why does a divorced downpipe give greater gain ? i know there will be less turbulence, but so what if there is less turbulence. a regular downpipe is a bigger hole which is less restrictive. The only way i see the divorce downpipe give greater gain if the pipe for the wastegate is not recirculated. But if the divorced downpipe is recirculated, how is that any better from a regular downpipe? How does that give greater gain? i want real evidence. want see proof using math or physics. possibly see some math equations or flow analysis using pro-mechanica, ANSYS, or solidworks. apply flow dynamics theory (want to see bernoulli's equation applied). or a dynosheet with the only thing being changed is the downpipe and nothing else.
prove to me a divorced downpipe is better then a regular 3"
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teamslow;1178633 said:
I cant really help you there. But it does sound insane when the wastegate opens with an external gate or divorced downpipe.
im not going to use a program, but i will use common sense when it comes to exhaust gas... and from what i've read about divorced downpipes.
basically if you have a divorced downpipe, and you have it recirculate within 6inches its worthless... it might as well just be a regular downpipe.
but if you have a nice long 24'' long wastegate tube, it gives the wastegate enough room for its gases to go, along with letting the turbo move MORE air though the downpipe seperate of the wastegate passage.
and on a true divorced downpipe thats VENTED. you get even more gains because your venting all of that bypassed exhaust gas OUT OF THE EXHAUST system, so its not longer in there, which creates more room for the gases in the pipe already.
so if your going to have a divorced downpipe, it needs to have a nice long tube, be smooth, and enter back in at a nice angle. the goal is to not create turbulance in the exhaust, the turbo does a fine job of that...
basically if you have a divorced downpipe, and you have it recirculate within 6inches its worthless... it might as well just be a regular downpipe.
but if you have a nice long 24'' long wastegate tube, it gives the wastegate enough room for its gases to go, along with letting the turbo move MORE air though the downpipe seperate of the wastegate passage.
and on a true divorced downpipe thats VENTED. you get even more gains because your venting all of that bypassed exhaust gas OUT OF THE EXHAUST system, so its not longer in there, which creates more room for the gases in the pipe already.
so if your going to have a divorced downpipe, it needs to have a nice long tube, be smooth, and enter back in at a nice angle. the goal is to not create turbulance in the exhaust, the turbo does a fine job of that...
you know, he does kind of have a point. Ive never seen a BIC ddp vs a BIC regular dp, for example. But yeah your also releasing the wastegate left overs into an atmospheric pressure environment, not the pressure-wave ridden, turbulent ehxuast system. This would make the flow out of the turbo smoother overall. I guess? They do sound cool tho, thats really the only reason i want one. The power is nice too tho :evil2:
most of what i read is from the subby guys... and they claim that an external wastegate gets them more hp/tq and faster spool... LOL... sooo yeah.
but the theory on the divorced downpipes make sense when you think about it, at least to me... 2 pipes flow better than 1... duhh. haha
but the theory on the divorced downpipes make sense when you think about it, at least to me... 2 pipes flow better than 1... duhh. haha
one big pipe has more volume than 2 smaller ones though, even if they are close to the original size. I think it more has to do with the flow out of the shorter pipe being easier than passing the rest of the exhaust. Im sure someone will chime in who knows the REAL reason instead of our guesses lol
Isphius;1178688 said:
i was just talking about downpipes... obvisouly a 3'' downpipe by itsself isnt going to flow as much as a 3'' pipe AND a 1.5'' pipe for the wastegate...
everything is a theory until truly proven, so i enjoy thinking.
and i cant wait to get my exhaust done... im doing dual 3'' pipes from the muffler right before the rear diff (single in, dual out)... i wanna see if it makes a nice power difference tagged along with a divorced downpipe and high flow cat.
We don't have to worry about theory on this one, folks. Randy has already done the real world testing - BIC DDP and regular 3" DP, dyno results have shown gains of 29 whp. Same car, same day, same dyno, same setup.
He might still have the dyno sheets somewhere, I guess, but to be honest he's a fabricator, not a paper pusher, so I wouldn't hold my breath.
He might still have the dyno sheets somewhere, I guess, but to be honest he's a fabricator, not a paper pusher, so I wouldn't hold my breath.
no one has still given me any hard evidence that a recirculated divorce downpipe is better then a regular 3" downpipe. :1zhelp:
Rennat;1178690 said:
but the bic downpipe isnt 3" and 1.5". It is smaller than 3 inches at the beginning of the downpipe. so how is a recirculated divorced downpipe any better from a regular 3" pipe. A regular downpipe has a 3" inch surface area from beginning to end.
I love mine.
Bottom line is that diverting wastegate gasses away from the turbine outlet decreases backpressure, increases the exhaust systems total flow area, and also increases the wastegates response in controlling boost.
The power difference, however, between a open (big mouth) 3" dp and a DDP, will depend on many factors, like boost pressure, stock/upgraded CT, ported wg, etc....
