360 degree header triple exhaust on L series?

[bradyzq]

Hi All,

 

Warning: this is just a dream/crazy idea I'm throwing out here for discussion. I don't think it has any practical use in the real world. But it's different....

 

After reading through that fantastic thread about flat-plane cranks and 180 degree headers over in one of the V8 sections here, I got to thinking. That's sometimes a BAD THING.

 

With an L series, we can't have 180 degree headers into a dual exhaust. But we can have 360 degree headers into a triple exhaust!

 

1 and 6 into a 1.5" exhaust,

5 and 2 into a 1.5" exhaust,

3 and 4 into a 1.5" exhaust.

 

That would have slightly more cross-sectional area than a 2.5" single exhaust, and, mufflers notwithstanding, could occupy a space only very slightly larger than a single 3" exhaust.

 

Why would one want to do this? Why not?

 

In theory, the exhaust pulses would be evenly spaced. They may even be too far apart at 360degrees.

 

The sound might be ridiculously cool, or not?!

 

There _may_ be power gains to be had.

 

It shouldn't be too hard to do, especially on a racecar. You could even use a standard 6-1 header and cut off the collector, then fab your own twisted 2-1 collectors.

 

Waadya think?

[BRAAP]

I'm glad to see someone taking that info constructively and wrapping their mind around it.

 

A couple of things as this applies to the inline 6.

The Datsun L-6 headers, (6-into-1, or 6-into-2, or 6-into-2-into-1 design), already has its exhaust pulses merging at even intervals, giving the L6 exhaust note its smooth crisp tone. For a 6 into 3 header design, (whether it is 6-into-3 with triple exhaust pipes or 6-into-3-into-1 single exhaust pipe), your pairing of cylinders is correct in pairing the opposite firing cylinders, 1-6, 2-5 and 3-4. But I don't think it will change the tone of the exhaust note any from the standard 6 into 1, or 6 into 2, or 6 into 2 into 1 designs. I short, so it wont make it any smoother or crisper sounding. Though having 3 exhaust pipes would be rather unique and exotic looking. If for nothing else other than begin different, triple exhaust could be tastefully ran out the back. Would definitely get a bit of attention at the car shows.

 

 

Though if you merged cylinders that fire in odd patterns, (such as pairing 1-2 or 1-3 or 1-5) you would get an odd rough tone like a V-8, Suby 4 cylinder or maybe the Audi 5 cylinder/Dodge V-10, depending on when you merged, which cylinders. (I personally don't like the sound of free flowing exhaust systems on Audi 5 cylinder or Dodge V10! Sound too much like a really old odd ball tractor, not a sports car or even a muscle car!). From an exhaust scavenging perspective, it wouldn't be ideal, but just as the Subies and domestic V-8's with their odd paired exhaust pulses, the merging of odd firing pulses isn't going to "hurt" performance to level you would notice.

[bradyzq]

I somehow thought you would reply!

 

And I notice that you used a very small font when mentioning the 5-cylinder exhausts. I am addicted to the sound of free-flowing Audi engines, 10V NA, 10V turbo, and 20V turbo. Got 'em all and none have stock exhausts.

 

Back to the discussion:

 

I remember seeing pictures of Ferrari 365GT4/BB exhausts with a trio of tips per side. I wonder what that sounds like, and why it was done.

 

Also, if I understand this correctly, if you have a X into 1 collector, where X is the number of cylinders the engine has, the pulses would be evenly distributed by definition, strange odd-fire engines notwithstanding. Right? BTW, Audi made a factory equal length (or close to it) 5-1 header on their 20V NA engines in 1990-91!

 

So, I guess my next question is this:

 

Is the fact that the exhaust pulses are even distributed enough to maximize the benefits (scavenging, smoothness, tone, etc)?

 

Or, does the length of time (in degrees here) make a difference too? In an equal-length 6-1 header, it would be 120 degrees spacing between pulses. In a 6-3 equal length header split as above, it would be 360 degrees spacing.

Edited October 18, 2009 by bradyzq
typo!

[johnc]

From an exhaust scavenging perspective, it wouldn't be ideal, but just as the Subies and domestic V-8's with their odd paired exhaust pulses, the merging of odd firing pulses isn't going to "hurt" performance to level you would notice.

