headers anyone?

[MrPbody]

WrightZ28,

The info provided is relating to making power with headers. I have no doubt, the TES system is better than the stock system. And a full length system skews the results from header installation, as well. When discussing headers specifically, it is generally accepted that the engine will be run with open exhaust when trying to make max power.

FWIW

Jim

[89IROC&RS]

Ok, to start, the whole "seat of the pants" measurement was given, because i havent taken the car to the track, otherwise, i would have posted times. My experience and knowledge about cars in general, and small block chevy's is not in question on this forum, so im not going to justify myself and sound like a braggart, suffice it to say, that i also know what i am talking about.

Now, It is true that "tuned" headers aim to sync the exhaust pulses to aid in evacuating each cylender on the exhaust stroke, but not all headers are "tuned", that includes shorties and long tubes. And yes, this all does operate on the principle of the speed of sound, and the stack of air moving at that speed up and down the tubes. As for flow... it is very important as the flow rate of the tubes has a major impact on backpressure in the exhaust which impacts the volumetric efficiency of the engine, you can tune the length of your headers till youre blue in the face, but if the primary pipes have the diameter or soda straws, youre not making any power, because you have little to no flow. by the same token, you can over scavenge the cylinders with pipes that are too large, and cause a low flow condition. so size of the pipes and their flow rate cannot be ignored.

Now in reference to sonic harmonics in tuning the engine, i believe you are a bit confused. The harmonic in the exhaust does not impact resonance tuning of the intake track. theres a little something in the way called valves.

Intake tuning by resonance was first experimented with by the "ram chargers" who worked for mopar back in the sixties. They found that the length of the intake runner would cause a supercharger like effect at a certain rpm, this is caused by airflow moving down the intake runner, to the cylender, when the intake valve closed, air would "stack up" and you would get a pocket of air right against the valve, that was denser than athmospheric pressure, this pocket would "bounce" off the intake valve, and move back up the intake track at the speed of sound, and when it hit the plenum, it would "bounce" back towards the valve and the resultant vacuum it left behind. By tuning the intake, you could time this pulse so that the dense pocket of air was just about to hit the intake valve when it opened, the resulting dense air charge being shot into the engine would cause a signifigant boost in volumetric efficiency, but only within a very small window of rpm operation.

Exhaust tuning, is a seperate animal, you arrange the exhaust pipes, so that they meet up at points where the previous exhaust pulse (which would be dense, compressed gas, would be passing just in front of the next one, in essence the previous gas pulse "pulls" the next one along due to its momentum. You do this to avoid all the gas pulses arriving at the same time at the same point in the exhaust and creating a "choke point" that would limit exhaust FLOW. yup, that critical point.

So your understanding of the idea of "ram charging" was correct, however you were a bit confused on to the components of the engine that effect it. It is impossible for the exhaust pulse to effect the intake, because the exhaust valve closes while the exhaust is still exiting the cylinder, and the intake valve opens after the exaust valve closes (except in very lumpy race cames that have to deal with overlap due to extreme high rpm operation). If neither valve is open at the same time, you are looking at what is in effect a plug in the system, that would not allow exhaust to travel back up the intake track. this is why we have EGR systems.

I really dont know what to tell you regarding the shortie headers operating better at high rpms, vs the long tubes, because it goes against everything i have ever seen in engine building. my uncle drag races, builds race engines, his friend builds racing boat engines, ive been spinning wrenches since i was 8, and am also a mechanical engineering major. with a minor in aerospace.

the speed (edit - frequency) at which the sound pulse goes back and forth within the pipe really has no effect on anything, except how long the pipe will be if you want the pulse to arrive at the valve at a certain rpm.

Now, in regards to my car, im afraid i may have confused you with my use of the term "complete exhaust system". i do not have an X-pipe, or true duals, i drive a third gen, which limits me to a single pipe. I have TES headers, into a high flow 3in cat, and a 3in american thunder exhaust system with a single pipe to a single muffler and dual outlets, just like the factory put on. I can trust my seat of the pants measurement, because im not trying to determine the exact trap speed or E.T. of the car, im saying i drove it before with stock manifolds for a period of time, i did the swap, and after driving it, could feel a very noticeable difference. The car was faster after the swap to a degree that i could very well feel. Your argument implys that if i were to drop an 8-71 blown 468 big block between my frame rails, i would have to take it to the track to "prove" it was faster, because my butt might lie to me. Probly the only way that setup would be slower is due to a lack of traction. Now, if i wanted to say how MUCH faster it was, i would need to go to the track and have before and after runs.

To that end, i will retract my statement that it felt like a 30hp increase, as i will admit, despite having alot of experience driving cars before and after modifications, and driving cars of different power levels, my butt is not a dyno, and i really have no basis for that numerical figure. But i can tell you the car was conciderably faster with the headers installed.

