Quote:
Originally Posted by Nigel_S
There are no explosions involved, the valves open smoothly on a smoothly curved cam, initially allowing a tiny flow which smoothly increases before being smoothly closed again. The exhaust gasses should flow smoothly out the ports and down the pipes. Even the burning of the fuel isn't an explosion as many people think, it starts burning at the spark and the flame spreads out smoothly through the piston giving a smooth increase in pressure.
If things start exploding then things are going wrong, that is what detonation is and that destroys engines.
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The use of the word "explosion" was hyperbole / non-technical-definition there (sorry for the imprecision) - the rest still applies though. Exhaust gas flow is one of those problems for which you don't need to consider laminar flow conditions
at all.
Quote:
Originally Posted by Nigel_S
The main job of the header is to transport the exhaust gasses, they will flow easier through nice straight pipes, putting extra curves in to get equal lengths seems very questionable to me.
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Yes, it's definitely questionable.
Extra curves
are going to introduce extra resistance that's a given (this is also true of adding extra length). On the other hand, extra length
is going to change the resonance and dynamic properties of the system.
The actual question, of course, is whether the tradeoff is worth it - and I definitely don't know the answer to that in this case
.
I do know that for many, many racing and 'high performance' applications, equal length headers are worth quite a few extra bends even in cases where they have the option of running 'zoomies', 'shorties' etc. - I don't imagine Nascar and F1 teams would put that much effort into something that didn't offer an advantage. Whether it's worthwhile for the other end of the spectrum is, indeed, another question.
As with any engineering tradeoff, any given amount of extra bend, bend tightness & length will be (in very crude terms) "worth" a certain amount of advantage from dynamic properties. How much exactly? Well, I reckon I can manage double length with a pipe layout with only an extra 210 to 240 degrees (depending), some of which can be at a fairly 'lazy' radius. A 'ram horn' adds about 180 to 240 of extra curves depending on the layout.
Some people claim that for raw "performance", the tradeoff between building a ram horn and having slightly shorter pipes definitely
is worth it (e.g. "the k-tuned" company - see the writeup here:
http://www.k-tuned.com/blog/products/ram-header/). Of course, their shorter headers may simply be the "wrong" length, as they're working with K-series (rear exh. ports) swaps, so their other headers might just be tuned for detrimental resonance - I'd be more convinced of course if they ran a comparison with an untuned but cleanly built 'shorty' tube manifold, of course if the shorty came out better than their standard 4-1 and 4-2-1 they'd have a bit of egg on their faces
not to mention that a shorty doesn't look as sexy as their other offerings..
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I strongly suspect I'll have to build, dyno, tune, and road-test two versions to answer the question in my own mind. On the upside, at least one of the versions
should be better than the stock manifold...