Anyone interestes in 4-2 Factory exhaust?

[hightec_redneck]

Hey everyone. OK, I am almost finished with Adrenalize and now have the exhaust issue. I had every intention of ordering a new 4-2 from Mac for this project, as it was the closest to factory that I found. But do to demand or manufacturing issues, Mac could not get it done. I will only listen to " I will get it shipped to you in 2 weeks" so many times. So I canceled my order and started reading. Now I know what I wanted, and I am lucky that my tools and abilities are better than adverage. So I found a 4-2 system that the header pipes were in good shape, but the mufflers were shot. The next step was to find an aftermarket muffler that was the same size and look for my application. And I found one at JC Whittney of all places. But that would not solve all the problems. While it would look great, I know it would not perform as well because the removal of the crossover would greatly effect the low and mid range torque. So not being one to leave anything alone, I decided I would figure out how the factory 4-2 worked and then reproduce the engineering that went into it. Then, because of this forum, I did something that I never do. I decided to take some pictures, just incase someone else was looking to do the same thing. I figured out how the crossover worked last night, and then figured out how to modify the Dunstall mufflers so that I would end up with a duplicate of the original exhaust. Of course it is not an exact copy of the factory exhaust system, as I did not want to completely build a new baffle. But I think it is an inexspensive alternative that will perform just as well. Now I know that the only way to prove it would be to put it up against a stock system on a dyno, and that I have no interest in doing. But I will evaluate the performance when I finish it, and let you know the results. The reason for this thread is to see if anyone else is interested in trying to make this type of system. Please understand that I am not looking for anyone's opinion of why this can't be done, or should not be attempted. I have already done it. And if it does not work out, I will be the first to say so. But in the interest of giving back to this site, I am interested in knowing if anyone else would find this information helpful to them. I just do not want to spend alot of time writting a tutorial with pictures of this mod, if knowone else wants to do it. Please let me know if you are interested, and if all goes well, I will make the tutorial.
Thanks everyone.

[Suckerpunch]

sounds very interesting. Run with it.

[RODS454]

Go for it

I'm very interested in seeing pics, and the results. I say if you have the time and the inclination, do it.
RODS454

[XSokieSPECIAL]

hightec_redneck.........

A very GOOD idea but I think what you are working on is completely unnessessary with this bike.

There are NO low end problems with this engine when properly tuned.

I am running a Mac 4 into 2 system WITH an 850 final drive and have absolutely no low end problems.

2K to 8k, power band starting around 3k -3.5k, it's smooth. No bucking at ALL.

Overanalizing this engine is just beating your head against the wall. The original engineers have already done an EXEPTIONAL job.


IMHO

[Ivan]

You'll know if it doesn't work pretty easily. Most exhausts let the thing top out at about 120. With stock exhaust and some properly tuned carbs and a looooong desolate paved road, its pretty easy to see 130 plus.

On that is straight through will have all the high end you want, but nothing in the low end.

I have fought this issue since I have had an XS11. Now I have a stock exhaust and a Jardine spaghetti for one scoot and a 4-1 on the 79. They all perform well. The 79 with the 4-1 has an extremely long muffler, it almost juts behind the rear wheel. It perforsa quite well, unlike other 4-1's I have tried, but the were all about a foot shorter. This leads me to believe volume is just as important as restriction. I think the Jardines are close, but have jst a tad too much restriction, as the low end is great, but buring along at 7k in high gear just doesn't work as well as with the stock exhaust.

I will be very interested in your results.

[WMarshy]

You'll know if it doesn't work pretty easily. Most exhausts let the thing top out at about 120. With stock exhaust and some properly tuned carbs and a looooong desolate paved road, its pretty easy to see 130 plus.

On that is straight through will have all the high end you want, but nothing in the low end.

I have fought this issue since I have had an XS11. Now I have a stock exhaust and a Jardine spaghetti for one scoot and a 4-1 on the 79. They all perform well. The 79 with the 4-1 has an extremely long muffler, it almost juts behind the rear wheel. It perforsa quite well, unlike other 4-1's I have tried, but the were all about a foot shorter. This leads me to believe volume is just as important as restriction. I think the Jardines are close, but have jst a tad too much restriction, as the low end is great, but buring along at 7k in high gear just doesn't work as well as with the stock exhaust.

