Dual straits on a diesel?

[6L PWR]

How about this:

If the single pipe is already flowing the maximum air it can flow, there will be no increase. If it's not there will be an increase, providing the overall length of pipe is the same.

Does that work?

I guess in my mind I'm already assuming it's flowing the maximum amount of air, but if it's not, then why would splitting still improve it? If it's not flowing the max, then it still wouldn't be if you split it. Right?

 

[Bricks]

Beats the hell out of me Todd lmao

I ain't no engineer....but I have a striped hat, and I got to blow the horn once

 

[dragogt]

Reduce pumping loses and the engine will perform better. A larger diameter exhaust is just another way to do this. The lower the backpressure, the more velocity, you should have in the system, helping the scavenging effect.

on June 01, 2009, 07:32:23 pm
Joel, I was looking at a one cylinder deal and wasn't talking about the collector. Would not the vacuum for scavenging (defined as 'pulling the remainder of the spent exhaust out of the chamber that hadn't been expelled via mechanical means') be created...at the piston via mechanical force and cylinder pressure combined? Meaning the release of retained cylinder pressure as the exhaust valve cracked, and the force of the piston at sweeping to TDC would allow the exhaust gasses to create a tug effect on the remainder of the exhaust in the chamber. This would also be positively impacted by a longer duration, lower lift (smaller orifice for 'draw') exhaust lobe I would think.



Granted, this can only happen if there is NO pressurized exhaust in the exhaust system to stop it up, which can be facilitated by pulse tuning off other cylinders at the collector as you said yes? I know this is getting away from the exhaust tubing...but I'm personally not sure what you're getting at here.

Cris

OK... let's stay at the cylinder for a while......

The way I look at it is that the scavenging starts the moment that exhaust valve starts to open. Why does the EVO starts BBDC?....... doesn't the "early" release of exhaust pressure prevent excessive mechanical loss or piston pushing gases ABDC?.... IOW, you want that vacuum or low pressure area leading the piston upward (Ham.... you were more than right). The mechanical travel is eased from BDC to TDC + by the time the piston reaches TDC, it also helps magnify that scavenging or vacuum effect..... or doesn't the piston also generate its own pulse at TDC? ...... This is exactly why valve timing + rate + ...+... or the whole combo, is what's really important. And obviously, the reason why some people do what they do.

I really wanted to focus on the end side of the scavenging pulses, since there are are more than a single scavenging "aid" pulse (this is another fact as already mentioned) yet.... it does help understanding the whole exhaust process right after the power stroke. Again..... dissect at will.....

I guess in my mind I'm already assuming it's flowing the maximum amount of air, but if it's not, then why would splitting still improve it? If it's not flowing the max, then it still wouldn't be if you split it. Right?

What size pipe is "stock'" 2.5/ 3" ?? and thats on a 6.9/ 7.3 CI engine..

Now if there saying a 3" pipe is Good for a 5.0 CI engine ; Do think that its not restricting a engine Twice its size?????

So if ya split it, than it helps reduce back pressure and increase performance...

Quoted from this thread _ http://sbftech.com/index.php/topic,19160.0.html _ --> Re: Topic #26: A 3" Exhaust System is too big for a 302 - Exhaust Back Pressure ..

 

[blacksnapon]

Its been common knowledge for years that too large of an exhaust pipe (immediately after the manifolds) will actually hinder power. A smaller exhaust pipe increases scavenging action. After the muffler, larger is better. But it will sound different with duals.

 

[dragogt]

Than can you explain this to me????????

Exhaust flow will never slow you down as I have EXPERIENCED.

May it affect the "dyno" yes. *But HP derived from exhaust is engine acceleration.

I have said this many times.

Back in the day when a "swap" from a stock H-pipe to an off road pipe was a "big deal", the gain to the tires was 7hp. *Read that again, 7HP. *If you ran the 2.5" off road pipe, it was 7HP. *So here come the corral type mentality that there was no difference in the two.

Really?

The FMS piece (2 1/4) would pick up 2.5 - 3.0 MPH. *At 3300# that is an average of 24HP.
The MAC piece (2 1/2) would pick up 3.0 - 4.0 MPH. *At 3300# that is an average of 32HP.

But the "dyno" only showed 7HP and it was the same....... :dunno

People show their true inexperience when arguing about exhaust HP. *There is a young guy on this board who put DUAL 3.00" exhaust on a V-6 3.8L Mustang and it picked up TONS of power.

I grow sick of these discussions on catfish boards by morons.

 

[Skandocious]

I'm honestly sick of arguing... I just keep saying the same thing over and over.

Lets drop it Aaron.

 

[blacksnapon]

Much depends on size of engine, rear differential ratio/trans gearing (if measured on a dyno), condition of emission controls, and other factors to accurately measure horsepower gains/losses. Because said vehicle gained different amounts means nothing when measuring another vehicle/engine/trans/diff combo.

 

[dragogt]

I'm honestly sick of arguing... I just keep saying the same thing over and over.

