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Just for fun: Unequal length headers on an I4 because noise

General engine tech -- Drag Racing to Circle Track

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BLSTIC
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Just for fun: Unequal length headers on an I4 because noise

Post by BLSTIC » Wed Feb 05, 2020 8:54 pm

So I recently discovered unequal length headers for Honda engines and they sound cool (like a WRX) but the cylinder grouping is 1&2 joining at about an inch with 3&4 joining similarly close but doing a literal loop before the final Y. Also they are big pipes, so no inertia tuning either. It's technically the worst header design I've ever seen but they sound awesome for an I4
FB_IMG_1580239818014.jpg



https://youtu.be/6Rro3Ls-QMU

I want to replicate that noise but without the general level of design crapness and for a nominally 120hp 2 litre rwd

I was thinking of 1&4, 2&3 grouping, with cylinders 1&2 going forwards and then back to the other two in their respective pairings. I want a minimum of 12" before the junction on the "short" primaries. The others will likely be in the 36" range. The combined length should be long enough to avoid any strange interference issues, even if they aren't long enough for proper tuning. 1 1/8" primaries as it's quite low power per cylinder

What do you think? Should I make a step up after 12" on the long headers to make some kind of unity between the cylinders? Any other design points I should introduce?
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Re: Just for fun: Unequal length headers on an I4 because noise

Post by ProPower engines » Wed Feb 05, 2020 10:21 pm

Some designs are based off firing order to promote scavenging thus increase power.

Look at so 180 degree headers used on V8 late model dirt or paved cars/engines stuff.
Some use a tri Y configuration with the firing order as well. IE 1+3 2+4 in a dual 2 into 1 into 1 stepping the tube up slightly from the port say from 1 1/2" to 1 5/8" or 1 3/4'' to 3'' end collector. seen a honda system like that on a customers ride it worked well and did sound better then the typical import stuff. I should add it was boosted as well but you get the idea. :D
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Re: Just for fun: Unequal length headers on an I4 because noise

Post by BLSTIC » Fri Feb 07, 2020 3:17 am

These will be 360 degree up until the second merge around the 30" mark on the short runners. I don't think one cylinder assisting another will be a thing on these, just inertia and primary length effects I think.

Is there some kind of anti reversion collector design i can use?

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Re: Just for fun: Unequal length headers on an I4 because noise

Post by Dan Timberlake » Fri Feb 07, 2020 9:50 am

" technically the worst header design .."

It would be fun to see some dyno results and some relatively unbiased reports of strip and track performance.

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Re: Just for fun: Unequal length headers on an I4 because noise

Post by ProPower engines » Fri Feb 07, 2020 12:04 pm

BLSTIC wrote:
Fri Feb 07, 2020 3:17 am
These will be 360 degree up until the second merge around the 30" mark on the short runners. I don't think one cylinder assisting another will be a thing on these, just inertia and primary length effects I think.

Is there some kind of anti reversion collector design i can use?
If you look at the design of what in the pic that is more of a just make it work system nothing more.
If this is a turbo deal thats a different story all together.
If its an N/A set up the best system will take advantage of the scavenging affect of the exhaust gas exiting the system.
There will be either a 4 into 1 set up as in 4 equal length tubes into a single collector or the other system I mentioned.

May be some thing like the PipeMax program can help with that design and tube and collector size and placement.
I have never used it myself but I know others that have for designing exhaust systems with great success when looking for power improvements.

If its just about "" How it Sounds"" well it will not be much help if the system you got now fills that bill [-X
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Re: Just for fun: Unequal length headers on an I4 because noise

Post by BLSTIC » Fri Feb 07, 2020 9:20 pm

ProPower engines wrote:
Fri Feb 07, 2020 12:04 pm
If its just about "" How it Sounds"" well it will not be much help if the system you got now fills that bill [-X
I don't actually have a system worth mentioning on there. I want the sound without the generally poor everything else the pictured header. If I was after optimal performance as the only goal it would be long-tube 4-1 as you imply. I'd probably also have a different engine (Silk purse, sows ear, all that. There are many far superior engines that use the same bellhousing and engine mount pattern).

