6-3-1 Header for I6

[540ZCar]

I just would like to know if a 6-3-1 header would be more efficient than a 6-1 header or better yet, how different would the torque and power bands be with the different set-ups? Not for a particular project or anything, just in a theoretical mood and wondering why I never see any 6-3-1s for inline 6s, I bet clearance/room is the biggest reason.

 

[Lou Scannon]

A 6-3-1 setup is not required for breathing and far from ideal for packaging. The ideal setup for an inline 6 is 6-2 (6-2-1 is ok but not optimal).

All this is assuming the front 3 and rear 3 are the groups in the 6-2 and it is a conventional 4-stroke inline 6. There is definite advantage to be had with this configuration over a 6 into 1 log. And it has been done on passenger cars, mostly imported.
As to how different/much improved, that's all in the details.

 

[540ZCar]

I don't know much about exhausts but I've read articles on L28s built in Japan making 400 naturally aspirated horsepower using the 6-1 design so I thought there was something with that.

 

[evelrod]

Here we have the same problem faced by every amature engine builder in my memory.
What must be considered in addition to "which header is better" is the combination of camshaft, CR, port design, design RPM, intended use and, a host of other factors that play a major part in the design.

Whether it's an Jag 6 or an L-20 (16 and 18) that I have worked on, it still best to actually build the engine to your specs and then simply test different exhaust systems. It may sound primitive and not at all PC...but, it's still the system used by most major engine builders when starting new engine design. Whether the 6-2-2, or 6-1 is best is dependent on all the above conditions. I've seen winning race setups done in just about every configuration imaginable.

Rod

 

[540ZCar]

What about the theories of fluid dynamics with the different designs? I always been told that having the companion cylinders connected together will increase scavenging which is why I started thinking about 6-3-1s.

 

[patprimmer]

Generally the pipes should be connected so that every second cylinder in the firing order is joined in a 6 into 2 arrangement. ie 240 deg between pulses.

Regards
Pat
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[gruntguru]

Yes but the OP is talking about 6 into 3 which would need pairing of opposite cylindesr in the firing order ie 1+6, 2+5 and 3+4. Obviously this would be a very awkward set of headers to package.

Engineering is the art of creating things you need, from things you can get.

 

[patprimmer]

I know he is talking about 6 into 3 and I am recommending against that.

Regards
Pat
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[evelrod]

One of the reasons, perhaps the major reason, that many engine builders/tuners tend toward a single collector...be that 6-1, 4-1, whatever is the "packaging" aspect. Another reason is that these "single tube/port" systems will perform well on just about any engine. However, if you wish to optimize the exhaust system for one particular purpose and not just overall, then a great deal of improvement in specific areas can be had by using a try-y or 6-2-2 or systems pairing cylinders for optimizing extraction and/or restricting reversion. It's not a 100%, but close.

I'm certainly not an expert on exhaust design outside my personal involvement with my race cars. I must say that what I see in independent operators is often NOT what I consider optimum. A lot of what I see at the track comes down to $$$$ and "packaging"...

Next question...Why should anyone pay attention to my ideas? Good one. Of the last 35 races I've placed in the top five 20 times and only have 8 races I failed to finish with three of those being crashes. Just because an engine builder has a great reputation does not always mean that they have the "best solution" to an engines performance.

By all this I mean that your solutions may be better than ours...Having said that, I still don't like the 6-3 arrangement even though I have not tried it. Let us know how it works out.

Rod

 

[SomptingGuy]

I think that "practical" means different things to different people. It can be related to safety, reliability longevity or economy (others?). Ultimate performance (check out the 5-1 F1 exhausts of yesteryear) pays its price.

The compromise is always packaging (cost??) and thermal requirements.

- Steve

 

[BrianPetersen]

One of the things you want to avoid in an exhaust system design, is for the pressure pulse when a given exhaust valve starts opening to travel down that cylinder's header pipe and backwards up an adjacent header pipe and arrive at that cylinder's exhaust valve just before it closes. It will cause a reversion pulse.

Whether you have 2 cylinders grouped, or 3 cylinders with even firing spacing grouped, in either case there is no (or negligible) overlap in the exhaust strokes. Even if you are using a really wild long duration camshaft, the length of the header pipes (if set correctly) combined with the speed of pressure wave propagation will ensure that the bad reverse pressure wave won't arrive at that adjacent cylinder at any plausible engine RPM in which the engine is making power. (It might happen with the engine at or just above idle speed, but for a performance engine ... who cares.)

So, that would suggest no first-order advantage of the hard-to-package evenly-spaced (360 degrees between firings) 6 into 3 arrangement, over the dead-simple-to-package (240 degrees between firings) 6 into 2 arrangement, or for that matter, the easy-to-package 6 into 3 arrangement with adjacent cylinders paired (240 then 480 degrees between firings on the outer pairs and 360 degrees between firings on the center pair).

A log manifold with all 6 cylinders into one will have overlapping exhaust pulses into that log at practically all engine speeds. A 6-into-1 or a 6-into-2-into-1 with short header pipes might have overlapping exhaust pulses at lower engine speeds depending on the length of the header pipes compared with the local speed of sound / pressure wave propagation, etc.

