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!!!!!

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)

Hi There Again Ted,

                    Thanks very much for your extra time in rehashing my question. that is much appreciated I assure you. Your answer is pretty much along the lines i had in mind also, but couldn't quite  rationalise it to myself. so again, thanks. Also, how did those heads ported to round exhausts perform on your tests? I had a bit of a search for it but didn't find it. As Aussie Bill said he had done that back in the day, so to had an Uncle of mine, though not on a Y-Block.

                    Hope all is well with you n yours, and another congrats on the EMC Project, fantastic result!

                                                                                                                                        yours Scotty!

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

Y-BLOCKS ROCK!!!!!

Ted has hit the nail on the head as to port match. The whole anti reversion theory is simply a band aid for a screwed up header to start with. How much time and money do you spend to blueprint the intake to head? The same should apply to exhaust port. It's even more critical as the exhaust pulses are traveling way faster. This week I'm building a set of headers on a 632ci drag car. The customer supplied the flanges with a 2.5" round port. The port is actually happy with a 2" tube. I spent a lot of time sleaving it down to 2". The collector is 2 3/8". The 2" at the port cones out to 2 1/4".

Thanks,

Jerod.


Jerry Jardine's Header Palace

307 455 3960

headers@jar-tec.com

That particular pair of heads with the round exhaust ports exhibited middle of the road performance gains when tested against other heads with conventional exhaust ports.  Here's the graphs showing how that particular set of heads did with three different sets of headers.

   

Lorena, Texas (South of Waco)

Thanks again Ted,

                    Reasonably impressive wouldn't you say Though well up there in rev range, and I would assume to though, that all these headers had the square port flanges still wouldn't they, and if so, surely none would have been large enuff to uncover/restrict, the ports?

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

Y-BLOCKS ROCK!!!!!

The fenderwell headers were the only set of headers of the three sets used in the round port head test that actually had round ports at the header flanges.  The round ported heads themselves were actually ported back in their day to match up to this particular set of headers.  The EMC and Sanderson headers have rectangular ports that were actually smaller than the ports at the heads and as a result, both sets had some flow obstructions taking place as a result of the mismatch at the heads.  But to look at the torque graph, the EMC headers outshined the other two sets of headers in the lower rpm band regardless of the port mismatch.

 

But as usual, there’s much more happening here than just a head to header flange port mismatch. The large dip in torque seen with the fenderwell headers has since been attributed to the collector size on that particular set of headers as being way too large.  Had this been recognized at the time of the round port head test, the fenderwell headers would have performed much better with downsized collectors.

 

Since doing that particular cylinder head test, the fenderwell headers have been tested again with a different set of heads on the engine but also with collector extensions that brought the collector sizes down from 4” to 3”.  With that change, much of the pronounced dip that was evident with the 4” collectors was removed from the lower rpm band of the curve.  Here’s the torque graph where the round ported fenderwell headers were tested on the mildly ported G heads that have rectangular exhaust ports.

 

Lorena, Texas (South of Waco)

Now THAT'S interesting! the mufflers did just exactly the opposite of what my intuition would have expected. More top end HP (TQ) and lower readings in the midrange. Splain that Lucy.

Frank/Rebop

Bristol, In ( by Elkhart) 

Gary R. (site member) had very recently shipped to me the latest Reds header offering for the ‘55/56 car chassis.  This new header is a four tube header design feeding into a very short 2½” collector.  Overall it’s still a shorty header but fares much better than the older two tube version that was tested.  Scoring is still calculated starting at 2300 rpms and ending at 5500 rpms.  I’ll add that this is also the best scoring chassis header that is designed to fit into the mid-fifties Ford cars.  All the other headers that outscored this particular set are either race car or dyno specific.  Here are the detailed results for this particular header. 

 

Reds 55/56 car 4 Tube 1.625” headers	Score	Peak HP	Peak TQ	Avg HP	Avg TQ	Mufflers
2” pipes 68” long w/mufflers	1690	287	338	231	313	Yes
2” pipes 66” long w/ no muffs	1730	290	344	236	321	No
2” pipes 24” long w/ no muffs	1726	303	344	237	319	No
2½” pipes 75” long w/mufflers	1729	292	345	237	320	Yes
2½” pipes 75” long w/ no muffs	1753	295	347	240	325	No
2½” pipes 28” long w/ no muffs	1746	307	349	240	322	No
2½” pipes 20” long w/ no muffs	1740	309	343	239	321	No
2½” pipes 12” long w/ no muffs	1721	304	332	236	318	No

 

 

And here is the revised chart showing the ‘best’ score for each exhaust system tested thus far. Keep in mind that the best score does not necessarily produce the best peak horsepower or peak torque values.

Description.	Score	Peak HP	Peak TQ	Avg HP	Avg TQ	Mufflers	Testing configs
Single exhaust with crossover pipe	1484	239	303	202	276	NO	2
1955/56 Dual Exhaust manifolds	1629	274	327	223	301	NO	4
Reds/Hedman two tube headers	1635	278	327	224	302	NO	3
1957 Dual Exhaust manifolds	1650	279	330	226	305	NO	4
Fenton cast iron manifolds	1663	282	332	228	308	NO	2
Tri-Y stepped shorty Tbird headers non-firing order specific - GB	1675	294	332	230	309	NO	4
Ram Horns w/2”into 2¼” pipes	1683	283	337	230	312	NO	2
Shorty 1.625” w/box collectors - DC	1693	284	336	231	314	NO	1
JC 4 tube car chassis shorty headers	1739	296	347	238	322	NO	6
Tri-Y pickup headers firing order specific-CC	1739	297	347	238	322	NO	5
Sanderson 1½” T-Bird headers w/2½” pipes	1751	297	350	240	324	NO	11
Sanderson 1½” Pickup headers w/2½” pipes	1751	300	350	240	324	NO	5
Reds 1.625” 4 tube hdrs for 55/56 car	1753	295	347	240	325	NO	8
Fenderwell headers 1.75” tubes - MW	1768	306	344	242	327	NO	5
Fenderwell headers 1.625” tubes	1769	308	346	243	327	NO	5
KC 4 tube Maxton Mile 1 5/8” headers	1775	310	351	244	328	NO	4
Rdstr 4 tube 1.75” gattling collector hdr	1778	309	355	244	329	NO	2
EMC headers 1.75”/1.875” stepped	1780	310	349	244	329	YES	4
FPA T-Bird hdrs 1.625”/1/75” stepped	1780	311	342	244	329	NO	13

 

Lorena, Texas (South of Waco)

Frank.  Those are the headers designed for the EMC competition and these actually work best with the mufflers in place.  Part of this has to do with the muffler inlet/outlets being larger than the actual collector size.  There is a 3” merge collector inside the 3½” header collector and the muffler sizing is 3½”.  This particular header and muffler combination ends up being a very nicely tuned exhaust system for the dyno and has thus far worked very well on a multitude of different Y combinations.

Lorena, Texas (South of Waco)