I will be very interested in your results.

My '79F has the Jardine 4-1 and I think its just the opposite, less restriction. Granted I dont have mine tuned quite right, it doesnt seem to have the low end torque my Dad's '79F does with stock pipes. I think above the 6000 rpm mark mine out performs his. In another couple of weeks I will have mine rejetted, valves adjusted, carbs synced and tuned, and will do the same (minus the jetting) to my Dads, then we will compare...

[CatatonicBug]

I think I would rather spend the money and order a brand new full set from Germany. Exact copy of the OEM setup.

[fredintoon]

- - - I found a 4-2 system that the header pipes were in good shape, but the mufflers were shot. The next step was to find an aftermarket muffler that was the same size and look for my application. And I found one at JC Whittney of all places. But that would not solve all the problems. While it would look great, I know it would not perform as well because the removal of the crossover would greatly effect the low and mid range torque.
- - -

Hi Redneck,
um, you won't actually know if the headers + JCW cans will lessen the mid-range until you try it?
My understanding of the crossover was that Yamaha were forced to make the stock cans so restrictive that it took both of them to let the exhaust out.
MAC and other replacement systems are not built like that.
FWIW, my own stock system had rusted through at the muffler to header weld both sides. I chopped through the sound metal as far back as I could and discarded the megaphones & cross tube. I welded 1½" extension tubes on & installed Triumph mufflers that came from a swapmeet at $35 the pair.
I can boast that they look real neat and far more importantly, report that the midrange is still all there.
And oh, that mellow sound.

[hightec_redneck]

Hey everyone, thanks for the XSive support on this experiment. Since there is an interest in the results, I will be writing and posting a "Get R Done" tutorial with pictures, after I finish the evaluation. I also wanted to add some information that I am not sure many people are aware of. My purpose of this experiment was to build a 4-2 system that looks and performs as close to the factory system as I could, for about $100 dolors. That being said, I did not know if everyone understands the physics behind scaving and wave form dynamics, as it is pretty difficult concepts to grasp without being able to see them in action. And I will not pretend to be an expert on this either. But the center crossover is not a passage way between the two sides of the exhaust system for increasing the airflow and reducing back pressure. It is allot more complex than that. It is actually two passages between both sides of the exhaust system. And the baffles in the mufflers form 2 separate paths for exhaust flow. The first crossover is straight through the inner tubing, which feeds the baffle system within the muffler. The second is for what passes through the baffle, and baffle packing material. This is the technology which I do not want to loose. Now comes the hard part. Without going into too much detail I will try to explain a portion of what I have learned. After a cylinder fires and reaches the end of the power stroke, the exhaust valve starts to open. At that time, a large amount of energy is released into the exhaust system. This is moving at 1700 to 2100 feet per second, and travels down the exhaust pipe. But this can not get out of the muffler due to it's restrictions. And at that velocity, nut much of it changes direction 90 degrees and travels through the crossover's first chamber. This is what happens. A portion passes through the baffle and out the muffler. A small portion is reflected back up the pipe twords the engine. A small portion is released through the first chamber of the crossover and into the inner tubing within the second muffler. The remaining energy passes through the baffle and baffle packing material. From there, it hits the outer wall of the muffler and is funneled back twords the engine in the space between the inner tubing and the outside wall of the muffler. This is directed into the second passage within the crossover, which is completely isolated from the first. It now passes through this second passage which contains another baffle made of perforated steel, and is released into the outer passage of the second muffler. From hear it can only go two places. One being back from where it came, and the other being through the packing material and the baffle of the second muffler. I know that is difficult to understand. But the effect is the energy is allowed a path to follow which is restricted, and allows it to dissipate in a non harmful way. It also allows the exhaust gases which are only moving 200 to 300 feet per second, to be released with less restriction and an increase in velocity. Without going into all the engineering behind scaving and wave form dynamics, lets just say that the location for the crossover was designed and tested for optimum performance, and not because it "fit well" where it was located. Because we all know that the exhaust system is 2 lbs of s#%t in a 1 lb bag. Couple that with the fact that detuning the engine for environmental reasons is too easy to accomplish with reducing intake air and jet sizes. And you have an extensively engineered and tested piece of equipment that was installed to increase performance. And that is what I did not want to loose. I hope this make sence.

