Interesting study of header-tube length; the conclusion is that short-tube headers may be just as good as long-tube headers in reducing pressure drop in exhaust gases. http://www.designfax.net/cms/dfx/opens/article-view-dfx.php?nid=4&bid=228&et=featurearticle&pn=06
It seems the short tube is better, but minimally. And both are better than stock. I suppose in a racing application, this slight difference could mean tengths of a second, which could be a win or lose at the track. It didn't mention pipe diameter. I wonder what that would be? My question would be how much difference is there when they are used in a full exhaust system? I guess in that situation, mufflers and pipe diameter would come in to play as well.
Back up the claimed, with dyno readings and track times and we have a winner. Else it resembles estimates, modeling, with some real world aspects via Concord, MA, Solidworks programmers. My read in fabricating headers is that tube diameter and length, affect torque and power curves.
This is great if all you want is reduced restriction - this guy totally ingnores the scavenge effect that a header is supposed to create - this is a very misleading article.
The analysis does not take into account the tuned organ pipe principle that can be a major advantage with headers. The flow in the individual runners occurs in pulses so that there is a negative pressure wave which travels back toward the engine. You want to have that negative pressure present at the valve for the next time the exhaust valve opens. The length of the header will determine the RPM that matches the "tune" of the pipe. For short headers the tuned RPM range would be way too high.
The following is copied directly from the article, and may give an indication of the accuracy of the conclusion. Both after-market headers showed a drastic decrease in pressure drop over the stock manifold. However, the long tube only had an edge over the short-tube pressure by 0.019 PSI. "Decrease in pressure drop" is NOT what the conclusion should be. It is an "increase" in pressure drop, or reduction of pressure. "Decrease in pressure drop" is a form of a double negative, and can be re-written to "increase in pressure". Credit goes to Mrs. Doris Egland, my 7th and 8th grade English teacher. I'm such an ass when it comes to spelling and diction.
^Agreed with Fritz Junior. They didn't take into account matching with running mates either.... blah blah blah, tear this whole article apart. But there is also something to be said about the sound of a long tube header vs short or stock. Thats worth the $75 to me
"Decrease in pressure drop" is NOT what the conclusion should be. It is an "increase" in pressure drop, or reduction of pressure. "Decrease in pressure drop" is a form of a double negative, and can be re-written to "increase in pressure". Credit goes to Mrs. Doris Egland, my 7th and 8th grade English teacher. At first read I thought it was wrong, too. But the pressure drop is, in effect, how much restriction the pipes add. If the pressure drop were zero - no restriction. If the pressure drop were high, lots of restriction. So if you decrease the pressure drop, that's a good thing.
I think you are confused here - by going from a stock manifold to a header, you will have a "decrease in pressure drop", or in other words, less back pressure or restriction on the engine. An increase in pressure drop would mean the header or manifold was more restrictive. I design exhaust systems for large diesel engines for a living - we live and die by inches of water column pressure drop (25" w.c. = 1psi roughly; so not alot)
All you ever wanted to know about header-tube length is NOT in this article. If he truly is an engineer then I would expect a much more in depth analysis and he would have found that "pressure Drop" is not the only or even most significant attribute in exhaust header design.
What is an 'Elite Application Support Engineer'??? Is he one of them guys that has his exhaust pipe bigger than his pistons?
Hmm..all due respect for trying, but he forgot a coupla things that play hand in hand with what he tried to do...but.. Ya needs to add in other factors...such as - Tube diameter Cylinder evacuation RPM changes/levels Gear ratios Manual or automatic trans. Stall speed Max. RPM Car weight etc., etc. Not quite that easy..! Mike
Sounds like he has enough calculation capability to be dangerous and not enough info to be effective. His article stems around a puny engine too 12.x cubic inches per cylinder
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