exhaust knowledge

[Camurai]

calm down there buddy. My post wasn't even referenced to you.

Anyone who's been here long enough knows what I was talking about.

That john l guy writes novels everytime he posts, just like owequitit.

I wasn't excited, just curious as to why it seemed like you were referring to me. Your post was just below mine with no other reference, so it was natural assume that the reference was to my post rather than the one 8 posts before me.

And yes, johnl definitely does write long posts, but he's extremely knowledgeable and well spoken, so I'm digging it!

[johnnyo032003]

ok some of ya'll take stuff way too seriously i wasn't making a freakin science project out of exhaust theory i was giving you basic examples. ok so here's what i guess i should say when you open up an exhaust with any modification headers cat muffler etc. it moves your power and torque to a higher rpm range too much and it's gonna eventually get so high that you won't be able to reach your peak horsepower or torque within the factory safety net the computer sets a.k.a. inside the rev limiter... say for example your peak torque with a factory exhaust is made at 2500 rpm then you put a high flow muffler or whatever on it may raise it to 3000 rpm with just one mod but when you let the exhaust flow too freely it may get to where your torque peaks at like 6500 rpms and you never get into it on the street say you put 2.5" headers a 3" collector a test pipe and a 4" exhaust on yeah it'll sound like the rice sound people love but it will cause exhaust reversion which is what destroys piston rings and you won't make any horsepower till like somewhere on the bad side of the redline i mean you will but your peak power will be uot there where you don't want it to be on a street driven vehicle

[F22HB]

Umm, hi exaust master. Hows it goin..
What can you tell me about unequal length headers? I've been thinking about making a set for my accord to give it the subi sound.

bump
spill your guts on this subject man! I want a novel. lol

[johnl]

bump
spill your guts on this subject man! I want a novel. lol

A novel, well I suppose that means you must mean me then?! I thought you were making some sort of flippant comment, 'subi' sound, well I couldn't take that seriously!

What do you mean by 'unequal' length headers? a four into two into one as opposed to a four into one. Or what?

[johnl]

Johnnyo,
Are you referring to me as “exhaust design master”? I don’t appreciate the sarcastic tone if you are (and this irritation is coloring the tone of my reply). I’ve never claimed to be an expert on exhaust system theory. In fact if you read my posts carefully you’ll notice I’ve gone to pains to point out that I’m not, merely an enthusiast with a general background knowledge, which may not be 100% accurate.

I respect your caution in recommending that people not go berserk with things such as pipe size etc, and tend to agree that this is unlikely to be a good thing for a moderately tuned street engine. I expect you probably can set up an exhaust system that is superior to a stock system and possibly better than some other people can, based on your empiric experience, hunches, and info from the product manufacturers (are you rigorously dyno testing the results of your efforts?).

But this doesn’t necessarily mean an in depth understanding of the dynamics involved. I used to come across this sort of empirical ‘knowledge’ all the time in karting, i.e. racer X will do Y to the kart and the kart will lap faster, but ask racer X for his explanation as to why and you’ll often get a confident mish mash of half understood physics and misconceptions as to why karts behave the way they do (a very complex series of interactions and effects). Racer X may often know what to do given a particular apparent problem, but doesn’t actually understand what’s happing at a dynamic level, so if the change doesn’t work or makes things worse, then they have no clue where to proceed other than trying something or other blindly on spec. Having bagged racer X’s understanding and approach, I will admit that having a better theoretical understanding won’t guarantee finding the solution to every problem with the kart, but will more often than if you have no clue at all about the physics.

I feel that you tend to make statements that are over-simplified and therefore misleading even when / if they may not actually be incorrect. You don’t seem interested in the fundamental science behind the theory, but if you have no handle on the basic science you’ll never actually understand exhaust system behavior, which is hard enough in any case even with a basic scientific understanding (and I don’t pretend to fully understand it myself, but do understand at least some of the basic physics).

To imply that back pressure is all that’s preventing the piston rings and head gaskets etc from being destroyed is in my understanding simply incorrect. You’re credibility took a big dive at this point, at least with me. You then later say that an overly large pipe with little back pressure (by implication) will cause reversion and also destroy rings etc. Which is it? Rings etc are in far more danger of being destroyed by detonation than from improved or impaired exhaust flow, though substantial reversion may be a contributing factor in some cases of detonation (hot gasses mixing with incoming charge, adding to compressive heat rise that causes detonation).

