st205 openions/feedback owners/ ex-owners

[sergei]

Although in my case is little bit extreme, every one was puzzled.
I even went to extent of jamming open the waste gate with no down pipe and still was getting boost ~1 bar.
My setup has only one straight through oval muffler, no crushes in the pipes either.

And turbo was brand new steel "CT20b" with XS power down pipe. Then custom Simon's down pipe and 1 external waste gate joining from two internal ports and stock flap removed. That evolved into two waste gates with adapter - the only working setup.

[iOnic]

That's a topic of people telling you they have no problems with their ct20b's and free exhaust systems......

It's pretty clear from that discussion that your problems are/were isolated to you/your car Don't automatically assume ALL upgraded exhaust systems are bad simply because you used a cheap and nasty downpipe that is known for causing that exact problem (seriously what were you expecting) and had trouble with it...I have designed several different exhausts/downpipes for ct26/20b turbos on my and other cars and have never had that problem. Besides, if the stock exhaust is as good as you say it is - why'd you upgrade it?

[cat007]

Reducing back pressure should theoretically reduce the boost as it is reducing the restriction.

nuff said

except its on the wrong side of the pump.....

[sergei]

That's a topic of people telling you they have no problems with their ct20b's and free exhaust systems......

It's pretty clear from that discussion that your problems are/were isolated to you/your car Don't automatically assume ALL upgraded exhaust systems are bad simply because you used a cheap and nasty downpipe that is known for causing that exact problem (seriously what were you expecting) and had trouble with it...I have designed several different exhausts/downpipes for ct26/20b turbos on my and other cars and have never had that problem. Besides, if the stock exhaust is as good as you say it is - why'd you upgrade it?

Because it was ST165 with rotten piping.
I will never upgrade exhaust on my ST205.
You have obviously didn't read the what I wrote, I have tried custom made down pipe with external waste gate same result.
I also tried no down pipe, no waste gate flap and it still was making boost.

what you are saying that after you installed free flow exhaust you get boost increase, if say waste gate was functioning correctly you should not get any boost increase at all. In most of the cases the "free flow" system is restrictive enough for waste gate to function more or less for people not to exceede 16psi (safe boost limit for stock ST205).

[sergei]

I find it funny when people say:
I put new I/C it gave me extra boost
or
I put new exhaust it gave me 2 more psi of boost

Think about these statements why people don't realise that there is something wrong:
The waste gate is pressure activated. So any decrease or increase of restriction would cause the wastegate to compensate.
I know for a fact that a lot of stock wastegates are in fact barely enough, hence there are boost spikes even on stock vehicle.
Look at this way, why the boost would climb to over a bar and drop on higher rpms to a steady 0.8bar on ST205?
Or I've seen subarus spike up to 1.5bars and then hold steady at 1.2bars (although this might be to ECU trickery to gain more torque, because they have a proper boost control unlike ST205).

Also my new wastegate setup on ST165 is holding steady any boost from 0.5bar and up (whatever I set it to on EBC), be that sudden full throttle on 5000rpm or steady build up of rmps from 3000rpm under load.

Also:
Boost is not measure of performance.

[iOnic]

You're right, boost is not a measure of performance - it is however a measure of restriction, which is what I was talking about to start with - not sure where you got that other idea from to be honest.

Why does boost climb and then settle? Well.....as rpm's climb there is more and more exhaust gas trying to cram it's way into the turbo's exhaust housing......all turbos have inefficiencies - at a certain point the exhaust housing is getting more gas coming in than it can send out fast enough......and that causes a restriction on the turbine wheel which in turn affects the compressor wheel which = less boost The wastegate isn't "compensating" for anything. The reason you "gain" boost from fitting a free-er flowing exhaust is that there is less of a restriction on the turbine wheel and therefore it can spin faster and in turn the compressor wheel is able to produce more boost with less effort .....it's not much more boost (not 2 bar that's for sure ) but there is a slight increase which is why less restrictive exhausts are usually the first port of call

This is why machining the exhaust housing of the CT26 is a popular upgrade - it allows more exhaust gas to escape the exhaust housing and therefore allow the turbo to continue producing the same amount of boost for longer - the ct20b is slightly more efficient/better designed in this respect but it is also by no means perfect and it has it's limits as all things do

There is more to a turbocharger than a wastegate - I'd suggest that you learn about the effects of restrictions on various parts of the assembly - it may stop you from saying things like this...

Reducing back pressure should theoretically reduce the boost as it is reducing the restriction.

nuff said

[cat007]

The waste gate is pressure activated. So any decrease or increase of restriction would cause the wastegate to compensate.
I know for a fact that a lot of stock wastegates are in fact barely enough, hence there are boost spikes even on stock vehicle.
Look at this way, why the boost would climb to over a bar and drop on higher rpms to a steady 0.8bar on ST205?
Or I've seen subarus spike up to 1.5bars and then hold steady at 1.2bars (although this might be to ECU trickery to gain more torque, because they have a proper boost control unlike ST205).

