Hybrid96EK

I just can't quite seem to grasp this concept. A friend of mine is trying to tell me that by letting the car "breathe" more that you will effectively gain boost without do any other mods. He claims the addition of an exhaust on his car got his 2psi. Its an 89 Supra we are talking about BTW. I just can't seem to grasp this concept since the boost is regulated by a wastegate. I mean, he could be seeing boost creep from a lesss restrictive part, sure.. but boost should still settle down to a pre set level which is dictated by the wastegate. Anyone else have info on this?

stockredej1

That ***** creeping

80884

I can comment from the sti side of this. If you take a stock sti and put a downpipe and 3" exhaust on the otherwise stock car you will most likely experience "boost creep" but it is really more uncontrolable boost and it never seams to come back down to the stock level. I know on my car which is suposed to be around 15psi stock that exhaust alone alowed boost to go as high as 23psi with no other mods. The sti's boost cut is set for 17.5 psi and it takes 5 secs or so for it to kick in once it reads over the 17.5. Needless to say i've hit it before plenty of times.

I guess it depends on what kind of wastegate and boost control setup you are using to determine if boost will increase or not. I'm just posting my personal experiences. I would guess that factory non turbo cars should not increase boost with better exhaust unless there is a problem with the wastegate/boost contol.

raene

Think of it this way... with a high-backpressure setup, lots of pressure in the manifold, so more gas escapes given the same amount of time and wastegate hole diameter. Simplistic example, but whatever.

Now if you remove some of that backpressure, and your wastegate can't keep up by opening up more, you get boost creep.

Hybrid96EK

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by raene &raquo;</TD></TR><TR><TD CLASS="quote">Think of it this way... with a high-backpressure setup, lots of pressure in the manifold, so more gas escapes given the same amount of time and wastegate hole diameter. Simplistic example, but whatever.

Now if you remove some of that backpressure, and your wastegate can't keep up by opening up more, you get boost creep. </TD></TR></TABLE>

I understand the idea behind boost creep and why its especially an issue with internal wastegates. I just can't see how adding BPU's would increase the overall boost level, but he says it does. I guess apparently its common knowledge amongst the supra community. Dunno.

Hybrid96EK

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by raene &raquo;</TD></TR><TR><TD CLASS="quote">Think of it this way... with a high-backpressure setup, lots of pressure in the manifold, so more gas escapes given the same amount of time and wastegate hole diameter. Simplistic example, but whatever.

Now if you remove some of that backpressure, and your wastegate can't keep up by opening up more, you get boost creep. </TD></TR></TABLE>

I understand the idea behind boost creep and why its especially an issue with internal wastegates. I just can't see how adding BPU's would increase the overall boost level, but he says it does. I guess apparently its common knowledge amongst the supra community. Dunno.

EF8 D-UNIT

like he said on the crappy diaphram wastegates on stock setups, they creep easily normally, so when eliminating/decreasing back pressure, it can't keep up properly. A proper boost management or a spring wastegate would be a good idea for your buddy!

-Rob

raene

Read over what I said a few times and like EF8 D-UNIT said it'll come clear to you

AP-Signworks1

It's creeping, the stock wastegate was designed to maintain boost levels at a certain flow. Exceed that, and it will creep.

Even on an aftermarket wastegate, if you're running on spring only, changing the exhaust will affect the boost levels. On my Maxima, I have a 38mm Tial with 7 psi spring. When I first did the turbo, I had a 2.5" crush bent exhaust on it and stock cat. Car made 267whp at 5.5psi. Put a 3" test pipe in, and 3" mandrel bent exhaust and the car hit 7psi immediately and made 301whp. With a boost controller, this wouldn't happen obviously.

raene

The boost controller can't lower boost except by making the wastegate open more. A boost controller wouldn't help your problem if the wastegate already can't keep up... you need to change your manifold setup or get a bigger wastegate.

tgreaves

Very true.. My old crx was running 9psi with stock exhaust and shitty downpipe.. I upgraded to a custom 3" exhaust and the boost was running 11-12psi..

AP-Signworks1

Sorry, I was only referring to my setup with the Tial. It never went past 7psi, I just wasn't hitting a full 7psi with the restrictive exhaust. But you're totally right, if the wastegate can't keep up, it can't keep up.

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by raene &raquo;</TD></TR><TR><TD CLASS="quote">The boost controller can't lower boost except by making the wastegate open more. A boost controller wouldn't help your problem if the wastegate already can't keep up... you need to change your manifold setup or get a bigger wastegate.</TD></TR></TABLE>