Designing a header for fuel economy (for a Metro G10 1.0L)

[Daox]

With all the theoretical designing done its time to move on to the practical design work. The next step involves the physical routing of the pipes, and keeping them as close as possible to the same length. This will really depend a ton of your vehicle and how much clearance you have to many different things. Of course, there are several different ways to approach this. I'll go over a couple.

1) Manually taking measurements and/or doing mock up work. This is not easy or quick, but you can take measurements and do some guess work as to how long each pipe needs to be. Possibly mocking something up with corrugated tubing (like smaller diameter dryer ducting), PVC tubing or something similar. Using a spreadsheet you can fairly easily add up pipe lengths with mandrel bends and see where you need to add/subtract length to make the primaries equal length.

2) Designing on a computer. This is also not easy for those who aren't familiar with the software, and even then it can be tricky to make sure things actually clear all obstacles around the header. You still need to take a lot of measurements when doing this. However, you can ensure that the header pipes are the same length and mess around a lot easier and quicker than mocking things up. Using this method it was quite easy and quick to figure out what tube should be on top/bottom, or left/right when they all come together. It also allows you to get exact tube cut lengths very easily for calculating how much tubing you need to order. Obviously, this is my preference. I use SolidWorks in my daily job so I'm pretty proficient using it. Another option would be google sketchup which is free. The learning curve may be steep though.



This was the initial rough in of the header I made on lunch one way.





From that, I was pretty easily able to tweak the design to a fairly finalized model that you see below. Each runner's length is less than a 1/16" variance in length.

I was able to tweak the 45 degree bend length on the center runner to dial in the exact length I wanted.





I got lucky with the outer runners and they ended up being fairly close. To dial in their exact length, I adjusted the distance from the exhaust manifold flange to the first bend. You'll notice the right runner comes out farther than the left most runner.





You definitely want to keep things as simple as possible. The less bends the better. Not only for efficiency sake (less turns is less velocity lost), but its also cheaper (less mandrel bends to buy) and quicker to make with less complexity. I'm also not the worlds greatest welder and the less joints the better. I was really hoping to not have to put in the two 45 degree bends, and just use one 90 degree, but it just wouldn't work out. If you have the choice, a larger bend radius is also a better option as sharp turns steal more efficiency. Unfortunately, there isn't often multiple bend radius choices to be had.

[oil pan 4]

For get about using PVC for mock up.
Get some heat exhaust manifold heat riser tubing. Its like an all metal clothes dryer exhaust vent, but a lot smaller.
It should be available down to about 1''.

Or if you want to use real small tube get some electricians to bend you up tubes out of 1/2or 3/4 inch EMT conduit. Electricians are great at putting smooth wide radius bends in tube to go around obstacles or fit in a tight space and then making copies of a tube.
You can even get stainless steel conduit.

You could have electricians bend up some cheap galvanized EMT in what ever size you desire, then once you know it works have them copy it in stainless.

Those bend radiuses in the drawing look pretty much exactly like what you get from a conduit bender.

[Daox]

Great idea on the corrugated tubing! I'll add it to the post.

The bends in the model are what I was able to find online for mandrel bends that I can buy.

[Daox]

Originally Posted by oil pan 4

With converging and diverging nozzles I believe 7 degrees is ideal.
There are companies that sell 7 degree reducers for intake and exhaust piping, they are kind of expensive.

According to this: http://www.spdexhaust.com/pdfs/02-11...Collectors.pdf

The best angle is a 12-15 degree convergent angle with a 3 degree divergent angle. Interesting that those are different.

[oil pan 4]

What was the official size going to be?
I saw 5/8, 3/4 and 1 inch talked about for primaries?

[Daox]

I'm not sure I'm even going to build it, but for the purposes of this thread/design I'm going with 3/4" OD 16 ga tube.

[Shawn D.]

Originally Posted by Daox

According to this: http://www.spdexhaust.com/pdfs/02-11...Collectors.pdf

The best angle is a 12-15 degree convergent angle with a 3 degree divergent angle. Interesting that those are different.

That style of collector is for use with an open exhaust, i.e. no exhaust system past the collector/transition. You will see these collectors on drag cars frequently, but I've never seen a street car with these AND an exhaust system.

[Daox]

I'd imagine the convergent angle would still be the same. The divergent may not. I haven't been able to find specifics on designing a collector with a venturi build in, so I've omitted any data on it.

[Shawn D.]

Originally Posted by Daox

I'd imagine the convergent angle would still be the same. The divergent may not. I haven't been able to find specifics on designing a collector with a venturi build in, so I've omitted any data on it.

Yes, you're right -- the convergent angle & merge are the same. It's the divergent part and slight convergence at the exit that are not used for a full exhaust.

[Daox]

Woohoo, getting close to done now. We are on to efficient collector shaping.





A collector is designed to bring tubes together into one larger tube. It should do this smoothly and efficiently to maintain exhaust velocity. The main problem of doing this is shown above. There is a gap between the pipes as they come together, so we need the collector to smooth the transition.





Ideally, you would order this freakin fancy Burns Stainless collector and call it done. However, they retail for $200 to $400, and the materials for this job are likely going to be under $100... So, lets talk about making your own!

You can try to make your own fancy collector like the one above. This is totally doable, but it really looks like it would take a ton of time. The alternative is you can use this slightly less efficient, but vastly easier to make collector.





This is Headers by Ed's suggestion. You can form the ends of the pipes together without a huge amount of hassle, then you weld the seams together.







Above is a collector I made for a header I started building a long time ago for a Toyota Tercel. I took a bunch of tubes the length I wanted, cut a big V in them, and then started forming the outlet diameter with a hammer. You can calculate the size of the V by figuring out the circumference of your inlet and outlet diameters. It takes a while to form it all, but as you can see its quite doable with just a hammer and vise.

This collector is fairly easy to weld up to the above seam welded pipes without having to worry too much about sealing things perfectly.