Dual Port Waste-gates

[Indi9xx]

A sad effect of turbo charged cars is that you get more exhaust pressure pre turbo, than you do post turbo, in the OE Wastegate you can suffer from the pounds per square inch behind the valve helping it open, so the reversed valve direction of a TiAL (Valve pulling in) is that the back pressure before the wastegate is helping keep it closed.

The main benefit of a proper dual port wastegate, like a TiAL, is that you have two ports either side of a diaphragm, one side to close or keep the wastegate closed, and on the other side a port to open it.

However in most traditional dual port mode plumbing of a MBC or EBC the pressure builds on both sides of the diaphragm until the target boost is achieved and then the boost on the "closing" side remains at that set pressure, while the "opening" side continues to rise which causes the valve to open.

One way of thinking about it is to imagine that either side of the diaphragm you have a balloon, if they both inflate to 18 psi, the diaphragm will be held tight, but as soon as one or other has 19 psi, there will be 1 psi more on one side so the diaphragm will move away from that pressure... the higher the target boost level, the more firmly the wastegate will be held in its closed state.

When you compare that to a single port wastegate, which with even a boost enhancer or improver, will have no pressure either side of the diaphragm until the target is reached, and then will have pressure in the opening side.

In the OE with BoostImprover method, you end up with pressure building higher and higher pre turbo, which then begins to open the valve in the wastagate, and as the BoostImprovers are static (set to one pressure) that increasing force trying to open the wastegate via the valve, causes the boost to decrease as RPM (and pre turbo back pressure) increases.

So, you always get a faster spool up (especially mid way between no boost and full boost onwards) and boost which holds on further through the rev range.. All bar other factors and restrictions of course.

 

[TTM]

ORIGINAL: Indi9xx
in the OE Wastegate you can suffer from the pounds per square inch behind the valve helping it open, so the reversed valve direction of a TiAL (Valve pulling in) is that the back pressure before the wastegate is helping keep it closed.

Are you sure? In both cases exhaust gases push onto the valve, and the Tial will work just the same as the std WG if it's plugged in single port.

 

[Indi9xx]

Yep, after all these years I am sure. All the tials we use pull the valve into the body and we plumb them in so the valve face is on the exit into the system and yep, a dual port wastegate plumbed in using only one port, is just that, single port and no better than a standard wastegate, other than better machining, exhaust back pressure pre turbo pushing the valve closed rather than open and it not being 25 years old.

A dual port would be a better choice than buying a used wastegate if you wanted to keep the car pretty much original I guess, but I think most people plumb them in as dual port mode anyway and buy them as a performance mod rather than as a replacement part.

 

[Indi9xx]

Oo-er.. just noticed that Paul's photo shows him his tial38 plumbed in the other way round... What car was that on Paul? was it LIL before we fitted the big tial with the 3.2??

 

[TTM]

ORIGINAL: Indi9xx
Oo-er.. just noticed that Paul's photo shows him his tial38 plumbed in the other way round

Well, this is the way a Tial should be installed, whence my surprise when you say you install it the other way around.

 

[Indi9xx]

The 944's suffer from higher exhaust ratios than many cars once you start tuning them, especially for right hand drive, where there are not easy off the peg crossover designs, if you fit them they way I have always fitted them, and the way I have always recommended they are fitted, then you are less likely, or not likely, to suffer the sloping boost slope as rpm increases on MBC cars which is caused by the rising back pressure in the crossover pushing on the outwards opening valve which is an element in the opening force.

Run our way round, with the right combination of spring and MBC plumbing you eliminate this. There was a discussion here in the days of the dynodays at WRC where people discussed this phenomena and I explained it then.

TiAL recommended we did this when we explained the issues of creeping boost on 944 turbo models and were looking for an alternative to the Lindsey Racing DPW we used to use 10 years ago.

With EBC cars we find that installing the DPW our way round also causes the solenoid to work much later and less frequently in each run, which therefore reduces its operations and increases its lifespan.

