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/~allan...ngth/pipe.html http://www.engr.colostate.edu/~allan...ngth/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/TechAr...ry/theory.html
http://www.engr.colostate.edu/~allan...e5/page5f.html
http://www.engr.colostate.edu/~allan...e5/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.


[Modified by grumpyvette, 6:31 PM 3/10/2002]


[Modified by grumpyvette, 6:31 PM 3/10/2002]

 

Hi grumpyvette. We are new supporting vendor. Here is a link to add to your list. Please let me know what you think. Thanks. :)
http://www.headerdesign.com/extras/design.asp

 

well I like what I see :D (those pop-up definitions of terms are a great help for most of the guys) and Im sure you will be a big help here with the questions that come up quite regularly on the site. and I hope you realize that what I posted was strictly for a NON-ENGINEER AUDIENCE now I could easily get in to reflective wave speeds, reflective wave disperesion and heat retention but as a retired engineer Ive found that peoples eyes glaze over and they find something else to do real fast if I even start quoteing temps in kelvin or secondary versue primary pulse strengths so I try to keep things simple!

but just as a question, how well do you think I simplfyied the concepts for the guys?

 

Lots of good info here! Thanks guys!

 

How do headers work? Pretty good I'd say.:) Just finished my HookerSC install.:)

 

Sorry for the delay in responding. Had catch the end of the race.

Thanks for your kind words. As to your question, speaking engineer to engineer, since what happens inside the header is anything but simple, it is very difficult to reduce it to a simple explaination. Though I think your coke can illustration certainly introduces the folks here to how exhuast wave action can be used to purify the intake charge. Your explaination also does a good job of dispelling the old 'backpressure' myth.

My personal favorite analogy is to imagine you are standing in a river waste deep looking downstream. There is a waterfall 15 feet downstream of you. You take a board and make a wave sending it toward the waterfall. Watch the crest of the wave because it will be returned as a trough. That is what happens when the blowdown wave is reflected from the collector back towards the exhaust port. It is actually this reflected suction wave that scavenges the cylinder. Of course the wave travels much faster than the water in the stream, as you said.

I have spent the past year modelling the actual behavior in the header pipe and collector and packaged the results in the program on HeaderDesign. I share your goal of producing a very simple solution to a very difficult problem. The information on the site is intended for regular performance enthuiast, who have at least some rudementary knowledge of engines. The program readily accepts the Desktop Dyno output and produces the optimal header configuration.

I look forward to participating in the community on this and other topics. Thanks again for your kind words. I am happy to discuss further if you like.