wdonovan

Sorry, it AIN'T definitive. It ain't correct. In fact, it ain't even close. You should find the person that told you that and beat him up.

wdonovan

Find the guy who sold you on this one too. He also needs beating up. What does it mean about "enter the collector in the firing order?" All engines do this. That's why it's called a "firing order".

Shark

I'll go with my 17 years of experience as a Mechanical Engineer, rather than whatever dubious opinion you have

wdonovan

I'll see your 17 years of mechanical engineering and raise you another 8 years. What's your field? I've been in race engine engineering, camshaft design, valvetrain eng'g and metallurgy for 25 years. You obviously are not in the automotive end of engineering to make a statement like you did. Since you graduated, "jammed together" has been replaced by wave dynamics. It's nothing to do with "kept seperated longer".

nick49

A high performance header is manufactured with a runner length calculated to maximize performance at a certain RPM. Usually short runners are for high RPM power and long for lots of low end torque. Length is calculated from exhaust valve to a point in the collector. Some systems pair cylinders together that fire 180 degrees apart and will have multiple collectors depending upon desired results.

The collector will increase velocity of the exhaust gas and create a low pressure area in the runner of the valve that is about to open helping to pull or scavenge the exhaust for that cylinder. Some headers will have a small restrictor or cone at the inlet which will help break up reversion sound waves and increase exiting gas velocity. These aid in lower and mid-range performance and help with cylinder fill. Some headers use a canister before the collector that will fill during low rpm use and get bypassed during high, some have mechanical valves that will alter flow depending upon RPM.
These designs work over a broader RPM range but are expensive to design and manufacture.

All headers should work to a degree if designed by someone who understands the basics of removing spent gases from an internal combustion engine. Different designs will yield different power characteristics. It should have been pretty easy for Porsche to design a header for the 996 that would enhance the power of the motor for street use and concentrate power gains lower in the power band . If racing and power output would want to be maximized a little higher up in the RPM range, then the runner length and collector design would probably be changed.

Oh...no degree, just perma-grease under my fingernails, lol

wdonovan

Thanks Nick. Are ya reading, Mr. 17 year experienced Mechanical Engineer?

Shark

I work in the heavy equipment industry, with Cat and Waukesha engines, and we deal with issues like these every day because engine performance can lose customers tens of thousand dollars per day. These are million dollar pieces of equipment. This isn't trying to hop up a Subaru or what ever the hell you do in "racing"

You made a stupid statement that advocates beating someone up which added NOTHING to the thread, same thing with your recent post....you have added ZERO, and are just insulting those with far more knowledge and class than yourself. Good job Mr. 50 post wonder

wdonovan

"Beating someone up" was a joke. Unless you're talking about beating up your old professors because whatever diesels they taught you to work on, you DON'T KNOW how an exhaust system works. Maybe you should listen to one of the seat-of-the-pants racers to whom you condescend. Playing you "E" card was obviously an attempt in proving superior knowledge, as was your "hop up a Subaru or what ever the hell you do in "racing".
If it helps validate my position to you, I am not a shadetree hotrodder, 25 years as chief angineer and metallurgist for an aftermarket race engine parts manufacturer. Much of my research has been in wave dynamics, a necessary part of the performance equation. This is the branch of physics that governs performance exhaust systems. I'm afraid that what you practise in your "million dollar" engines has no practical value here, given the operating range of those "million dollar" engines. We're not hotrodding cranes, they're sportscars.
I apologize for saying to beat up your old professors, you should ask them to beat you up. And.... before you pull the "E" card again, you should KNOW WHAT THE HELL YOU'RE TALKING ABOUT. One way to start would be to read what Nick49 posted. This is accurate and verifiable. Your explanation IS NOT.

Here's a free education for you that they obviously thought would have been over your head when training you for deisel engineering. You long primaries work with your combination because it takes a long time for a positive wave to travel down the header and then the subsequent negative wave to travel back up and scavenge the cylinder. It's nothing to do with delaying the merging of pressures that create backpressure. There is no backpressure. There are negative pressure waves (vaccuum waves). That was the statement of yours that kind of gave away that you had no clue. You know, it's alright to ocassionally say "I don't know" or just don't post at all.

