Looks like I’m going to do another of those lengthy explanations here. For the most part, if you can put a dollar sign to the question, you’ll find the answer. In this case, it costs much less for the header manufacturer to utilize round ports at the header flange as these are much easier to produce than the ‘square’ ports at the flanges. That’s the dollar sign answer.

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But the essence of your question boils down to laminar flow versus turbulent flow at the exhaust port exit. With a round header port matching up to a square exhaust port at the head, there will be more turbulent flow at that point and part of that is due to ‘eddies’ that are being produced at the edges of the port. Those ‘eddies’ come about due to the extreme irregularity of the two different shaped ports being mated up to each other. When both the exhaust port and the header/manifold are similar in shape, then the flow becomes more laminar and as such, overall flow potential is increased simply due to the reduction of eddy currents in the air flow where the header meets the head.

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Besides the flow properties of a square or rectangular port on the head going to a similar shaped port on the header being an improvement over that of a round port, space utilization at the exit area on the head with a square or rectangular port is also better. An example is a 1.625” round port will have a square surface area of 2.074 inches. A square port that’s 1.44” X 1.44” will have the same cross-sectional flow area at 2.074”. Although the cross-sectional areas are the same, the non-round shaped port will have a greater flow capability than the perfectly round port.

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On the stock heads, round ports at the headers are typically not a serious detriment in regards to flow obstructions or gasket sealing as the corners of the ports on the heads are still within the boundaries of the round port at the header. When increasing the head exhaust port sizes beyond stock, then the outside boundary of the round header port size can be exceeded which makes for a flow inhibiting obstruction for the exhaust to make its way past. At this point, the square ports become a necessity if the ports at the heads retain the overall square configuration.

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I’ll also add that the exhaust port gasket sealing area on a rectangular head exhaust port is substantially increased when using a similar shaped header port. Going to a round port on the exhaust manifold or header where the head port exit is rectangular will minimize gasket sealing on the vertical and horizontal centerlines at the edge of the ports.

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Here’s a link to the thread showing some various ports and how the gasket sealing area is affected when doing a rectangular versus round port at the head. Obviously with a round port at the head, it’s also going to take a round port at the header as it would be a monster sized square port to compensate for the round port size.

http://forums.y-blocksforever.com/Topic46226-3-2.aspx

Lorena, Texas (South of Waco)

           Thanks all for your comments/replies, the use of round pipe was never in question, it was the point of using a "square" port flange and re-shaping the pipe to suit. Why all the extra effort, when the relevant sized tube for the port would be so much simpler/cleaner. When in dedicated racing use, more often than not, that is exactly what is done. Now I realise horses for courses, which brings me back to the line of thought, that there must be a valid advantage/reason. Sorry if I seem dumb, or sound like a broken record, but could try explaining again.                                                           

                                            Thanks again, Scotty!

"MY TWO BOBS WORTH!" (Twenty Cents AUD)

Y-BLOCKS ROCK!!!!!

Charlie.  Even with an expansion chamber, any restriction at the muffler would be seen at the engine and ultimately bring down the power numbers.  But once the restriction part is taken care of, an expansion chamber could be used to move the torque curve around.  The mufflers being a straight thru design over a chambered design are expected to show up as an advantage in this case.  The mufflers on the EMC headers are a straight thru design while all the other mufflers tested were the chambered design.

 

The crossover pipe being used in this particular test is the H design.  Here are a couple of pics of the crossover pipe that’s being used.

   

 

Here’s the graph comparing the open FPA headers without mufflers to the EMC headers with and without mufflers.  Because the horsepower is so similar on both, I’m displaying only the torque values which gives a better resolution.

 

Lorena, Texas (South of Waco)

Since the score continues to increase as the pipe diameter is increased, might some cone shaped expansion chamber help to achieve the higher numbers while still using a pipe and possibly a muffler.



The crossover pipe, is it an H or an X?



How does the open header graph compare to the EMC header graph?


Lawrenceville, GA

Here’s some more information that adds two more sets of headers to the list of those that have already been tested. These were also tested on the same engine combination as all the other exhaust systems which keeps comparisons equal.  Whereas only the best scores for each exhaust system were previously posted regardless of the number of configurations tested, here are the scores for each tested configuration for these two sets of headers.  The scores are still based on the overall performance in the 2300-5500 rpm range.

 

As in the previous tests, the mufflers continue to be appropriately sized based on the size of pipe that’s used in each test.  In the FPA header test chart below, there were three different pairs of mufflers being used.  The Ford Powertrain Applications (FPA) headers were unique in that the best numbers achieved were without any exhaust extensions being used and part of this could be attributed to the merge collector design being used at the ball shaped muffler connection at the end of the headers.  Many of the headers being tested did like some form of exhaust extension in which to improve their overall performance.

