i was mistaking your question. i thought u were asking how to figure out the length of pipe required for a bend. the picture you provided has slip joints rather than butt joints, and thats why its different. in a mandrel bend the diameter isnt changed, and thats why its used.

 

Yes. I know that a mandrel bent pipe still has the same diameter.
But it FLOWS a different amount of gas than a straight pipe will.

I'm trying to find the formula for how much less the curved pipe will flow.

 

Lotta variables go into header design. I'm not trying to be a prick but bend diameter wouldn't be high on my list of issues to solve.

And to answer your question: Beats the hell outta me.

 

May I ask what other issues you would be trying to solve?
I'm quite a noob when it comes to header design, but apart from packaging and actual pipe diameter, I have a rough idea of what I'll want to do when it comes time to build a header.

 

Learn to use google. If you really want to know, read this. You probably wont care enough to try and understand it completely lol. I didnt.

http://www.springerlink.com/content/...3/fulltext.pdf

http://www.sciencedirect.com/science...f&searchtype=a

You're making this too difficult...just make the bends slightly bigger and flare the straight sections to fit...

 

What R P M range do you want the headers to be most effective? Are you going for more torque or more HP? What will the exhaust gas velocity be? This is all assuming you already have the motor built the way you want it.

Do a search on exhaust gas scaveging. That should answer a few questions and raise a few more.

I dunno man. Building a set of pipes is no easy task unless maybe you're building them for a top fuel dragster. Other than that there are quite a few things to think about and after you've thought about them all the damn things gotta fit.

It's a good question though. Good luck on finding the answer. Post it here when you do, I'd like to know it.

 

i build manifolds and headers. i doubt what you want to do will make that big of a differenced in performance. you generally want to make each runner as simular as possable. the companies that calculate this kind of stuff do it with computer programs that are specific to that.

 

there was a thread started in here a few weeks back that linked over to another forum that was talking about header design and building a custom header. It didn't directly answer your question, because there are so many variables, but it did discuss the answer to your question, and even went into details as to why the computer programs aren't 100% right either. dig through the posts, maybe even a page or two back, and find it. I seem to recall it being titled something obvious.
header design really is a lost art... and subtle differences between two otherwise identical headers can make a notable difference when it comes down to the resulting power.
The thing that I believe Chronik Fab (or at least hope) was trying to say is that unless you're trying to break some record or racing competitively with a huge budget or trying at least trying to squeeze every last bit of power out of your race car engine, then it isn't worth trying to design and build the "perfect" header.
While I did say that those subtle differences make a notable difference, we are talking less than 2 hp... or maybe a few hundred rpms difference in the powerband. Something that the average car guy, or hell, even the above average purpose built car guy would notice.
the saying "you spend 10% of your money making 90% of your power and 90% of your money of the remaining 10%" is very much true when it comes to header design.
So, is that extra 1whp worth the trial and error it is going to take to build the header that produces it?

 

Pipe size is dictated by the engine parameters in header design and not the number of bends typically. The rshared_pm and valve events will largely play into overall length of tubes. Valve size, engine size, and port size are the main parameters that determine the tubing ID and steps. When you send off to burns for them to design a header they provide a properly sized collector for you and tell you the length, diameter, steps and step locations for the header as designed around your engine using their analysis. Their designs arent always the absoltute best but they are real close. You just have to do the math correct to figure the linear pipe length for each bend depending on the degrees of the bend which is simple math.

What you are describing is kinda like the equivalent straight length method of sizing tube/duct based on pressure loss of the elbows which is useful for fluid systems but pretty much discarded in header design. Less bends the better though.

 

Hmmm...I'm going to do some digging around and see if I cant find a rough equation for this...I'm going to have to assume that the only way to accurately guage this would be to put a bar and cfm gauge at both the inlet and outlet of the pipe to determine how much the barometric pressure changes as the exhaust gasses pass through the header design along with the total cfm of exhaust gasses the engine will put out if flowing freely versus how much it is putting out after passing through the header...as KJ said though...the less bends the better...but I'll work on finding out how much difference it would make if you can tell me the pipes ID, and the total number and degree of bends you plan to put into the pipe...I would most likely assume that after the first bend the amount of cfm flow reduction would be a diminishing return as the first bend would dampen the exhaust gas flow down to the maximum allowable amount through out the rest of the exhaust manifold...however...that's not entirely ruling out the idea that the flow could pick up velocity again in the straights. But seeing as how there is nothing to provide additional inertia behind the slowed gas flow aside from the same slowed gas flow, I cant imagine this being the case.

Another thing to consider in this equation is that forcing super heated gasses downward is also sure to slow it's flow...knowing the downward slopes of the header design would also be helpful in determining flow capability...along with the approximate EGT throughout your powerband...AND the ambient temperature of the area you are running the car in (to determine total thermal resistance)in other words...there are A LOT of variables.

Ultimately, the best design to evacuate exhaust gasses would probably be to have straight pipes angled squarely away from the engine at a 40 to 45 degrees upward angle...but I doubt seriously you want your car to look like the dragula car from the rob zombie video lol.

Something like this lol.