Lets drop it Aaron.

Chris, and anybody else that interested; Go here http://sbftech.com/index.php register login and get 10 posts in, than read the Myths and Rumors forum....

I promise it will be an eye opener.. Right Jurgan......

 

[73F100Shortbed]

LOL I think one post out of 3 pages gives an opinion and/or answer to the original post. Poor guy. I hope he found the answer

 

[Fellro]

From an engineering and physics standpoint: 1/2 density * (volume 1) ^2 + Pressure 1= 1/2 density * (volume 2)^2 + Pressure 2

So what this means is that the pressures will vary, the density will vary, the speeds will vary, but the total mass will remain the same. In essence, the amount of actual flow will remain constant. (See mass flow rate) conservation of mass dictates that this will be equal.

This does not mean that perhaps there can be a little power gained, but when you add a turbo, it reduces any gains. On the OP's vehicle, it is a non turbo application, so that is moot. As with headers, there is exhaust pulses that help to scavenge, but not in the way of a two stroke. The velocity of the prior cylinder expulsion helps to actually pull the air coming from a following cylinder's expulsion. That is what is meant by exhaust scavenging on a four stroke engine. Long tube headers gain this effect at high RPM's, while the old tri Y headers had this effect earlier, therefore making better torque over better HP gains.

With the setup the OP wishes to use, the pressure would initially be higher, then get lower at the y connection of the dual exhaust. This can be beneficial if set up correctly, or detrimental if not. It is dependent on how long the distance until the pipe y's off. The longer the pipe is, the more it simply builds pressure, making more resistance to flow. If it were to be kept fairly short, it could actually create a pulling effect (think venturi) that may help a little in the power area, but it would be the minimal gain as shown in the dyno results above. ( a few HP)

Chris, you weren't totally wrong in your thinking, except one problem: Exhaust is air, air is compressible, so more can be shoved into the same area. Water in a garden hose is not compressible, so the amount in has to equal the amount out at the same rate. In both cases, the amount in equals the amount out, just that gasses can be forced through in greater amounts, with actually theoretically no limits unless it were to be come liquid. Once a liquid, it is maxed.

Efficiency is a whole 'nother matter... the higher the pressure, the lower the efficiency. There are so many variables to why these motors can do better with a different mod... I can't view the rumors and myths area, and don't have the time to mess with it, so I will just kick out this from my physics and engineering classes.

Basically, my assessment is that it depends upon how long of a single pipe it will be as to how much effect it actually has on performance. Diameter is key as well, too small initial pipe will negate any benefit of putting large pipes after it. Most semi's I have seen with the dual pipe were running 4" tubes which split into 4" tubes.( Have actually seen some that did go from bigger to smaller pipes) My personal opinion is that these diesels had too small of pipes to start with, so to use the original type y-pipe would be useless for any kind of power gains. I did gain some power and throttle response by reworking my y-pipe to have the passenger side pipe flow straight back into the single pipe, rather than straight down into y-pipe. Then I connected the original pipe with the modified passenger side pipe into a 3.25" pipe that I happened to have (combine exhaust stack) and then went to a muffler I designed and built that had a 3.5 pipe out from that. (used pipe from a medium-heavy duty truck salvage yard) This is just a single pipe system that improved a lot from my 6.9. Sound wise it improved nicely...

So to address the original poster's actual question, it would help the sound, but will still remain loud, but may muffle it some due to the reduced velocity of the exhaust at the outlet. The velocity is what actually makes the sound waves...

 

[Skandocious]

Chris, you weren't totally wrong in your thinking, except one problem: Exhaust is air, air is compressible, so more can be shoved into the same area. Water in a garden hose is not compressible, so the amount in has to equal the amount out at the same rate. In both cases, the amount in equals the amount out, just that gasses can be forced through in greater amounts, with actually theoretically no limits unless it were to be come liquid. Once a liquid, it is maxed.

Allow me to correct you, because I have taken my fair share of physics and chemistry classes too.

Exhaust is a gas, water is a liquid. For the purposes of discussing compressibility and maximal mass of gas/liquid in a pipe/hose, they can be treated in the same way. Liquids compress the same way gasses to, except that they less compressible because of having greater molecular density. But compressibility doesn't matter when we're talking about maximal mass that a pipe or hose can hold or flow. Even if the exhaust gas is more compressible than water, there is an upper bound on how much mass you can flow through the pipe without bursting it. This is obviously the same principle as the water in a garden hose scenario-- pump water into the hose faster than it can be pumped out; it will gradually pressurize until the hose expands and breaks. All of the same rules apply to gasses in an exhaust pipe. So no-- I'm not wrong on that point. For the purposes of that point which you're trying to make, a liquid can just be treated as a very dense gas and conversely, a gas can be treated as a very sparse liquid. Water is, in fact, compressible.