 

Crossover pipes were also tested and you can make your own assumptions based on the numbers.  Sometime in the near future, I’ll post the lower rpm band information which is where the crossover pipes appears to make the most difference when comparing the graphs.

 

 

FPA T-Bird 4 Tube 1.625”/1.75” stepped headers	Score	Peak HP	Peak TQ	Avg HP	Avg TQ	Mufflers
2.25” pipes 64” long w/mufflers	1738	298	346	238	322	Yes
2.25” pipes 64” long w/ no muffs	1749	298	348	239	324	No
2.25” pipes 18” long w/ no muffs	1761	306	352	242	325	No
2.25” pipes 64” long & 2” dia crossover pipes and w/mufflers	1735	300	347	238	321	Yes
2.25” pipes 64” long & 2” dia crossover pipes and w/ no muffs	1757	303	349	241	325	No
2.25” pipes 18” long & 2” dia crossover pipes and w/ no muffs	1761	304	352	242	325	No
2½” pipes 64” long w/mufflers	1748	297	348	239	323	Yes
2½” pipes 64” long w/ no muffs	1757	297	349	241	325	No
2½” pipes 18” long w/ no muffs	1763	306	354	242	325	No
3” pipes 64” long w/mufflers	1748	300	346	240	323	Yes
3” pipes 64” long w/ no muffs	1764	303	349	242	326	No
3” pipes 18” long w/ no muffs	1774	308	356	244	328	No
No pipes – open headers	1780	311	342	244	329	No

 

Roadster 1.75” tubes 31” long with 18” long 3” dia collectors & no mufflers	Score	Peak HP	Peak TQ	Avg HP	Avg TQ
Without evacuation system hooked up	1768	307	354	243	327
With evacuation system hooked up	1778	309	355	244	329

 

Lorena, Texas (South of Waco)

Ted,

Thanks for the reply about the ram horns and the pics to help explain it.  I am on the fence about ram horns or sanderson truck headers.  Like the look of the ram horns and clearance on my truck.

Here's my two cents worth.  The only straight thru mufflers used in the extensive exhaust test were the Magnaflow mufflers used with the EMC headers.  Those mufflers had 3½” inlets and 3½” outlets which was a perfect match for the outside collector diameter on the EMC headers.  On the EMC headers, the Magnaflow mufflers actually improved the score over no muffler at all.  Part of this is a result of the muffler sizing actually being larger than the actual downsized opening within the collector itself.  I was running a 3" merge collector within the outer 3½" collector.  All the other systems when tested with mufflers used a chambered muffler design which were overall quieter but also more restrictive.  Based on this, a straight thru muffler would be better from a performance standpoint than a chambered muffler.

Lorena, Texas (South of Waco)

I'm wondering if a muffler with a "straight through" design like a glass pack, or steel pack muffler would piss the Y Block off. I'm planning on running either Porters, or Smithy's. But if "ALL OTHER SYSTEMS DIDN'T PARTICULARLY LIKE MUFFLERS" then I may end up running straight pipes. What are you thoughts all wise one?

Heber City, UT (15 mins outside of Park City- basically it's in the mountains)

55 Effie

Don.  The Sanderson headers were tested with 2”, 2¼“, and 2½” pipes but the Rams Horn manifolds were only tested with 2½” pipes.  If using the Sanderson header test as a basis for pipe sizing in general, then the 2½” pipes will still work best on the Rams Horn manifolds even if the 2” outlet on the manifolds is maintained.  The key here is keeping the 2” to 2½”transition on the exhaust pipe itself as short as possible.  But taking this a step further, any enlargement that can be done to the RH manifold outlets will be beneficial so I’d recommend doing some custom work in that area when initially fitting up the pipes.  A 2¼” outlet on the RH manifolds would obviously be better and if you could work a 2½” outlet in there, then even better yet.  Here are pictures of the exhaust pipe used in the test with the Rams Horn manifolds and a 2” outlet to give you an idea of how the exhaust hookup was made to achieve the 2½” pipe diameter.

 

 

Lorena, Texas (South of Waco)

Ted,

Thank you for the reply on the Ram horn and muffler recommendation.  One thing you mentioned going from 2 inch on the manifold to 2.5 inch pipes.  I see on the test it said 2.25.  Would you recommend 2.5 or 2.25 pipes from the exhaust manifolds?  Appreciate the help.