external wastegate question

[dylan5084]

Ive got a stage 3 ct26 fensport hybrid turbo and 4 branch s/s manifold, and have issues with boost creep, I know I'll need to weld up the internal gate.

My question is, can I put the wg onto one of the branches of the manifold, where it's easy to fit, or do I need to put it where the 4 branches meet?

Would there be issues if I fitted it to a single branch? My thinking is that the exhaust gasses would take the path with least resistance, which should be the wg, am I wrong?

Thanks dylan

[Ryan S]

You have to have it on all 4 or you'd only be getting 1/4 of the exhaust gas into it

[Ryan S]

Is it a rev2 you have? I have a stainles 4 branch manifold with a wastegate port on it, brand new and unused

[shinny]

I know I'll need to weld up the internal gate.

That seems to be the general wisdom. I'm not sure why, though... it just removes any flexibility / resale value in your setup later. The actuator will keep the wastegate shut well enough. (As well as it ever did, and people don't tend to complains about internal gates creeping open before)

I've got a GT28 turbo kit with external wastegate and still had bad boost creep... so I've just taken the unusual step of adding an internal wastegate and running both the internal and external gates at the same time. With a well chosen actuator pressure, it's working a treat!

I did get a CT20b converted to external gate and had the wastegate welded up... and I regret that now, because noone wants to buy a turbo with a welded up wastegate

Sheppy is right though, you want to dump from all four runners if possible... three might suffice, but one won't be good enough.

[dylan5084]

Is it a rev2 you have? I have a stainles 4 branch manifold with a wastegate port on it, brand new and unused

It is a rev 2, how much you after for it? Save a bit of faffing about!

[dylan5084]

I know I'll need to weld up the internal gate.

That seems to be the general wisdom. I'm not sure why, though... it just removes any flexibility / resale value in your setup later. The actuator will keep the wastegate shut well enough. (As well as it ever did, and people don't tend to complains about internal gates creeping open before)

I've got a GT28 turbo kit with external wastegate and still had bad boost creep... so I've just taken the unusual step of adding an internal wastegate and running both the internal and external gates at the same time. With a well chosen actuator pressure, it's working a treat!

I did get a CT20b converted to external gate and had the wastegate welded up... and I regret that now, because noone wants to buy a turbo with a welded up wastegate

Sheppy is right though, you want to dump from all four runners if possible... three might suffice, but one won't be good enough.

So, with the actuator without vac pressure should this generally keep the internal wastegate shut?

[Ryan S]

Is it a rev2 you have? I have a stainles 4 branch manifold with a wastegate port on it, brand new and unused

It is a rev 2, how much you after for it? Save a bit of faffing about!

PM replied to man, I forget you're just over the road, feel free to collect this any time

[shinny]

So, with the actuator without vac pressure should this generally keep the internal wastegate shut?

Exactly! However even if it does get pushed open a fraction at high boost/RPM the external gate will already be open to control the boost, so it's not a problem.

I'm sure you could argue that welding up the wastegate makes sure that this doesn't happen, but I honestly don't expect it's going to make any real-world difference. You can't un-weld the turbine housing if you change your mind or decide to swap turbo later...

[2mad]

So, with the actuator without vac pressure should this generally keep the internal wastegate shut?

The actuator spring will hold tension (the gate shut) best it can .. you could fit shims (shimming the wastegate) to hold it closed with more force .. welding it shut after testing it works ok is probably your best bet.



I would shim the wastegate unless the turbo needed removing, then id weld it shut ... just my 2p

[shinny]

The actuator spring will hold tension (the gate shut) best it can .. you could fit shims (shimming the wastegate) to hold it closed with more force .. welding it shut after testing it works ok is probably your best bet.

Exactly how easily will the wastegate be pushed open? It's not like it's going to start opening at 0.5bar! Let's not forget that many owners regularly run 1.2bar with the standard actuator and no-one seems to complain about the actuator being pushed open early by the exhaust gasses. Without a vac hose on the actuator, the wastegate will be held shut more firmly than running MBCs or EBCs without much gain configured. Why does it suddenly become a problem when there's another wastegate actually doing the boost control instead?

