Re: Stebro questions...
 

The expansion event in this system did no happen until further back, 2.5" resonators followed the collectors the into the expansion event which was placed just behind the rear X-member. If I had measure the length I would imagine it was about 20" further back. OT might have pictures floating around of how it all came together.

Tom

Re: Stebro questions...
 

I want this......

Re: Stebro questions...
 

Harvey, I'm not understanding the benefit of having the 3 pipes run into the expansion chamber without the use of a collector. And please don't get me wrong, I'm not questioning your knowledge. In fact I'm certain that you know more about the voodoo of engine tuning than I do, that's why I ask. But from what I have read from David Vizard, power is made in the collector. He even says that equal length primaries are not as important as a correctly tuned collector. Is the difference in the type of engine? Vizard generally writes about old V8's. As you explained in your camshaft thread, there are differences in what our engines like and what those like. Is this another one of those instances?

Re: Stebro questions...
 

Ok, went back and reread everything. You did say an expansion chamber or a collector. But I still am curious if it would be beneficial to have a properly tuned collector on this engine or not.

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You read quicker that I write.

Harvey.

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That’s ok mate, I know that it runs across the accepted theory, but as you say, it is another one of those instances.
The older ‘low engine speed’ theory, is based on the inertia of the exhaust gas flowing down a pipe, to create a low pressure behind it. They used this pressure to start the flow of inlet gas into the cylinder, during the over lap period. There is the theory that the flow would suck the exhaust gas out of the next cylinder. That worked up to a engine speed that was low enough, and the overlap was long enough to do it, but as this gas flow only travels at about 300 ft/sec, it was too slow for engines that had to develop there torque at 6/7000 rpm. The main function that a V8 header has is that, when the long overlap is used, there is a huge amount of interference between cylinders, some only 90* apart, so the header branching had to be very long to prevent it.

To the present, the exhaust that we have is the modern high-speed type; it does not rely on the inertia and overlap to induct the inlet air. It uses the sound wave pressure that is developed in the engine pipes, from the exhaust valve down to the third cat. This wave travels at 1700 ft/sec, fast enough for the highest engine speeds. This is the difference that changes the way we design headers, because, they have different functions to do.

We have three cylinders (the other side will be the same) they exhaust 240* apart, there is no chance that one cylinder will push exhaust gas into another cylinder, so the branching is kept as short as possibly. The three cylinders then use the exhaust pipe, from the exhaust valve to the 3rd cat, as its own tuned length resonate system, returning all the negative pressure back to the cylinder that needs it, to induct its air. It works the same as Toms three pipe header, but only needs one pipe, to do it.

To answer your question “, I'm not understanding the benefit of having the 3 pipes run into the expansion chamber without the use of a collector”.
The three pipes have to serve the three cylinders, the same as the STD single pipe does. It’s the end of the pipe that makes it or breaks it. Each pipe has to enter the chamber separately to return its energy back to its cylinder, when the three pipes join into a ‘collector’ pipe, the wave will divide into three, sending one third of its pressure up the other two pipes. The original one third enters the expansion chamber to return a weaker negative wave back to the end of the three pipes, divide into three again. Leaving precious little to work the cylinder that started it.

The exhaust gas inertia and the sonic wave can’t be treated the same. Exhaust gas has mass, hence inertia. It can flow gas pressure past another pipe and draw a low pressure in it. The sonic wave will divide send the same pressure up both pipes.
That is why we keep the branching short and the whole header system as compact as possible to preserve the pressure returned to the cylinder.

Does this answer your next question?:D:lol:

Harvey.

Re: Stebro questions...
 

Makes much more sense now, at least as much as I can comprehend. But I believe I get the just of it. Thanks:)

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I think Tom was just limited by the collectors he could find for less than an arm and a leg. Those look like the hooker formed collectors which are 2.5"x10". They certainly do represent an expansion event and from what I've read the negative pressure wave is almost exclusively returned through the pipe it came from and barely enters the others at all which is obviously contrary to Harvey's understanding. I didn't study this in school or anything so I can't swear what I've read is right and Harvey's understanding is wrong--it's clear there is a dissagreement by our sources though.