The power difference, however, between a open (big mouth) 3" dp and a DDP, will depend on many factors, like boost pressure, stock/upgraded CT, ported wg, etc....
teamslow;1178633 said:
i dont think there is anyone here willing to take their sweet time to pull out a physics book to to give you your theory's and equations. its not that i think we dont have people on here capable to do this, only they dont want to devote this much time to prove to you and whoever else that a ddp flows better.
take a moment and think about what rennat said: 3" is going to flow less then ~3"+ ~1.5" (but thats only with the wg open). with that said, dyno numbers arent enough to prove this? or do you just want to know the phyics?
I'm not about to go and pull a million equations off the shelf to satisfy you. Sorry man, but in my opinion, if you don't understand this in 'layman's terms' then you certainly aren't going to understand the technical aspects behind it.
I suggest you look up 'laminar boundary flow'
To make it short and sweet, the majority of the gas flows through the turbine itself. Look at the design of the turbine housing - the smoothest flow of exhaust gas is right through that turbine. The wastegate, on the other hand, DESTROYS flow (by a major increase in turbulence)
By keeping the most turbulent of air flowing through a separate path, you maintain a clean (relatively speaking) flow through the turbine.
When the DDP recirculates back into itself, the turbulence has straightened out, and the flows merge nice and smoothly.
The biggest restriction to power in the stock setup, is the stock turbine. The small size (relative, again) allows for FAST spool, but with poor flow. The DDP allows the best possible flow out of the restrictive turbine side.
If you want proof, ask Randy for his dyno graphs, if he still has them around.
I suggest you look up 'laminar boundary flow'
To make it short and sweet, the majority of the gas flows through the turbine itself. Look at the design of the turbine housing - the smoothest flow of exhaust gas is right through that turbine. The wastegate, on the other hand, DESTROYS flow (by a major increase in turbulence)
By keeping the most turbulent of air flowing through a separate path, you maintain a clean (relatively speaking) flow through the turbine.
When the DDP recirculates back into itself, the turbulence has straightened out, and the flows merge nice and smoothly.
The biggest restriction to power in the stock setup, is the stock turbine. The small size (relative, again) allows for FAST spool, but with poor flow. The DDP allows the best possible flow out of the restrictive turbine side.
If you want proof, ask Randy for his dyno graphs, if he still has them around.
Well theory should coincide with real world.
And in this case it does.
The biggest thing WHY it does actually have a power decrease has to do with two things.
One.
The Divorced downpipe is not reintroducing those gases back into the exhaust. Instead they are being "vented" to atmosphere. This causes an increase in venting diameter that you don't have when you reintroduce the gases back into the exhaust system. (ie instead of a 3 inch exhaust, now you have a 3 inch exhaust PLUS 1 inch wastegate vent for a total of area of 31.41 inches instead of 28.25 inches)
two.
Lowers the pressure ratio of the turbo on the turbine side. Depending on where on the turbo's efficency map, It might lead to a better efficency zone than when the pressure ratio is higher hence an automatic gain in power from just being a better suited efficency zone. Almost as good as increasing the A/R of the turbo but in reality just letting the current A/R do it job more efficently.
three.
Fluid mechanics and all of its associated parts still play a part here. Incredible what turbulance can do huh? But it should be no surprise. After all a turbulant enough wake up in the air can take a massive 747 out of the sky instead of the air plane being able to fly. Turbulance is a lot of energy to overcome and the exhaust gases are no different in interaction with said turbulant wind & boundary layer air that is located within the exhaust system.
And in this case it does.
The biggest thing WHY it does actually have a power decrease has to do with two things.
One.
The Divorced downpipe is not reintroducing those gases back into the exhaust. Instead they are being "vented" to atmosphere. This causes an increase in venting diameter that you don't have when you reintroduce the gases back into the exhaust system. (ie instead of a 3 inch exhaust, now you have a 3 inch exhaust PLUS 1 inch wastegate vent for a total of area of 31.41 inches instead of 28.25 inches)
two.
Lowers the pressure ratio of the turbo on the turbine side. Depending on where on the turbo's efficency map, It might lead to a better efficency zone than when the pressure ratio is higher hence an automatic gain in power from just being a better suited efficency zone. Almost as good as increasing the A/R of the turbo but in reality just letting the current A/R do it job more efficently.
three.
Fluid mechanics and all of its associated parts still play a part here. Incredible what turbulance can do huh? But it should be no surprise. After all a turbulant enough wake up in the air can take a massive 747 out of the sky instead of the air plane being able to fly. Turbulance is a lot of energy to overcome and the exhaust gases are no different in interaction with said turbulant wind & boundary layer air that is located within the exhaust system.
Rennat;1178679 said:
the reason an exterenal waste gate woudl make more power/ tq is because they open @ the exact psi desired. internal and stock waste gates start to open prematurly to prevent over boost. they are actualy designed by the factory in this way to make a less performance oriented result to insure thesafety of the motor. external waste gates also are more spool effiecient is again casue they arent open when the turbo spools. just saying not being a dick
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