6-3-1 header for inline 6?

[Streichholzschächtelchen]

Ok, been digging through articles on flat plane v8s and got to thinking... if exhaust scavenging on a flat plane v8 is better than cross plane, is there any way the inline 6 can have it's exhaust done differently for better scavenging? Usually the pattern is 6-2-1, with 1,2,3 joined in one manifold, 4,5,6 in another.

I have seen online many Triumph owners have reported a benefit in 6-3-1 headers, pairing 1to6, 2to5, and 3to4, then merging those 3 pipes to 1. I know that VK Holdens in Australia had this style of exhaust as well. This puts the paired cylinders 360° off of each other, both at TDC at the same time, but opposite points in the 4 stroke process. Is this beneficial in terms of scavenging? Also, would it hurt performance to go 6-3 and run 3 pipes all of the way back to a triangle of tips like an LF-A, compared to 6-3-1?

I think if nothing else it will sound unique.

Another theory, haven't looked into it yet, would be to link odds in one manifold, evens in another, 6-2-1. If the firing pattern is 153624, that would put cylinders firing back to back to back in one manifold, followed by the same thing in the other, kinda like two horses galloping opposite of each other (well, two three legged horses but you know what I mean).

Technically a 6-3-1 can also be done by pairing back to back cylinders in the firing pattern by pairing (1to5, 3to6, and 2to4) or (5to3, 6to2, 4to1), the latter keeping the ports for the pairs a little more evenly spaced. I don't think this would be ideal though.

6-3-1 as proposed, pairing 1to6, 2to5, 3to4

6-2-1 as seen on BMWs and most inline 6s


Burns stainless v12 boat, essentially two 6-3 exhausts tied together.
http://www.burnsstainless.com/V-12ExhaustDesign.aspx

[BDawg94]

I realize this post is dead and you probably figured your answer out but I'll give it a shot. So you're not wrong, if you wanted to do a 6-3 header you would want to pair 1-6, 2-5, 3-4. Then all paired cylinders would be 360* out of phase. The challenge this brings about is how does one connect 1-6 with the same length of primary as you would 3-4? Short answer, you wouldn't. So you'd have to run you're 3 secondaries all the way out the back just like the LFA, or merge and degrade your scavenging. If you do a traditional 6-2 header then you can pair cylinder 1-2-3 & 4-5-6. Then instead of firing every 360*, you fire every 240*. This arrangement is easier to fabricate with equal length primaries. It also allows your primaries to be shorter due to the smaller amount of engine rotation between firing. If you run dual exhaust back from this and make the total length of the exhaust an clean multiple of your primary length you'll optimize your scavenging effect. However, secondary scavenging is pretty much negligible if you have catalytic converters or a muffler (glass packs allow some scavenging to happen still but chambered mufflers... fuggetaboutit). Hope this helps!

[digger]

You can connect 6 and 1 with same length as 3 and 4 but it’s a packaging nightmare that results in a primary length that may not be as short as required for the intended engine rpm. It is fairly common here with some Holden and Chrysler inline 6 but these are rarely high rpm engines maybe 7500rpm tops which is still easily long enough to get 1 and 6 together. Forced firebird made a set a few years back for an m20 there is a thread somewhere.

Personally I don’t see any need to have 360 spacing unless camshaft is extremely large duration there is plenty of separation for a 6-2 engine. i was never able to find any benefit in the 1D simulations. certainly not enough to want to spend a large sum of money to test it out.

The effective length of secondaries (more correct is effective total pipe length) is critical for bottom end torque, clearly a cat or glass pack is not ideal but it is still very important to have the length suitable if you want the engine to not be a dog sub 4000rpm. High flow metal cats work fairly well compared to OEM catalysts. There are also means to decouple those items including chambered mufflers from the engine. David Vizard calls it a pressure wave termination box that makes the engine think it has essentially open headers.