Has anyone gone from 60 mm TB BACK to stock?

[johnc]

John, forgive me if this is a stupid question, but that cam doesn't look eccentric. How would it help?

 

It is. The cable runs down inside the groove on a progressive cam.

[Tony D]

The stock linkage gives the pedal much less authority at the beginning of the travel and much more authority as the throttle is opened more.

 

I am quite fond of how it works.

 

When using the same articulation of the linkage, I notice no difference in response between the 50 and the 60.

 

 

You might be suffereing form Diabetic Nuropathy...If you can't tell the tip-in characteristics are different from a 50 and 60mm T/B using stock linkage. There is most definately a change. It's what all the butt-dyno experts attribute as 'horsepower increase' after installing the 60mm.

 

But this is straying from the OP's issue of on-boost modulation which is a VERY sensitive subject compared to ANY N/A car. A larger T/B will make the tip-in touchy and more power will exacerbate this. If you can feel it in a stocker with 140HP, it's worse on a turbo car with 300+!

[col]

Why not have the electric boost controller connected through MS to the TPS. That allows you to program in how much boost against throttle. Say half boost at lower throttle grading up as throttle goes up. With this system you will still get boost just as quick if you mash the peddal.

[Zmanco]

MS controls boost by reducing the pressure applied to the wastegate actuator, thus causing it to open at a higher boost level. It cannot cause the waste gate to open at a lower pressure than the internal spring provides.

[col]

But if you use a softer spring you can use the MS to control It . So it will want to open at say half your desired boost at low tps , then as tps goes up the bleed changes the curve.

Or do I have something wrong, Quite possible!

[Zmanco]

If it was an external wastegate, then I could change the spring. But it's an internal wastegate with an enclosed (not sure how else to describe it) actuator. The spring is inside it and it's all sealed up. I cannot set it at less than 8 psi unless I change actuators, and I haven't seen any that will fit on a T3/T4 hybrid (needs a bent arm).

 

I'd be thrilled if someone could show me an affordable 4 psi actuator

[Bernardd]

If it was an external wastegate, then I could change the spring. But it's an internal wastegate with an enclosed (not sure how else to describe it) actuator. The spring is inside it and it's all sealed up. I cannot set it at less than 8 psi unless I change actuators, and I haven't seen any that will fit on a T3/T4 hybrid (needs a bent arm).

 

I'd be thrilled if someone could show me an affordable 4 psi actuator

 

Lengthen the arm on the actuator. Buy a turnbuckle and get it welded onto the arm and adjust to desired boost level. I've got one in the garage at the farm that can be set to 0psi.

[Zmanco]

Lengthen the arm on the actuator. Buy a turnbuckle and get it welded onto the arm and adjust to desired boost level. I've got one in the garage at the farm that can be set to 0psi.

 

You must have a different type than I do. The minimum force to move the actuator correlates to about 8 psi of boost. I can't see inside it but I'm guessing the spring is already compressed. Lengthening the arm just causes the wastegate to leak.

[Tony D]

There are controllers which are rpm sensitive, but this sidesteps the proper control of the turbo: keep it's wheel at proper tip speed (near maximum rpms) and bleed off excess flow during periods of low throttle opening to avoid minimum flow surge.

 

Arguably the latter is FAR more responsive to a sudden WOT demand (such as seeing the corner exit and having all things hooked up and ready to go straight down the road...) than anything that OPENS the wastegate to slow down the turbo to make it have less boost.

 

Keeping a turbo at a constant fixed speed and blowing boost overboard may sound strange to people, but this is what they did on Indy Cars for years to keep manifold pressure constant at 47 inches of mercury no matter what the throttle position. Instant N/A like response, but with MUCH MORE horsepower from the engine.

 

Using a wastegate is not the same solution, and goes about it totally differently.

[col]

For racing on a track , or driving on a road for that matter, I feel it better to relate boost to tps. That way you have it both ways, power modulation at part throttle and quick to full boost at full throttle. I think you could use the bleed system with tps, maybe that would be better. As you put the foot down it would be there instantly, in proportion to tps ,no lag. But I don't think at high revs , when already bypassing gas through the gate, there would be that much difference. Using the gate is simple and uses what is already on the car.

[johnc]

Arguably the latter is FAR more responsive to a sudden WOT demand (such as seeing the corner exit and having all things hooked up and ready to go straight down the road...) than anything that OPENS the wastegate to slow down the turbo to make it have less boost.

 

An aside here: if you're waiting to see the corner exit before squeezing the power down your car is either an ill handling pig or you're still learning how to drive...

[Tony D]

Ill handling pig... Lighting up 265's and looping it doesn't look good at the AutoX.

This was not an issue at Willow Springs, though. Then power could be applied and the car actually pushed to the outside of the track, scary fast.