The reason I'm advising against welding is because I'm speaking from experience of someone who did get a CT series wastegate welded up to go external gate and wishes he hadn't.

With that said, shimming the actuator is a great idea if you're really worried about the wastegate being pushed open

Finally, if your creep is so bad that the external wastegate doesn't do the trick by itself (as mine didn't on my CT28 kit) then you always have the option of running both internal and external gates... unless you weld up the turbine housing!

[2mad]

Yeah I have to agree with shinny now, welding the wastegates abit final, no going back from that.

Best of luck what ever route you take.

[C35Rob]

The actuator spring will hold tension (the gate shut) best it can .. you could fit shims (shimming the wastegate) to hold it closed with more force .. welding it shut after testing it works ok is probably your best bet.

Exactly how easily will the wastegate be pushed open? It's not like it's going to start opening at 0.5bar! Let's not forget that many owners regularly run 1.2bar with the standard actuator and no-one seems to complain about the actuator being pushed open early by the exhaust gasses. Without a vac hose on the actuator, the wastegate will be held shut more firmly than running MBCs or EBCs without much gain configured. Why does it suddenly become a problem when there's another wastegate actually doing the boost control instead?

The reason I'm advising against welding is because I'm speaking from experience of someone who did get a CT series wastegate welded up to go external gate and wishes he hadn't.

With that said, shimming the actuator is a great idea if you're really worried about the wastegate being pushed open

Finally, if your creep is so bad that the external wastegate doesn't do the trick by itself (as mine didn't on my CT28 kit) then you always have the option of running both internal and external gates... unless you weld up the turbine housing!

that's actually incorrect..

wastegates DO have a "cracking" pressure.. where they'll start to open, so for someone running 1ish bar it probably is somewhere around half a bar, internal gates don't just snap open at the desired pressure.

do it properly, weld the internal wastegate up, or at least mechanically hold it just by replacing the internal gate with a flat plate so you can bolt a rod solid to it.

as for the wastegate, a 38mm wastegate should be adequate for 99% of MR2 set ups, bearing in mind it'll need to be in a place on the manifold that feeds from all four runners, so you will loose some of the twin scroll effect.

I'd suggest the boost creep issue on the CT28 was probably/potentially down to the exhaust housing being too small.[/i]

[dylan5084]

Is it possible I could buy an adapter plate to sandwich in between the turbo and manifold, with an offtake for the external wastegate there? Where would I source one of those?

[dylan5084]

http://thumbs3.ebaystatic.com/d/l225/m/ ... jL624g.jpg

Like this but the ct26 bolt pattern

[Ryan S]

entirely possible but you;d struggle to find a ct26 to ct26 adapter, if you took that manifold off me you could easily get a T3 to CT26 adapter

Bear in mind your turbo will sit lower and in turn so will your decat which then won't line up with your exhaust.

http://www.ebay.co.uk/itm/CT-26-to-T3-C ... 1e89f44851

although...If you got one of these made up (or bought this one) then I doubt you'd have to modify the downpipe at all.

[shinny]

Is it possible I could buy an adapter plate to sandwich in between the turbo and manifold, with an offtake for the external wastegate there? Where would I source one of those?

Such a block would muck up the location of the coolant lines, oil lines and downpipe... the oil lines are solid and would need replacing with braided lines (NOT the rubber lines like JD Modified twice used on my car which caused two identical breakdowns when they burnt through!). You'd also need to fabricate a new downpipe!

wastegates DO have a "cracking" pressure.. where they'll start to open, so for someone running 1ish bar it probably is somewhere around half a bar, internal gates don't just snap open at the desired pressure.

Cracking pressure, AFAIU, is all about when the wastegate starts to move when applying boost pressure to it. So yes, a 1bar actuator will start moving at around 0.5bar boost. This is why EBCs have the concept of gain. However, that's not what we're talking about here - I'm suggesting leaving the actuator seeing zero boost. Exhaust pressure alone is not going to open the wastegate at the cracking pressure This is exactly how EBCs provide gain... they show the actuator zero pressure to keep them firmly shut past their cracking pressure until you're closer to your target boost. If it didn't work, there'd be no point doing it.

