Python021

does this design ever cause an issue with one charge side flowing into the other where they meet or do they just flow perfectly due to negative pressure from the engine (not being any sort of issue at all)
just a thought

bingS4

No problem. Pretty sure the answers would be in a fluid dynamics physics textbook.

complacentsee

It just forces the pressure to be equal in both halves. The flow will not be equal abut the pressure at the TBB will be. All of the pressure drop from the piping/intercoolers aids with equalizing pressure at the turbos.

shawnoc2003

Agreed, it all evens out. One turbo would have to be substaintially slow/stopped to get air to flow backwards in the system.

complacentsee

Now that I'm off work I can go into more detail. Unfortunatly I have to convert things into electrical analogs to explain it (in my head) so it doesn't really help others much.

Here is the theory to twin parallel turbos. (IMO)

The intake manifold pressure will be equal for both banks. On average the mass of the air forced into each cylinder will be the same. The amount of fuel sprayed in (assuming matched fuel injectors) is equal for each cylinder. Therefore the amount of both air and fuel in each bank is approximatly equal.

Now we make the assumption that the turbos are well matched. Maybe within 5% of each other (my guess). The amount of exhaust gases between the banks will be equal, as per above, so the turbos should be very close in output to each other. (A side note is that the wastegates are both fed from the same source and must be very closly matched.)

There will be some differance between flow of the turbos, however they both find thier equalibrium points. This might mean that the one turbo will push slightly more air at a given pressure level. Another thing to take into account is the large volume of air that the innercoolers hold. This also acts as a way to equalize the flows accross each bank.

My explanation isn't as good as I would have hoped. But if you conver everything to electronic analogs it makes perfect sense.. lol

Python021

that seems to exlpain what i was thinkin. it just seems twin turbo sounds cool but a single big turbo or a combo of a little turbo and a big turbo would have been a better design,

bingS4

Putting a big turbo in the mix causes more lag. Two smallish turbos do just fine. The guys who put in bigger turbos often end up upping their rev limits to the top of redline ($$$$) so they can take advantage of that top end power and make up for the lag time spent in the lower rpms.

complacentsee

And, the exhaust manifold routing of a single turbo design on a V6 car make it near impossible. Audi would have had to design a new engine to make it work. (or waited for the VR6)

Now with FSI you can have the intake maifolds on the exterior of the engine and a single exhaust manifold between the V. This allows for a single turbo much easier.

jamesdmanley

v8 guys do it all the time. its not that bad and makes intercooler piping more simle

complacentsee

Not at all a fair comparison since they typically have room to make the piping easy.