 

Actually though, I was equating it to the 917's. The driver would have to flatfoot it somewhere in the corner due to turbo lag, and in one's words: "Pray like hell you were pointed straight down Mulsanne when the boost hit."

 

This is the kind of reaction you will ALWAYS have by connecting WASTEGATE to anything (like TPS). That is CONVENTIONAL wisdom. NEXT GENERATION wisdom (or, if you prefer, mid 80's wisdom and not 1960's wisdom) is to control excess flow off the turbine by dumping overboard and keeping the Turbine at peak efficiency.

 

By regulating boost by a WASTEGATE on the turbine side, you change the speed, and therefore the response characteristics of the turbo (see the post from the guy in Trinidad in the turbo section). If you instead optimize the wastegate control to STABILIZE turbine speed at optimum for the flow point (peak efficiency) of the turbo, and then dump excess flow overboard via BOV modulation, you get a turbo which is ALWAYS at speed, and ALWAYS has 100% airflow available. The ONLY thing that will influence the response of the boost coming on is the closing or opening rate of the compressor bypass (BOV).

 

What you do with this control scenario is divorce the variables. By making the Turbo in essence a fixed speed operation, the curve only moves horizontally on the chart at any given pressure, as opposed to vertically AND horizontally when wastegate controlled.

 

Wastegate control changes TWO variables at the same time. When you try to control TWO variables at the same time the control scenario (read all these 'fuzzy logic' controllers and 'predictive' controllers out there) is unecessarily complex. If you set the wastegate to control to a set RPM for instance, you nail what your compressure surge point will be. It will be on a two axis chart. With wastegate control your surge line is a three-axis variable and control against that kind of curve will be far more difficult.

 

The theoretical TPS control will ALWAYS induce lag into the system because it changes flow by varying speed of the turbine. (And moving the surge line around.) The most efficient form of control would be to fix the speed within a reasonable limit and then dump flow. This is standard industry wide in process compressors. Quickly opening and closing inlet valves induce surges to otherwise stable processes when interruptions in flow occur. When the cecntrifugal compressor is operating with full flow through it, and the only variable is NATURAL surge as opposed to Suction Throttle Surge, the incidence of surging is dramatically reduced. This would be the excess flow venting proposal. Suction Surge (throttled surge) will not be an issue as the venting always accomodates the fixed surge line at that speed or mass flow area.

 

Now, if you are relating boost to tps, meaning changing boost LEVEL so that it's lower at lower throttle openings for easier modulation, it is more efficient to AGAIN vent excess pressure and lower it that way than by slowing down the turbine speed to produce less pressure. This makes for even MORE lag as you drop pressure from say 17 to 8 and then must walk the surge line back up to 17 as the throttle opens. Back to a three axis surge line chasing instead of 2 axis.

Edited June 9, 2010 by Tony D

[Zmanco]

I know we've left the world of passenger cars driven on the street now ... but I'm curious how the turbo is kept spinning at its optimum speed in the scenario you describe Tony? It seems to me that the ECU would need to maintain some minimum throttle position when the driver lifts off the gas far beyond what we normally know as idle in order for the engine to still expel enough exhaust to keep the turbo spinning.

Edited June 9, 2010 by Zmanco

[Tony D]

"As best it can"

 

Obviously when the car is totally drop-throttled the exhaust energy drops considerably.

 

But with a modulated vent on the intake tract, the wastegate is closed far faster keeping turbine speeds up further than they would be in conventional wastegate control scenarios.

 

If you were to have flat-shift capability in the ECU, then fuel enrichment and ignition retard would add fire to the turbo and keep it spooled as an external combustion turbine. You can get full boost at idle if you play with it (megasquirt) enough. You can also melt the brazing on your oil feed line and make your paint on the firewall blister due to the excess heat in the turbo....

 

But we aren't discussing total drop-throttle, we are discussing modulation above boost threshold. In this case there may or may not be a requirement to vent the wastegate and divert exhaust gas. On modulation (partial throttle) it's simply a matter of controlling the wastegate more from a turbo tachometer for constant speed than referencing a crude boost signal. The control of the turbine speed is then a VERY simple matter of a direct tachometer to wastegate position. The curcuitry is relatively simple, you could even use a stepper motor to control it (like the VNT's use a PWM circuitry to alter nozzle position)...

 

Which brings us to modern diesels. The VNT turbos with the PWM control are doing more to speed the turbo to optimum speed FIRST, then using the VNT to keep it there WITHOUT having to activate a wastegate (there is a reason it's called a WASTEgate---you are throwing free recoverable energy away...) Once at optimum speed, then boost control becomes part of the control loop.