 

[TTM]

Ok, but that would not be necessary on a very low back pressure set up, would it?

 

[Indi9xx]

If you have a left hand drive car with an aftermarket crossover, or a quite low power modified car it would be less of a problem, but having said that, on the dyno league a lot of people were suffering from a sloping boost profile even on relatively low power cars.

Not only this, but it also seemed to help with spool up, which I suspect might be a sign that the wastegate was floating or creeping a little even at lower rpm as the boost came in.

Lots of things seem to impact the pressure in the crossover in the millions of combinations of tuning levels and parts, a restrictive exhaust system, a turbo reaching its limits of efficiency, fueling strategy (especially as the boost rises), EGT's.. Some of which can be used to benefit the spool up of the turbo even though they may seem undesirable, some of which limit top end power..

A good example would be what we did to try and get maximum torque from cars with standard turbo's but other tuning parts used. Using fueling and ignition adjustments to create low rpm and early in the boost curve high EGT's help spool up through increased exhaust gas volume, velocity and heat, which would bring the turbo on to song sooner, but would increase the crossover pressure to levels you would expect later in the rpm and boost profile, but at a time when the actual boost is quite low, so therefore the pressure used to control the DPW was quite low, which resulted in you having to use a higher pressure spring in the wastegate, which we used to try to avoid, as it stops you from being able to have the ability to run a low boost level for winter driving (for example), but fitting the TiAL in the way we recommend actually solves this issue.

I just thought everyone did it this way...

It does not take long to try it, and if anyone is used to the tial being fitted the other way round, I am sure that after resetting their boost controller, and possibly opting for a lower pressure spring, they will be able to feel an improvement.

Its lots of little things like this that really make a difference, and why you might see that some cars tuned by us, with very similar parts to what are on other cars, make more torque and power.

Its not just the parts you use, its how you fettle them, improve them (even if just a little) and how you fit them which often makes a real difference.

 

[TTM]

I wasn't aware RHD cars had a different cross pipe...

Mine is LHD using the standard cross pipe with a 3" Lindsey exhaust and I see 1.3 bar of turbine inlet pressure at 1.2 bar of boost, which is very good.
I would expect cars using KKK turbines to make a lot more backpressure, with a backpressure/boost ratio somewhere between 2.0 and 3.0.

I played with reducing ign timing in order to increase EGT at lower rpm but it made the car way too slow to justify a possible increase in spool that I did not even get, for what it's worth...

 

[Diver944]

ORIGINAL: Indi9xx

What car was that on Paul? was it LIL before we fitted the big tial with the 3.2??

It sure was. I took that pic the day I fitted it over ten years ago. Plumbed in to the Greddy it held 18psi to the redline and was running on very early Danno chips from back in the day.

I remember I was one of half a dozen UK guys who got in on a Group buy from Speedforceracing and we all plumbed them in that way (as do pretty much all of the Rennlist photo's I've just looked at). It's interesting to see you've managed to get them in the other way round which sounds much better in operation. My memory is rusty but I think my TiAL physically would not fit in any other way without using a lumphammer to the underside of the car []

I'm sure I have a pic of the big 48mm you fitted somewhere [8D]

 

[Indi9xx]

ORIGINAL: TTM

I wasn't aware RHD cars had a different cross pipe...

Mine is LHD using the standard cross pipe with a 3" Lindsey exhaust and I see 1.3 bar of turbine inlet pressure at 1.2 bar of boost, which is very good.
I would expect cars using KKK turbines to make a lot more backpressure, with a backpressure/boost ratio somewhere between 2.0 and 3.0.

I played with reducing ign timing in order to increase EGT at lower rpm but it made the car way too slow to justify a possible increase in spool that I did not even get, for what it's worth...

They are not different, but right hand drive has a steering shaft going through it which makes all the usual off the peg manifolds, like speedforce ones, not fit and any custom solution an awkward item to fab and design.

