2017: Revisiting 4:2:1 vs 4:1 headers w merge collectors in the modern era

General engine tech -- Drag Racing to Circle Track

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Re: 2017: Revisiting 4:2:1 vs 4:1 headers w merge collectors in the modern era

Post by psychomotors » Sat Nov 11, 2017 3:38 pm

Never mind , I just checked and they no longer sell them.
Everyone appreciates your honesty , until you're honest with them , then you're an @$$hole.

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Re: 2017: Revisiting 4:2:1 vs 4:1 headers w merge collectors in the modern era

Post by modok » Sat Nov 11, 2017 5:43 pm

After sleeping on it I can explain the choke thing!

The more constant the flow is through the choke....the smaller you can make it as compared to HP. It's a matter of what is coming OUT of the secondaries.
A four cylinder with fairly short 4>1 header you might have 8 somewhat evenly spaced flow pulses coming at the choke so you can go quite small.

With the tri-y on the other hand you get 4 big periods of flow out of the secondaries. At the higher rpms the positive periods of flow out of each secondary will exceed 180 degrees and begin to overlap, making a large peak flow at that point. Choke has to be larger to accommodate that.

Simple right :P
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Re: 2017: Revisiting 4:2:1 vs 4:1 headers w merge collectors in the modern era

Post by modok » Sat Nov 11, 2017 5:52 pm

So the firing order and the cam timing can make a huge change the "pattern" going into the choke, which I think is the main reason you end up at totally different designs from one engine to another.

yeah the tri-y does a great job fighting the 180 overlap interference, which does become a big factor using wilder cam timing on a four banger. i wonder if you just twisted the crank 20-30 degrees to get over that 180 interference and use an ODD paired tri-y could get even more power overall. MIGHT BE TRUE :P But I won't dwell on it.
IMO the odd pairing and very unequal lengths just sounds like crap. Good a reason as any. But some people like it better. A lot of kids today think the subaru sounds really "mean", they want their honda to sound like a subaru. I think the subaru sounds like it's hitting on 3cyls :lol:
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Re: 2017: Revisiting 4:2:1 vs 4:1 headers w merge collectors in the modern era

Post by Erland Cox » Sun Nov 12, 2017 3:40 pm

I started with a 4-1 header that I modified and I had to connect cylinder 1-2 and 3-4 together.
So it is not an even firing system, it is just like on a inline 4 bike engine.
Previous best was the stage 3 with short primaries and long secondaries.
That header was a little better above 7200 rpm but the new one has a little more max hp and 5Nm more torque.
And it takes gas from idle.
A little lean stutter if floored to fast and a fat dip around 4000 rpm but not a big dip.
The new header is totally 41" for primary and secondary and the stage 3 is 40" and that can be why it has the better top end.
I will post the dyno test as soon as my son sends it to me.

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Re: 2017: Revisiting 4:2:1 vs 4:1 headers w merge collectors in the modern era

Post by Erland Cox » Sun Nov 12, 2017 4:58 pm

Red is the old header and brown is the new one.
No lambda for the red.
But compare to the other header I tested and posted earlier.

Image

Short primary with shorter 54mm secondaries, total length 34"

Image

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Re: 2017: Revisiting 4:2:1 vs 4:1 headers w merge collectors in the modern era

Post by hoffman900 » Sun Nov 12, 2017 5:34 pm

Shorten up the primaries a bunch if you can. You said they're at 28" now?
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Re: 2017: Revisiting 4:2:1 vs 4:1 headers w merge collectors in the modern era

Post by mtrhead » Mon Nov 13, 2017 8:07 am

What is the opinion on the old school 1 5/8's to 2.5 collector Tri-y like Dougs, Stans, Thorley's for a street 383 or 400 sbc?

Example: 383-400 sbc, 195-210cc heads, hydraulic roller, stick shift, dual plane, standard hotrod for the street. Most street builds, like mine have 1 5/8 or 1 3/4 full length brand x or y standard 4:1 headers.

The question would be for STRICTLY street up to 6000 rpm operating range.

Would a typical street SBC benefit from the old school Tri-y's?