 

The possibilities are endless. Ideally you would have a VNT to alter the A/R of the turbine from the smallest possible turbine to drive the compressor, with a Wastegate for high rpms (if the VNT was not capable of enough A/R change) and a vent on the intake side. This would all be ELECTRONIC CONTROL with no pneumatic requirements for motive force. Right now most of the stuff uses boost to control actuators. Take that requirement out of the system and the control possibilities expand quite a bit.

 

Time for lunch, my cohort will likely get cranky if he doesn't get fed soon. TTFN!

[Bernardd]

 

You must have a different type than I do. The minimum force to move the actuator correlates to about 8 psi of boost. I can't see inside it but I'm guessing the spring is already compressed. Lengthening the arm just causes the wastegate to leak.

 

You'll have no problems setting the boost to 4psi by lengthening the arm on a stock 280zxt turbo actuator. The stock actuator spring tension is increased when the arm is installed onto the wastegate arm on the turbine housing. If you have to pull the actuator arm out a bit to install it onto the turbo you should have enough to do the same with your wastegate. Hope that makes sense. Usually an internal wastegate starts moving well before the set pressure.

Edited June 9, 2010 by Bernardd

[Tony D]

Usually an internal wastegate starts moving well before the set pressure.

 

And this is precisely why they are so prone to poor response characteristics when compared to the alternative scenario I have been discussing.

 

If you had PWM Variation of the Nozzle (or hell, the wastegate for that matter) to allow for control of speed of the turbo for maximum efficiency, then controlling ultimate pressure via a simple dump overboard on the intake side is a piece of cake.

 

The difference in the control scenarios is you are in one case (Wastegate) taking motive force and varying it's input, which will always have to overcome rotational inertia of the wheel to come back up to speed, etc...

 

When you work on compressed air flow blowoff, you are working with product, and not motive force. Much easier to control, and slightly more efficient in the 'modulation' scenario. Off-boost performance would also be slightly better as the blowoff would act as a bypass valve keeping load off the turbo in N/A running (allowing a quicker spool), as well as keeping the wastegate completely closed until AFTER peak efficiency speed of the turbo has been reached. Then, and only then should speed on the motive force end of the equation be regulated. Overspeeding shouldn't be an issue with that scenario. Having proper 'fail open' or 'fail closed' logic on the valves would give a limp home N/A mode as well, instead of the typical blown diaphragm overboost till it blows scenario inherent in most Wastegate only control scenarios.

[col]

If you want to get into a lengthy development needing mods in the system [i don't think venting blow off would be enough] your pressure bleed would work well. The wastegate method only needs MS tuning and a softer spring. I still don't think lag would be a problem [ not instant like your system but ]. With the engine at racing rpm bypassing a heap of exhaust then slaming the wastegate shut should bring boost on verry quickly. Both systems should work fine in practice.

 

Also you seem to think surge will be a problem if I read right. I don't think so, to my knowledge surge happens when the exhaust is not producing enough torque through to the compressor to pump to cope with the flow-pressure on the inlet side. If the car does not surge with a normal waste gate set up, it should not do so with this system. There should be more exhaust available than comming from idle at WOT.

Edited June 9, 2010 by col

[Tony D]

If you want to get into a lengthy development needing mods in the system [i don't think venting blow off would be enough] Curious -- it works all over the world, as well as in the aforementioned racing series. Exactly why don't you think bleeding flow will 'be enough'? What is your logical basis for this other than 'thinking' this or that?your pressure bleed would work well.It does, as stated, all over the world. Why are you stuck using 1960's control scenarios which are inherently inefficient. They work "good enough" but are NOT by any means the optimal way of controlling a hot-side turbine driving a compressor. BLEED AIR is the standard in aircraft engines with motive force control for STATIC COMPRESSOR SPEED. When's the last time you saw a 'wastegate' on a jet engine? Same theory at work, good engineering looks for alternative solutions which are applicable. These systems are available now and in use. It is only a matter of time before they become commonplace offerings in the aftermarket. Some OEMS are incorporating this type of control now. Ever wonder why? The wastegate method only needs MS tuning and a softer spring.Really? "Only" needs it to return an inferior control method. You have ignored the inherent disadvantage of wastegate-only control. You continue to ignore the inherent shortcomings of wastegate-only control. Trying to explain it further is probably useless, but one more time... Though I can't convince someone who is totally ignoring facts being presented and just repeating 'I think, I think, I think'. Damn dude what PROOF do you have that this is the way it will work---you are radically altering boost via TPS in phase?---ADDING tip in modulation exacerbation! Do you know what control hysterisis is? Modulation works with a CONSTANT power output. You are varying power (boost) output as you're engaging in TPS Based modulation. This will add MORE reaction time to tune out, can't you SEE that? My 'proposal' at least there are people using that scenario to great effect in both competition and street cars. I still don't think lag would be a problem [ not instant like your system but ].BUT WHAT!?!? You don't 'THINK' lag will be a problem, but then ADMIT it will NOT likely be as responsive as the alternative. Think more.You are adding lag by various methods of control. With the engine at racing rpm bypassing a heap of exhaust then slaming the wastegate shut should bring boost on verry quickly. Both systems should work fine in practice. Here we go again talking about things not being discussed. We are talking about MODULATION i.e. PARTIAL THROTTLE movements. Nevertheless, taking your example your proposed solution will have MOTIVE FORCE LAG through frictional losses and inertial lags to get the wheel up to speed. With a venting blowoff system, the wheel is ALREADY at speed (so you loose that lag), and the intake system is already at FULL BOOST (so you loose that lag for repressuirzation) and additionally you can now program HOW the boost 'comes on' --- TOTALLY programmable via simple PID loops on a valve controlling overboard dump.

