TeamSwift

As some of you know, I play quite a lot with header design. I have come up with several reasonable designs, but the holy grail of header calculations still alludes  me. It is easy to design headers that are well suited for a specific (but small) range, but there will always be large downfalls acociated with fixed tube designes. 
I do not dispute whether your header "works good" or what works for the boys in NASCAR, but i will say that  beneficial scavenging effects happen within a narrow window, and can actualy impede performance once out of that window.
Pressure waves within a fixed primary tube will only be beneficial to scavenging while operating within the frequencies in which the primary was built to accommodate. (where a negative "vacuum" pulse arrives at the exhaust valve during valve overlap, assisting the scavenging process). Once the frequency changes (change in RPM), the beneficial pressure waves occur out of phase with valve events,  all scavenging effects diminish and there is even a risk of recharging (be it on a small level) cylinders with exhaust gasses.
This often results in a peeked torque curve which is often not desirable in a vehicle intended for street use.

So, how can we flatten our torque curve? How about we dissipate the the potential "good" and "bad" wave forms and remove the problem all together. This way the average pressure at the port is at around 0  during valve overlap instead of fluctuating as a result of resonance.   The trick hear is to build a manifold that has the ability to slow down and "weaken" the initial pulse quickly. This way, if there is any energy reflected back to the port, it will have lost amplitude and will arrive well before valve overlap. By doing this, the pulse can be overcome by the still high velocity charge being driven out by the piston. 
The result is a very consistent pressure curve at the port through the range of engine operation. In short, a flatter torque curve.
Another concept I have been contemplating is the temporary but complete removal of back pressure @ the manifold via use of Venturi effect. With use of a high pressure gas, one can create a strong vacuum within the manifold to exponentially increase scavenging. For brief periods of time however. The result is a little extra power when you need it. Like a week shot of NOS.

Just some ideas I've been chewing on... I will be trying this all out on my next build-up. I'll keep y'all posted.

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95% of the canadian population say "Oh shit!" before hitting the ditch.
The other 5% are good 'ol Alberta boys saying "Hear, hold my beer... NOW WATCH THIS!!!".


May not always be pretty, but Rednecks Git'R'Done Good!

Some thought provoking discussion you bring up here.

With the goal being to manage two different but related systems, the physical pressure wave system, and sound wave reflection system, it might be necessary to mix and match traditionally successful header attributes on the 3 holer.

Edelbrock has made some attempts at flattening torque curves by using 2 different primary lengths/diameters to get 1/2 the holes maximizing one rpm range, and the other half further up or down the rpm range. So how about a 1.25 dia primary on hole 1, a 1 3/8 primary on the next hole, and a 1 1/2 primary on hole 3? With custom IR intake tuned to the appropriate rpm range for each hole? So they each produce max torque 500 to 1000 rpm apart. Then worry about crank harmonics after it throws your flywheel into the cockpit...

The next thought would be to manage both reversion (reduce negative pressure at valve) as well as sound frequency (harmonics, 1/2 waves, 1/4 waves, whatever waves are available through readily available tubing) by stepping dramatically.
1.25 dia primary for the first few inches (need to calc sometime), 1 3/8 for next several inches, then 1.5 into a merged cone collector of approx 1.5x-2x diameter at the secondary pipe choke point. All this stuff is available off the shelf (parts) from the 914 racer supply houses. I'd say 1 3/4 for the secondary pipe for around 2 feet length into an expansion chamber (resonator, glass pack, whatever) that the engine "sees" as atmospheric, simulating an open header in an enclosed full system. 2ndary pulse stops and reflects from the entry into the chamber and gets progressively muddled as it makes it's way backwards against the (reversed) stepped down primary. At least 3 different sound waves arrive at the valve at least 3 different wave speeds, possibly opening up the rpm range of that system.

It's enough cut and try to wipe out the wallet, but that's what makes it fun.

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95 Metro hatch "Tequila lime" now demonically possessed by Lil Evil.
93 Metro wagon teenage schoolbus
90 Metro hatch "fugly duckling" next up for freeway suicide duty
89 'GT3' chassis in the house
Looking for another 95 to drag home...
92 Tracker 2 dr rwd stock
93 Sidekick 4 dr 1.9 vw TD, WVO conversion, 6" lift over 33's

i'm a fan of anti-reversion type pipes. those use an inner cone to keep the reverse pulse from traveling up the walls of the pipe and back into the port.

you can use them on the exhaust tip as well to keep atmosphere from being sucked back into the pipe. that keeps exhaust gas moving out of the pipe, effectively getting rid of or reducing the reflected pulse.

pretty much as a standard, you have guys that want to open up the exhaust ports and match the manifold gasket to the outlet with the mental process being that it will smooth and maximize flow. i've found that the 3 banger is really quite sensitive to that sort of thing and runs better, in my opinion, if you leave a step between the outlet and the manifold flange. in effect, that does the same type of thing as the anti-reversion cones in modern headers. it stops the echoed pulse from travelling back along the pipe walls and back up into the exhaust port.

exhaust gas pulses as the valves open and close. in the interval where the valve is closed and gas flow stops, you need to maintain some flow because it takes some small amount of time and considerable energy to get it going again after it stops. i typically let the tuned front end of the exhaust open up into a larger diameter pipe which affords some extraction in the overall system. as the gas expands into the larger cross section of the pipe, it will bridge the tuned frequency of the front pipe and help to keep gas flowing, even though the velocity slows as it expands into the larger pipe.

