The flow through a forced induction engine

[muhhan]

I'm just trying to get my head around the various parts that make up a FI engine. Apologies if this should be in the noob section.

From my understanding once the exhaust leaves the cylinder it goes into the turbo manifold then into the turbine housing, spooling up the compressor in the process, it then leaves the turbocharger.
This is the part that I am not sure of. From here does it enter the dump pipe? What other names are given to the pipe that comes off the main exhaust and wastegate exhaust? Are these 2 exhaust outlets plumped through the same pipe or are they separated? If they are separated do they eventually join back together and if so when do they join back together? Is the set up the same for turbos with external wastegates as it is for those with internal wastegates, except for the fact that the wastegate exhaust will be coming from a different position?
Now from this pipe my understanding is that it connects to the catalytic converter then from here to the b-pipe and muffler much like on a NA engine.

On the compressor side of the turbo the air is forced through the intercooler and then through the throttle body into the intake manifold, ready to take its journey back through the engine.

I guess my main areas of confusion are where the exhausts flow once it has passed through the turbo.

Thanks for all your help!

[destrukshn]

depends if it's external/external wastegate.
the wastegate is there to get rid of excess exhaust gases

internal, it just goes through the normal exhaust piping/dump pipe.
external, well the external gate connects to the manifold via another pipe, and the other end of the gate is where it will expell the exess gasses via another pipe, either plumbing it back into the exhaust system, before the cat, or in the atmosphere which is illegal, so having an external gate dumped into the atomosphere is just like having another exhaust with no cat, resonators/mufflers.

and normal gasses, just exit via the rear of the exhaust housing, which is the exhaust system

[muhhan]

Thanks, destrukshn. I think I may have found the answer to my own question as well. I was reading in Hot 4's magazine about exhausts today and found info on the dump pipe.
Apparently, turbos with internal wastegates, as destrukshn mentioned, often have their exhaust plumbed through the same pipe but it is possible to get dump pipes with separate piping for wastegate and main exhaust. This sort of exhaust is supposed to give better results according to the article.

[destrukshn]

Thanks, destrukshn. I think I may have found the answer to my own question as well. I was reading in Hot 4's magazine about exhausts today and found info on the dump pipe.
Apparently, turbos with internal wastegates, as destrukshn mentioned, often have their exhaust plumbed through the same pipe but it is possible to get dump pipes with separate piping for wastegate and main exhaust. This sort of exhaust is supposed to give better results according to the article.
apparently so, but i've seen a dyno, using the the separating pipes, and normal pipe, same results.

[saxman]

on a well designed set up, having the wastegate tube seperate of the exhaust will make a difference.


on something like a stock internaled honda motor with lots of compromises in the set up, it may not.

[destrukshn]

on a well designed set up, having the wastegate tube seperate of the exhaust will make a difference.


on something like a stock internaled honda motor with lots of compromises in the set up, it may not.
yes i've heard, but haven't seen any myself of any gains.
but hey, i guess they do it for a reason.
lol.

[poid]

yeh often that reason is because its easier to fit a pair of smaller pipes in the cramped engine bay than a single 3" dump pipe, esp if using a normal log style mani and keeping the air con.

[destrukshn]

yeah but the thing is the pair of smaller pipes turn out to be a bit wider than a normal 3 inch dump pipe, beucase of it's design.

[saxman]

yeh often that reason is because its easier to fit a pair of smaller pipes in the cramped engine bay than a single 3" dump pipe, esp if using a normal log style mani and keeping the air con.
has a lot more to do with flow turbulence when the wastegate exhaust is introduced into the normal exhaust line.

[muhhan]

Thanks for all the info guys.

Saxman, I read that the turbulance issue was why it was more beneficial to have the exhaust gases separated as well. Although destrukshn made a good point about poorly designed dump pipes that separate the flow actually having negative effects on power output, but I guess that is the same with any part.

So final verdict, if you can get a good quality dump pipe with separate piping for main and wastegate exhausts go for it, even on a stock turbo?

[poid]

has a lot more to do with flow turbulence when the wastegate exhaust is introduced into the normal exhaust line.

ya...

as you said before however, it often makes very little difference on a low boost street honda setup. So the other reason you sometimes see such a split pipe is for packaging reasons. This was my point...

[poid]

yeah but the thing is the pair of smaller pipes turn out to be a bit wider than a normal 3 inch dump pipe, beucase of it's design.

well the idea is that you have a limited amount of clearance between the turbo and the a/c...so sometimes a 3" pipe wont fit in that area while two smaller diameter pipes side by side will do so

[saxman]

Thanks for all the info guys.

Saxman, I read that the turbulance issue was why it was more beneficial to have the exhaust gases separated as well. Although destrukshn made a good point about poorly designed dump pipes that separate the flow actually having negative effects on power output, but I guess that is the same with any part.

So final verdict, if you can get a good quality dump pipe with separate piping for main and wastegate exhausts go for it, even on a stock turbo?

yes... running seperate pipes is ideal... you should see gains in any set up with this, just going to be much more pronounced when everything else is in check.

[Sexc86]

www.howstuffworks.com

Very very good site for things like this

[muhhan]

Just adding a bit more info onto everything else people have contributed to my question...

http://www.motoractive.com.au/article53.htm

It's info from the www.motoractive.com.au website about exhaust systems covering both NA and turbo setups, mostly turbo though. It's a video clip so no need to read anything ;) Helped make things even clearer for me.