BruceP

I wish people would pay more attention to posts like this. SO MANY mods, if they do anything at all, don't find "more power". They just change where it occurs, often at the expense of what you can actually feel. Breathing mods, at either end of the motor, often add power at high rpms, at the expense of grunt at low rpms. You get more bragging rights, but a less lively feeling car. Fine if that's your choice. But every time I see someone popping off about how they found power that Porsche didn't know was there, I strike them off my list of credible sources.

jw996

Did another dyno run after gasket was correctly installed. The results was still not what stock headers produced. Lost 11 lbs. tq. & 13 hp. After reinstalling stock headers seat of pants dyno seemed to give back low end tq. and power. Seems like if Porsche could of designed a more efficient header they probably would have. Cost would have not been much difference because you still have to weld 3 pipes into a collector. JMHO. Also installed RSS plenum from group buy. Butt dyno seems like response was more aggressive and would say more power. Won't dyno unless I get bored or feel like spending another $125. On 6 speed board there is a new mod being developed for appx. $200. Check out and give opinion. JW

RayGT3

Before you beat any one else up, this is "What does it mean". Lets say the engine fires first in cyl 1 then 2 then 5 then 3, 4 and 6 ( just as an example) one header collector would have cyl 1, 2 & 5 and the other 3, 4 & 6. And by the way, all engines do not do this.

The name "firing order" did not come from header design.

And who put you in charge of "beating people up"?

Just maybe, you should beat your self up.

wdonovan

All engines release gas into the headers in the firing order. Not necessarily into one collector. That would mean there could be only one collector. Firing order is 1-6-2-4-3-5 in a 996. One, two and three are on one side, four, five and six on the other. So one collector sees 1-2-3-1-2-3.... The other sees 2-4-6-2-4-6.... The order is staggered but it is even and by rights, requires equal length primaries for best performance. An exhaust system that collects gas in the firing order of the entire engine would require one collector. That would mean running headers over the top or under the bottom. It is not practical in an engine with more than one bank of cylinders. What I was saying is that the order in which the cylinders fire is the order in which the gases exit. That is true of all engines. Never said the term comes from header design. Just that the gases enter the collector in the same order that the engine fires.

2000wrx

I find this a little odd... I can think of a lot of cars that see nice gains from headers.

Mustangs (any year) see nice gains (03-04 cobras = huge gains)
F-cars (any year) nice gains
EVO's VIII-IX nice gains
WRX and STi see okay gains
C4, C5, and C6 Vettes see nice gains
LS1 & LS2 GTO's see nice gains


Porsche like many auto makers has to make compromises.


It would be nice to see a group header dyno on one car in one day to test many sets of headers. This was done on NASIOC for the WRX and was a great wealth of info. FYI all headers performed better than stock, though this is a turbo application.

RayGT3

In my origonal post I stated that this method is impracticle in most cases and does require additional plumbing, one side of the engine to the other as well as matching runner lengths. But has been used in drag circles with some success multi cyl motorcycle engines and I believe even in early F1 engines. But bottom line still being, there are power gains to be had using this system on boxer and V engines. Again, I admit to this system being somewhat obscure, primarily because of the complexity, but going fast is all about choices and keeping an open mind.

wdonovan

Ray, I was just teasing you because it sounded like you were saying "the sky is blue because the sky is blue". Guess you didn't catch my implication that the order fired is the order expelled. In reply to your last post, yes there have been multiple bank, single collector setups but they generally require such long primaries that they are tuned for either too low an RPM or too late a pulse harmonic where they serve little use. Multicyl. M/C engines, if inline are a breeze as they are a single bank of cylinders. On the Porsche, you may be able to engineer a single collector setup that meets centrally under the engine. Interestingly, the primaries on my 996 911 are the same length but meet at intervals along a collection manifold (for lack of a better term). If Porsche tuned the length of these pipes, they should scavenge cyls 2,3,5,6 the same with a different signal for cyls 1 & 4. There may be within, the key why the Porsche headers outperformed a different set of equal length headers. The other strong possibility is that the aftermarket ones are either the wrong length tubes or are too big of a diameter to maintain velocity.