Bottom line is that you have to use theory to get the primary pipe lengths and diameters in the ballpark and then test, test, test.

 

[NickJ67]

In the world of tuning elderly Triumphs (TR5s, TR6s, GT6s, Vitesses & 2000/2500 saloons) with inline 6 engines, the 6-3-1 design is well regarded and considered to give better low end / midrange than 6-2-1 designs and 6-1 designs. The 6-1 would be the weapon of choice for high rpm race use though. The 6-3-1 has the 360º pairs linked (1-6, 2-5 & 3-4).

I'm a bit puzzled as to why it is the 4-2-1 manifold is considered a good bet for I4 engines and is widely used, whereas the 6-3-1, which is only applying the same idea to the I6, is a much rarer beast and not generally well regarded.

They are a bit trickier to make it's true and good ones for the Triumph engine are not easy/cheap to come by, which is a pity as they do seem to work.

Nick

 

[BrianPetersen]

6-3-1 with 360 degree cylinder pairings is not seen very often for one very simple reason ... packaging. A lot of drivetrain layouts don't have a lot of room beside the engine to make that work. In OEM applications with mild camshafts, the exhaust tuning doesn't matter too much, so they're designed with log manifolds because they're compact and "good enough".

Here is an OEM exhaust manifold from a BMW

http://www.worldcarfans.com/204071812802/bmw-6-cylinder-engine---in-depth#10

Bunch more pictures and some discussion found here -

http://forum.e46fanatics.com/showthread.php?t=395393

Looks like the BMW world groups the front and rear three cylinders in every case I could find, as one would expect, and in case one thinks there's something special about a BMW high-tech engine, how about headers for the good old pushrod two-valve Chrysler slant six. (Click on the catalog.) Same thing - front and rear three are grouped.

http://www.cliffordperformance.net/

I fully realize the "that's the way everyone else does it" trap, but at the same time, usually when that's the way everyone does something, there's usually a reason behind it!

 

[patprimmer]

Presuming you want even separation, with a 4 cylinder you have the choice of 720 deg, 360 deg or 180 deg separation, all with simple easy to achieve packaging with only the centre two pipes crossing each other.

With a 6 cylinder you have the options of 720 deg, 360 deg, 240 deg or 120 deg. 360 deg is by far the most complex to fabricate and 240 deg still gives adequate pulse separation so one exhaust pulse follows close behind the one in front.

Even exhaust pulses per bank and the resultant ability to get at least a consistent 180 deg separation without real complicated packaging is also the reason for flat plane cranks in some V8s.

Regards
Pat
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[evelrod]

Worked on a 180 setup on a Chebby V8, tubes all over the place, routed over the bellhousing, etc. Also a flat plane 454, much easier exhaust system. Both had a phenomenal sound. Kinda like a six cylinder Jag on steroids. Don't know if either car ever became a winner...Do know that you never see all the extra tubing on the NASCAR circuit cars.
Just a guess--- perhaps the "massive improvement" spoken of so fondly by the magazines was not so "massive" after all.

Rod

 

[patprimmer]

I also was led to believe (I don't know from where) that some F1 cars had the exhaust in the valley and the inlet on the outside to help in exhaust system development. It could also simply be to carry the heat away from the inlet air as the top of the engine is in the main air stream on a F1.

Regards
Pat
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[evelrod]

Here ya go, Pat.

http://www.streetlegaltv.com/forum/obscure-engines-1964-ford-dohc-indy-3889.html

Rod

 

[540ZCar]

So what I'm gathering is that as long as the tubes are the right length and diameter, that the style of the header only give marginal increases?

 

[Tmoose]

"Pete Hagenbuch was a Chrysler engine development engineer in the engines area from 1958 through to 1987; he worked in valvetrain, performance, emissions, and other areas. His work covered Chrysler’s most legendary engines — the 426 Hemi, the B/RB-series big blocks, the LA small blocks, the 2.2 turbos, and even the Australian Hemi Six.
Read more at

http://www.allpar.com/corporate/bios/hagenbuch-interview.html?ktrack=kcplink"

http://www.allpar.com/corporate/bios/hagenbuch-interview.html

"I wanted in the worst kind of way to have a twin exhaust system because, man, will that do wonders for a 6. You put one, two and three, and four, five and six together and you run ‘em down about 6 or 8 feet and bring them together in one tailpipe and you’ve added great huge gobs of output. Engines, especially engines that are low output, the things you can do, the things you can get for just a little bit of effort are just unbelievable sometimes. But to turn that 225 from what I always thought was a real slug, but a dependable, durable slug, into one hell of a nice engine that was a fun program.
Read more at

http://www.allpar.com/corporate/bios/hagenbuch-interview.html?ktrack=kcplink"

 

[Lou Scannon]

I wouldn't say the inline 6 is an under-appreciated configuration, but its fan club does seem to be a smaller, if more passionate group, than say, that of the ubiquitous American V8.