Ever wonder which is best 2.5 or 3 inch pipes? What about balnce tubes? Is there a "right" place to put the muffler? Are tailpaipes the hot ticket? And how do I choose or build the best header for my engine?

Get your calculator out, put your feet up, and start designing your own header and exhaust system, for your specific combo.With these exciting, ok, tedious, formulas straight from various engineering texts.

I use these for my stuff and have seen a 6 hp gain across the board and 10 at peak on a chassis dyno when replacing the best of the prebent X pipe stuff with a system designed like this....


1. First calculate individual cylinder volume.

(((Bore x 2.54) x (Bore x 2.54)) x (Stroke x 2.54) x 6.2832) / 8 = individual cylinder volume

2. Select desired peak horsepower rpm (i.e. 6000 RPM, from your dyno sheet if possible)

3. Identify exhaust valve opening BBDC (Before bottom dead center) in degrees (i.e. 67 degrees BBDC, from your cam spec sheet)

4. Calculate ED. Add 180 to BBDC spec (i.e. 180+67= 247)

5. Identify collector diameter inlet (almost always 4 inches)

6. Identify collector diameter outlet (almost always 3 inches)

7. Collector cotangent angle of taper will be 7 to 8 degrees for most headers

8. Calculate header primary tube length.

(ED x 850) / (Peak power RPM – 3) = primary tube length in inches.

9. Calculate primary tube inside diameter (ID)

Square root of ((Individual cylinder volume / ((Primary length + 3) x 25))) x 2.1 = primary ID in inches

10. Calculate collector length.

((Inlet diameter – outlet diameter) / 2)) x cotangent angle of taper = collector length in inches.

11. Calculate intermediate (collector to muffler)pipe ID

Square root of ((Individual cylinder volume x 2)/((Primary tube length + 3) x 25)) x 2 = pipe ID from end of collector taper to front of muffler

12. Calculate intermediate pipe length

(Primary tube length+3)-collector length = intermediate pipe length in inches

13. Calculate balance tube ID

1.5 x Primary tube ID = balance tube ID in inches

14. Tailpipe. Same ID as Intermediate. Minimum 8 (12 is better) inches long to scavenge the muffler. It can be any length as long as it’s not shorter than 8 inches.

The header you just designed will ensure that the sonic reversion pulse travels back up the pipe to the exhaust valve precisely at the right time at peak power RPM. The exhaust system will support the pulse timing and scavenge the header and muffler. See, it's simple.... :confused:

Gary

Thanks for the formulas! :cool:

Now, hmm, let's see... graemlins/angry.gif ... Excel spreadsheet? redface.gif ... :confused:

That's some really great info.....but, you lost me after #3 tongue.gif If I knew those specs, it merely a matter of plugging in the numbers, no biggie, but how would one find them?

hmmm, something not right about #1.

(pi)(R)(R)(stroke)

Should work a little better.

COOOOOOOOOOOL stuff, I saved it for future reference.

This gets cyl. volume a little easier Bore x Bore x .7854 x Stroke gives one cylinder's total volume.

What Harold said. That's the easiest way I've seen. .7854 is pi/4 if anybody wonders where that came from.

Tom

5. Identify collector diameter inlet (almost always 4 inches)

6. Identify collector diameter outlet (almost always 3 inches)

Identify? What does that mean? A 283 needs the same collector size as a 502?

8. Calculate header primary tube length.

(ED x 850) / (Peak power RPM – 3) = primary tube length in inches.


Would that be:

(ED x 850) / (Peak power RPM ) – 3 = primary tube length in inches.

Subtracting 3 from 6000 makes very little difference.

The header you just designed will ensure that the sonic reversion pulse travels back up the pipe to the exhaust valve precisely at the right time at peak power RPM. The exhaust system will support the pulse timing and scavenge the header and muffler.

Where does this reversion pulse come from? Would there be more than one? What RPM's are the waves out of phase and detrimental to the scavenging?

Collector inlet size is almost always 4 inches, because you have to pack four primary tubes into it. Larger primaries, larger collector inlet.Smaller, smaller.It is not a critical dimension beyond being able to construct the header.

Outlet size will be the same as your intermediate pipe diameter (i.e. 3 inches or 2.5 inches.)Then knowing that the cotangent angle of taper wants to 7-8 degrees you can determine collector length.

onovakind67 is right on number 8, I typed the paren in the wrong place.

The sonic reversion pusles travel backward up the exhaust system and header and ideally arrive at the exhaust valve at the precise time to halt the flow of gases out of the combustion chamber to prevent over scavenging. This is how headers are really "tuned", not the tribal knowledge version which is eqaul pipes and gasses entering the collector, blah, blah, blah.Properly designed headers are specific to a given camshaft.

Gary

The sonic reversion pusles travel backward up the exhaust system and header and ideally arrive at the exhaust valve at the precise time to halt the flow of gases out of the combustion chamber to prevent over scavenging.


What creates these sonic reversion pulses? How intense are they? Does the temperature of the exhaust gas affect these pulses? Does the placement of the balance tube have any effect on the timing of these pulses?


This is how headers are really "tuned", not the tribal knowledge version which is eqaul pipes and gasses entering the collector, blah, blah, blah.Properly designed headers are specific to a given camshaft.

I don't know what the manufacturing tolerance of your header operation is, but most work with fixed tube sizes, like 1-5/8", 1-3/4", etc and can control the lengths of the primaries within +/- 1/2" or so. This would significantly broaden the application range of a set of headers, not just to one specific camshaft. Do you account for the port length in your calculations?

