Synapse

If your boost goes up to, say 10 psi, and then backs down to, say 8 psi, can you reply back with your boost levels and which type of Wastegate you have and what size it is? Do you have a boost controller, and what fixed it.

This also applies to 8 psi then back down to 5, the theme here is boost spikes up then drops by redline.

AbitAvenger

what wastegate do you have? what manifold? what kind of boost controller if any? or is this just a technical question and your wondering why it does that?

some manifolds just creep and spike just due to their design and not letting enough manifold pressure to the wastegate at certain times

Synapse

I don't need to know why it does this. Just taking a pole of the what guys have which WGs and see this happening. I understand why it does this.

flangemastermike

got the same problem, boost goes to 8 holds and then at 6300 + it starts to drop to 5-4 psi , cant fiqure it out. oh im runnin a pfabrication log mani , xs power wastegate . 3" downpipe. was using a cheapO manual boost controller. got rid of it and just used a bigger spring , didnt fix the problem.

tony1

95% of the time when this happens without a boost controller installed, it's because the turbo is too small to keep up. 95% of the time when it happens with a boost controller installed, it's because of the boost controller. An electronic boost controller that's a PID type closed loop controller will compensate solenoid duty cycle to maintain a constant boost pressure. It has to do with a constant "bleed" being applied by manual boost controllers and the backpressure changing. With constant pressure on the diaphragm, you're back to spring pressure vs. exhaust backpressure. Backpressure increases with rpm causing the wg to be pushed open at high rpm, which results in more boost early on, and boost falling off up top.

Synapse

You should try to figure out what your backpressure is by redline. My theory is that you're producing more backpressure up top, instead of staying 1:1 with the intake.

Tony1- It sounds like backpressure is going up faster than intake mani press and he's not going into crossover.

tony1

It takes a pretty big turbo to get into cross over, i'd say 90+% of turbocharged engines will never be there at any respectable boost level.

From my experience, at 30psi, it takes bigger than a Q trim wheel be be in crossover on a B series motor.

Synapse

Here's another hypothesis that needs testing.

When you pressurize a chamber, you have the time it takes to fill that chamber, then pressure rises once the volume is exceeded by the pressure source. If it is a flexible bladder, like a diaphragm, you have to stretch it until it exerts back enough force to generate the pressure, right? But if there is a bleed, or small leak, then the pressure source, be it a compressor, or a turbo compressor, has to spin more RPM and produce more volume to exceed the bleed rate before being able to exceed the chamber volume enough to produce pressure.

What if, a leaky valve stem in most wastegates, is delaying the pressure rise that lifts the valve? So the turbo makes 8 psi, then when the compressor is finally making enough volume to pressurize the diaphragm it lifts the valve a little more and the wastegate then bypasses more exhaust and boost drops to 5 psi.

Just a thought.

AbitAvenger

poor design of the spring/wg?

tony1

That makes sense, but we're talking about very small chambers to "expand" and a big volume of air available to do it with. I think that being able to see the duty cycle of a boost solenoid running in closed loop, and compensating for backpressure to maintain boost pressure will make it easier to understand. i'll see if i can post some screen shots of datalogs that will make it easier to see.

93supercoupe

i think thats what hes getting at

AbitAvenger

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by 93supercoupe &raquo;</TD></TR><TR><TD CLASS="quote">i think thats what hes getting at</TD></TR></TABLE>synapse is referring to the wg opening early and bleeding off manifold pressure cuasing the turbo to spool harder for more boost

tony is stating that an ebc would compesate for the boost drop off and even it out

or at least thats what i got from the both of them but im kinda lost as to what we were first talkin about lol

SOHC_MShue

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by tony1 &raquo;</TD></TR><TR><TD CLASS="quote">95% of the time when this happens without a boost controller installed, it's because the turbo is too small to keep up. 95% of the time when it happens with a boost controller installed, it's because of the boost controller. An electronic boost controller that's a PID type closed loop controller will compensate solenoid duty cycle to maintain a constant boost pressure. It has to do with a constant "bleed" being applied by manual boost controllers and the backpressure changing. With constant pressure on the diaphragm, you're back to spring pressure vs. exhaust backpressure. Backpressure increases with rpm causing the wg to be pushed open at high rpm, which results in more boost early on, and boost falling off up top.</TD></TR></TABLE>
so what your saying makes sense about why it would fall off in high rpms's running just off wastegate spring witout a bleeder style boost controller, but why does the bleeder make it likely to spike worse? From what i've seen the boost controllers make spiking much worse.