going back to the days when i designed exhaust systems for schnurle principle 2 strokes, i used to play with the forward and reverse pulses to help stuff spilled over fresh charge back into the exhaust port just before the piston rose into it's secondary compression mode and closed off the port. with 4 stroke engines you have a mechanical valve that closes off the cylinder on the compression stroke so you don't much need the reverse pressure wave to assist. that's where the anti-reversion and extraction techniques come into play. keep the flow velocity up in the front pipe and let the gas expand into the next section(s.)

i've seen 3 different pipe diameters used in some trick exhausts. another thing i used to do was to convert gas flows and engine rpm into frequency and crunch the numbers that way. you would be amazed at how close the math is between mechanical and electrical engineering. things like spring rates can be solved using the same equation as that for an electrical oscillator.

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1991 Blue Geo Metro Convertible highly modified 1.0L Turbo3 5 spd. - 1991 Red Geo Metro Convertible customized 1.0L 5 spd. - 1992 White Suzuki Swift GT

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Dunno about the three bangers but Ken Yoshimura came up with a simple concept of balance pipes on the header between cylinders 1-3 and 2-4. volume stays the same but the pulse see double the space and the wave fronts dissipate that way.

how to revert that principle into a 3 legged header.... hmmmm

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Understeer is when you hit the wall with the front of the car and oversteer is when you hit the wall with the rear of the car.HP is how fast you hit the wall, torque is how much you push the wall out.

I figured y'all would over engineer this... (lol)

The solution is surprisingly simple, short exducer runners (less than 4") that taper from 1.5" to 3" (not in steps either, a straight taper) and dump into a large collector, trapizoidal in shape.
If one is looking to disperse energy, why give it time and room to build momentum... Instead, let it do it's thing very quicky while it has no ability to interfere with scavenging due to the still high cylinder pressures, and let the unimpeded flow of exhaust take the course of nature.
The only potential problem with This setup is the high potential for cross-talking between cylinders. But, it's going to happen anyway, so f**k it! Show me a header that has all primaries ajoined by one collector that dosnt have cross-talking issues. (may as well call them party lines! Lol)

A very quick and dirty explanation, but hey... It's a bitch to type a long winded explanation on an iPhone!!!!

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95% of the canadian population say "Oh shit!" before hitting the ditch.
The other 5% are good 'ol Alberta boys saying "Hear, hold my beer... NOW WATCH THIS!!!".


May not always be pretty, but Rednecks Git'R'Done Good!

actually, very often you'll find that engines really like slaved pulses. there are some infamous v8 engines that run like poop if their dual exhausts aren't cross connected.

i think that it's way more important that the pulses are balanced against each other.

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1991 Blue Geo Metro Convertible highly modified 1.0L Turbo3 5 spd. - 1991 Red Geo Metro Convertible customized 1.0L 5 spd. - 1992 White Suzuki Swift GT

My Turbo3 Project

My Cardomain Page -Ol' Blue

My YouTube Channel

My Photo Gallery

SAAB Sonett II

It is to my understanding that many v8 engines run better with a crossed dual exhaust due to the colaps of pressure waves due to the length of the system. Not so much due to the reflection of waves.
Either way, the approach I am taking simplifys much of the research I have done. The added plus is the fact that it is rather cost effective to produce, and is far more compact than other headers I have designed.
I am rather excited to see if the Venturi scavenging system i will be incorperating really works... I will have to get some dyno results to confirm the gains if it dose.

_________________
95% of the canadian population say "Oh shit!" before hitting the ditch.
The other 5% are good 'ol Alberta boys saying "Hear, hold my beer... NOW WATCH THIS!!!".


May not always be pretty, but Rednecks Git'R'Done Good!

let me know if you will be making ex. headers. i'm in the market for one for SOHC 16valve.

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Silver 2000 Firefly 4DR; 16V SOHC, 3 to 5 speed swap, install PS and AC, remote and auto start, PL, PW, kill and start switch, Valentine 1, behind-bumper CAI, 55MM TB with coolant-bypass, polyurethane-fill engine/shifter mounts, modified to short shifter, upgraded electrical system, CS130 alternator, 90/160W headlights + relay mod, ceramic H4 plug/harness
To do: finish stereo, 4000K H4 HIDs, short block replacement
'sponsored' by Captain Crunch, Lordco, Felpro, Permatex, Royal Purple

I would be interested as well. Since there seems to no longer be any kind of parts source for the three banger headers anymore.

And damn, all u guys from the North.....ur heads must hurt from all that knowledge gained from spending the long winters indoors.

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Things that go "BOOM" in the night ! Hopefully not the 1.0.
Member#3307 ??

Spending the winter indoors??!! I guess, when I'm not re-certifying service rigs, hunting coyotes or ice fishing... Lol. I just like to make things suit my own needs. If it means re-engineering something, so be it.

Once I prove or disprove the design, we'll talk about building more...

_________________
95% of the canadian population say "Oh shit!" before hitting the ditch.
The other 5% are good 'ol Alberta boys saying "Hear, hold my beer... NOW WATCH THIS!!!".


May not always be pretty, but Rednecks Git'R'Done Good!