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Re: 2017: Revisiting 4:2:1 vs 4:1 headers w merge collectors in the modern era

Post by ptuomov » Mon Nov 13, 2017 11:37 am

I have a question about what to do to fight pressure pulses when the primaries are way, way too short. But instead of getting this thread off track, I posted my question to a new thread:

viewtopic.php?f=1&t=51430
[b]Paradigms often shift without the clutch[/b] -- [url]https://www.youtube.com/watch?v=cxn-LxwsrnU[/url]

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Re: 2017: Revisiting 4:2:1 vs 4:1 headers w merge collectors in the modern era

Post by NewbVetteGuy » Mon Nov 13, 2017 1:17 pm

ptuomov wrote:
Sat Nov 11, 2017 10:21 am
I found this explanation of the 180-degree exhaust blowdown interference fairly intuitive to a novice like me:

Image

http://www.mazda.com/en/innovation/tech ... kyactiv-g/
4-2-1 Exhaust System
One option to significantly reduce residual gas is the adoption of a 4-2-1 exhaust system. As shown in Fig.3, when the exhaust manifold is short, the high pressure wave from the gas emerging immediately after cylinder No. 3’s exhaust valves open, for example, arrives at cylinder No.1 as it finishes its exhaust stroke and enters its intake stroke. As a result, exhaust gas which has just moved out of the cylinder is forced back inside the combustion chamber, increasing the amount of hot residual gas. With a short exhaust manifold, the high pressure wave arrives at the next cylinder within a short amount of time, causing this adverse effect to continue from low to high engine speeds. However, with a long 4-2-1 exhaust system, since it takes time for the high pressure wave to reach the next cylinder, the effect mentioned is limited to extra-low engine speeds, making the reduction of residual gas at almost all engine speeds possible.

In addition, a pipe length of over 600mm was necessary to elevate actual-use torque, but space was saved by adopting a loop shape.
I also like how they focused on getting the pipe long enough to keep the worst of the reversion below the highway cruise RPM. Maybe that's all you need to do. Just make enough AR tweaks to push the worst of the reversion below the RPMs that you'll be using anyway.


Adam

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Re: 2017: Revisiting 4:2:1 vs 4:1 headers w merge collectors in the modern era

Post by Erland Cox » Mon Nov 13, 2017 3:49 pm

hoffman900 wrote:
Sun Nov 12, 2017 5:34 pm
Shorten up the primaries a bunch if you can. You said they're at 28" now?
That is very hard to do and besides I had 13" primaries before.
Both these headers nearly overlap their curves, the short and the long primary header.
I have to build a completely new header to change the dimensions.
I will try that later but my next test will be a windage tray.

Erland

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Re: 2017: Revisiting 4:2:1 vs 4:1 headers w merge collectors in the modern era

Post by ptuomov » Mon Nov 13, 2017 4:11 pm

NewbVetteGuy wrote:
Mon Nov 13, 2017 1:17 pm
I also like how they focused on getting the pipe long enough to keep the worst of the reversion below the highway cruise RPM. Maybe that's all you need to do. Just make enough AR tweaks to push the worst of the reversion below the RPMs that you'll be using anyway.

Adam
I think (but don't know) that the factory _wants_ 180-degree exhaust interference at low cruise rpm, at low load anyway. They call it passive exhaust gas recirculation! They think they get better emissions and fuel consumption if they don't fully evacuate the combustion chamber at low load low cruise rpm. To do that, they make the tri-y header of a four banger just long enough to get rid of the 180-degree interference at rpms where things get interesting, but not so long that it's gone at cruise rpm. Wild speculation on my part, of course.
[b]Paradigms often shift without the clutch[/b] -- [url]https://www.youtube.com/watch?v=cxn-LxwsrnU[/url]

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Re: 2017: Revisiting 4:2:1 vs 4:1 headers w merge collectors in the modern era

Post by Erland Cox » Wed Nov 15, 2017 4:58 pm

I have one question about the choke.
I have been testing dimensions in my exhaust system in Engmod 4t and the engine seemed to like a choke and a diffusor on the last pipe.
How small can the choke be compared to the diameter in the dual pipes?
Can the choke be smaller than the dual pipes?

Erland

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Re: 2017: Revisiting 4:2:1 vs 4:1 headers w merge collectors in the modern era

Post by modok » Wed Nov 15, 2017 8:12 pm

The computer sims told me that too, enough to make me try it more times than I'll admit, but it just killed the resonance of the whole thing.
I have heard of a case where they were the same size, strange as it seems. It was an odd-fire tri-y on a honda.
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Re: 2017: Revisiting 4:2:1 vs 4:1 headers w merge collectors in the modern era

Post by Erland Cox » Thu Nov 16, 2017 11:32 am

What I tried in the sim was instead of going from 48mm ID to 60mm ID on the last step
I had a cone that went from 48 ID to 60ID over 375mm:s.
That was better everywhere according to the sim and since my exhaust is modular
I can easily change the last collector to see if it works in the real world to.

Erland

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