At the time we were just looking for speed and volume...

 

[quote author=asilitch link=board=7;threadid=22079;start=30#msg208602 date=1068592149]
So -- what number (or algorythm if ya's got that fancy) did you use for VE?
[/quote]

I cant remember, but I do know it was >1, and <2

 

[quote author=Diesel Freak link=board=7;threadid=22079;start=45#msg208610 date=1068593142]
At the time we were just looking for speed and volume...
[/quote]
That works ALMOST as well, as the turbocharger tends to modulate the pulses leaving the exhaust manifold.

The frequency is obtained by the interior volume of the exhaust pipe itself, and what its natural resonant frequency is (notwithstanding that stainless has a different Fs than aluminized steel)
unfortunately, the 'tuning' is RPM limited (compromised) as the rpm's climb above or fall below the tuned threshold. No free lunch in the audio or physics world for that matter.
The equations were utilized from the audio program LEAP Loudspeaker Enclosure Analysis Program.

 

[quote author=Mudinford link=board=7;threadid=22079;start=30#msg208511 date=1068577684]
Great posts!! I have learned soo much and lots of new words to use in everyday conversations! haha...anyway....this is why i had the questions i did...check this out...this is a quote from the Magnaflow web site from a PSR article:

The Turtle V was then moved to the prototype department where Richie took over. A master welder and fabricator by any scale, he explained that it is important to have the proper back pressure on the stock Power Stroke's turbo to allow it to spool up quickly for maximum boost and torque off the line. To this end, MagnaFlow uses a 3 1/2" down-tube before blending it into the full 4" system. Here is the link: http://www.magnaflow.com/05news/magazine/05psr.htm

Also, i have another question for yall. What happens when you put dual pipes on the truck? How does that effect the out come of the exhaust? We dualed out my Bosses Ford and it ran better than the single 4". here is my guess why from the before posts. The exhaust is going good in the 4" pipe until it hits the dual 3" pipes. Once it hits those, the velocity increases and thus reducing back pressure???
[/quote]

Mudinford
Remember to have velocity a restriction is required. Worst yet, to move exhaust past a restriction to make that velocity it takes force. To maintain velocity the restriction would need to maintained. To increase the velocity an increase in the restriction would also be needed. I did a calculation of the area inside two 3" circles and compared it to a 4" inch circle and found that the combined area of the two 3” pipes has an increase in area of 4.92". What happened was the restriction was reduced, velocity was reduced and the force to move the exhaust out the end of the pipe was reduced. In my opinion maintaining velocity is a negative in a diesel exhaust system. The only goal is to reduce the force it takes to move the exhaust gases out the end of the pipe.

Edward

 

Edward, on the money. All this hooplaw over velocity in the exhaust downstream of a turbocharged diesel engine is nonsense. Velocity of the exhaust gasses leaving the exhaust port of a naturally aspirated engine, particularly one with a large camshaft and subsequent valve overlap, is important for sure. On a turbo diesel it means nothing. For turbocharger performance, all you care about is the delta enthalpy across the turbine, which means quite simply, the highest possible temperature of exhaust gas entering (within material limits), the lowest possible pressure after the turbo and the least amount of flow restrictions on its path out the tailpipe.
Any statement saying that backpressure is required for quick turbo spool up is positively ludicrous and indicates the company making the statement has no business in business.


Once again, I am telling you that you all should be insulating your exhaust manifold and exhaust system if you are serious about quick turbo spool up. Think of it this way.... What turns your turbo is the change in enthalpy across the turbine. Enthalpy comes essentially from temperature/pressure difference between inlet and outlet. So you are cruising along and your EGT's leaving the cylinder head are say 500°F, and your manifold which is un-insulated is running an average of 400°F with the gasses entering the turbo at 450°. Now you smash the throttle down for some delightful Cummins power. The EGT's leaving the cylinder head quickly increase up to say 1100°F, but the manifold is still at 400° and is shedding lots of heat into the engine bay, so the gasses entering the turbo only start ramping up in temperature gradually at say 1/4 the rate of increase that the gasses leaving the head ramp up at, while that hunk of cast iron heats up. Compound the problem by the fact that as the manifold does heat up, it sheds more and more heat into the engine bay, so at 1100° gas temp entering, you may only have 900° leaving the manifold and entering the turbo until a considerable amount of time has passed. Add into the mix the inertia of the turbine/compressor wheel... voila... lag.

You want the lightest possible manifold, well insulated, to have the quickest spool-up. Granted, mechanical/structural considerations, not the least of which is the fact that the manifold supports the turbo, prevent substantial thinning of the manifold. But insulating the manifold is a no brainer.

