Here are dyno results showing what happens to the power output when a particular set of headers are used with and without mufflers on the 322” dyno mule.  The headers in this test are the EMC headers with 1.75”/1.875” stepped tubes going into a 3½”/2½” combination collector.  These are essentially the same headers used on the 2010 Engine Masters Challenge entry with the exception of 3” merge collectors being inserted within each  collector since this particular test took place.  On the EMC headers, the mufflers are an integral part of the exhaust tuning and scoring ends up being significantly lower without the mufflers in place.

The engine used in this test is a +060 over 312 with the cast pistons 0.025” in the hole and the heads are unported G’s with a light mill.  The compression ratio is 9.2:1.  Camshaft is a Crower Monarch with 238° @ 0.050” duration, 0.420" lift before valve lash, and using 1.4:1 no name rockers.  The intake is the Edelbrock ‘573’ 3X2 using Stromberg 97’s.

Scoring is as follows:

With mufflers -      1667pts.

Here are some additional dyno results showing the differences again with and without the mufflers as well as another set of headers throwed into the fray.  The engine in this case is a 375” Y with nicely ported iron ‘113’ heads and 10.2:1cr.  Camshaft is 254°/258° @ 0.050” and 0.595”/0.602” intake & exhaust lifts respectively with 1.6:1 roller rockers.  Intake manifold is the Mummert dual plane with a 824cfm Holley carb.  The EMC headers are the same ones described in the above post.  The racing headers are 1.75” diameter ~31" long tube headers with 18” long 3” diameter collectors and are the ones used on my Y powered altered roadster with a 337” Y.

Scoring in this instance is as follows:

EMC headers with mufflers –  2129pts

EMC headers w/o mufflers –   2096pts

It’s all in the combination but if the muffler itself is too restrictive, then topend performance is going to suffer regardless.  Magnaflow mufflers with 3½” inlets and outlets are being used and the mufflers essentially becomes an extension of the collectors without much in the way of a flow restriction while also exhibiting some good sound deadening qualities.  The EMC headers have header tubes that are larger than normal for a Y and collector tuning in this instance makes a lot of difference.  The larger tubes are needed for the topend horsepower numbers while the mufflers helps to restore some of the lowend by being a part of the collector tuning.  A longer collector can be made to do essentially the same thing as adding the mufflers so look at mufflers in this instance as being a part of the header and not necessarily just a sound deadening device.  Controlling the exhaust pressure waves in the collector area is key here and the mufflers become a part of that equation. 

Without the dyno, it would be difficult at best to quantify what works and doesn’t work in regards to some of the subtle changes being made on the exhaust system.  The general rule I adhere to is always err to the large side when dealing with exhaust systems and especially where wide open throttle performance is being optimized.  If an engine is running at a steady state 2200-2500 rpms day in and day out, then small tubes will be more efficient than large tubes.  The volume of air that must pass through the tubes at a light throttle opening is obviously much less that the volume that must pass under wide open throttle conditions.

Here’s an interesting tidbit regarding some past experiences with headers on my drag car.  The 427 HiRiser in my ’64 Fairlane doesn’t like mufflers at all.  Adding 4” inlet and outlet mufflers to the ends of the existing collectors kills performance on this car to the tune of  two tenths in the eighth mile.  That’s a bunch and especially considering that the mufflers are only 12” long and appear to be a wide open hole all the way through them.  But a little history on this particular exhaust system.  The headers started life out as 2.125” tubes going into 3½” diameter 6” long collectors.  I changed the collectors out to a 4” diameter collector the same length and the car still ran the same et’s but sixty foot times slowed while the mph picked up.  I then added 4” diameter 18” longer collectors to the existing collectors and picked up the missing 60’ times while not losing any of the gained mph.  Exhaust tuning is greatly improved at this point.  Adding mufflers to that conglomeration then kills what was gained on both ends of the track.  What hasn’t been tested on that combination is simply removing 12” of collector length and replacing it with the 12” long mufflers and seeing what the performance differences are.

When I was drag racing my F engined '57 Bird a couple years ago, I changed from the stock mufflers and 1 3/4" unresonated tail pipes to 2" in and out mufflers and 2 1/4 tail pipes and picked up a good 1/2 second in the 1/4 mile.  I didn't re-tune the carb or timing after the change, I probably could have helped it even more.

   I run a 2 1/2" system with an "X" pipe and Flowmasters on the factory manifolds. The car runs the same ET's and speeds with this as it did with open pipes, or A set of Hedmanns and 2 1/2 collecters. I removed about 75 lbs with the Hedmanns by removing the manifolds and the entire exhaust system, yet the car gained nothing in et or mph.

