No matter how much additional air is forced into the engine, no additional HP will be made unless additional fuel is also added. The energy that makes HP in an engine comes from the combustion of the fuel, not only the air. In general, every two HP produced requires one pound of fuel per hour. When modifications are performed that increase airflow into the engine, more air is available for the combustion of fuel. The combustion of the additional fuel is what translates into additional HP.

Air flow is not just influenced by the size (area) of the paths it takes into and out of the engine. It is also influenced by the speed at which it moves.

Specific Port Flow (cubic meter/sec) = Flow Velocity (m/s) x Average Path Area (m²)

Whenever an engine modification increases the average area of the airflow paths into and out of an engine, there is a chance the velocity of the flow will decrease. Most of the time the factor of velocity decrease is very small compared to the area increased, so flow is generally increased. If modifications are taken too far, the velocity will decrease more than the area increases, so flow is adversely affected (example - four inch exhaust system on a 1.6 liter engine).

1. A "shortie" or a "block hugger" flows better than a stock manifold, and helps to produce more power than stock. However, it is not technically considered a header. They are easier to install in a stock style exhaust system, which makes them attractive.
2. Bigger diameter primary tubes are NOT better in most street applications.
3. The torque/power boost available from a header will occur at a specific RPM that can be easily determined. The price paid for this boost is likely lower power at other RPMs. All engine design is compromise.
4. Equal primary tube length is very important for tuning and power output, but not to the point of obsessing over it. A regular Tri Y or 4-1 header will work wonders over the stock manifolds.
5. A long and smooth collector is a good thing.
6. Just like header tube size, be reasonable with the size of your exhaust system.

Those "facts" are browsed from internet, not my head.

http://www.fabshopheaders.com/header-facts.html

The more you read, the more you get new ideas...

http://www.otter-ag.ee/files/Header%20design.pdf

That doesn't really answer the question about sizes but it is otherwise interesting to read... I like the trial and error method more friendly for my wallet...

This one has more graphs and runner lengths calculated by rpm range

http://tom.marshall.tripod.com/exhaust.html

And this Merge Collector thing interests me more and more.

http://www.spdexhaust.com/pdfs/02-11_Merge_Collectors.pdf

And this is easy to read. Understanding is another dilemma...

http://www.popularhotrodding.com/tech/0310phr_jack_burns_exhaust_manifold_header_tech/index.html

When the heads and intake manifold dyno testing is concluded, an extensive exhaust system test is planned.  At this point I have the following exhaust systems on hand in which to test.

EMC four tube stepped headers with 3½” X 10” collectors w & w/o mufflers

EMC four tube stepped headers with 3½” X 28” collectors w & w/o mufflers

Fenderwell 1 5/8” four tube headers with 3” collectors

Fenderwell 1¾” four tube headers with 4” collectors

Pickup Tri-Y 1 5/8” headers with 2½”  collector opening.  Lead pipes being considered.

Thunderbird short tube Tri-Y 1¾” headers with 2½” collector opening.  Lead pipes being considered.

Reds/Hedman short tube headers with 4” long 2” diameter lead pipes

Rams horn exhaust manifolds with 4’ long 2½” diameter lead pipes w & w/o mufflers

Stock 1957 exhaust manifolds with 4’ long 2” diameter lead pipes

Four tube 1¾” headers with 3” collectors w& w/o mufflers (built for dyno testing)

Four tube 1¾” headers with 3” collectors (custom for a ’56 Ford racecar)

This looks to be a minimum of fifteen different test variables and likely at least 30 dyno pulls on the engine as each variable is normally tested twice.

The EMC headers have a 3½” collector but the collectors are now double walled with a 2½” smaller collector inside the larger one which helped the EMC engine.  That same header is currently being used on the 312 dyno mule without any changes from when it was used in the EMC competition.  I’m currently building some new 1 ¾” tube headers for the Y dyno engine with 3” collectors and without the stepped tubes as are currently being run.  There’s also another set of 1¾” tube headers of a slightly different design available that were just built for a ’56 Ford drag car that’s currently going together.

It must be remembered that dyno testing is WOT testing and smaller sized headers are not necessarily bad at low rpms and at a cracked open throttle operation.  It’s only when the engine is at full throttle that a larger volume of ingested fuel air mixture must be purged from the engine and that’s where sizing becomes critical as scavenging becomes a major player.  As a general rule, being too large on header tube size is not as detrimental to overall engine performance as being too small.

Bob Hedman made these for this car after Vic Sr. finished the engine. They're slightly different (flanges) than the T-bird headers the Hedman started to produce shortly thereafter. They're very similar to the ones that you can buy at Red's Headers, but these have 1 3/4" primary as opposed to 1 5/8"...neither version has a typical header collector. It's a slip joint/clamped connection.

