turbo exhaust help

[2dot4]

I like the sound of my dumped exhaust right now, but I kinda wanna clean it up a little. I'm looking to see if anyone knows a place that can do a nice 3" straight pipe (maybe 4") for a modest price. Compare Automotive quoted me $450, but that seems ridiculous for a straight pipe.

And who wants to help me install an intercooler? I was told it's a good, two-man job. If you're interested, let me know. Thanks.

[_Keith_]

I like the sound of my dumped exhaust right now, but I kinda wanna clean it up a little. I'm looking to see if anyone knows a place that can do a nice 3" straight pipe (maybe 4") for a modest price. Compare Automotive quoted me $450, but that seems ridiculous for a straight pipe.

And who wants to help me install an intercooler? I was told it's a good, two-man job. If you're interested, let me know. Thanks.

you wont want that big on the tc.

[Nebster]

the only reason you'd want a 3" is if you have a fully built engine with like a big ass turbo.

you'd want a 2.5" and you can get those from agency power or zpi.

if your set on a 3" zpi makes a true 3" mandrel bent that is fucking nice.

[Krdshrk]

3" is too big unless you're at high boost w/ a built motor. You'll lose too much backpressure. 2.5" for cheap? Get the Tsudo N1 Catback - 2.5" catback. Throw on a ZPI or Megan or whatever other S-Pipe and you have 2.5" all the way back. I went mix & match - ZPI S-Pipe, Tsudo N1 Catback's Midpipe, TRD Axelback. Sounds awesome.

[2dot4]

Isn't backpressure bad for turbos? I am currently running a dumped exhaust from a 3" downpipe (which equals virtually no backpressure) and my car loves it - amazing boost response and almost no turbo lag. When I connected my stock exhaust (which is like 2 1/4", right?), my car peaked, performance-wise, at about 4500-5k rpms, and my boost peaked at 5psi (with a 7.3psi wG spring). The car was quiet as hell, but I lost like 15-20hp easily. So i disconnected it again. The car pulls hard all the way through redline, max boost at about 4300rpms and my boost is back up to 7.3psi now. So I know a restrictive exhaust is bad. Plus, I plan on running high boost in the future, as well as doing some engine work. I don't want to have to pay for an exhaust twice. That's why I'm looking for a 3" exhaust, and $900 is flippin ridiculous for an exhaust - for that price, it better be titanium.

[Nebster]

you have a problem.

you shouldn't be peaking at 5psi with a 7.3 psi spring. somethings not right with your setup

[2dot4]

My boost only drops when I connect my stock exhaust to my turbo downpipe. When I dump the exhaust after the downpipe, 7.3psi @ 4300rpms easy. When I connect it, it struggles to hit 5.5psi, even at 6200rpms.

I've disconnected and reconnected it quite a few times. And I've had the same results each time.

My only theory is that the restrictive exhaust is causing too much back pressure, and in high rpms, with high exhaust volume, the backpressure registers a "False" 7.3psi to the wastegate, causing it to open, when the compression side of the turbine is only putting out around 5psi. Think of it this way - if the car wasn't running, and we pressurized the turbine side of the turbo, the manifold, and the downpipe to 7.3psi, without moving the turbine wheel - the wastegate would open, while the compression side registers 0 boost, correct? The only other variable I can think of is the wG actuator...and if that's the problem, how do I fix it?

The next time we get together, I can have one of you check out my setup and tell me what you think is wrong, but the car doesn't have any problems (other than a rough idle and very seldom stalling problems), so I can only assume it's a back pressure issue. So in the meantime, my exhaust dumps after my downpipe. It sounds badass, and it lets me reach full boost.

I am gonna try a couple things tonight...I'll let you know what happens.

[Krdshrk]

Too much backpressure isn't good... The general rule of thumb is that the back pressure should be under 2x the boost pressure. Too little backpressure isn't good either, I believe... the turbo spools and creates backpressure.

[2dot4]

I can't imagine an instance where any backpressure is good for a turbo. The more exhaust you can get the spin the turbine, the better - any back pressure just slows the spooling of the turbine. In a N/A setup, backpressure is beneficial, but when it comes to turbos, you've got plenty of backpressure on the cylinders themselves (all 4 cyl. dump their exhaust into a manifold that merges to a 2"x3" hole), but after that, you want the exhaust to get the fluck out of the way, and let the turbine spin freely and easily, increasing boost response, and eliminating turbo lag.

That would make the most sense to me, but this is my first turbo car...I could very easily be wrong.

[2dot4]

so apparently my exhaust wasn't the problem....

Turns out the same day I worked on my exhaust, I was screwing with the wastegate. Well I have a rubber vacuum line running to the compressor housing from the wastegate, and the heat made it rock hard and brittle, so when I was fiddling with it, the hose cracked underneath causing a vacuum leak, lowering my boost. I replaced the hose and got some high-temp insulating tape and wrapped it along with a couple other vulnerable hoses and such.

Problem solved.

I've decided to get the tsudo n1 catback anyway.

[Krdshrk]

Cool. That's what I roll with.

[Binder86]

Most exaust systems are turbo compliant.
The challange is finding one that will optimize
the power of the turbo. Right now I'm using a skunk2
Mega Power exhaust w/ a turbo @ 10 psi i have yet to run
into any problems.

:wave:

[Souljah]

you don't want any backpressure. however, it is a common mistake to think bigger is better. you only want 2.5" because you'll lose exhaust speed/temp with a larger exhaust. when that happens it creates turbulance. hope that helps

[Nebster]

all exhaust coming out is turbulent. if you think otherwise you have no knowledge of fluid dynamics or flow properties

[2dot4]

turbulance is just a change in flow.

I know you want to keep exhaust as hot as possible until it leaves, because it flows a lot easier. Colder air is more dense, so you don't want it in the exhaust. Larger diameter pipe increases surface area which increases cooling, and creates negative turbulance. It makes sense. It's the same reason you want to change your oil while your engine is still relatively hot - hot oil flows easier than cold oil.

I just assumed you needed a 3" for optimal turbo performance.

[Souljah]

all exhaust coming out is turbulent. if you think otherwise you have no knowledge of fluid dynamics or flow properties

you are correct, i should have said "more turbulance".