Here’s another muffler versus no muffler dyno test using the EMC stepped tube headers.  Completely different engine combination this time as it’s a 314 incher.  Engine particulars include a 3.810” bore (+060 over 292 block), 312 crank with turned down mains, C2AE truck rods, ported ‘G’ heads, 12½:1 compression ratio with Dykes rings in the top lands, extrude honed Blue Thunder aluminum 4V intake, Isky 505-T cam with 254° @ 0.050” duration ground on 108° lobe centers and installed at 106° intake lobe centerline (2° advance), 1.6:1 Dove rockers, and a 830cfm Holley vacuum secondary carburetor sitting atop a 2” HiFlo spacer.

Scoring:

With mufflers – 1713.0 pts.

Obviously  what you have works well. Do you suffer any performance loss with the blown out gaskets?

No, I haven't tried copper.  Actually it's no big deal, I only replace them when the headers are off for some other reason.  Have had the flanges ground flat, also have put a weld bead around the openings and had them ground flat but not ground to the flange, left themn sticking up a little.  The reversion thought may be what I'm dealing with, never considered it.

Frank.  You’re absolutely right in that the mufflers in the various tests using the EMC headers are essentially collector extensions from a design point of view.  I’ll add that on the drag cars I’ll use a 45° cut on the collector outlets which has always proven to be a benefit.  On the EMC engine itself, I was using ~8' of additional 3½" tubing behind each muffler as part of the tuneup on that engine.  Torque curve saw a drastic shift when the extra pipe was added.  When the extensive exhaust test on the +060 312 dyno mule is performed, I’ll include a variety of 3½” diameter extensions on the EMC headers just for the additional information it will generate.  A general statement on exhaust testing performed thus far is that each engine combination requires a different setup on the exhaust to insure optimum engine performance.  The testing on the dyno mule will give some generic guidelines but as is already evident in using the EMC headers on several different engines, the torque bands vary depending upon the total engine combination.

Here’s the pic of the EMC headers and mufflers that are being used.

EMC Headers – 1¾ X 1 7/8” stepped tubes with 3” merge collectors installed within the 3½” collector shells.  The Magnaflow mufflers are 3½” I.D. and add 18”  to the current collector length.

http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&item=270630324210&viewitem=

marv

       I have seen formulae for the primary lengths, but never the "Collecter" lengths. We used hear that you cut the collecters at the "Blue" lines on the pipes, I always used ET's to determine where to stop. In many cases the added low or mid range torque got the car through quicker than just top end HP. I spent about three months getting a 67 Pontiac Sprint (OHC-6) right. Car would go 12's with 230 ci and break store windows two miles off. The big deal then was the square Box collecter, never could make that work.

    John's tubing diameters are too small for the HP he makes, BUT, it's an automatic and fairly heavy. So maybe the mid range torque actually helps out of the hole. He's TWO SECONDS quicker than my car, with a 6-8 mph advantage. Something works!

I don't understand the 45 degree thing unless it spreads the torque curve out.  

 Marv: I'd think the copper would be annealed by one or two passes. Exhaust gas Temps will exceed the melting point of aluminum, or 1100 degrees. More than enough to anneal copper.     

Charlie.  There are plans to run the single exhaust system with the overhead pipe but no plans to take that particular system and test as a dual exhaust conversion.  There’s just not enough material here to fab up an extra pipe to test that particular scenario.

The ’57 car manifolds are laid out for a dual exhaust test which should be sufficient in quantifying the basic differences between a single and dual exhaust sytem.  The Rams Horns and Fenton manifolds will also be tested in a dual exhaust configuration.  After that, it will be a myriad of headers with various exhaust combinations being tested.  At this point, I’m waiting on header flanges that can be welded to the various pipe extensions before proceeding any further.

Frank.  The beveled cut on the end of the collector makes for a larger exit area for the exhaust without actually enlarging the diameter size of the collector.  This allows for an easier transition in the differential pressure between what’s in the collector and what’s outside the collector.  Reduced back pressure within the collector is the net result of the angled cut on the end of the collector.  This also has an effect on the db or noise level at the collector outlet.

The analogy to this is a water pipe that stands vertical with its exit or drain at the bottom.  With a straight cut, the reduced (and constant) surface area at the exit permits the water to actually stand within the pipe without draining.  This is atmospheric pressure actually holding the liquid in place.  With an angled cut, the difference in pressure is varied at the pipes exit from one end of the cut to the other allowing the water to freely drain without atmospheric pressure being able to hold it in place.  I trust that makes sense.