 

Semantics. Odd firing pulses (waves) going through the exhaust doesn't hurt but it doesn't help either. I keep harping on the TransAm guys but converting to 180 degree firing in the exhaust and running a 5" or 6" single exhaust got them a 10% increase in horsepower.

 

Also, if I understand this correctly, if you have a X into 1 collector, where X is the number of cylinders the engine has, the pulses would be evenly distributed by definition, strange odd-fire engines notwithstanding.

 

Yes. That's the thinking behind a 6 into 1 exhaust, except that the primary lengths on the currently available 6 into 1 L6 header are unequal. In practice that header does not have even pulses at the collector merge.

 

Is the fact that the exhaust pulses are even distributed enough to maximize the benefits (scavenging, smoothness, tone, etc)?

 

Or, does the length of time (in degrees here) make a difference too? In an equal-length 6-1 header, it would be 120 degrees spacing between pulses. In a 6-3 equal length header split as above, it would be 360 degrees spacing.

 

Depends on where in the rpm range you want to maximize scavenging. A 6 into 2 into 1 gives two somewhat narrow places in the rpm band where scavenging can be optimized. A 6 into 1 gives one somewhat broader place in the rpm band to maximize scavenging. The 6 into 1 can give a higher horsepower number then the 6 into 2 into 1 but the latter can give a broader range of power.

 

All of this assumes a lot of development work and optimization.

[Daeron]

All of this assumes a lot of development work and optimization.

 

Quote of the Month!!!!!!!!!

[bradyzq]

Depends on where in the rpm range you want to maximize scavenging. A 6 into 2 into 1 gives two somewhat narrow places in the rpm band where scavenging can be optimized. A 6 into 1 gives one somewhat broader place in the rpm band to maximize scavenging. The 6 into 1 can give a higher horsepower number then the 6 into 2 into 1 but the latter can give a broader range of power.

 

Could one conclude in a general way that 6-2-1 is best for low-midrange torque, 6-1 for higher RPM torque, and 6-3 ????? (maybe REALLY high RPM torque)?

 

The longer the primary and the fewer primaries with which it merges, the more a cylinder will feel like it has its own dedicated exhaust pipe, right?

 

And this would be ideal for top end torque?

 

Any benefits anywhere else?

 

All of this is on the assumption that all needed development work has been done!

[ezzzzzzz]

My old school Janspeed s/s 6-2-1 header can be seen here. http://www.classiczcars.com/photopost/showphoto.php?photo=18972&ppuser=7128&sl=e

The primaries are very close in equal length and the slip-on collectors are way long. This header dumps into 2.5" s/s mandrel bent tubing, straight-thru resonator and muffler.

[johnc]

Could one conclude in a general way that 6-2-1 is best for low-midrange torque, 6-1 for higher RPM torque, and 6-3 ????? (maybe REALLY high RPM torque)?

 

No.

 

The longer the primary and the fewer primaries with which it merges, the more a cylinder will feel like it has its own dedicated exhaust pipe, right?

 

You're assuming the optimum is to have an individual pipe/exhaust for each cylinder. That's only (in rare cases) true for forced induction engines. For normally aspirated engines there are huge benefits to wave tuning using multiple cylinders to work with each other.

 

And this would be ideal for top end torque?

 

No.

 

Any benefits anywhere else?

 

Yes.

[LLave]

Ummm... What about weight? Sounds weighty to me. I think the weight would probably offset any performance increase.

[bradyzq]

Quote:

Could one conclude in a general way that 6-2-1 is best for low-midrange torque, 6-1 for higher RPM torque, and 6-3 ????? (maybe REALLY high RPM torque)?

No.

OK, then, what, if anything, could one conclude in a general way about the above?

 

Quote:

The longer the primary and the fewer primaries with which it merges, the more a cylinder will feel like it has its own dedicated exhaust pipe, right?

You're assuming the optimum is to have an individual pipe/exhaust for each cylinder. That's only (in rare cases) true for forced induction engines.

 

Not really assuming that, actually. And that would be in VERY rare cases for turbo cars , as we would talking one turbo per cylinder! For blower cars, I can think of big dragsters (like Funny cars, etc).

For normally aspirated engines there are huge benefits to wave tuning using multiple cylinders to work with each other.