The question is about whether exhaust pressure alone can overcome the spring on your wastegate. Certainly if you've had the boost line fall off an actuator, as happened to me once on a test drive, you'll know you'll build boost very quickly and hit fuel cut. Building boost really isn't a problem if your actuator doesn't have a vac line!

Let's look at it a bit scientifically - on the standard actuator let's say the size of the diaphragm is about 3 times the area of the wastegate (a bit of a guestimate based on the size of the actuator and the wastegate ports). If you test the wastegate off the car and it starts moving at 0.5bar, that means the preload of the spring inside is overcome by the force exerted on the diaphragm at 0.5bar. Now, to get the same force just by applying pressure to the wastegate flap, which is only 1/3rd the area, you would need triple the pressure being applied, ie 1.5bar. However that's not 1.5bar absolute pressure above atmospheric because there's still some backpressure from the exhaust, so it's only the difference accross the turbine that counts. AFAIU turbines present backpressure to the enigine proportional to the backpressure presented by the exhaust. So if a turbine had a 2:1 pressure ratio (which seems to be a ballpark figure for a CT26 from my googling) and the exhaust presented a pretty high 1bar backpressure, the engine would see 2bar back pressure and the pressure difference acting on the wastegate flap would be 1bar - still not enough to crack the CT26 wastegate open by my back-of-an-envelope calculations. With a free flowing exhaust, the absolute pressure difference drops, making it even less likely the exhaust pressure will be able to crack the wastegate.

as for the wastegate, a 38mm wastegate should be adequate for 99% of MR2 set ups, bearing in mind it'll need to be in a place on the manifold that feeds from all four runners, so you will loose some of the twin scroll effect.

From my experience I would agree. I didn't notice the slight loss of twin-scroll, probably because being able to confidently slam the boost in at the desired level beats a perfect twin scroll that's creeping up to your desired boost level.

I've had three different manifold / turbo combinations with 38mm wastegates. The only one that has given me creep is the GT28 one and I would put that down to the adaptor taking the dump pipe off at an angle greater than 90º to the gas flow. Here's a diagram taken from a turbosmart document to demonstrate how best to add your wastegate:



My GT28 kit has 38mm wastegate on a take-off at 90º to the gas flow which then immediately curves another 45º, so would probably be under the "not recommended" section. Not a big surprise that it creeps; when making your own wastegate mounting, don't make the same mistake.

[dylan5084]

entirely possible but you;d struggle to find a ct26 to ct26 adapter, if you took that manifold off me you could easily get a T3 to CT26 adapter

Bear in mind your turbo will sit lower and in turn so will your decat which then won't line up with your exhaust.

http://www.ebay.co.uk/itm/CT-26-to-T3-C ... 1e89f44851

although...If you got one of these made up (or bought this one) then I doubt you'd have to modify the downpipe at all.

Looks a not bad option that countersunk plate, you make a not bad salesman

[shinny]

entirely possible but you;d struggle to find a ct26 to ct26 adapter, if you took that manifold off me you could easily get a T3 to CT26 adapter

Bear in mind your turbo will sit lower and in turn so will your decat which then won't line up with your exhaust.

http://www.ebay.co.uk/itm/CT-26-to-T3-C ... 1e89f44851

although...If you got one of these made up (or bought this one) then I doubt you'd have to modify the downpipe at all.

Looks a not bad option that countersunk plate, you make a not bad salesman

That countersunk plate is for a single entry CT26... it's not suitable for the twin entry turbo found on the MR2 or Celica.

[Ryan S]

Haha, not trying to sell it man, just trying to help you out. There is twin scroll adapters available, one thing i didn't think about was oil and water lines. I'm not sure where the turbo would sit with that manifold i have, you would need the t3 adapter as i said. It's a lot of mucking about so it depends on how much benefit you'd see from the external gate.