A turbocharger is a heat recovery device. After youve burnt the fuel and expanded the gasses in the cylinder why waste that energy heating up the engine bay? Let the heat recovery device recover it.
Just for fun, look around the internet at large diesel engines like marine engines and large diesel gen sets where efficiency if of paramount importance, and try to find one without the manifolds, turbo and exhaust insulated.

As for insulating the exhaust downstream of the turbo, you want to do that to keep the gasses as hot, and thus at minimum density as possible to minimize flow restriction and keep the gasses flowing.


Long one, sorry :
Zino

 

Thermal barrier coating inside and out of a manifold would seem to be a great idea on our engines. You could probably benefit from even doing the turbine housing and down pipe as well.

Justin

 

An insulated thin wall manifold is the shiznit in this situation!

 

Freak is right. The only time you dont want to retain too much heat is when the heat is already too high for the components to take in the first place...before the barriers, etc. are applied. Additional heat retained...say in sled pulling competition or drag racing is not a good thing for the turbine, bearings, etc.

Don~

 

On the subject of the dual 3" pipes, I know it increases the area of pipe. BUT since it is a smaller pipe, just 2 of em, would that keep turbulence down to a min and keep the exhaust moving? I am just wondering why the dual pipes seemed to work better than than the single 4". Kinda goes against what’s been said here.

 

[quote author=Mudinford link=board=7;threadid=22079;start=45#msg208957 date=1068669270]
On the subject of the dual 3" pipes, I know it increases the area of pipe. BUT since it is a smaller pipe, just 2 of em, would that keep turbulence down to a min and keep the exhaust moving? I am just wondering why the dual pipes seemed to work better than than the single 4". Kinda goes against what’s been said here.
[/quote]

truth be known, I did not go with dual pipes for performance, I did it for the coolness factor! 8)

Below 35 mph, I get two distinct swirling clowds of soot!

above 35 mph, it looks like the air turbulence of a F-18 at full bank swirling off the wingtips, then all the soot gets sucked in behind the truck into one huge hanging clowd.

 

Well heck....that goes with out saying! Not everyone can say they have 12" of stainless tip on their truck! haha......

O YEAH! What about the tip? Can you gain performance from the........im just kidding.....haha

 

I have heard that those cool tips with the LED's that light up are good for at least 5 HP per LED.

 

[quote author=Diesel Freak link=board=7;threadid=22079;start=45#msg208979 date=1068671864]
I have heard that those cool tips with the LED's that light up are good for at least 5 HP per LED.
[/quote]

I read that article too.... it was entitled "Are you Rice Enuf"

 

Heck, an extra Cummins emblem should net you about 75HP right?

 

I have to disagree with this portion of your post. You are correct in what you say about turbocharger performance. But there's more to the engine than just a turbo. There's still an engine that needs to exhaust spent gases.

Velocity DOES play an important role in BOTH NA and TURBO engines. Why? Because exhaust gases have mass, and therefore, INERTIA.

How do you explain the loss in HP and turbo response noted by some users of 5" exhaust? If YOU are correct, the larger the pipe, the better, plain and simple. This, because a larger pipe would give more delta P.

Shall we model exhaust flow as pulsed or constant? While that affects resonance (and its effect on flow), it doesn't much affect the intertia aspect of the flow. Everything in nature tends to be self-correcting. You increase temp of a compressed gas, you see more pressure and less density. It's all a trade-off.

Since the flow cools as it travels down the pipe, it also slows down. It also increases in density as it cools. This increases in density reduced the slowing effect on the flow because it now has more inertia.

So what is the IDEAL exhaust system?????


1. The downpipe would be the same inner diameter as the turbine outlet.

2. The downpipe would have a gradual bend.

3. Transitioning to a larger diameter pipe would be done GRADUALLY-- like a 6" transition for an change of 3.5" to 4".

4. Overall pipe diameter would be sized based on the backpressure/velocity ratio I described earlier.


True, a diesel is different than a gasser, and a turbo engine different than NA. But the diesel is not as different as you want to think. Same with the turbo vs NA. While we aren't "tuning" our turbodiesel exhaust like an NA gasser would (to help scavenging), There IS DEFINITELY an "optimum" exhaust diameter for each given level of fueling (temp) and airflow.

Unfortunately, this optimum only exists for a split second-- everything else it's slightly off.


Just as an aside, I would like to see dyno tests of the different B1 turbos with outlet variance. The "true" B1 outlet of 4" is larger than the HX40 outlet, and much larger than the HX35 outlet. Shouldn't the largest outlet yield the most delta P and the best turbo performance?????

Justin