As far as your comparison of the dodge to the pontiac and how much faster the dodge felt than the pontiac, but the fact that you still won, has more to do with power curve, and the way the engine makes power. you could make the same comparison of a hemi cuda vs a z28 camaro with a DZ302. off the line the hemi would feel like it would eat that "tiny" V8 alive no questions asked. in fact the 302 was often described as being anemic off the line, however, once that 302 rev'd up to 8000rpm it pulled hard on its own right, and the two were actually quite well matched at the track. with the hemi being slightly faster if i remember correctly.

but i digress, this is a different discussion for a different thread.

my point here, is to agree that seat of the pants measurements are hardley scientific, but i have seen a man with enough experience that he used an impact gun to set the torque on a pinion nut, and when i checked it with a torque wrench he was spot on, so there is something to be said for experience. And i also have driven enough cars to be able to feel a signifigant difference in power from adding something like headers and exhaust.

also, just because my first post wasnt a thesis regarding the subject at hand, dosnt mean im not concidering all the factors at work, it means i didnt feel the need to launch into a complete explenation of them all. And i am very well versed in the design and construction of high performance engines.

-erik

[instantkevin]

I won't step in (and don't really care to) on such an involved discussion, but I will say that it is proven fact that shorties generally produce better peak power numbers in the lower rpm range and higher torque numbers. Long tubes produce better power in the high rpm range and produce higher horsepower (not torque). Lastly, shorties are more than marketing ploy... they offer very significant performance gains over stock cast iron manifolds.

I won't spend much time on this, but if you would like me to provide independent test results (dyno) and also manufacturer results, I can. It's proven fact. (obviously different engine combos react differently, but this is most often the case.)

Also, no one knows everything, but having been around here for many years, I can attest to 89IROC's knowledge. There are several of us who are aware of the deep technical aspects of performance and go well beyond the typical shadytree mechanic.

[instantkevin]

Also (contributing to the original question), I have Headman shorties on my third gen. I did the V6-V8 swap, so I dont know if you O2 sensor location is any different, but the O2 comes well after the header so it wasn't a big deal to reuse it.

It was a simple cut of both sides, weld-in the collectors, and connect the collectors to the new headers. Since the O2 came later in the piping it was not affected.

As with any tpyical header install, its a pain to tighten the last header bolt on the passenger side (much easier with the engine out). My headers are designed for angled spark plugs, and its no big deal. 1 or 2 are a little more difficult to get out, but nothing really significant. Being smart and using the right tools makes it simple.

[89IROC&RS]

oh almost forgot about the spark plug issue, there is a tool you can buy on ebay, or at least you used to be able to, or you can make one yourself, makes life a helluva lot easier.

get a 5/8in socket with a 3/8 inch square hole for a ratchet, but with a hex head on the outside, im not sure of a part number off the top of my head. you cut half the length of the socket off, and drill the center out to a larger size, i dont know off the top of my head, the bigger hole lets the spark plug stick through the center, and you can put a wrench on the hex head to break the spark plug loose, i think mine is a 3/4 size hex on the outside of the socket.

worth its weight in gold after the header install.

oh and instantkevin, appriciate the ego stroking feel free anytime

[MrPbody]

I'm not confused. The valves ARE open at the same time in EVERY automotive engine. It's the "overlap" period you speak of. Older design high performance cams had more overlap than current thinking. But current thinking still includes it. The scavenging effect relies COMPLETELY on the overlap period. If there was none, there would be none... In a supercharged application (or turbo or any other "positive pressure" method), overlap is kept to an absolute minimum to prevent pumping raw mixture out the exhaust. But even they have SOME overlap.

This was not intended to start an "I know more than you do" debate. I don't care what you know. I care what is propegated to the general public, and how confusing many people see issues like this. I know what I know, and am very secure in it. It has served my customers well for many, many years (more than 30). I'm not a shadetree or a hobbyist. I do it for a living.

Lastly, there are many more engine families out there than small block Chevy. What works for one, may or may not work for another. Having been to many races, pro and ammetuer, I have yet to see a real hot race car with shortie headers on it. All the small block guys I support run full-length, and some WILL spend the money to have true "equal length" primaries made to fit their car.

Bantering about this is counterproductive. Suffice it to say, when you have a full exhaust system, headers won't do what they're supposed to do, nearly as well as they do when "open". So we're just sitting here beating a dead horse.

PAX

Jim

[89IROC&RS]

i will respect a truce.

if we go all the way back to the beginning, my whole objection to the post you made, was that shortie headers were ineffective, and long tubes were the best way to make power.

in your last post, you say that all "real" race cars youve seen run long tubes, well that makes sense, because as ive stated, long tubes make power at high rpms, where race cars run. My argument against them is that he is driving a street car, which will probly NEVER see those rpms, and the shortie headers would produce a powerband much better suited to his application. Which is why i supported the install of the shorties.

and as for peak power with or without a full exhaust, there actually have been dyno runs, where the lack of an exhaust reduced backpressure too much, and when the full exhaust was installed, they picked up a few ponies. not all engines mind you, but in street applications there have been engine setups that responded well to a bit of backpressure.

so aside from a few points of disagreement, were actually saying the same thing, its just that youre writing from a race car perspective, and im writing from a street car perspective, or at least thats how it looks to me.

nothin wrong with some spirited debate opcorn:

[MrPbody]

Truce accepted.

I must say our perspectives aren't exactly as you say, though. While I AM talking about race cars, true, I am also talking about street cars. I suppose the biggest difference is I'm not trying to maintain the entire catalyst system and work within the confines of stock replacement. Sometimes we stray from the beaten path...

Jim