Exhaust Debate... Back Pressure, Or Velocity?
04-23-2013, 11:08 PM
#21
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Vehicle: 2010/Hyundia/Genesis Coupe 2.0T Track
My fault, I read your post wrong.
You were saying that intake is 'flushing' out exhaust in overlap so scavenging isn't needed....ok that makes sense. My fault, sorry again, I thought you were trying to say intake pressure pushes the piston down which is the opposing force that pushes exhaust out so the exhaust piston takes no tq away. Which as expalined above made no sense and why I had to break it down so in depth to expalin how this isn't happening, though I see now you never claimed that in the first plave lol.
Though I understand what you are saying now and agree. Though IIRC, your origional statement was tied to Garett in that scavenging isn't needed or doesn't occur past the turbie outlet. In which case overlap has nothing to do with that. As there are two scavenging occurances, one post and one pre turbine. Though again, it is possible and makes sense that the turbine takes away so much energy that scavenging can't affectly occur post turbine and maybe that is why an open dump is best.
I edited my post to take out that stuff written while confused at what you said so as not to confuse.
I guess to make it more clear, I would say due to IM under pressure and valve overlap. That makes sense and I agree with that. But again, I though you were implying pressure of the IM was causing the piston to go down forcing the other pistons to push exaust out easier....Which I don't know how I got that from what you said, but now maybe you understand the in depth explanaation required to show that doens't occur. And I also went into such depth because I knew 187 knew his crap and if he was agreeing with you, In my going so far in depth, maybe you would understand waht I was thinking and tell me where I was wrong. Though I guess you couldn't tell me where (which step or thought process) I was wrong, becuase I wasn't in the explaination of what I was trying to explain to what I thought you were saying which though was correct, was comletly unreated and even more confusing to you who knew what you were talking about lol.
So big misunderstanding. All the OP needs to know is that exhaust is tuned/optimised for a certain rpm range with NA, open exhaust is for max power (peak hp) NA/FI, and scavenging doens't play nearly as strong of a role with FI than with NA. So generally speaking, the larger exhaust is better if you have a turbo. And turbine A/R has the largest impact/effect on tq loss and exhaust pressure/velocity/turbo spool. Agree?
You were saying that intake is 'flushing' out exhaust in overlap so scavenging isn't needed....ok that makes sense. My fault, sorry again, I thought you were trying to say intake pressure pushes the piston down which is the opposing force that pushes exhaust out so the exhaust piston takes no tq away. Which as expalined above made no sense and why I had to break it down so in depth to expalin how this isn't happening, though I see now you never claimed that in the first plave lol.
Though I understand what you are saying now and agree. Though IIRC, your origional statement was tied to Garett in that scavenging isn't needed or doesn't occur past the turbie outlet. In which case overlap has nothing to do with that. As there are two scavenging occurances, one post and one pre turbine. Though again, it is possible and makes sense that the turbine takes away so much energy that scavenging can't affectly occur post turbine and maybe that is why an open dump is best.
I edited my post to take out that stuff written while confused at what you said so as not to confuse.
So big misunderstanding. All the OP needs to know is that exhaust is tuned/optimised for a certain rpm range with NA, open exhaust is for max power (peak hp) NA/FI, and scavenging doens't play nearly as strong of a role with FI than with NA. So generally speaking, the larger exhaust is better if you have a turbo. And turbine A/R has the largest impact/effect on tq loss and exhaust pressure/velocity/turbo spool. Agree?
04-24-2013, 01:01 AM
#22
Super Moderator
It'll probably help you to understand what's going on if you only think about one cylinder. A 4 cylinder engine is just (4) 1 cylinder engines stuck together.