To imply that the O2 sensor can’t measure oxygen content adequately if exhaust flow is too high due to lack of back pressure is I think equally suspect. If you want us (me) to take these sorts of statements seriously then I’m afraid you’re going to have to back them up with hard info or at least some credible theorizing, and to be clear in you’re language when doing so. If you are trying to convey complex information then if you make little attempt to be clear (and this includes such mundane things as correct punctuation and use of capitals etc, sentence structure is boringly important to being understood) then you might as well not bother, even if you’re right you will be misunderstood and misinterpreted. You tend to make statements that are sweeping generalizations with no qualification or actual explanation, yet seem to expect us to take them seriously based on nothing more than your self proclaimed guru status, sorry not good enough.

To suggest that “any modification” to the exhaust that increases exhaust flow will result in the power band being moved farther up the rpm range is IMO not credible. In many instances it may well have this affect, but not in all cases by any means. The results of changes to exhaust systems can be quite unpredictable, something that in theory ought to have X affect may well not have the expected result, and really needs to be tested, preferably on a dynamometer. Sometimes what may feel like the power has been moved up the rpm range may not actually be what it seems from the butt dyno, it may be that no change at all occurred lower in the rpm range, but at higher rpm a substantial gain did occurr. This wouldn’t be a case of ‘moving’ the power band up the rpm range, but of simply finding additional power somewhere in the band, or even extending the band, but it might feel like the power had been moved up. Affects like this could occur up and down the rpm range, backwards and forwards.

I think you are probably correct in implying that to obtain optimum performance after any significant changes to the exhaust system (or any changes that will affect air flow INTO the engine) then looking at the ECU programming is a good thing, but this really means proper dyno testing and adjustment / change to maps based on what the dyno tells you.

Of course all this is merely my opinion. If you disagree then feel free to do so, but please provide a clearly expressed argument if you do.

[d112crzy]

I bet this is owequitit with a different name.

[owequitit]

I bet this is owequitit with a different name.

Nope. It is not me. I have no reason to post under a different name.

I also have no carting background, although I sure do wish I did.

I think Johnl is from Australia, and honestly, he is doing this stuff pretty well, so I don't have to any more.

[Camurai]

Johnnyo,
Are you referring to me as “exhaust design master”? I don’t appreciate the sarcastic tone if you are (and this irritation is coloring the tone of my reply). I’ve never claimed to be an expert on exhaust system theory. In fact if you read my posts carefully you’ll notice I’ve gone to pains to point out that I’m not, merely an enthusiast with a general background knowledge, which may not be 100% accurate.

I respect your caution in recommending that people not go berserk with things such as pipe size etc, and tend to agree that this is unlikely to be a good thing for a moderately tuned street engine. I expect you probably can set up an exhaust system that is superior to a stock system and possibly better than some other people can, based on your empiric experience, hunches, and info from the product manufacturers (are you rigorously dyno testing the results of your efforts?).

But this doesn’t necessarily mean an in depth understanding of the dynamics involved. I used to come across this sort of empirical ‘knowledge’ all the time in karting, i.e. racer X will do Y to the kart and the kart will lap faster, but ask racer X for his explanation as to why and you’ll often get a confident mish mash of half understood physics and misconceptions as to why karts behave the way they do (a very complex series of interactions and effects). Racer X may often know what to do given a particular apparent problem, but doesn’t actually understand what’s happing at a dynamic level, so if the change doesn’t work or makes things worse, then they have no clue where to proceed other than trying something or other blindly on spec. Having bagged racer X’s understanding and approach, I will admit that having a better theoretical understanding won’t guarantee finding the solution to every problem with the kart, but will more often than if you have no clue at all about the physics.

I feel that you tend to make statements that are over-simplified and therefore misleading even when / if they may not actually be incorrect. You don’t seem interested in the fundamental science behind the theory, but if you have no handle on the basic science you’ll never actually understand exhaust system behavior, which is hard enough in any case even with a basic scientific understanding (and I don’t pretend to fully understand it myself, but do understand at least some of the basic physics).

To imply that back pressure is all that’s preventing the piston rings and head gaskets etc from being destroyed is in my understanding simply incorrect. You’re credibility took a big dive at this point, at least with me. You then later say that an overly large pipe with little back pressure (by implication) will cause reversion and also destroy rings etc. Which is it? Rings etc are in far more danger of being destroyed by detonation than from improved or impaired exhaust flow, though substantial reversion may be a contributing factor in some cases of detonation (hot gasses mixing with incoming charge, adding to compressive heat rise that causes detonation).

To imply that the O2 sensor can’t measure oxygen content adequately if exhaust flow is too high due to lack of back pressure is I think equally suspect. If you want us (me) to take these sorts of statements seriously then I’m afraid you’re going to have to back them up with hard info or at least some credible theorizing, and to be clear in you’re language when doing so. If you are trying to convey complex information then if you make little attempt to be clear (and this includes such mundane things as correct punctuation and use of capitals etc, sentence structure is boringly important to being understood) then you might as well not bother, even if you’re right you will be misunderstood and misinterpreted. You tend to make statements that are sweeping generalizations with no qualification or actual explanation, yet seem to expect us to take them seriously based on nothing more than your self proclaimed guru status, sorry not good enough.