I've been told that this design doesn't flow as well as the full-length Bird headers available ($$$$) but they are better than the Sanderson headers for the T-bird with straight exit from the engine and smooth transitions...though they do make plug changes even more of a nightmare...

The driver's side still installed before tear down:

And here's the passenger side, removed from the car:

Here are the Red's Headers version:

320497055363   just over a day left

I have an extra set of Sanderson 1 1/2" plain steel headers.  If they are what you are looking for, I would be happy to send them to Ted.  These are the same kind I use on the race truck except we use ceramic coating.  I doubt if these would work well on larger cu. in. engines, but the little 258" Y doesn't seem to mind.  Jerry C has been trying to get me to change them for some time with no success (he especially hates the collectors), (what collectors?).

And here’s a picture of the headers that were worth an additional 22 horsepower with mufflers in place over the ones pictured above.

Did you try a set of Jerry's rear dump headers? I'd like to know how they do on a Dyno. Chuck in NH

I am curious what the price difference would have been between john,s rams horn headers and these? Thanks.

On the rams horns, are you testing originals or John's, or is there any difference? I am sure John must have some info for this question.

Kenny.  If it’s not too much trouble, do drop your headers off at my shop while you’re passing through.  I’ll include them in the test.

Mark.  Thanks for the offer but it appears that I’ll not need your particular set of headers at this time.  I have a set of headers already here that should be representative of yours.

http://www.ssheaders.com/header.htm

Also,

Does anyone have experience with Speedway Motors chassis headers for Y-Block F100's.  If anyone has a set of these they can donate to the dyno cause I know I would be interested in the results.  I'm sure Charlie would be too.

Thanks,

Greg

ps.  This is my first post here....fantastic site.  I have two 1956 F100's.  One big window and one small window.  Both Y-blocks!

DeTomaso Pantera 180 deg exhaust manifolds as mentioned in previous link. Hard to fit, but...

The Hedman style T-Bird headers took a 339HP engine down to around 295HP

With regard to design: I have found from a lot flow bench testing that the Y-Block exhaust port is seriously hurt by any tube smaller than 1-3/4". The problem seems to be that the exhaust exits in  uncontrolled multiple paths. I call it a scatter-gun.  It appears that the large tube is needed to bring the multiple streams back into a single stream.

Regarding length: a very short header can work very well. The primary tubes need to be 20" or less. From there I believe that the tubes should be 36"+. The short headers seem to be too short to create standing waves while the longer headers take advantage of tuned waves. I think that lengths in between are long enough to be tuned but to an RPM that is outside the normal operating range of a Y-Block.

I'm not even close to knowledgeable in this field but this thread has prompted a lot of reading.  So, in attempt to help answer the tubing size issue, I found this from the Burns Stainless web site, part 4 of a 5 part series on welding headers.  It can be found under their Technology header...

"So, when fitting the header pipe at the head, it is critical that the exhaust pipe be either “port-fit,” or slightly larger (0.030” or less) than the exhaust port for proper flow.  The top of the port is the most critical section as this is typically the place of highest gas velocity during blowdown.   It is best that the header tube be oriented parallel to the top of the port.  Also, we prefer that the transition from the port to the primary tube be as smooth as possible over at least the top 90 degrees.  Some header builders prefer the “step” at the port reasoning that the step will minimize back-flow or reversion.  If this method is employed, the step should only be used at the bottom of the port."...

Also, from all my reading it appears for the RPM ranges most common to "street engines" the longer 36" primary tubes would be prefered.  If you have the room. 

John,

What were the primary tube sizes on these headers? Was that a contributing factor?

Regarding the Hedman style headers, they were 1-1/2" tri Y style that fit in a T-Bird. I think the flat top exhaust manifolds would have just as well.

It seems that headers with 26-30" primary tubes will be tuned to RPM levels above 7000RPM so probably won't work well for street engines.

Regarding flanges a local engineer named Jim Feuling used to make headers with a large oval cone that mated the flange to the primary tube with large end welded to the flange. His theory was that the exhaust would shoot right past the mismatch, but it would prevent reversion at low RPM.

I just did a quick search on the web for Jim Feuling anti reversion exhaust and found some interesting things. His later design went in-line in the primary tube.

Food for thought!

Charlie Mc,

You are very perceptive.  Tim is just finishing a third new 258" Y for the brick.  Today we discussed more chassis dyno runs and one of the comparisons will be different headers.  Perhaps we will make Jerry C smile after all (remember, he wants me to toss these Sandersons).

Ted's research will be closely scrutinized as well.  Headers are one of the last frontiers that we have explored and perhaps we have had our priorities a little out of line.  We will share any new positive data.