 

[Fellro]

I don't see the engine even begin to approach that point at all , it would take some serious boost to ever burst the pipe with simple exhaust pressure... However, I may have gone a bit far in the statement... but for this application, compressibility is a factor to address. If it wasn't we could just use compressed air for brake systems. Liquid of course is much more efficient to use.

 

[Skandocious]

I don't see the engine even begin to approach that point at all , it would take some serious boost to ever burst the pipe with simple exhaust pressure... However, I may have gone a bit far in the statement... but for this application, compressibility is a factor to address. If it wasn't we could just use compressed air for brake systems. Liquid of course is much more efficient to use.

It would be very possible to use air for brake systems. In fact, it happens all around you! Big rigs use air brakes, amongst other things.

My point was that you said water is not compressible, but it is. I never said anything untrue in my above posts.

 

[Fellro]

Water is nearly incompressible as a liquid. Otherwise we could not make the statements liquids are incompressible... Their density can be considered independent of their pressure, while density of gases IS dependent upon their pressure...

Big rigs do not use air pressure to apply the brakes, they use it to release the spring pressure that does apply the brakes. You have to have air pressure to move the trucks to counteract the springs in the brake chambers. When an air line breaks, the brakes set. Much different from using air pressure to apply the brakes. There are some systems that do not have the dual springs to apply the emergency brakes. Lucky for my uncle, his truck was one of them. (I got it out of the burning shed it was in...) Most of the big rigs though do not use air pressure to apply the brakes. Ever seen a rig going down the road with the brakes smoking? That is because the air pressure was too low and the brakes set. Also, they use massive surfaces in comparison to give more pressure advantage (more surface area to apply the pressure to) while hydraulic brake systems use minimal surface area by comparison. Not real practical on the daily driver. That would be why they aren't used on the average vehicle. I was referring more to use in hydraulic type systems, if the gas were so easy to have work like a liquid, it would be useable in hydraulic systems.

 

[fordman76367]

....damn ...physics n chem all ove again...can we just pass me w a C like the teacher did?

 

[Skandocious]

Water is nearly incompressible as a liquid. Otherwise we could not make the statements liquids are incompressible... Their density can be considered independent of their pressure, while density of gases IS dependent upon their pressure...

Well you could make the case that water is relatively incompressible; that is, relative to the compressibility of its gaseous state-- water vapor. But if you told a chemist that liquid water was incompressible I'm sure he'd give you a nice lecture about the importance of fine grain measurements.

Big rigs do not use air pressure to apply the brakes, they use it to release the spring pressure that does apply the brakes. You have to have air pressure to move the trucks to counteract the springs in the brake chambers. When an air line breaks, the brakes set. Much different from using air pressure to apply the brakes. There are some systems that do not have the dual springs to apply the emergency brakes. Lucky for my uncle, his truck was one of them. (I got it out of the burning shed it was in...) Most of the big rigs though do not use air pressure to apply the brakes. Ever seen a rig going down the road with the brakes smoking? That is because the air pressure was too low and the brakes set. Also, they use massive surfaces in comparison to give more pressure advantage (more surface area to apply the pressure to) while hydraulic brake systems use minimal surface area by comparison. Not real practical on the daily driver. That would be why they aren't used on the average vehicle. I was referring more to use in hydraulic type systems, if the gas were so easy to have work like a liquid, it would be useable in hydraulic systems.

I'm actually not sure what we're arguing about here, to be honest...

 

[Fellro]

Well, we could argue to fine points on the compressibility issue forever, as the physicists and chemists apparently do, don't care to follow suit. However, the properties between the compressibility of a liquid and gas are considerably different.

On the big rigs, you take the air pressure away, and the e brakes will set. It is not due to air pressure, but rather the lack of it. Also, the way they work is also different, as the springs in the average big rig typically are what apply the brakes, not the air pressure. I have worked on and replaced the brake chambers on more than a few. The only truck I have ever seen that used air pressure was my uncle's Chevy grain truck. It had only the band brake on the transmission for an emergency brake.

 

[Skandocious]

Fair enough. I can agree with most of the things you said. I just took issue with you calling me "wrong" when I clearly wasn't. Calling water "incompressible" is wrong.

 

[1970Custom]

Water in an engine doesn't compress (relatively speaking) it just breaks stuff...

 

[A_G]

and with one header,,,,,dual stacks is ****in useless

To make it even a somewhat normall idea (still useless) youd haft to have a 12" from thee header to the Y then to two 6" pipes for it to even make some sense.

and if you were trying tgo make more power then yes, the more your out the exhaust the more power it makes (scavenging, someone had hear it) thats why your tractor pull guys (lil dq) have exahust sticking out the hood. the faster they get the exhaust out the more they can cram into the cylinder.

cylinder scavenging works by duration of valve movement. when air is entering a cylinder under pressure from the turbo the exhaust valve isnt quite closed to allow the boosted air to push most of the remainiong of the exhaust out....

i have just lost my self somewhere in this post...not sure how i got a scavengine. But read it...enjoy it....iono

Anthony