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Old 01-16-2002, 11:09 PM   #1
Keiho
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Default Header design

Having read through some of the header threads in here, I still have a few questions.

A mechanic at Technik Motorwerks (the turbokit guys) has mentioned to me he's interested in custom making headers for me. He's thinking along the lines of MRT, two equal length runners that merge into the midpipe. His idea does not include cats. Now normally I'd be all for it, but I'm lazy and don't want to have to swap to the stock header/cat setup everytime I go for emissions. There's also the question of throwing CELs. I don't want that.

So ideally, I'd like to have the equal length headers, with cats in the mix somehow and retaining as much of the stock "property" so CELs don't come up.

Where should the cats be positioned in this proposal? I assume I'd need to have two high flow cats to retain both O2 sensors to prevent CELs right? And ideally ceramic coated to retain the heat correct?

So any engineering guys want to throw in some ideas for placement of cats and sensors for the least likelihood of throwing CELs? Oh yea, he mentioned something about having a 4 to 1 setup...which would be better for a daily driver? I vaguely remember 4-1 header setups being used for top end power.
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Old 01-17-2002, 12:42 AM   #2
AllWheelDrift
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I believe you only need a single cat with one O2 sensor before the cat, and one after.

The CE light is usually related to cat efficiency. As you've probably read, the problem is with an equal length header design, the cat ends up being much farther from the exhaust ports. Additionally, the the system will flow much better especially when combined with a cat back system. Further, most headers aren't heat shielded like the stock one. This all means the cat doesn't heat up enough to work well, which is detected by the second O2 sensor. The solution is to ceramic coat and/or wrap the header to retain more heat.

As to 4-1 design, none of the pics seem to work anymore, but I think this is the way Brullen made their header. Based on the dyno results, it seems to have improved torque throughout the rev range so there wouldn't be any issues for a daily driver.

An idea might be to fit a single cat in each runner as close to the head as possible. You'd proably want to run small cats since you've only got 2 cylinders to heat them. (No need for high flow cats for the same reason.) Both O2 sensors would have to go on a singe runner (for argument's sake lets say the right one) one before the cat and one after. Your ECU would only be monitoring the A/F ratio on right cylinders, but you'd hope that they would be running as rich/lean as the left cylinders (If they aren't there's nothing the ECU could do about it even if you had the stock system!) With this kind setup you could make a true dual exhaust system if you chose not to merge the runners.

It's a crazy idea, but it just might work.
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Old 01-17-2002, 01:00 AM   #3
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Actually after lots of research and watching the gang at Brullen pull their hair out, cat placement is not as important as O2 sensor placement.

Now consider this. Cat + O2 sensor placement together is really critical. Even 1inch difference in placement will change how the O2 Sensors and Cat interact with each other.

The front O2 sensor is more critical, too close to the exhaust stream and the ECU will overcompensate by running too rich resulting in carboning up the cat which results in 0420 code.

Running the O2 sensor too far will result in the O2 reporting a too rich (cold) situation and the ECU overcompensating by running too lean 0310 code.

Been there done that. Now other considerations, after you find the ideal location in the exhaust stream to match the 3 way cat location, the next step is to decide on the depth of the O2 sensor into the exhaust stream, we are talking 3D here.

The problem is not related with cat light-up, as it is related to placement of all the components.

That's why companies like Brullen / Syms / Maxim works etc. spend thousands of dollars testing and re-testing hoping that all the bugs have been worked out. Only when it is released to the general population will you ever see a proper cross-section of utilization that will result in other items cropping up.

Even with good smog results (see attached for the Brullen setup) life is not necessarily perfect.

Good Luck, if you need more info, let me know and I'll do my best to answer your questions.

I know the pain that you are about to go through.

The hand written notes on the smog test are the max allowable numbers for California emissions.
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Old 01-17-2002, 03:44 AM   #4
Keiho
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Thanks JoeT.

To be honest I'm not sure if I will go through with anything yet, it's all just in the "talking" stages. It'll probably be easiest to just build a catless system anyway.

Would using the same diameter piping size as stock, just in equal length help? Try to emulate the position of the two cats and the O2 sensors as well.
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Old 01-17-2002, 08:45 AM   #5
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Yes it would.

The length of the pipe will determing what RPM you want to affect. For example, if you make "Shorties" depending on how short the equal length runners are, may affect the engine beyond the usable RPM range.

The stock ones have about 8" primaries and 1 5/8" tubing. If you were to calculate what RPM this was meant to scavenge at, you would be looking at beyond 10 000RPM. In reality, the stock primaries never get to the efficiency point to scavenge exhaust gasses.

Long tube equal length headers are ideal for our cars, in the range of 28 - 34 inches with 1 7/8" primaries. This kicks in and works extremely well within the stock RPM range.

If you change the cat, and change the primaries it's back to square 1 with regards to proper positioning of the O2 sensors. But that would be a good place to start.
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Old 01-17-2002, 09:07 AM   #6
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The Brullen is not a 4-1 header. It's not even a 4-2-1. Technically, you would probably call it a 4-3-2-1 setup. The primaries on the passenger side collect to one pipe. Then the primaries from the driver's side dump into that collected pipe one at a time. This means you have a pipe collecting two cylinders, and then further down the stream you find the same diameter pipe is now handling all four cylinders. At least, that is what I gather from the pictures I have seen. I have yet to see dyno sheets showing more than a 9HP gain from the full system. It just doesn't seem like a good design to me.
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Old 01-17-2002, 10:22 AM   #7
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i'm still waiting for the Revolutions header and the Greddy header to see what comes up.

i say if you are looking for just better than stock performance, use a header that will bolt up the same way, just re-route the piping to make equal length and up the size slightly. this way you won't have to worry about re-locating the cats.

but i don't know much about this so it's merely a suggestion
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Old 01-17-2002, 11:32 AM   #8
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Joe, very good points about the O2 sensor placement. This is very interesting, and the first I've come across such ideas (well, two threads this morning, but it's still new).

Trojan, there wouldn't be much point in making a new exhast manifold/header that bolted to the stock system. See Borla. It's a convoluted design that doesn't really take advantage of much of anything except using bigger tubes. Gains will be seen in going with something along the Brullen/MRT lines.

It would be somewhat easy to make a system that bolted to the stock mid-pipe, however. Though, still, using stock system pieces in your design will limit gains.
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