Ok, the dual exhaust question has been beaten to death. As of late, I haven't read anything that would help answer my question, so here it is.

Say you've got your average inline-4 Honda engine, h23, h22, f23, b18, etc. Ok well more specifically, I'm thinking of a built H22a with a T03/T04, 1bar boost. Now say it's turbo'd and is creating some serious exhaust flow. What if you had a y-pipe with a valve in the intersection of the Y-shape, allowing you to choose which pipe was open at any given time. Then, the turbo would be plumbed after the y-pipe. Say, one pipe is a thinner diameter, for high flow velocity in the low-end and increased scavenging, and the other pipe is larger diameter, for the upper revs when the thinner diameter piping would start to cause too much backpressure. Would the thin pipe's ability to create a faster velocity in the lower revs help a turbo to spool up faster? And then, when the revs are higher, the larger pipe could feed all that exhaust into the turbo? Perhaps the switchover from the small to large pipe could coincide with the VTEC-cam engagement? Or would it make more sense to have the y-pipe and valve placed after the turbo?

 

Ok, a turbo is spooled by two things: exhaust flow, and heat energy.

Now, [this is all theorhetically speaking, I don't know who may have ever tried this] a smaller primary leading to the turbine would create more backpressure and heat at lower RPM, so it would be possible to spool the turbo early. By switching over at some later RPM value though, you risk cutting away some of that heat energy, or staying with the smaller pipe too long and limiting how much boost can be generated.

Then there is the issue of why you'd want boost earlier than the ~3200-3600RPM a t3/t4 would spool on an H22 anyways, since it would take some serious traction to keep from wasting that torque at low speeds.

Also take into account the longer distance between the exhaust ports and the turbo you'd have to have to accomodate a 'y' pipe, and I start getting the feeling that the potential losses far outweigh the slim potential gains.

 

Good points, thanx for the feedback!

 

I think the Y pipe is going to see a bunch of turbulence, and cause more backpressure than a straight back 3in. A straight design will induce laminar flow, and you will benefit from the constant flow velocities.

I've considered the idea of a constriting downpipe to increase velocity, and help spool, but I think the simpler solution is to just spray a shot. Or to have a nicely sized turbo to begin with.

-PHiZ

 

He's talking about a y pipe before the turbo, not after.

 

Are you saying I can't read??!!

Oh wait, I can't read.
-PHiZ