Does external wastegate dump increase effective exhaust size under boost?

So I have a 2.5 inch exhaust from essentially the turbo back. I also have an open cutout pre cat which is loud and getting on my nerves.

I never stopped to think about whether or not the 1.5 inch EWG dump adds to the 2.5 inch exhaust for a total of 4 inches diameter under boost.

If not, does it at least equal a 3 inch exhaust under boost? I have been googling this and it seems like 2.5 inch exhaust + 1.5 inch exhaust = 4 inches under boost period. That would be too good to be true but I would be happy if it were.

Thoughts?

Thanks

 

I just thought about it and the answer would be NO...since the wastegate won't be open until after target boost is exceeded. /ubbthreads/images/graemlins/frown.gif

 

hmmm...I think I was right the first time. Exhaust will free up right when target boost is reached and target boost will stay there....this could work out if I have it correct...not sure if I do though. /ubbthreads/images/graemlins/mad.gif

 

[91_427]

Quoting blkchr91:
So I have a 2.5 inch exhaust from essentially the turbo back. I also have an open cutout pre cat which is loud and getting on my nerves.

I never stopped to think about whether or not the 1.5 inch EWG dump adds to the 2.5 inch exhaust for a total of 4 inches diameter under boost.

If not, does it at least equal a 3 inch exhaust under boost? I have been googling this and it seems like 2.5 inch exhaust + 1.5 inch exhaust = 4 inches under boost period. That would be too good to be true but I would be happy if it were.

Thoughts?

Thanks



One 2.5 inch pipe plus one 1.5 inch pipe does not have the same flow as a 4 inch pipe because the areas of the two pipes is still less than the area of the 4 inch pipe.

 

Would the 2 pipes together meet the "magical threshold" of 3 inches that everyone these days is seeking for an e316g?

If so, I am content.

Thanks

 

[91_427]

Try using basic math. Compare the area of the 2.5 inch pipe plus the area of the 1.5 inch pipe against the area of the 3 inch pipe. If you don't remember the formula for the area of a circle it is 3.14 times radius squared.

EDIT:SPELLING

 

[Barnes]

Area of the following pipes:

1.5" = 1.77 sq-inches
2.5" = 4.91 sq-inches
Combined = 6.68 sq-inches
3" = 7.07 sq-inches
4" = 12.57 sq-inches

Rule of thumb: As diameter doubles, area quadruples.

So technically you will have less flow area than one single 3" pipe. However, area is not the only factor related to flow. A dumped 1.5" pipe that is very short has little resistance compared to a pipe that has to go all the way back to the rear of the car. Without doing any math I would submit that a 2.5" exhaust with a 1.5" external dump would flow as well, or better than a full 3" exhaust carrying all the exhaust.

 

Not good at math, but probably better at most things than you will ever be. Thanks for the help.

Quoting 91_427:
Try using basic math. Compare the area of the 2.5 inch pipe plus the area of the 1.5 inch pipe against the area of the 3 inch pipe. If you don't remember the formula for the area of a circle it is 3.14 times radius squared.

EDIT:SPELLING

 

Thank you, I wish that I had something definitive to go on. I used to be great at math but have lost it. If you really think so, then I don't see why not.

Quoting Barnes:
Area of the following pipes:

1.5" = 1.77 sq-inches
2.5" = 4.91 sq-inches
Combined = 6.68 sq-inches
3" = 7.07 sq-inches
4" = 12.57 sq-inches

Rule of thumb: As diameter doubles, area quadruples.

So technically you will have less flow area than one single 3" pipe. However, area is not the only factor related to flow. A dumped 1.5" pipe that is very short has little resistance compared to a pipe that has to go all the way back to the rear of the car. Without doing any math I would submit that a 2.5" exhaust with a 1.5" external dump would flow as well, or better than a full 3" exhaust carrying all the exhaust.

 

[Barnes]

Another way to think of how equal flow area does not mean equal resistance to flow imagine the following:

A 3" exhaust

A 3" exhaust which is stuffed with little smaller pipes, like straws.

The flow area is the same as just the 3" pipe. (Neglecting the material thickness of the straw sized pipes of course.) But due to the increased surface area, and other possible flow effects, the resistance to flow will be GREATER than just a single 3" pipe.

 

Pondering what you are saying and that analogy makes complete sense, but are you now thinking that the overall resistance of this combination may actually be greater than having a 3 inch exhaust? I ask because "the little straw" would be outside of the 2.5 inch exhaust. Really want to know if you have changed your mind on it or if you still think that 2.5 inch exhaust plus that 1.5 inch dump would still exceed the overall flow of just a 3 inch exhaust. I assume that resistance is the inverse of flow PERIOD? Just like in electronics where resistance is directly inverse to current PERIOD?

Thanks

 

[Barnes]

That analogy only applies if the pipes are the same length. I.E. If you had a 2.5" pipe from your turbo outlet all the way to the tail of the car, AND a 1.5" pipe from the waste gate all the way to the tail of the car.

So in your case the analogy does not apply because your 1.5" pipe is very short.

 

Gotcha, that clears it up. Thanks again.

 

[91_427]

Quoting blkchr91:
Not good at math, but probably better at most things than you will ever be. Thanks for the help.

Quoting 91_427:
Try using basic math. Compare the area of the 2.5 inch pipe plus the area of the 1.5 inch pipe against the area of the 3 inch pipe. If you don't remember the formula for the area of a circle it is 3.14 times radius squared.

EDIT:SPELLING





Clean the sand out of your vagina dude. /ubbthreads/images/graemlins/bawling.gif

 

[CutlassJim]

Does external wastegate dump increase effective exhaust size under boost?

Yes


/End thread