 

Also you seem to think surge will be a problem if I read right. I don't think so, to my knowledge surge happens when the exhaust is not producing enough torque through to the compressor to pump to cope with the flow-pressure on the inlet side.Your understanding is wrong. Think more, what you describe is 'slip' and a different phenomenon. If you don't understand the basics of the dynamics of turbocompression, do you really 'think' your suppositions will work in real life? Sometimes problems will arise you didn't 'think' would, and it's usually from misunderstanding how things work while engaged in the front end of the engineering process. Read the sticky in the turbo section about 'what is surge' and get the basic primer down. What your 'understanding' is leads you astray. If the car does not surge with a normal waste gate set up, it should not do so with this system. Again, incomplete knowledge. Read the sticky. There are several scenarios which will precipitate surge. You may not hear it, but it is happening. And when it does flow is interrupted. I will warrant that a wastegate control will induce a surge through underspeed situation and the flow dropping down and to the left on the compressor map. I could show you this on a chart, centrifugal compressors surge on startup, they surge on shutdown. All due to operating outside set wheel tip speed parameters. Point here being the turbo IS surging with a wastegate setup, and WILL ALWAYS surge with only crude wheel-speed control. IT IS INEVITABLE. The ONLY way to stop a centrifugal compressor from surging is to control it's pressure via an overboard dump (referred to as an 'unloading valve' in the industry.) Where is that 'unloading valve' in an automotive system? The BOV? What controls it but crude pressure and preset springs? With those SET parameters, the compressor WILL cross the surge point while spooling up and down. There should be more exhaust available than comming from idle at WOT. This is a non-starter, but makes assumptions which gloss over so many nuances of proper centrifugal compressor control that it's not funny.

[Tony D]

One of the primary advantages of a overboard controlled flow dump is that a situation like is occurring on Big Phil's GT35R could be tuned around. A MIDRANGE RPM surge situation would be eliminated and the car could launch at a HIGHER boost pressure due to not coming to a minimum-flow situation at midrange rpms.

 

The overboard modulation will solve 'improperly applied' oversized turbocharger issues with these very aggravating midrange (not racing speed) surge issues.

 

Like I previously posted, the implementation of a two-phase control of the turbo would allow running the smallest turbine wheel coupled to the largest compressor it could turn (on the ragged edge of slip ratios) and have extrordinary low-speed boost response (full boost off-idle) while allowing for much higher horsepower levels at the upper range of the engine's RPM range. It makes a turbocharger effectively a supercharger in response, still with the advantage of 'being able to be shut off' during cruise for economy.

 

I have run a system that would deliver 17psi at 1700 rpms (actually the natural surge point was 21psi...and it would reach that by 2000rpms!) and it's not your typical turbo non-linear power delivery setup. The disadvantage was the compressor was small (hence the relatively low natural surge point) if this proposed system was available then, I could have upsized the compressor accordingly, and made considerably more horsepower under the curve---and a BIG curve it was, running from 1700 to 5500. That would have been extendable to 7000 rpms easily, and probably 25psi of boost at 1700 rpms.

 

It simply was not possible with wastegate only-control, as had I installed a larger compressor then, I would have run into EXACTLY the same midrange surge that Big Phil has on his car. Turbo fine for high end power, but way too much compressor for down low.

 

What you are missing col, is that my proposed system allows MIDRANGE boost at much greater levels than a simple wastegate-only control scenario. Speed doesn't come from lowering the boost at partial throttle, it comes from sticky tires, grip, and maintaining that higher boost level through the midrange. This system is engineered for midrange performance, the wastegate will only ever work at racing speeds, and then only be crudely, partially effective.

[rayaapp2]

Just another thought on the eccentric throttle cam: The Infiniti Q45 90mm throttle body has a similar setup. The cam is not eccentric, but the cam does not directly drive the throttle shaft. It is connected to a a linkage with a roller that rides in a curved groove. The curved grove gives the eccentric motion. Its been a month or so sine I looked at one, but it may be fitted to other nissan throttle bodies.