I'm a little tired now, I'll come back to you all later

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Re: Just for fun: Unequal length headers on an I4 because noise

Post by modok » Fri Feb 07, 2020 11:09 pm

I'm glad some people DO like the subaru sound, and I know some do. Personally I think it sounds like a box of rocks but that has to do with your personal taste and what not.
On a PROPER straight or flat, four or six, the engine vibration and sound CAN BE so consistent and rhythmic that any thing you hear even slightly "off time" is usually a misfire or problem.
If your used to that, a subaru sounds sick, not in a good way.

But there are a few asymmetric novel header designs for a four, that "should" work but you don't ever see.

One possibility is the "three tube header", same as a standard four into one....except the two center ports are close enough that they could be combined into one and share a tube. The two center ports are close enough that the diameter could be kept small, and step up into the header tube. While the outers are really too far apart to pair up effectively because you end up with too much volume in the Y join them into -one- normal primary pipe.

Another possibility is a header that is HALF a longtube four into one, and half a tri-y. I'm sure it would sound a bit odd.

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Re: Just for fun: Unequal length headers on an I4 because noise

Post by ptuomov » Sun Feb 09, 2020 8:59 am

How pulses are combined in the header will change the sound, I predict.

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Re: Just for fun: Unequal length headers on an I4 because noise

Post by BLSTIC » Sun Feb 09, 2020 4:17 pm

modok wrote:
Fri Feb 07, 2020 11:09 pm

On a PROPER straight or flat, four or six, the engine vibration and sound CAN BE so consistent and rhythmic that any thing you hear even slightly "off time" is usually a misfire or problem.
That might be why Honda 4 fours sound like they do. I can't help but note that the honda engines (and any others) that "sound like Hondas" have basically zero cylinder to cylinder variance except for the inlet plenum shape possibly throwing things off. Certainly all the runners, exhaust lengths and ports are all the same.

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Re: Just for fun: Unequal length headers on an I4 because noise

Post by modok » Sun Feb 09, 2020 9:58 pm

Honda has really mastered small four stroke engines, and achieving very close to all cylinders running equal.
Tho "all four cylinders running exactly the same" was initially motivated by port fuel injection systems having no way to correct for variations.

I don't actually believe it is always the best choice tho.
If you have to make all the cylinders run only as good as the worst one..... that's not helpful.

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Re: Just for fun: Unequal length headers on an I4 because noise

Post by MadBill » Sun Feb 09, 2020 10:34 pm

In the old cowboy movies, I always wondered how it was that a posse of 12 pursuing a single bad guy could stay in a tight group for miles and still not lose any ground to him. Drafting? :-k
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Re: Just for fun: Unequal length headers on an I4 because noise

Post by Kevin Johnson » Sun Feb 09, 2020 11:01 pm

MadBill wrote:
Sun Feb 09, 2020 10:34 pm
In the old cowboy movies, I always wondered how it was that a posse of 12 pursuing a single bad guy could stay in a tight group for miles and still not lose any ground to him. Drafting? :-k
Synergism.

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Re: Just for fun: Unequal length headers on an I4 because noise

Post by modok » Mon Feb 10, 2020 4:08 am

Exactly
Is the power balance of all four legs equal?
Most engines can probably gallop faster than they can trot. :wink:

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Re: Just for fun: Unequal length headers on an I4 because noise

Post by modok » Mon Feb 10, 2020 4:45 am

ProPower engines wrote:
Wed Feb 05, 2020 10:21 pm
Some use a tri Y configuration with the firing order as well. IE 1+3 2+4 in a dual 2 into 1
It's quite accurate to say that a logtube tri-y with the ODD firing order GALLOPS.
The even firing order, can only trot. So past some certain combination of primary length/ cam timing/ and rpm, exceeds the fourth harmonic of the secondary length, you can change to the ODD firing order and keep going HIGHER, as that way the Y pairs are not limited to the fourth harmonic. Galloping :lol:

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