Those with boost gauges at stock boost- question

[rocketspeed]

Does your boost tail off at higher RPM's? Mine does and I don't think it is unusual, but I was thinking about why it would today.

So, why? Is it because the little turbo can't keep forcing air in at high RPM's, tuning to protect the engine or what?

Of course, i searched for answers and I'm sure its out there somewhere, but I dind't find it.

[t3ase]

its called a boost spike. most, if not all, cars have it even those with ebcs.

[AutoBox]

tease i think he is sayin the boost falls off at higher rpm...my stock setup does also.....in the mid range its about .46 bar (i got a dtt)...by redline it drops to .35 bar......one thing also...when i removed my stock s-pipe back and put in 3" all the way back i hit .7 bar at 4k and it held all the way to redline...i think the stock cats cause too much backpressure and the turbo slows down some at high rpm :)

[rocketspeed]

Spike, huh?

Mine shoots up to just north of 7 psi, holds there until maybe 4-5k , then tails off to probably 5-5.5 by redline. What's the cause? Higher RPM's mean more air getting sucked in, must make it harder to keep boost up- is that the reason?

[ViksMSP]

its called a boost spike. most, if not all, cars have it even those with ebcs.I'm not sure he's talking about boost spike, he's running stock boost, and it doesnt' spike but fade off, or tail off, what ever you call it.
Anyways, it's kind of normal, but it's not because of the small turbo but because of the wastegate setup. The turbo will be more then happy to supply you of never-ending 15psi fun, but the wastegate takes all the fun out of it.

BTW, what happened to all the old threads? I searched for "Profec" and came up with nothing and a month ago there was like 50 posts???

Vik

[jersey_emt]

The plastic intercooler pipes expand under boost...that's why the pressure drops.

Same amount of air in a larger volume = less pressure

[rocketspeed]

tease i think he is sayin the boost falls off at higher rpm...my stock setup does also.....in the mid range its about .46 bar (i got a dtt)...by redline it drops to .35 bar......one thing also...when i removed my stock s-pipe back and put in 3" all the way back i hit .7 bar at 4k and it held all the way to redline...i think the stock cats cause too much backpressure and the turbo slows down some at high rpm :)
Yeah, that's what I'm saying- boost gradually tails off as RPM's rise once I pass probably 5k- its hard to watch the tach and gauge at the same time to say exactly where.

[rocketspeed]

The plastic intercooler pipes expand under boost...that's why the pressure drops.

Same amount of air in a larger volume = less pressure
That makes some sense. You'd think the turbo would just keep feeding more air to compensate, no? I'm not up on the inner workings of the wastegate.

[yashooa]

Not my crazy ass turbo it blows like a little possessed beast now. I will be taking it back to the dealer because it is causing me some concern. At part throttle it blows 5 PSI and at WOT or high revs it blows 14! But it never falls off until I shift.
I think my wastegate has freaked out.

[ViksMSP]

Not my crazy ass turbo it blows like a little possessed beast now. I will be taking it back to the dealer because it is causing me some concern. At part throttle it blows 5 PSI and at WOT or high revs it blows 14! But it never falls off until I shift.
I think my wastegate has freaked out.Yep, your vacuum line to the wastegate might be off or have a really bad leak.
So how does 14 psi feel??
The wastegate is what really controls the spooling and all the good stuff of the turbo.
Vik.

[t3ase]

[reply removed]

[boostaddict]

If it is the pipes then they're gonna have to be expanding like a *really* big baloon to reduce the pressure that much considering the amount of air oing through.


The plastic intercooler pipes expand under boost...that's why the pressure drops.

Same amount of air in a larger volume = less pressure

[jersey_emt]

Hehe...you've never seen them expand then, have you...they DO expand like a balloon :)

Along with that the engine moves a whole lot because of the crap mounts.

[rocketspeed]

I'd think the wastegate would just allow more pressure through to compensate for expanding pipes, no? As best as I understand, it cares about air pressure, not air volume- I could be wrong.

Anyway, any other folks with input? Does your boost fall off slightly at high RPM's?

[yashooa]

[reply removed]How come your reply was removed ? You say something CRAZY? No not T3ase he would never do that (fight) <V:p</V:p<O:p</O:p

No sir he is as soft as Bambi's coochie. Although Bambi was a guy so that's physically impossible.

<O:pI have nary a leaketh for my hose is a strong as a Homeless person's breath (cryhard) </O:p
<O:pThe boost she is a-good el Capi-tan but just a leetle too strong.</O:p