11. Calculate intermediate (collector to muffler)pipe ID

Square root of ((Individual cylinder volume x 2)/((Primary tube length + 3) x 25)) x 2 = pipe ID from end of collector taper to front of muffler

Somehow I keep coming out with pipe sizes in the 3/4" range. i.e. 33" primary tube, 41.4cu.in volume, I'm taking the square root of 82.8/900 and multiplying it by 2 for an ID of .606"

Collector inlet size is almost always 4 inches, because you have to pack four primary tubes into it. Larger primaries, larger collector inlet.Smaller, smaller.It is not a critical dimension beyond being able to construct the header.

Outlet size will be the same as your intermediate pipe diameter (i.e. 3 inches or 2.5 inches.)Then knowing that the cotangent angle of taper wants to 7-8 degrees you can determine collector length.

onovakind67 is right on number 8, I typed the paren in the wrong place.

The sonic reversion pusles travel backward up the exhaust system and header and ideally arrive at the exhaust valve at the precise time to halt the flow of gases out of the combustion chamber to prevent over scavenging. This is how headers are really "tuned", not the tribal knowledge version which is eqaul pipes and gasses entering the collector, blah, blah, blah.Properly designed headers are specific to a given camshaft.

Gary

I've tried my best but my head is swirling, the entire calculation is just too complicated for me.

Interesting and beyond my math skills ....... but FWIW did some testing on dyno with header sizing and collector sizing .......my 427 630hp .......Stahl Adjustable headers spec'd for my combo as shipped 2" primary 3 1/4 collector and a 3" x 20" split collector

Tried off the shelf 1 7/8 hedman with 3" collector , hooker 2 " 3 1/2 collector & shop 3 1/2 shop slip fit collector on Stahl 2" headr

ended up with Stahl 2" primary
BUT the 3" diameter 20"long collector made within 7hp of the 3 1/2 at peak rpm but torque was up all the way across the band by approx 15ft lbs ............. dyno guy / racer could not beleive that "little" collector worked so well and yes Jere Stahl wanted my cam specs when I ordered the headers .only cared about peak rpm and HP range I thought motr would be at ....... told me in general rpm and HP mean more than cubic inches when designing a header

Ever wonder which is best 2.5 or 3 inch pipes? What about balnce tubes? Is there a "right" place to put the muffler? Are tailpaipes the hot ticket? And how do I choose or build the best header for my engine?

Get your calculator out, put your feet up, and start designing your own header and exhaust system, for your specific combo.With these exciting, ok, tedious, formulas straight from various engineering texts.

I use these for my stuff and have seen a 6 hp gain across the board and 10 at peak on a chassis dyno when replacing the best of the prebent X pipe stuff with a system designed like this....


1. First calculate individual cylinder volume.

(((Bore x 2.54) x (Bore x 2.54)) x (Stroke x 2.54) x 6.2832) / 8 = individual cylinder volume

2. Select desired peak horsepower rpm (i.e. 6000 RPM, from your dyno sheet if possible)

3. Identify exhaust valve opening BBDC (Before bottom dead center) in degrees (i.e. 67 degrees BBDC, from your cam spec sheet)

4. Calculate ED. Add 180 to BBDC spec (i.e. 180+67= 247)

5. Identify collector diameter inlet (almost always 4 inches)

6. Identify collector diameter outlet (almost always 3 inches)

7. Collector cotangent angle of taper will be 7 to 8 degrees for most headers

8. Calculate header primary tube length.

(ED x 850) / (Peak power RPM – 3) = primary tube length in inches.

9. Calculate primary tube inside diameter (ID)

Square root of ((Individual cylinder volume / ((Primary length + 3) x 25))) x 2.1 = primary ID in inches

10. Calculate collector length.

((Inlet diameter – outlet diameter) / 2)) x cotangent angle of taper = collector length in inches.

11. Calculate intermediate (collector to muffler)pipe ID

Square root of ((Individual cylinder volume x 2)/((Primary tube length + 3) x 25)) x 2 = pipe ID from end of collector taper to front of muffler

12. Calculate intermediate pipe length

(Primary tube length+3)-collector length = intermediate pipe length in inches

13. Calculate balance tube ID

1.5 x Primary tube ID = balance tube ID in inches

14. Tailpipe. Same ID as Intermediate. Minimum 8 (12 is better) inches long to scavenge the muffler. It can be any length as long as it’s not shorter than 8 inches.

The header you just designed will ensure that the sonic reversion pulse travels back up the pipe to the exhaust valve precisely at the right time at peak power RPM. The exhaust system will support the pulse timing and scavenge the header and muffler. See, it's simple.... :confused:

Gary
Yes it is simple call the companys that built them for a living

I am lost at this one...

9. Calculate primary tube inside diameter (ID)

Square root of ((Individual cylinder volume / ((Primary length + 3) x 25))) x 2.1 = primary ID in inches

Square root of ((44.389498 / ((27.861538 + 3) x 25))) x 2.1 = 0.120820869

Square root of 0.120820869 = 0.34759296454330024

So I need a primary tube ID of .3475" :(

Ya, there was obviously typos made.

thread only 6 years old, maybe a few parens fell off during the storage? :)

thread only 6 years old, maybe a few parens fell off during the storage? :)

LOL

I took the easy way out and spent $40 to purchase Larry Meaux's Pipemax program when I built the current set of headers & exhaust.

thread only 6 years old, maybe a few parens fell off during the storage? :)


Wow I hadnt noticed that!

if you have to run exhaust...is it worth 5 or 6 hundred bucks for 7 horsepower?

i can see it if you are racing for a living.

building for streetable fun is key if you see street use.

How does this formula adjust for exhaust gas temperature? Speed of the returning wave differs with different temp. That's the reason these formula are a guestimation, and usually need some tweeking in length to get things optimum. Most people use collectors that are too large in diameter, and too short or too long. Most power comes from proper collector sizing. See PipeMax.

Thanks for that information.

My friend owned a pypes axleback,Im going with the the flowtech