more like the inlet manifold but a combination of these two headers
with the square tubing of the valiant inlet manifold if it makes sense.

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Slant 6 style??

True but I always wanted the old hot rod manifold look :)
straight out level with the exhaust ports to the flange
then curved downpipe. The inlet ports would be curved
over the rocker cover and inlet on spark plug side.

The step for harmonic bounce only needs to be about 1mm and round pipe will allso allways flow better as the is the least possible surface area for given volume.

Well for some people like us with none to mediocre welding ability.
I thought of using square tubing for more area with less tube diameter
and also Jmac suggestion of larger diameter outlets so there is a step
to stop flowback pulses.

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I recomend a book "performance tuning in theory and practice" by Graham Bell. it gives you the primery, seconday lengs but ya need to know ya cam specs and desired RPM range. If ya real keen it even has mathamticle equation's for messurments down to decimals

Hi,

Thanks for the idea mate.
I'm not at that level yet Where I need to fine tune the primary and secondary pipes, but thanks for drawings, and the build order.

Gandalf, did you missed the "I have no welding experience" part?

I can't promise you any thing as I think it will be a struggle just to build one, and at a Software Engineer rates ... it will a very expensive sub standard one! (just kidding!)

daniel

If you have the time/interest to try a few experiments, you might take a look at this option:

Basically make the headers in 3 main sections (1 2 3 in the picture) you can weld up the primary collectors to the secondary pipes, but don't weld them to the primary pipes for now. Same goes for the final collector - leave it out (but construct the secondary pipes so that they will fit the collector.

Then you could get short lengths of pipe - a couple of inches long, and expanded at one end (so they slip over) - which are like mini extensions to vary primary or secondary pipe length and do some testing. You could start with no extensions at all like in 5, or otherwise could add to the primary length a couple of inches, or the secondaries (or even both) as in 6. This is basically making them like lego - and you can alter the lengths to find the best powerband. You could probably even (for racers) run longer primaries or secondaries on tighter racetracks, and shorter ones for high speed/long racetracks. You could keep them modular like that and adjust them as needed, instead of having to have 2 complete sets of extractors/headers for different tracks.

Naturally you'd have to also check whether they will all fit into the engine bay without hitting something, I just presented the idea because I just got back from work and can't get to sleep!

Daniel,

I'm interested on a exaust manifold too, but can't find any in Portugal, if you are gone make one, are you interested in making 2 and sell me one?? After making the first the second should be better :P

Tiago

I remember this post from ages ago, it has got some great info on the theory of exhaust making, Jmac has sheds some great information, it will be beneficial.

Let us know how it goes!