Also my new wastegate setup on ST165 is holding steady any boost from 0.5bar and up (whatever I set it to on EBC), be that sudden full throttle on 5000rpm or steady build up of rmps from 3000rpm under load.

Except you're forgetting that an engine is purely a pump - the faster the air can get in/out the better

The turbo is already doing the in part, the 'bigger' exhaust helps with the out....

[AJz]

oh right i see how this relates to the OP.....

[iOnic]

OP's question was answered looong ago he'll drive both and see which one he likes more This is just typical off topic goodness (quite informative in a roundabout way ) Should get a mod to split it and clean all the crap out as there is plenty of info in here other people may want to know

[AJz]

lol its like that flamewar vid, cept irl

[sergei]

The waste gate is pressure activated. So any decrease or increase of restriction would cause the wastegate to compensate.
I know for a fact that a lot of stock wastegates are in fact barely enough, hence there are boost spikes even on stock vehicle.
Look at this way, why the boost would climb to over a bar and drop on higher rpms to a steady 0.8bar on ST205?
Or I've seen subarus spike up to 1.5bars and then hold steady at 1.2bars (although this might be to ECU trickery to gain more torque, because they have a proper boost control unlike ST205).

Also my new wastegate setup on ST165 is holding steady any boost from 0.5bar and up (whatever I set it to on EBC), be that sudden full throttle on 5000rpm or steady build up of rmps from 3000rpm under load.

Except you're forgetting that an engine is purely a pump - the faster the air can get in/out the better

The turbo is already doing the in part, the 'bigger' exhaust helps with the out....

Engine is not purely a pump. As there are two things happen you convert liquid to gas and you heat it up at same time.
While why the boost suddenly settles, there is an efficiency curve of a turbocharger aka compressor map, and the rpm of turbocharger is not proportional to boost or flow.

My point is the boost spikes are only there because wastegate system is not sufficient.

[iOnic]

The only "improvement" that you will get from 3" no restriction, no cat, on the the stock turbo is over-boosting (uncontrolled, beyond 2 bars).

My point is the boost spikes are only there because wastegate system is not sufficient.

Sort out your contradictions please. First the boost spikes were only there because the exhaust was less restrictive and now it's the wastegate system?

And yes......in it's simplest form, an internal combustion engine is, in effect......a pump. A complicated pump but a pump nonetheless....

[sergei]

The only "improvement" that you will get from 3" no restriction, no cat, on the the stock turbo is over-boosting (uncontrolled, beyond 2 bars).

My point is the boost spikes are only there because wastegate system is not sufficient.

Sort out your contradictions please. First the boost spikes were only there because the exhaust was less restrictive and now it's the wastegate system?

And yes......in it's simplest form, an internal combustion engine is, in effect......a pump. A complicated pump but a pump nonetheless....

What is contradicting there please?
You basically do not understand what causing over boost.
Here simple explanation:
The gas flow "prefers" going through turbine than wastegate system with larger pressure difference between the turbine housing and turbine exit. As the exhaust more restrictive the flow goes through wastegate more than with less restrictive exhaust.
As simple as that.

Otto cycle engine is an adiabatic process at some degree, so it is not a simple pump.

[iOnic]

I give up

[sergei]

I give up

Next.

[Lith]

What is contradicting there please?
You basically do not understand what causing over boost.
Here simple explanation:
The gas flow "prefers" going through turbine than wastegate system with larger pressure difference between the turbine housing and turbine exit. As the exhaust more restrictive the flow goes through wastegate more than with less restrictive exhaust.
As simple as that.

That would have to assume that the wastegate was venting externally, right?

[sergei]

What is contradicting there please?
You basically do not understand what causing over boost.
Here simple explanation:
The gas flow "prefers" going through turbine than wastegate system with larger pressure difference between the turbine housing and turbine exit. As the exhaust more restrictive the flow goes through wastegate more than with less restrictive exhaust.
As simple as that.

That would have to assume that the wastegate was venting externally, right?

That applies to internal. Flow dynamics is not simple subject.
But roughly speaking there is some venturi effect on the wastegate ports (from inside the turbine housing of course) when there is low pressure after turbine wheel .
See on the CT20b the ports are drilled at 90' into the housing, having also a narrowing in there and faster than designed gas flow would cause reduction in flow of through the wastegate ports.

[sergei]

http://en.wikipedia.org/wiki/Venturi_effect

[dnalunchie]

hey guys I hate to throw a curve ball into the mix but how would an evo two line up against the chaser/205? in terms of performance and reliability?

[Mr Revhead]

nnnnnnnnnnnoooooooooooooooooooooooooooooooooooooooooooooo
dont add ANOTHER tangent