[C35Rob]

Cracking pressure, AFAIU, is all about when the wastegate starts to move when applying boost pressure to it. So yes, a 1bar actuator will start moving at around 0.5bar boost. This is why EBCs have the concept of gain. However, that's not what we're talking about here - I'm suggesting leaving the actuator seeing zero boost. Exhaust pressure alone is not going to open the wastegate at the cracking pressure This is exactly how EBCs provide gain... they show the actuator zero pressure to keep them firmly shut past their cracking pressure until you're closer to your target boost. If it didn't work, there'd be no point doing it.

I understand that, however, I think you're getting mixed up with the 'gain' setting, on every boost controller I'm aware of the 'gain' setting is there to provide boost stability - i.e counteracting the tail off of boost at higher revs, having gain dialled in will give exactly the symptoms of "boost creep" - whereas a -ve gain setting will see boost drop off at higher revs.

what you're talking about is what is called the "start" pressure on greddy controllers (others may call it something else) i.e the solenoid clamps the actuator from seeing any pressure untill say, 12psi(or whatever the set level is) in order to increase boost response

Let's look at it a bit scientifically - on the standard actuator let's say the size of the diaphragm is about 3 times the area of the wastegate (a bit of a guestimate based on the size of the actuator and the wastegate ports). If you test the wastegate off the car and it starts moving at 0.5bar, that means the preload of the spring inside is overcome by the force exerted on the diaphragm at 0.5bar. Now, to get the same force just by applying pressure to the wastegate flap, which is only 1/3rd the area, you would need triple the pressure being applied, ie 1.5bar. However that's not 1.5bar absolute pressure above atmospheric because there's still some backpressure from the exhaust, so it's only the difference accross the turbine that counts. AFAIU turbines present backpressure to the enigine proportional to the backpressure presented by the exhaust. So if a turbine had a 2:1 pressure ratio (which seems to be a ballpark figure for a CT26 from my googling) and the exhaust presented a pretty high 1bar backpressure, the engine would see 2bar back pressure and the pressure difference acting on the wastegate flap would be 1bar - still not enough to crack the CT26 wastegate open by my back-of-an-envelope calculations. With a free flowing exhaust, the absolute pressure difference drops, making it even less likely the exhaust pressure will be able to crack the wastegate.

I'm not sure I follow here..

obviously there is pressure in the exhaust manifold, pre turbine, and that pressure will nearly always be greater than the boost pressure, the smaller the exhaust housing and turbine wheel the less able it is to flow gas and the greater the pressure - a turbo with a small hot side (i.e mismatched to the engine) will be harder to control boost on, and in these cases a larger EWG would be beneficial

back pressure in the actual exhaust system is highly undesirable, you certainly shouldn't be seeing a bar of pressure in what is essentially a 3" open ended pipe! - that is, unless you're driving a boat with a submerged exhaust.

as for the wastegate, a 38mm wastegate should be adequate for 99% of MR2 set ups, bearing in mind it'll need to be in a place on the manifold that feeds from all four runners, so you will loose some of the twin scroll effect.

From my experience I would agree. I didn't notice the slight loss of twin-scroll, probably because being able to confidently slam the boost in at the desired level beats a perfect twin scroll that's creeping up to your desired boost level.

I've had three different manifold / turbo combinations with 38mm wastegates. The only one that has given me creep is the GT28 one and I would put that down to the adaptor taking the dump pipe off at an angle greater than 90º to the gas flow. Here's a diagram taken from a turbosmart document to demonstrate how best to add your wastegate:

Image Replaced With URL For Quote http://shinny.co.uk/toyota/wastegatemounting.png

My GT28 kit has 38mm wastegate on a take-off at 90º to the gas flow which then immediately curves another 45º, so would probably be under the "not recommended" section. Not a big surprise that it creeps; when making your own wastegate mounting, don't make the same mistake.

Agreed, wastegate placement is paramount - I've seen a single 38mm EWG being used on a 570bhp RB20 engine, comfortably controlling boost, because it had a properly designed manifold and 4" exhaust (yes, 4", from turbo back)

so, really.. there should never be any requirement to run an internal and external wastegate, a properly placed external gate will do the job.. internal wastegates are fitted as standard to most turbos because of cost and packaging requirements, from a performance standpoint they're gash. why introduce another potential point of failure into the system when you can just weld it up and be done with it