[Arns85GT]

I'm working with a v6. The books call for 36" primaries. But, one side of the engine is really cramped and I need to put in at least 3 bends to make it fit. (The other side is no sweat)

I have an initial 70* on all 3 pipes, then the second bend which varies between 90* up to 180* on a 2" radius , followed by 2 - 90*s on a 3" radius. It's all pretty tight until it goes to the collector, which is a Shoenfeld.

We're talking pretty much a backwards "S" shape on #5 cylinder vs. a kind of "d" on #1.

So the question is how much length changes with, say, a 90* bend vs. a 180* bend, etc. Does anybody have some good data on this?

I can either shorten or lengthen to suit.

Thanks for the help,
Arn

[Rick WI]

Although it is almost impossible in some cases we try and make all the tubes the same length, without any account for flow restrictions due to the bends. Although I am sure there is some loss with bends the total length of tubing is SOOO short in the grand scheme of things its not worth going to the 4th decimal in calculating it out. For complex jobs just trying to get tubes within an inch or two of each other is a major endeavor. Concentrating on the correct primary tubing size and length, plus collector length is where we find the most gains on the dyno.

[Arns85GT]

Yeah, I hear you.

Some local guys have sort of said the same thing to me. The reason I am asking is that the one side is sort of like spaghetti if you get my drift.

I'm still curious if there is any research on it.

Thanks,

[chrisflock]

I don't recall where, but I read a project log where a guy actually flow-metered a variety of tubing of different diameters with different bends, and the results he got were a little surprising, but basically what it came down to was that bends were far less important than the length and diameter. If the bend changes the cross sectional area of the tubing, that will make a big difference because it is effectively dropping the diameter of the tubing, but otherwise he found that the overall length of the tube was a much bigger factor. Like, the difference between a straight tube 4 feet long and the same diameter tube coiled up (again, this was mandrel bends or what not, so the overall diameter stayed the same) was only a few %.

Anyway, I'm sure that Google would yield some technical papers on the subject that would probably turn your BRAIN into spaghetti...

[Rick WI]

Spaghetti is putting 2" equal length headers in a 70 Camaro stock stub car with AC while trying to maintain sparkplug and starter clearance. So yeah, I got your drift what it's like, a nightmare.

I'm sure as Chris mentioned there is data out there and if I got out my fuel gas code book I could give you some data on the losses per bend type. BUT, after being in mechanical engineering for 20 years the losses versus the actual mass flow and tubing length make it a pretty mute issue.

I worked with Bruns, Stahl, and others redoing a set of stainless headers on my car this past winter. I fabbed them up from the flanges out. All the time was spent on tubing diameter, lengths of steps (I step sized this set) length of primaries and collector design and length. No matter how you get there with the bends and folds in the pipe lengths the key was trying to keep them as equal as possible. In my case that was trying to be within a couple of inches.

Schoenfeld are great folks and we work with them all the time on the circle track stuff. They know their stuff and their headers make power. They would be my guiding light for any questions you have as you get more into it.

[Arns85GT]

Thanks guys.

That is really good advice. You've answered my question really well.

I am doing up mine from the flange out as well. I have laid out the bends on plywood, and, using copper wire 36" long, I've been able to lay out plans that are very close, and likely within 1/4 to 1/2" of being the same across all 6 pipes.

I'm using Schoenfeld slip on collectors and a custom laser cut flange. They should be nice if I don't screw up.

Arn

[Crazy Mopar Guy]

I made my own headers and wondered the same thing- one side looks a little bit on the "spaghetti" side.

In something that is low velocity with not much force behind it, I think the bends in the pipe would come into play more, as the static pressure difference would affect the two types of pipe greater- straight versus bends.
The more I tlked to header guys, the more I came to the conclusion that there is so much force in such a little distance, that the primary diamter and length were more important than the bends, so I went with diameter and length.

[Crazy Mopar Guy]

passenger side

[Arns85GT]

Very nicely done and thanks for the info.

I just wish I could weld as nicely as you obviously can.

Arn