Yes, I understand that. It's what made me this thread!

 

Quote:

And this would be ideal for top end torque?

No.

 

Where, if anywhere, would this setup be ideal?

Quote:

Any benefits anywhere else?

 

Yes.

 

Where would there be benefits then?

 

I appreciate your taking time to participate in this thread, but I get the feeling you'd rather be doing something else. Simple "Yes" or "No" answers that immediately require followup questions are frustrating.

 

Or... you could just be messing with me. I hope it's the latter!

 

So, reply or not. Either is fine.

[bradyzq]

Ummm... What about weight? Sounds weighty to me. I think the weight would probably offset any performance increase.

 

I hadn't thought of that!

 

Assuming equal wall thickness of the tubing, the piping would weigh a whopping 80% more than a single 2.5" exhaust. If the exhaust is short, the actual weight gain could be quite modest, though.

[johnc]

I appreciate your taking time to participate in this thread, but I get the feeling you'd rather be doing something else. Simple "Yes" or "No" answers that immediately require followup questions are frustrating.

 

There's so much mis-information on the Internet and in people's "common sense" regarding internal combustion engine exhaust that attempts at explanation on an Internet message board are futile. It just turns into "my friend who has xxx made yyy horsepower with a zzz header so that means all headers made by zzz are the best."

 

Exhaust tuning is very, very vehicle and engine specific and extrapolating what worked on my 325hp, 14 to 1 CR, 310 duration cammed L6 engine to whatever you have in your car is a waste of everyone's time.

 

You, yourself need to find the books and do the reading to come to a conclusion that's appropriate for your car.

[bradyzq]

Depends on where in the rpm range you want to maximize scavenging. A 6 into 2 into 1 gives two somewhat narrow places in the rpm band where scavenging can be optimized. A 6 into 1 gives one somewhat broader place in the rpm band to maximize scavenging. The 6 into 1 can give a higher horsepower number then the 6 into 2 into 1 but the latter can give a broader range of power.

 

All of this assumes a lot of development work and optimization.

 

I'm with you on the misinformation front. But I don't see any signs of this thread degenerating to of those "This is the Best" type threads, which are thankfully not allowed here anyways!

 

I reread the thread and came up with the above quote as the trigger. It's where I had difficulty, and is the reason I asked the questions I did after you posted it.

 

My logic is as follows:

Effective scavenging removes more spent gases from the cylinder thereby allowing more space for fresh mixture to be ingested.

 

More ingested mixture is synonymous with increased volumetric efficiency, which means more torque where the VE is improved.

 

So I came to the conclusion that better scavenging equals more torque.

 

For the 6-1 with its one broad area of increased scavenging to be able to make more power than the 6-2-1, it must be at higher RPM than the 6-2-1's areas of optimized scavenging.

 

But then you say that the 6-2-1 can give a broader range of power than the 6-1, despite its two narrower areas of optimized scavenging.

 

This seems to contradict your 6-1 comment of higher power, with a broader range of optimal scavenging....

 

Unless my max scavenging => VE increase => torque increase line of logic is wrong.

 

If I've missed something, I apologize for the WOB.

 

Cheers,

[johnc]

But then you say that the 6-2-1 can give a broader range of power than the 6-1, despite its two narrower areas of optimized scavenging.

 

This seems to contradict your 6-1 comment of higher power, with a broader range of optimal scavenging....

 

OK, this is pretty broad and really only specific to the engine I had in my car, but here goes:

 

With the 6 - 2- 1 header its possible to tune its two torque peaks (not really peaks, just high points I guess) to span some band of rpm. The area between the peaks remains relatively flat so the torque curve may not be as high as with an optimally designed 6 - 1 header but you can end up with a broader torque curve and possibly more area under the curve. It takes a lot of dyno time (15 hours in my engine's case) and involved a lot of work in other areas of the engine but it can be done.

 

Notice all the vagueness with words like "can", "possible", "possibly", "may", etc. Without testing you'll never really know what you've achieved.

[Daeron]

brady:how much math have you taken in school?

 

The reason john is coming off as snippy is very complex and subtle. That reason is, this entire field of exhaust wave pulse tuning is...... complex and subtle. SUBTLE. *I* certainly don't really know enough to ansswer your questions fully, but I think I can get a good handle on why your questions cannot really be answered...

