Quick turbo question ---

This is Tj --
Here's the situation:
My BMW is running non-intercooled. Think of the way my engine is positioned just like the ca18et engine, where the TB faces the exhaust manifold. I run a straight shot from the turbo to the throttle body with 2 inch piping. One special charge pipe contains the BOV and 2 nipples for vacuum, it also goes from 2 inches to 3 inches for the throttle body. The turbo charge outlet is 2" big.
With me so far?

What if I changed the pipes to 2.5 inches. I would go from 2" to 2.5" directly out of the turbo, straight up, then turned to the special charge pipe, which would knock it back down to 2" (then up to 3" haha).

Would I recieve any gain by doing this? Or would it be a total waste of time and money?

For that short of a distance you would probably not see any significant difference...and depending on the air charge temperaturein the new setup the air could become less dense...which would decrease power...

save your $$ to put into an intercooler later on down the road. But this all depends on the boost level your running as well. (what is the compression of the motor?)

compression is 8:1 -- This engine can safely take 15psi non-intercooled if I have a rising rate fuel pressure regulator with my 30# injectors(10psi with what I have now). I'm running 6-7psi right now.

I always think of it this way; An engine can flow only as much as the greatest restriction. So if you change to a bigger intake without changing throttle body sizes, you probably wouldn't notice any difference. Now I know that this is not entirely true, as many things affect flow, but that is just my opinion, and I've found that it makes a great base for intake theories. Also, since air is compressible, it would change the amount of air that needs compressed without changing the orifice that the air is restricted by (the throttle body). That means that with a greater area to pressurize, and the same amout of air flowing out of that area, it would have to work harder to pressurize the area to the same level. Now, I don't fully understand turbocharger air flow, but assuming that the turbo outlet and the throttle body are the same size, I would assume you would get more turbo lag, although probably not any noticeable amount. Again, these are just my theories, if anyone has any arguments I ask that they please share them.

the throttle body is 3" on the bimmer so we dont think that its a problem. It is the turbo outlet that is 2", but remember, you are presurizing those pipes, so many things come into effect.

OK, if you have a 3" throttle body, I could see making the intake pipe bigger worth your while, since right now I would think it is the greatest restriction in your intake. I think that the turbo inlet, although small, doesn't have as great an effect on the system, since the air flowing through it is at a higher pressure than anywhere else (The source of pressure should have the highest pressure, right?).

OK, if you have a 3" throttle body, I could see making the intake pipe bigger worth your while, since right now I would think it is the greatest restriction in your intake. I think that the turbo inlet, although small, doesn't have as great an effect on the system, since the air flowing through it is at a higher pressure than anywhere else (The source of pressure should have the highest pressure, right?).
Well the air pressure will be the same within the confined area, but with less volume the pressure within the pipes will be higher (in theory) than if you put more, or bigger piping...but it still comes down to what the turbo can deal out...and I too would save for an IC, that will give you more benefit than a couple more inches of 3" piping...

Yeah, Alex, you're right. If he spent the time and money making the intake tube bigger, that tube would be obsolete if he decided to intercool it down the road. Plus, he would get a larger benefit from an intercooler. I would say combine the two, and make an intercooler with larger piping running to and from it.

Roger guys, thanks for the brainstorming!
-Tj

I was just curious what year bmw? I also own a bmw and would like to turbo mine! :burnout:

87 535is with M30 engine