ztan

Something else I've heard from people's setup..

Start with 3" and taper down to 2.5 inch at the muffler.. The air starts off flowing fast, but as it travel further, it slows down. Tapering the pipe can speed up the exhaust velocity at the end.

bumblezc

My 14b has a 2.5 to 3" on it and the turned down to my DP. You can see it sort of here. I just went to the parts store and asks for the adaptor.

bumblezc

Not 100% True. I will have to crack out my Fluid Dynamics Tect to reveiw this. Yes a smaller diameter increases velocity, but increases pressure also. Think of it like this, Area-Down, Pressure-Up. Turbulence is a whole nother factor, Turbulence is more based on the viscocity of the fluid your flowing, In this case gas, viscosity is really low. Take it from a person running 3", I saw an decrease in spool time, This is not just from Butt Dynos, But logged in ECUControl.

chinoy

Well since this is the only exhaust thread of mine working Ill continue here.

1. First the issue of the down pipe Dia. The reason for the confusion was because. You guys are ficing your down pipe to the trubo manifold if I did that I could too use a 3" pipe. But Im not. I have dumped the Turbo manifold and have fabied my down pipe direct to the turbo. Reasons for doing this

a. Reduce weight. Must reduce weight everywhere. That turbo manifold that joins the wg and turbo exit with the O2 bung weighs 5 Kgs.
b. Im pretty sure that the flow from the wg will disrupt flow.

So I have my WG opening to open air. Funny thing is its not really loud at all.
This means I only have to worry about the Turbo exit which is 2".

So I need to dump the 3" parts and just buy 2" bends i.e. do the same as above but with a 2" pipe.

Which will reduce to 1.5" at the end.

Now about my questions.

1. Im quite familar with Blairs books for two strokes and four strokes. And the gas dynamics discused. I also have two stroke and four stroke engine simulators we use to design customer NA engines.
By going from a wide pipe to a narrow pipe we are actually seting up a reflection for the waves. This is the setup we use on two strokes to reflect waves back at the exhaust port. In order to setup a suction pulse and flow better the taper direction should be the other way i.e. from narrow to broad.
BUT
On a number of TUrbo forums I see this mod of going from Large Dia to small dia. Pipes being recomended. The reason given is that when the air exits the turbo it is swirling a lot. And this mod helps straighten out the air and provides better laminar flow. In this case would a simple honeycomb or even a single straight play do a good job.
This is confusing me.

2. Second question. Any harm in venting the WG to open Air ?

chinoy

Bump
If not do you know any Car forum where I could get answers to these questions.

Cray91

The harm in venting the WG into the air is that it gets soot everywhere. So it is a lot cleaner to just run it back down the exhaust. If you are venting it in the engine bay it can also melt stuff. It is comming almost right off the head, so it is extremely hot.

The reducing exhaust diameter is not a large issue for most set-ups. You would be best to go with the largest pipe possible for the outlet and continue that size or larger on down the line.