[XJOK2PLAY]

Hi,

I think I commented earlier in the week in one of your earlier threads about JCW mufflers... I believe you asked if anyone had tried them.

I remember mentioning the crossover pipe, and losing it if you go that route.

Just wanted to add, that as far as performance, I saw -0- loss w/ JCW's. It ran great, sounded great.

What I did see was excessive vibration at the rear of the mufflers, which led to breaking not only welds, but the pipes themselves... and losing that crossover pipe, at least on the XJ, (which has shorter mufflers that the XS) contibuted to the XSive muffler shake. It just doesn't tie the two sides together, and doesn't brace them as well.

BUT... that was MY experience, on an XJ... my buddy that has run the longer Dunstall mufflers on his Standard, has no crossover pipe, used the JCW universal brackets... and they've worked great for years.
As they say... YMMV.

Hope I haven't totally confused you...
I know on cars, an 'H' crossover adds lowend torque. But as was previously stated by one of the other members... I don't think that was Yamaha's intentions when they put those in the stockers... it was probably to reduce the backpressure some, and to make the exhaust system more ridgid.

Bob

[WMarshy]

Dont worry, you wont lose us all as some of us have a formal engineering degree and have researched the topic of gas dynamics and intake/exhaust tuning. Even then, there are others without a formal engineering degree that have as much and maybe even more knowledgable about the topic. In anycase, I had a difficult time reading your flow logic as I am a visual learner dislike reading a huge paragraph like yours.

As you've stated, it is a complex topic and unless you are an expert in it I try not to evaluate/critique the Yamaha engineers decision on how/why they designed the exhaust the way they did, I just dont have that amount of time or resources at my hands...yet... There is a lot of reading that one can do and even simplified models that an average joe with good math skills can apply to imitate the system. Do some searching about Helmholtz resonator theory, it will give you a simplified way to calculate the rpm in which peak torque is acheived from the given intake/exhaust system.

Basically, there are going to be about 3 or 4 groups that everyone will fit in regarding this subject.
1. Dont care, think there is an easier way like aftermarket exhaust.
2. Care, but it doesnt mean anything without proof, I.E. Dyno that there is power gain not loss.
3. Dont care if there is a huge gain in power or a slight loss, just want an easy way to add a cross over.
4. Dont have any interest at all.

[Ivan]

I was with you until you started talking about the dual passages in the cross over. I just put a stock exhaust on and its just a tube between the two.

[XSokieSPECIAL]

OK...here goes,

Having been into stock car racing back in the mid 80s I learned a lot about the crossover pipes and the X pipe configuations. Here is how I understand what I learned.

If you take a glass of water, for example, and put a straw into it and blow some compressed air across the top of it a vacuum will be created in the straw and the water will be sucked up and out of the glass.

This effect works the same with a crossover pipe in an exhaust system. It scavenges the gas volume of the other pipe as the rushing gasses pass over the opening creating a negative pressure in the other pipe allowing more air/fuel mixture to enter the cylinder that pipe is connected to.

Header collectors create the same effect but the crossover multiplies that and it was discovered in auto racing ( NASCAR) that the X pipe multiplies it even more because of it's DOUBLE scavenging design.

That is how I understand the dynamics of the thing.

[MaximPhil]

Following your thread with interest. Still confused but on a much higher level Mine has hand crafted cross over on original header pipes and Harley mufflers. presently feel the system is too open for good bottom end and fuel consumption.
Maxim Phil

[yamtom]

go man go

Hi,
Go with the experiment, I am very curious as to how the crossover affects performance, Ive heard it helps power overall, but am curious as to how this is measured. I have a setup similar to Phils, Hardley muffs , but dont have the crossover at all. The bike seems a bit slower than my old 79 standard with the crossover and stock muffs.