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I know it's strongly advised to keep the H pipe intact due to needed back pressure. In regards to executing a good looking exhaust wrap, would a custom H-Pipe set up similar to this still provide the same needed back pressure? Or is there more going on down there?



 

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I know it's strongly advised to keep the H pipe intact due to needed back pressure. In regards to executing a good looking exhaust wrap, would a custom H-Pipe set up similar to this still provide the same needed back pressure? Or is there more going on down there?







I will look at the MAC tonight and see if anything is in the 2-1 part, but as long as you re-jet I don't see why you can't do something like that.



Mike
 

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Discussion Starter · #3 ·
I will look at the MAC tonight and see if anything is in the 2-1 part, but as long as you re-jet I don't see why you can't do something like that.



Mike


I mean I could do it, but I guess my question is would there still be a loss in power as if you were removing the H-pipe, or would a setup like this create the same back pressure condition as stock. That way I retain stock back pressure, and can now wrap the exhaust much easier.
 

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Well the H-pipe is really for balancing the backpressure between the cylinders. Without it, it's kind of like not having your carbs synced. There may be some backpressure introduced in the stock pipe, so you may need to adjust your jetting.



I think it'll be just fine. Make sure you check your plugs to see if you need to adjust the jetting.



Looks good though.
 

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Well the H-pipe is really for balancing the backpressure between the cylinders. Without it, it's kind of like not having your carbs synced. There may be some backpressure introduced in the stock pipe, so you may need to adjust your jetting.



I think it'll be just fine. Make sure you check your plugs to see if you need to adjust the jetting.



Looks good though.
The H pipe also sends the exhaust from the left bank out through the right pipe and right through left ,to allow for the fact that one bank is i front of the other .


I have a micron system 2 into 1 exit on the right,but I have a pair of harley take offs, 1 with a cat so I will need an H box .Nearly back to silverwing spec just wiring to go and paint (vw canyon red pearl)
 

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The H pipe also sends the exhaust from the left bank out through the right pipe and right through left ,to allow for the fact that one bank is i front of the other .


I have a micron system 2 into 1 exit on the right,but I have a pair of harley take offs, 1 with a cat so I will need an H box .Nearly back to silverwing spec just wiring to go and paint (vw canyon red pearl)


A 2-into-1 doesn't require an h-box. Unless you are meaning you're going back to dual pipes, then yeah you'll need one.



Not quite sure what you mean by one bank is in front of the other and the crossing stuff....



H pipe will help to keep the pressure between cylinders the same, so you don't have tuning issues. Same reason they run H and X pipes on the 80s-90s Mustangs.
 

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Moto, not sure what mufflers you are going to run, but if you want to keep from rejetting, you can play with the outlet size on your mufflers. i.e. keep restricting it til your plugs look good. I'd just rejet
 

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Rejet and do what you want.



The hbox does have a tube from each side that funnels it into the cross over section. But some other bikes have had less complicated cross overs and they work just fine. With a rejet it will be fine.
 

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H-Box allows for added exhaust length, and proper tuning.



Exhaust tuning theory is actually fairly simple, it’s all about getting the negative (and, hence, scavenging) pressure pulse to arrive at the exhaust valve as it is opening. To do this we have to set the pipe lengths and diameters correctly.



The formula for Primary pipe length is:



P = [(850 x ED) / RPM] - 3



Where:

RPM is the engine speed to which the exhaust is being tuned.

ED = 180° plus the number of degrees the exhaust valve opens before BDC.

P = Primary pipe length (on a 4-1 manifold), or Primary pipe length plus Secondary pipe length (on a 4-2-1 manifold), in inches.



Generally road engines will require the manifold to be tuned to the max torque rpm whereas race engines will be tuned to work either at max bhp rpm or a speed midway between the max bhp rpm and max torque rpm.



Ideally the Primaries should come off the cylinder head in a straight line for around 4 inches before any turns occur.



some engines it can be useful to have a 'step' between the exhaust port and the Primary (ie the Primary bore is greater than that of the exhaust port). This tends to be the case in engines with rectilinear exhaust ports.





The design of the collector should be such that the inlet pipes terminate abruptly otherwise the tuned exhaust pressure wave will carry on into the tailpipe and the calculations done to get the negative scavenging wave back to the exhaust valve on time will all be wrong.


To gain a more complete understanding of how mufflers and headers do their job, we must be familiar with the dynamics of the exhaust pulse itself. Exhaust gas does not come out of the engine in one continuous stream. Since exhaust valves open and close, exhaust gas will flow, then stop, and then flow again as the exhaust valve opens. The more cylinders you have, the closer together these pulses run.



Keep in mind that for a "pulse" to move, the leading edge must be of a higher pressure than the surrounding atmosphere. The "body" of a pulse is very close to ambient pressure, and the tail end of the pulse is lower than ambient. It is so low, in fact, that it is almost a complete vacuum! The pressure differential is what keeps a pulse moving. A good Mr. Wizard experiment to illustrate this is a coffee can with the metal ends cut out and replaced with the plastic lids. Cut a hole in one of the lids, point it toward a lit candle and thump on the other plastic lid. What happens? The candle flame jumps, then blows out! The "jump" is caused by the high-pressure bow of the pulse we just created, and the candle goes out because the trailing portion of the pulse doesn't have enough oxygen-containing air to support combustion. Neat, huh?



Ok, now that we know that exhaust gas is actually a series of pulses, we can use this knowledge to propagate the forward-motion to the tailpipe. How? Ah, more of the engineering tricks we are so fond of come in to play here.



Just as Paula Abdul will tell you that opposites attract, the low pressure tail end of an exhaust pulse will most definitely attract the high-pressure bow of the following pulse, effectively "sucking" it along. This is what's so cool about a header. The runners on a header are specifically tuned to allow our exhaust pulses to "line up" and "suck" each other along! Whoa, bet you didn't know that! This brings up a few more issues, since engines rev at various speeds, the exhaust pulses don't always exactly line up.


Honda put the H-box in there for a reason, If it were up to me and I had the option I'd leave it be.



This









I can't imagine having the desired effect of tuning the pulse. But that's just me.
 

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Has anyone gutted the H-box, and ran a hollow set-up. I'm thinking of it with pod filters and 90/120 jetting. I'll see how that treats the plugs.
 

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Has anyone gutted the H-box, and ran a hollow set-up. I'm thinking of it with pod filters and 90/120 jetting. I'll see how that treats the plugs.


Except for the crossover pipes, it already is hollow, and those pipes are obviously hollow as well.



Notice in Stich's pictures the right cross over is longer than the left, to compensate for the cyl head spacing.
 

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This was my solution to the dreaded "H" pipe. Stepped, Ceramic coated, although now I have a different "can" on. Sounds great, light weight, and fits very well.

Cheers, 50gary







Nice pipes Gary. Too bad we don't all have access to the equipment to make something like this. Hell I can't even use a cheap 110v welder in the garage unless I upgrade the circuit
 

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Some thoughts I have looking at your design...



Its great that a cross-section of a stock H-Pipe was posted...you can see that you would have a plenum effect with the main box on the stocker. Problems you may have with your design is there is no reservoir to collect or have a summation of the pressures from each cylinder. Depending upon the lengths of each pipe there would be some sort of resonance of the flow and pressure wavs, and the exhaust back pressures might cause or create a strange harmonic imbalance--you can imagine this would change with varying RPM. I would imagine that you would have different bands that would be in tune, others that would not. I don't think the cross portion would have a mixing or cross-over of exhaust streams that you are hoping for...each exhaust stream would cause a pressure drops where you have your cross piece. I think your design would be like running two independent pipes.
 
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