Help with Home Made Exhaust.
 

Im keen to improve my crappy shotck exhaust.
The mufler Ive got on is ok.

Ok question. 1
You guys talk about 3" and 3.5" Exhausts. So I got into the 3" mode or at least 2.5"
Went out and bought all the parts. Striped the turbo and went Duh!!. The Exit from from my turbo is only 2" where do I put the 3". Even the 2.5" is covering the mounting bolts.
So how big is your Exhaust hole on the turbo. If your using a 3" down pipe. Trying to figure out the ratio your using between turbo out and your bend pipe.
The pice you see in the pic I dont juse. We vent the blow off direct to open air and have welded on a flange to the turbo out.

Anyway here are the bits I got. The plan is to first just do the down pipe.
Instead of worry about whitey bends and other stuff I just went to a plumbing shop and asked him for a 2.75" 90 Deg bend. 3$ Then 2$ for each of the reducers.
It takes me from 2.75 to 1.5 inch in stages. Only disadvantage is the stuff is heavy wall thickness is 3.5mm

Re: Help with Home Made Exhaust.
 

waste of time...that ---- is pointless to go from 2.75 to 1.5 :-X

Re: Help with Home Made Exhaust.
 

The question wasnt if it was a good idea or not.
The question was on the ration of turbo exit to start of down pipe dia.

If I promise to keep it 2.75 all the way.
Wil somebody give me a straight answer :D

Re: Help with Home Made Exhaust.
 

do you have a dp flange to weld it to?

Re: Help with Home Made Exhaust.
 

why dont u use the reducers the other way around

btw those pipes look super heavy cuz there for plumbing ;)

Re: Help with Home Made Exhaust.
 

look at the pics of fook's setup, he has his DP/dumptube done very nice

Re: Help with Home Made Exhaust.
 

Yes
flanges are not an issue. Can cut them up and ready it in a few hours.

Ok Ill try one last time.
How big is the hole on your turbo exhaust exit.

Re: Help with Home Made Exhaust.
 

on a t3 .48 its about 2.5 inches

you mash in the pipe with a hammer a bit where the bolt holes are to make it fit
The pipe u bought will need a huge ass beating to even bend a little

Re: Help with Home Made Exhaust.
 

it depends on what turbo, more specifically what stage turbine wheel, you have. mine personally is 2.5", but i also couldn't get a 3" pipe directly on to the flange without interfering with bolt holes, so i have about a 1" piece of 2.5", then it steps up to 3" the res of the way. and yeah why the hell even bother with the 3" if you're stepping it down smaller? it will be no different starting big and getting smaller than if you just used the small stuff all the way, i promise.

Re: Help with Home Made Exhaust.
 

A few of my friends have taken some classes in fluid dynamics, so they've always told everybody else to just run whatever size the turbo outlet is and keep it that way. If you switch piping diameters too much it can cause too much turbulence and will reduce the velocity.

Re: Help with Home Made Exhaust.
 

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.

Re: Help with Home Made Exhaust.
 

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.
http://www2.propichosting.com/Images/421611201/10.jpg
http://www2.propichosting.com/Images/421611201/11.jpg

Re: Help with Home Made Exhaust.
 

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.

Re: Help with Home Made Exhaust.
 

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 ?

Re: Help with Home Made Exhaust.
 

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

Re: Help with Home Made Exhaust.
 

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.