 

A given engine has its volumatric efficiency and its number of cylinders, which are the first variable. We've got siz, so there is one pulse every 120 degrees of crank rotation. Six into one is one single function: f(n)=nXyXa, where n is your torque fat point (I am bluffing here to make a metaphorical point, just bear with me) y is your number of pipes and a is the length of the primaries.

 

when you get to something like a six>3>1 or 6>2>1, there are two or three more steps in that function, and they get multplied together, and exponents are involved, and things spiral out into a multitiude of meaker responses.. you get, instead of tuned for one big fat torque pouint, two, or three, or more torque peaks that are correspondingly less stark, but can be made into a broader, more comfortable vault-like torque curve.

 

 

I THINK that is sort of the gist of it. There is alot of math involved in even coming close to knowing what you are doing, and that is why John says you need to study a book... because he would need to write that book for you heree and now for you (and I) to really GET this, and I wasn't planning on paying him for that... so we need to find someone who HAS been paid to write said volume, and purchase it and then try, try, try again and THEN we will understand.

 

 

 

 

Thats why all I really think about is pipe sizing and construction quality. When I am in the range of playing with real exhaust tuning, then maybe I will figure these things out with more precision and to greater detail. You get to a point where some things, you just leave it to the guys who are REALLY trying to win races and spending the money to eke it out of their motors, and then ogle it.

 

That last 5% of the power is a b!tch to squeeze out.

[letitsnow]

There are a lot of books out there on this subject, but depending on your math background, you might not understand a word of it. You might want to see if you can find "Design and Simulation of Four Stroke Engines" by Gordon Blair in a library, it's about $100 on amazon.

[bradyzq]

Hi All,

 

I have (had, actually, as most of it was long ago) a very high level of math education. I find it very strange that I had to type that sentence, BTW.

 

Dyno time is not an issue either, as I have one right behind me as I sit. (chassis, though, which would make it harder for 30 minute header/exhaust mods). I am a dyno tuner. I must admit, though, that 95% of the cars I see are already built, and all I can do is optimize what's in front of me. So I don't design exhausts...

 

But, as I posted in the first paragraph of this thread, this was to be a hypothetical scenario. I'm not trying to get a radical exhaust system designed for free through this forum!

 

And, yes, I understand that this topic is a deep one, and that one must experiment to get it right on a specific application.

 

But there are general trends and guidelines. A long tube header may work better one a given engine than on another, but it should have a similar relative effect on both (like for example improving high RPM torque).

 

Finding out, or even just discussing, that trend was all I was after.

 

Read my questions. They were all very general in nature. This was not an accident. Then, when 6-2-1 and 6-1 headers were introduced into the mix, I asked more general questions, in an effort to position the hypothetical 6-3 header relative to the other 2, and flesh out the discussion.

 

Apparently I didn't do a good enough job, since the whole idea of 6-3 got buried.

[zcar?]

(I personally don't like the sound of free flowing exhaust systems on Audi 5 cylinder).

 

 

How can you not like a sound like this?:

 

[BRAAP]

How can you not like a sound like this?:

 

 

That sounds Sah-weeet!

 

I was talking more on the odd tractor sound I have heard from some 5 cylinder ratty Audi's on the street with and open exhaust Vipers!

[Daeron]

Hi All,

 

I have (had, actually, as most of it was long ago) a very high level of math education. I find it very strange that I had to type that sentence, BTW.

 

I want to apologize, I somehow omitted to state what I meant to state after posing that (rather judgmental-sounding) question. That was: It starts getting into derivatives, and calculus, and goes far above my head (at least, where it sits now..) but I hadn't intended to leave it hanging out there like a bald accusation.

 

I am certainly no one to condescend; to achieve the rank of "Peer" here is my humble aspiration and I didn't want to convey anything other than: the specifics of a given extractor are tuned literally to the engine, and any more complex understanding than that requires specific research and education (wrenching and reading books, and of course asking questions like these.)

 

Once more, sorry if my mistaken omission caused an insult. For the record, I had excellent skills in math until I started calculus, and at that point decided I had learned enough math for my own tastes, and I could pick this back up later if my path seemed to warrant it. So my answer to my own question is basically, "Far enough to see the light, but not enough to really understand it."