Synapse

either the solenoid can't cycle fast enough, or the processor of the electronics doesn't have the resolution to keep up with the fast events. It may be electronics, but how fast they switch depends on how fast they control.

I'm going to try to setup a test on the bench to verify this.

SOHC_MShue

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Synapse &raquo;</TD></TR><TR><TD CLASS="quote">either the solenoid can't cycle fast enough, or the processor of the electronics doesn't have the resolution to keep up with the fast events. It may be electronics, but how fast they switch depends on how fast they control.

I'm going to try to setup a test on the bench to verify this.</TD></TR></TABLE>
oh i was talking about a purely mechanical bleeder valve

Synapse

Whoa! same thing. if a bleeder valve makes it worse, then a wastegate that leaks at the valve stem has a built in bleeder valve.

Once you exceed the bleed, then the valve can actually lift. I need to take one of my WG's and stick a bleeder on it and see if it does it.

Synapse

I'm watching this video again and realize that the leak at the valve stem isn't just some small leak. It is puking alot of air. Look at the size of the bubbles, regardless of the flow, because look at how small the feed line is.

http://www.youtube.com/watch?v=WjNbMTLzZck

HiProfile

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Synapse &raquo;</TD></TR><TR><TD CLASS="quote">I'm watching this video again and realize that the leak at the valve stem isn't just some small leak. It is puking alot of air. Look at the size of the bubbles, regardless of the flow, because look at how small the feed line is.

http://www.youtube.com/watch?v=WjNbMTLzZck</TD></TR></TABLE>

lol, I think boost-head that has a fish tank will buy another TiAL now.

What methods do you think could be used to correct this, besides using a better valve guide? AFAIK, EGTs at that point will be well over 1000F, which means at least 800F at the top of the valve. Silicone is only good to upper 600's from what I remember, at least for a reasonable cost.

Synapse

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by HiProfile &raquo;</TD></TR><TR><TD CLASS="quote">

lol, I think boost-head that has a fish tank will buy another TiAL now.
</TD></TR></TABLE>

Sweet idea, I gotta get a fish tank for the office and put a wastegate in it.

This would only work for drag racing, but you could take it apart after every run, use silicone lube. Do another run, take apart and lube again.

Otherwise the whole thing just needs to be redesigned.

matt k

the tail wastegates leek allot around the valve take your air compressor turn it down two 20pnds and hook it up to your bottom port i was surprised tony what kind of back pressure are you seeing on the 42r at 25 to 35 psi and does it change from one gate to the other on your divided manifold

Synapse

I just played with one on the bench and I think Tony is right. Probably more like the backpressure going up higher at higher rpms.

LeGeND4LiFe

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by bob menuts &raquo;</TD></TR><TR><TD CLASS="quote">the tail wastegates leek allot around the valve take your air compressor turn it down two 20pnds and hook it up to your bottom port i was surprised tony what kind of back pressure are you seeing on the 42r at 25 to 35 psi and does it change from one gate to the other on your divided manifold </TD></TR></TABLE>

Similar yet different question, mostly for tony1 or for anyone who can answer from actual logged data. If all else including boost pressure remains constant throughout, does backpressure decrease going from a smaller gate to a larger one?

TiAL

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote &raquo;</TD></TR><TR><TD CLASS="quote">I'm watching this video again and realize that the leak at the valve stem isn't just some small leak. It is puking alot of air. Look at the size of the bubbles, regardless of the flow, because look at how small the feed line is.
http://www.youtube.com/watch?v=WjNbMTLzZck
</TD></TR></TABLE>

AGAIN, since you arn't able to comprehend this: we designed the wastegate to leak down the valve stem...that isn't a bad thing

i'd say our 13 years of success is more than enough proof

LeGeND4LiFe

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by TiAL &raquo;</TD></TR><TR><TD CLASS="quote">

AGAIN, since you arn't able to comprehend this: we designed the wastegate to leak down the valve stem...that isn't a bad thing

i'd say our 13 years of success is more than enough proof</TD></TR></TABLE>

Could you elaborate on why, and the pros and cons of a leaking vs non leaking design?

TiAL

yes I can, there are no pros or cons for either, we don't do it because it provides absolutly ZERO benefit, there is no need to do it. nothing will be effected either way. it's like trying to decide what color you want to paint a room