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Originally Posted by mid_life_crisis
Has anyone ever come up with an understandable explanation for this? It just seems odd. I believe it, but it still seems odd.
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This is probably the best explanation I've seen:
Quote:
Originally Posted by david borla
Hi,
This is David Borla from Borla Exhaust.
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Now let’s address the whole equal length versus unequal length headers thing. First of all, those of you who have noticed that neither of our headers are truly equal length are correct. It was not our intention to make the primaries equal length and we apologize if we mislead anyone. The reason we have two different designs are for differences in sound for an otherwise mostly stock set-up and to give enthusiasts who make other modifications options that may or may not show a performance increase and or durability advantage depending on their setup. Please note that these headers both perform the same on the dyno. I hate to get too deeply into this because it gets into theory of fluid dynamics, engine management, engine dynamics, physics etc. and I have spent hours and hours debating this with enthusiasts but please understand that “equal length” does not automatically result in “maximum performance”. In fact, even “equal flow” may not give you the most power available. You can easily decrease performance by making header primary lengths equal. When designing headers for street cars, in most cases you are at the mercy of packaging and you have to make compromises to keep primary lengths equal. Unlike on a race car, we don’t have the option of moving other critical components on The FR-S to maximize the flow of every primary. We only have a certain amount of space to work in. What winds up happening is that you take a primary/cylinder which is flowing better than the others and decreasing flow on that primary/cylinder to make it equal to others which aren’t flowing as well or in many cases the worst performing one. You don’t want to decrease the flow of any primary and that’s what you wind up doing in the quest for an equal length or even an equal flow header on a street car in most cases (not every case but most). What you really want is maximum flow, the most you can get from every cylinder. I can’t say it enough, maximum flow is where it’s at. You don’t want to decrease the flow of any primary. Another important aspect of this is that maximum flow does not mean the largest primary size available, primaries that are too large in diameter will also decrease flow. It depends on the engine characteristics and essentially how much air is being pushed by each cylinder. Bigger is not necessarily better, neither is equal length or even equal flow. Sure, in a perfect world, where every primary’s flow is maximized to its full potential, there are possible benefits to equal flow, again only if every single primary is flowing as much as it possibly can. If the flow of one or more primaries is limited by packaging, the only way to get equal flow is to limit the flow of the other primaries which will only hinder performance. Our intention was to design and manufacture bolt on headers that add as much performance as possible while sounding awesome and remaining highly durable. We are confident we have achieved this combination and back it with our million mile warranty.
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It's kind of long winded, but if I can extrapolate a bit, I think what he's saying is that the length of the two shorter primaries on UEL headers is probably the ideal length to promote exhaust flow in the torque dip range (3200-4500 RPM).
You can lengthen the shorter primaries to create an EL header, but in so doing, you lose that ideal primary length you had on two of the cylinders.
That is just how I interpret his statement, but could be wrong...
BTW I think if you extend the primary length enough, you eventually reach another resonance frequency that would generate ideal exhaust flow for that torque dip range. I think that is what Nameless was going for with their EL header, which is why the primary lengths on that header are so long. It's also a 4-2-1 design.