very informative.. Thanks to all who are posting. Keep the results coming !!!
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Re: 540 Lycoming 300 hp exhaust size 2.5 or 3"?

Postby Cody25911 » Wed Dec 23, 2015 6:52 pm

Curious if anyone had any new findings with this. I bought a AV 200 a few weeks back and it had a set of 3 inch open headers that were on their last leg. Went and bought 2.5 headers and mufflers. I guess we will see if I can feel any seat of pants difference.

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Re: 540 Lycoming 300 hp exhaust size 2.5 or 3"?

Postby chuckitt@earthlink.net » Sun Jan 24, 2016 9:43 am

This boat has a Lyc 0-320 with 4 into 1 tuned headers. All down tubes are 1.75 inch and 32 inches long. The merge collector is spring mounted and 2.25 inch collector with a 2.25 inch X 12 inch open resonator for a muffler. All Ceramic coated inside and out. This boat was viewed and ran at the Sun&Fun Airshow for a week before being shipped to a special customer in Alaska. He did not mind paying 1500.00 dollars for the exhaust system. He knows what makes power and owns some of the fastest toys in Alaska.
Thanks, Chuck
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Re: 540 Lycoming 300 hp exhaust size 2.5 or 3"?

Postby chuckitt@earthlink.net » Sun Jan 24, 2016 9:48 am

4 into 1 Tuned Headers.
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Re: 540 Lycoming 300 hp exhaust size 2.5 or 3"?

Postby chuckitt@earthlink.net » Sun Jan 24, 2016 9:59 am

0-540 SV 3 into 1 tuned headers with 2.25 inch collectors and mufflers. Down tubes were 32 inches long. By the pitch and rpm of the prop we estimated a 25 HP gain.
Thanks, Chuck
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Re: 540 Lycoming 300 hp exhaust size 2.5 or 3"?

Postby SkinnerBack » Tue Jan 26, 2016 11:42 am

I have the Norman Clay 3" headers with mufflers on my 540, very throty good sound..... I put some 3" shorty stacks that were about 8-9" long...... I lost the torque roll when mashing on it but gained 150rpms & it was a little snappier...... & honestly not as loud in my opinion!

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Re: 540 Lycoming 300 hp exhaust size 2.5 or 3"?

Postby Gary S » Wed Jan 27, 2016 6:36 am

SkinnerBack wrote:I have the Norman Clay 3" headers with mufflers on my 540, very throty good sound..... I put some 3" shorty stacks that were about 8-9" long...... I lost the torque roll when mashing on it but gained 150rpms & it was a little snappier...... & honestly not as loud in my opinion!



So your saying open stacks are quieter than headers with mufflers?????

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Re: 540 Lycoming 300 hp exhaust size 2.5 or 3"?

Postby SkinnerBack » Wed Jan 27, 2016 9:12 am

I probably shouldn't have said quieter, my headers with mufflers have a deep tone to them @ 3k rpms, the shorty stacks didn't have that deep tone to them....... It was a high pitch tone......

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Re: 540 Lycoming 300 hp exhaust size 2.5 or 3"?

Postby glades cat » Wed Jan 27, 2016 1:21 pm

Many things happen during the exhaust phase. Combustion gases/particles are released and a pressure wave also travels down the pipes. The idea is to get the particles out with the assistance of this pressure wave. A common theory is that bigger is better…not the case. An ideal tuned exhaust should produce a low pressure wave at the time the exhaust valve opens, which will assist chamber evacuation and allow a more complete fresh intake mixture. To do this requires the proper equipment or trial and error. Properly sized tuned primary tubes, collector and muffler will all influence pulse timing and desirable pressure drop at Exh Valve Opening. Longer length headers raise back pressure and delays the onset of scavenging, while shorter lengths reduce the ability to contain a fully developed, powerful wave. It's more than meets the eye.
Do some more research and learn what's been done to the 300 hp Lyc o-540 and the results obtained.
Here's a link to some good reading on tuned ext on aircraft engines:
http://www.wemakeyoufly.com/tuned-vs-eq ... t-systems/

I would take the advice and info Chuck offered in his posts above and consider them to be very valuable. He does a lot of homework and has been on the cutting edge of air boating a long time. He will surely steer you in the right direction and keep you from chasing an exhaust rabbit down a bad path.
Last edited by glades cat on Wed Jan 27, 2016 1:50 pm, edited 1 time in total.
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Re: 540 Lycoming 300 hp exhaust size 2.5 or 3"?

Postby glades cat » Wed Jan 27, 2016 1:44 pm

Take a look at these AV exhaust systems. Talk about nice! And they're supposed to be tuned and make more power…on dyno and testimonies.
http://www.wemakeyoufly.com/cessna-airc ... st-system/
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Re: 540 Lycoming 300 hp exhaust size 2.5 or 3"?

Postby dshaw94 » Wed Jan 27, 2016 9:58 pm

glades cat wrote:Take a look at these AV exhaust systems. Talk about nice! And they're supposed to be tuned and make more power…on dyno and testimonies.
http://www.wemakeyoufly.com/cessna-airc ... st-system/


Neither one of that companies published power numbers hold water when applied to the horsepower formula, the factory hp is inflated by 11 hp, and the hp with there super tuned jobs is over twenty hp off. If they are going to conduct false advertisements they should at least make there numbers work.
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Re: 540 Lycoming 300 hp exhaust size 2.5 or 3"?

Postby chuckitt@earthlink.net » Thu Jan 28, 2016 10:04 am

A formula to determine the HP of an engine is very general. It has nothing to do with the real world of building engines. A formula don't know what cam, heads, or pistons you used. The formula don't know how much internal friction you freed up when you built the engine. When a GM recommended fine tuned 750 cfm carb on a new GM ZZ383 was removed an a fine tuned 650 cfm installed, we picked up 18 HP. This was done on United Speed World's Dyno.
If a fine tuned carb can increase HP, then why not fine tune the exhaust.
If your GM car produces 260 HP and I can load a calibration file in the ECM that lets your engine produce 300 HP, what formula will take that into consideration?
On a 6 cylinder aircraft engine, you can make just as much increased HP with a 1500 dollar exhaust system as you can with a 3000 dollar top end job adding high top pistons.
All airboat headers are made to be affordable. They are not designed to make power.
A custom set of tuned headers with 32 inch down tubes, mandrel bends, merge collectors, ceramic coated inside and outside can cost about 1500 dollars. If these headers were made in a production setup they may only cost about 800 dollars. Manufacturers want invest in setting up production of these performance parts just to have them set on the shelf because airboaters want pay that much for headers.

Thanks, Chuck

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Re: 540 Lycoming 300 hp exhaust size 2.5 or 3"?

Postby Dirtman » Thu Jan 28, 2016 10:20 am

Chuck, how did you come to determine the length of the primary tubes to be 32"? Were you the one who built the headers?
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Re: 540 Lycoming 300 hp exhaust size 2.5 or 3"?

Postby chuckitt@earthlink.net » Thu Jan 28, 2016 10:30 am

I did lots of research on header design for performance. Some performance header manufacturers helped me with info.
I built those headers. That is why I know how much time and material it takes to make a custom set.

Chuck

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Re: 540 Lycoming 300 hp exhaust size 2.5 or 3"?

Postby JPerkins323 » Thu Jan 28, 2016 4:55 pm

What does the ceramic coating do as far as performance. I'm about to put my boat back together and I just had my 3" headers and flex pipe ceramic coated but to be honest with you I only did it because it looked good lol I've never ran mufflers either but I got a set of mufflers too. Anxious to put it back together and see if I can gain something from it all.
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