JKav

iTrader: (8)

Oh yeah, the swirl decays as it progresses down the exhaust.

Experiments have been made to take advantage of the low pressure region dead smack in the middle of this swirl at the turbine discharge. The goal being to to reduce backpressure by essentially sucking out the wastegated flow. There might even be patents on doing this....

03whitegsr

iTrader: (8)

This got me curious to get a rough idea of the pressure drop in a length of pipe under the conditions of a turbo motor. These numbers are just rough numbers with lots of approximations and assumptions made.

Keep in mind that 60 pounds/min of motor flow does not mean 60 pounds/min of exhaust flow unless you have your wastegate plumbed back into the exhaust.

Here are the results of my calculations. This is based on 10 feet of straight tubing and is just made to gauge the approximate pressure losses of an exhaust system.



Here is the moody diagram. I was thinking the flow would be fully turbulent, but to my surprise, it actually operates in the transition range.

The Red is the 3", blue is 3.5" and purple is 4". The further to the right, the higher the airflow for a given tube size.


Feel free to correct/own me if I messed something up.

crcain

Sorry to divert from the more technical side of the discussion but...

In my most recent post in this thread I stated a smaller exhaust creates load on a motor and that ends up building boost sooner, which then creates more torque. But I think I'm second guessing that theory too. Is it possible that a smaller exhaust can create more torque all other things being equal?

C6C6CH3vo

iTrader: (9)

I think so, but the overall result probably won't be significant. Below are two log sessions overlayed,

- Background log (dotted lines) was with:- Exp log (solid lines):Note: Any changes in HP/TQ are assumed from rate of rpm change, or rpm slope. Also, spark lead appears lower from picture but for given rpm the slower log actually had slightly more advance due to ECUload

Pulls were from about a 10 MPH roll (1-2-3). Disregard the first gear portion of exp log due to tire spin. But if you compare the lower rpm portions of 2nd and 3rd gears you can clearly see a steeper rpm slope with the dotted graph (restrictive exhaust) initially, signifying more torque. This did not do squat though because the restrictive run was about 0.7 seconds slower by the end of 3rd marking a significant difference, even though it displayed a little more torque initially. One thing interesting that you can't really notice from the image alone is when you slide the overlay to zero in the rpm at a certain point, and on other logs as well, is increases in power for me have almost always been associated with a higher MAF hz respective to boost, sometimes with less boost.



Just note this is with my car, doesn't mean it's set in stone.