bored at work

so i thought you would like to see my exhaust in the making tell me what you do and dont like

Instead of the right angle before the mufflers you could just do a Y. It be equal lengths and have the same flow out of both outlets. Better airflow

i was gonna do that.. but i want back pressure at low rpms. and with the stock valve in this set up i think i will get a really good low and top end power

diggin it, get one made, test it, then make me one!!!

looks like a D&D with a valve.

looks like a D&D with a valve.

Click to expand...

so a D&D that might be better!

oh i will, the gut that helped me pull my bike off the road has a dyno

If you were to get mufflers that have some baffles in them you could get tge back pressure needed couldn't you?

im not sure^^ [confused] im going to make this coming up soon and im getting free dyno time on with this, so im gonna try to dyno my bike stock, then this pipe with no ecm then and ecm remap and will let everyone see the results but im so busy with 3 jobs im not sure when im going to have the time to make the pipe

Please don't take this the wrong way, but...

http://www.rbracing-rsr.com/exhausttech.htm

We are going to state this very clearly...Backpressure does not increase horsepower. Period.

An often heard statement from the well-informed is "You need a bit of backpressure for an exhaust to work". Usually this comes from someone who is not a tuner or someone who is faced with a situation where he does not have the tools or means to adjust things. Anything you do in the exhaust will change the flows, the pressures, or velocities somewhat. The correct scenario is that the exhaust has to be properly designed and then you optimize the jetting, ecu data inputs, camshafts, port dimensions, valve sizes and the like. The exhaust has to be designed for the intended use.

This all dates from the early 1980's when Supertrapp invented a muffler designed for dirtbikes to trap potential sparks, or burning, carbonized, bits, so it could have US Forrestry Approval for off-road use. The "trapp" tells what the intended purpose was. If you wanted a Harley to barely work you had to stick a couple of pounds, or about 23-25 of these discs in the end of your exhaust. Of course this didn't really work, which is why they ended up putting a hole up the middle anyway. You don't tune an exhaust.

Your engine has 15 psi (1 Bar) of atmospheric pressure sitting at the inlet and another 15 psi lurking at the end of the tailpipe. The inlet stroke creates a pressure differential and the atmosphere goes rushing inward. The exhaust valve opens and there is a pressure rise in the tube followed by a strong vacuum signal as the gases head down the pipe. Note that we said "vacuum signal."

Click to expand...

I do NOT know everything there is to know about building or modifying an exhaust system. I get "lucky" more often than not though.

From what I understand about the exhaust valve that was in the stock XB pipe is that it changes the effective volume that the engine "sees" at a specific rpm range.

I think the valve is to change the volume, flow capacity, at particulary RPMs, low end torgue you want some back pressure to keep from burning valves, high RPM spin-up you want low back pressure, am I right?

It's not backpressure, it's changing the tuned length of the pipe. Short for high rpm (higher hp), long for low rpm (more torque). There's too many other variables though, shape, diameter, bends, total volume, etc. Then you have to look at the intake also. Lots to consider, or just throw it all to the wind and go with what your gut tells you. You might just get lucky.

If back pressure wasnt in issue you would never have to tune a car

Destroying a myth.



Some say that "an engine needs backpressure to work correctly." Is this true?

No. It would be more correct to say, "a perfectly stock engine that cannot adjust its fuel delivery needs backpressure to work correctly." This idea is a myth. As with all myths, however, there is a hint of fact with this one. Particularly, some people equate backpressure with torque, and others fear that too little backpressure will lead to valve burning.

The first reason why people say "backpressure is good" is because they believe that increased backpressure by itself will increase torque, particularly with a stock exhaust manifold. Granted, some stock manifolds act somewhat like performance headers at low RPM, but these manifolds will exhibit poor performance at higher RPM. This, however does not automatically lead to the conclusion that backpressure produces more torque. The increase in torque is not due to backpressure, but to the effects of changes in fuel/air mixture, which will be described in more detail below.

The other reason why people say "backpressure is good" is because they hear that cars (or motorcycles) that have had performance exhaust work done to them would then go on to burn exhaust valves. Now, it is true that such valve burning has occurred as a result of the exhaust mods, but it isn't due merely to a lack of backpressure.

The internal combustion engine is a complex, dynamic collection of different systems working together to convert the stored power in gasoline into mechanical energy to push a car down the road. Anytime one of these systems are modified, that mod will also indirectly affect the other systems, as well.

Now, valve burning occurs as a result of a very lean-burning engine. In order to achieve a theoretical optimal combustion, an engine needs 14.7 parts of oxygen by mass to 1 part of gasoline (again, by mass). This is referred to as a stochiometric (chemically correct) mixture, and is commonly referred to as a 14.7:1 mix. If an engine burns with less oxygen present (13:1, 12:1, etc...), it is said to run rich. Conversely, if the engine runs with more oxygen present (16:1, 17:1, etc...), it is said to run lean. Today's engines are designed to run at 14.7:1 for normally cruising, with rich mixtures on acceleration or warm-up, and lean mixtures while decelerating.

Getting back to the discussion, the reason that exhaust valves burn is because the engine is burning lean. Normal engines will tolerate lean burning for a little bit, but not for sustained periods of time. The reason why the engine is burning lean to begin with is that the reduction in backpressure is causing more air to be drawn into the combustion chamber than before. Earlier cars (and motorcycles) with carburetion often could not adjust because of the way that backpressure caused air to flow backwards through the carburetor after the air already got loaded down with fuel, and caused the air to receive a second load of fuel. While a bad design, it was nonetheless used in a lot of vehicles. Once these vehicles received performance mods that reduced backpressure, they no longer had that double-loading effect, and then tended to burn valves because of the resulting over-lean condition. This, incidentally, also provides a basis for the "torque increase" seen if backpressure is maintained. As the fuel/air mixture becomes leaner, the resultant combustion will produce progressively less and less of the force needed to produce torque.

I was always under the impression a "two into one" pipe has the best performance. Like the hawk, jardine, race can, etc.

i think theres something to the 2 into 1 into 2 design. Like the d&d and stock v-rods and others. I think it has to to with volume and pressure regulation between the two cylinders... hell i dunno.

I feel realy dumb now (incomparison) after readin anrkizm's post that was quite possibly the best explination that i could ever imagine bravo[up]

It was copy/pasted - It's been on the net awhile but still a good read. Google rules. - Back Pressure Myth

well still good job for findin it am i right about the 2-1-2 style exhaust?