how headers work

[grumpyvette]

how do headers work

I was asked about a previous post,my example of how do headers work? (my explanation for non-engineers)what I think your refering to was when I was trying to explain how headers help pull the exhaust out of the cylinders by useing the energy from the previously fired cylinder mass of exhaust rapidly moveing away from the exhaust valve causeing a negitive pressure at the exhaust valve that helps scavage the cylinder. what I said was you can demonstrate that negative presure caused by a rapidly moveing mass by getting a 2.5"x5' long section of pvc pipe hold it horizontally and insert a full coke can with some tape wrapped around it so that it just slides easily into one end of the 5' long pvc pipe, now put your hand over the end of the pipe you just installed the full coke can into and rapidly drop the other end strait down, as the coke can slides too the floor you will feel the negitive pressure on you hand caused by the falling mass. now a cylinders volume of exhaust moveing through a primary header tube works in much the same way, while it weights much less than the coke can its moveing far faster and carries enought energy that the same negitive pressure is formed at the exhaust valve by the slug of exhaust gas traveling in the header primary tube, if the header primary tube is long enought to still contain the mass of exhaust gas at the rpm that matches the cam timeing and cylinder volume, now temp. cylinder volume, cam timeing and interior pipe dia. all effect the rpm range that this effect peaks at effiency wise but in most v-8 engines a dia equal too the exhaust port and about 32"-39" will put that negitive pressure wave caused by the previous fired cylinder at the exhaust port in the 4000-6000rpm range, look at this chart, http://www.engr.colostate.edu/~alla...ength/pipe.html http://www.engr.colostate.edu/~alla...ength/pipe.html

now figure that exhaust is 1300f or 977k so thats about 25" at 6000rpm and about 39" at 4000rpm to get that pressure wave to work for you scavageing the cylinder(helping to pull exhaust out and the new intake charge into the cylinder.)hers stuff to read,

http://www.burnsstainless.com/TechA...ory/theory.html

http://www.engr.colostate.edu/~alla...ge5/page5f.html

http://www.engr.colostate.edu/~alla...ge5/page5f.html

http://www.feuling.com/randd/articles/art11.htm

 

BTW it should be obvious why shorty headers don,t make as much power,....the primary tubes being much shorter are also much less effective at controling that negitive pressure wave timeing and strength.

[Two40MuscleZ]

Grumpy:

 

Question: To overcome that lack of pressure draw when using "shorty" blockhugger headers, couldn't you add a "stinger" to the end of the collector, thus giving you additional draw pressure? It wouldn't necessairly be of any great length, but would allow for a greater increase in draw and correct the problem?.

 

Comps,

Van

[Mikelly]

That is an excellent question Van. Most of us are stuck with few header selections and the most common is obviously the shorty blockhugger. When you run the numbers for a number of these headers in DD2000 you find that shorty headers aren't costing as much HP as I had previously thought.

You do lose power, but not as much as many would think.

Mike

[johnc]

The draw (also called scavenging) effect is still there because that exhaust slug is now moving down the exhaust pipe. Unfortunately, the "force" of the draw is reduced because the "force" is now being distributed across all the primary pipes in the collector. You might also run into situations where the exhaust pulses from other cylinders on the collector run into each other due to unequal length primaries and/or bad collector design.

 

A Tri-Y header might help in this regard if you are limited to short primary pipes, but I'm thinking that if you can fit the bigger OD duals from a Tri-Y next to the block, you should be able to fit all 4 primaries.

[grumpyvette]

Mikelly;

first thing is that DD-2000 can,t give you a good idea of what the shorty headers are costing you in flow/power/torque over the full length headers because there is no input in the data for primary length or really for size as they just use an average for(large or small tube)you will be closer useing the high performance manifold choice.but read this whole article http://www.feuling.com/randd/articles/art11.htm

notice how anti reversion baffles can gain a bunch of power and a second set just past the MERGE COLLECTORS would help the mid range too.

 

Two40MuscleZ

Grumpy:

Question: To overcome that lack of pressure draw when using "shorty" blockhugger headers, couldn't you add a "stinger" to the end of the collector, thus giving you additional draw pressure? It wouldn't necessarily be of any great length, but would allow for a greater increase in draw and correct the problem?. if the collectors are the merge type( http://www.ssheaders.com/Collectors.htm ) and you include anti pulse reversion dams internally, yes they can be made to work up to a point.but notice

 

http://www.engr.colostate.edu/~allan/fluids/page7/PipeLength/pipe.html

that each square on the chart is about equal to 8" in length and you can,t get down to about 16"-25" in length(typically shorty header primary length) till above 6000rpm, so those shorty headers are not doing alot for you below 6000rpm.

[biohzrd]

i found a set of full lengths that look like they may work but i'm not hundred % sure.

go to this site and look at the part # thy-327y

http://www.thorleyheaders.com/gm_headers.html