To suggest that “any modification” to the exhaust that increases exhaust flow will result in the power band being moved farther up the rpm range is IMO not credible. In many instances it may well have this affect, but not in all cases by any means. The results of changes to exhaust systems can be quite unpredictable, something that in theory ought to have X affect may well not have the expected result, and really needs to be tested, preferably on a dynamometer. Sometimes what may feel like the power has been moved up the rpm range may not actually be what it seems from the butt dyno, it may be that no change at all occurred lower in the rpm range, but at higher rpm a substantial gain did occurr. This wouldn’t be a case of ‘moving’ the power band up the rpm range, but of simply finding additional power somewhere in the band, or even extending the band, but it might feel like the power had been moved up. Affects like this could occur up and down the rpm range, backwards and forwards.

I think you are probably correct in implying that to obtain optimum performance after any significant changes to the exhaust system (or any changes that will affect air flow INTO the engine) then looking at the ECU programming is a good thing, but this really means proper dyno testing and adjustment / change to maps based on what the dyno tells you.

Of course all this is merely my opinion. If you disagree then feel free to do so, but please provide a clearly expressed argument if you do.

Pwned. 'Nuff said.

[F22HB]

Did I just get pwnd? I don't even know.. I don't think so.
I was just wondering what you guys could tell me about unequal length headers. I have experience in racing karts for about four years and I've been racing midgets for two years now. That doesn't make me any better than anyone on this site.

[bcjammerx]

glad I read through to the second page...great replies

man the a1 header...pardon...exhaust manifold...sucks donkey's balls...nasty bastards

[johnl]

Pwned.

"Pwned"??

[bcjammerx]

yeah it's this weird variant of "owned" these kids are using...I tell ya...kids these days ;P

[johnl]

I was just wondering what you guys could tell me about unequal length headers. I have experience in racing karts for about four years and I've been racing midgets for two years now. That doesn't make me any better than anyone on this site.

I have 10 years karting experience, and as far as I'm concerned it makes me superior to almost anybody! Well, of course not really, but I've run across a number of people in karting who won't even grunt at you unless you've at least won a state title. Racing snobs, what a pita!

Unequal length headers, well it's a new concept to me, but I'll have a crack at it. I'll proceed on the assumption that such headers have primary pipes of differing lengths for each cylinder (?). Everything that follows is pure speculation on my part.

It seems likely to me that such a set up would be intended to spread the power band of the engine, i.e. cylinder A might have a long pipe that tends to move that cylinder's power band farther down in the rpm range, cylinder B might have a somewhat shorter pipe that makes better power a bit further up in the rpm range at the expense of power where cylinder A makes it's best power with it's longer pipe. Cylinders C and D would be more of the same moving the power band of each cylinder progressively further up the rpm range.

I doubt this would mean substantial differences between the power bands of each cylinder, the power bands of each substantially overlapping the power bands of the others. The sum effect would be a fatter / broader power band, though peak power would probably suffer somewhat.

The progression of pipe lengths may not follow the firing sequence, but some other possible sequence based upon achieving the least 'pulsating' power delivery possible with each two revolutions of the crank (considering that each power stroke from a given cylinder at any given rpm won't be equal to the power stokes from the other cylinders at any rpm), and maybe minimising vibration due to unequal strength power strokes at any given rpm (?).

That's my best shot, of course I could be competely wrong!

[johnl]

yeah it's this weird variant of "owned" these kids are using...I tell ya...kids these days ;P

'Owned' as in (roughly translated) 'I agree'?

I dunno, can't keep up with the relentless onslaught of new idioms these days, makes me feel a bit old, and I'm only 48!

Kids nowadays, think they invented 'cool'! Can't wait till 'groovy' comes back into fashion... well maybe I can!

Hell, flares are back (at least this week), now there's a backward retro step, they were awful first time around!

[bcjammerx]

'Owned' as in (roughly translated) 'I agree'?

I dunno, can't keep up with the relentless onslaught of new idioms these days, makes me feel a bit old, and I'm only 48!

Kids nowadays, think they invented 'cool'! Can't wait till 'groovy' comes back into fashion... well maybe I can!

Hell, flares are back (at least this week), now there's a backward retro step, they were awful first time around!

ha ha ha...I think groovy came back but then ran away again...

owned...is more like...showing someone up in general...and doing this in such a manner that the person is made to look like a noob or unlearned person.