If Tom were to take a sawzall to those collectors and replace the body of them and some of the tubing behind them with 16" of 3.5 tubing they would be an excellent match for a race car running the ECUtune 264 exhaust cams and shift maps or a manual transmission.

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http://i149.photobucket.com/albums/s...x/IMG_6641.jpg

This is what is under my car now...

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pics on car pics on car:pics: on car

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May be Tom would like to answer this first bit,:)but I thought it was more a case of cams and ignition advance.

Mike you are obviously reading the wrong magazines. You must have learned at school that "pressure acts in all directions equally". The sound wave meeting a junction of three pipes, will divide equally, to enter each pipe, with the same, one third of the orignal pressure.

When you dyno your 'race engine' with 264* exhaust cams, we will all see what you mean.:)

Harvey.

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Harvey,

I did get A's in University Physics at the University of Miami back when i took the courses; however, what little I remember of what we studied about the effects of waves on gases only reminds me that I don't know enough to presume any such thing. The best I can do is hope the sources I have read give correct rule of thumbs and you are the only source I have read that claims that. Please feel free to provide the literature to explain otherwise to me.

If I remember correctly that .5 second improvement in et from putting on his headers was the low of a series of runs Tom did with the high being a full second improvement over before the headers. I feel confident the improvement he thinks he saw with his headers is genuine. Maybe some other design would give him even better improvment but I haven't seen any other source supporting your design suggestion other than you. His design is fairly close to what I would come up with using most online calculators or by going off the rules of thumb on wikipedia.

Maybe you are right and I'm certainly open to being convinced. Saying the same thing again like it is a given won't do it though. How about sending me a copy of what you are reading?

Re: Stebro questions...
 

Yes Harvey, the collectors I used were not the ones I would have like to use. I did buy them for roughly $75 a piece. The collectors I really would have liked to have were slip on formed collectors that cost roughly $275 a pop. Now considering the cost, which avenue would you have chosen?

Now along the lines of 1/4 times, I always take my times with a grain of salt. A .1 or .2 increase or decreasein ET w/ 2-3mph differences in trap speeds are more than likely driver error. But .5sec in ET and 6-7mph in trap speeds is not a mistake.

Tom

Re: Stebro questions...
 

OK Mike, I suppose I have been pushing this barrow for a while. I first wrote about the SVX exhaust design about 10 years ago on the Yahoo forum.
As you well know I have often been the lone voice for the technology.:)

As for the technical information that I use. I haven’t kept that a secret, the two main textbooks that I use are, THE HIGH-SPEED INTERNAL COMBUSTION ENGINE, by Harry Ricardo, for engine operating principals, and THE SCIENTIFIC DESIGN OF EXHAUST AND INLET SYSTEMS, by Philip H Smith, based on the experiments of John Morrison. Smith wrote this book, but Morrison did all the research work.

These will provide the basic technical facts for building on. The rest of my knowledge was gained from experiments carried out on Bike engines both 2 and 4 stroke. These are a lot cheaper to develop than a 6 or 8 cylinder engine; after all, it is the cylinder that you are trying to increase the Volumetric Efficiency on. Now days I use an Engine Simulation program to carry out experimental changes on, to save all the expensive, and time consuming work.:cool:

From what I can see, most of the ‘on line calculators’ are based on work for the domestic V8. Using long primary pipes (branches) to separate the cylinders exhaust gas from entering other cylinders. The SVX does not have this problem, so the exhaust system design can be directed to filling the cylinder, using the sonic wave technology.

Harvey.

Re: Stebro questions...
 

I don't intend to run out and make any book purchases. If you could post the exerpt/exerpts that explains/explain that the negative pressure generated from the sound wave entering the expansion chamber is evenly split between the primary tubes we could make some progress though. The citation without the referenced material isn't very illuminating.

Actually the material I've read online along with the calculators says that they are calculating the length of the primary tubes and the length of the collectors so that the negative pressure generated from the soundwave leaving the primary tube returns to and continues through the ideal timespan at the same cylinder that it came out of and they ignor the other cylinders because the % of the negative pressure that enters the other primary tubes is negligable.