Really unusual pressure readings you got on your turbine inlet to boost ratio, normally I find they are much higher, are you sure you were getting a true pressure reading from the turbine inlet and not a venturi or other gasflow effect which may have been giving a false reading?

I would be interested in knowing a bit more about your engine, turbo, crossover and engine management details as it might shine some light on your findings of higher EGT's not helping spool up as well as why you might have the exhaust turbine inlet to boost ratio you have.

What kind of rpm do you manage to achieve full boost at and in what gear and what boost level?

 

[TTM]

These are pretty normal backpressure readings for a Garrett GT turbine.
Some other folks who also have removed most of the restriction in their much-modified engines have also noticed little to zero gain by reducing timing to improve spool - things change quite radically when you upgrade the turbine's breathing ability.

Most of my engine is discussed here. Check the last 10 pages or abouts.

 

[gajh]

Hi Jon, have I understood it correctly that my setup where I have the Tial with the pipe from the cross over going into the side of the waste gate and the bottom of the wastegate going to the exhaust is how you recommended it be setup with a MBC.

Gavin

 

[Indi9xx]

ORIGINAL: TTM

These are pretty normal backpressure readings for a Garrett GT turbine.
Some other folks who also have removed most of the restriction in their much-modified engines have also noticed little to zero gain by reducing timing to improve spool - things change quite radically when you upgrade the turbine's breathing ability.

Most of my engine is discussed here. Check the last 10 pages or abouts.

I will have to sit down and have a good read of your engine thread this evening, but it sounds like you are running a modified crossover and a non KKK hot side, so it is less amazing your are not getting the back pressure in the crossover which causes the sloping boost curve experienced by MBC's and Dual port wastegates, or even the challenges to holding boost completely and getting great spool up on a more typical install.

The thermal efficiency of the GT hot sides (housings and turbines) is an improvement over even Garrett wheels in modified KKK housings, but a lot of people do not want to go through the effort or expense of a modified or replacement crossover with using the GT hot side, or the replacement mount and oil drain of the whole GT series turbocharger.. Which is a shame, but everyone has their limits. Well done to you for going further.

 

[Indi9xx]

ORIGINAL: gajh

Hi Jon, have I understood it correctly that my setup where I have the Tial with the pipe from the cross over going into the side of the waste gate and the bottom of the wastegate going to the exhaust is how you recommended it be setup with a MBC.

Gavin

Thats how we do it, we also make some modifications to the wastegate as well as has been mentioned elsewhere, but for mounting it I would recommend another modification to anyone fitting a TiAL in either orientation.

Make sure you do not have threads in both the TiAL flanges and the same holes in the adapters.

It is a schoolboy error that many people make, which is one of the reasons some people have seen them coming free.. If you have a thread on the same bolt hole in the Tial's body flange and the adapter, you end up with a wastegate which can work loose or leak, as you will never be able to clamp down the body to the adapter as the threads will be synchronised.

Make this modification and you should not need lockwire and the wastegate will not work loose or leak, even without the torque tube mount of the original wastegate.

 

[gajh]

Thanks Jon nice to know mine is correct and all ok. []

ORIGINAL: Indi9xx

ORIGINAL: gajh

Hi Jon, have I understood it correctly that my setup where I have the Tial with the pipe from the cross over going into the side of the waste gate and the bottom of the wastegate going to the exhaust is how you recommended it be setup with a MBC.

Gavin

Thats how we do it, we also make some modifications to the wastegate as well as has been mentioned elsewhere, but for mounting it I would recommend another modification to anyone fitting a TiAL in either orientation.

Make sure you do not have threads in both the TiAL flanges and the same holes in the adapters.

It is a schoolboy error that many people make, which is one of the reasons some people have seen them coming free.. If you have a thread on the same bolt hole in the Tial's body flange and the adapter, you end up with a wastegate which can work loose or leak, as you will never be able to clamp down the body to the adapter as the threads will be synchronised.

Make this modification and you should not need lockwire and the wastegate will not work loose or leak, even without the torque tube mount of the original wastegate.