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XR6-T Torque Limiter (Actual Workings)

5K views 13 replies 6 participants last post by  XR_Strider_GuY 
#1 ·
Ok i now know the theory of how this 450Nm torque limiter is achieved on the XR6-T.

A maximum boost of 6psi is achieved at "i think" 3000rpm and for every 1000 rpm there after the boost drops a certain amount say 1psi. So by the the time redline is reached the boost tails of to almost nothing.
Now from the seat of your pants, this makes the XR6-T behave much like a bigger capacity engine rather than your typical japanese turbo powered cars that tend to have a big top end rush.

What my question is how is the boost at the turbo lowered as the rpm increases?? I mean since the turbo itself is driven by exhaust gas's is there a mechanism that limits the exhaust gas's spinning the turbo, or is there a diaphram on the intake end that restricts air comming into the intake.
 
#2 ·
It's called a wastegate Strider. Come on, surely you know about this stuff?
 
#3 ·
Aussie Pete said:
It's called a wastegate Strider. Come on, surely you know about this stuff?
Yeah mate, i do know how a wastegate works, but i thought it kept the boost at a maximum, so if the maximum is set to say 6psi then waste gate would open to keep it at that boost. Sounds like wate gate is electronic controlled to achieve the de-boosting effect.
 
#4 ·
XR_Strider_GuY said:
Yeah mate, i do know how a wastegate works, but i thought it kept the boost at a maximum, so if the maximum is set to say 6psi then waste gate would open to keep it at that boost. Sounds like wate gate is electronic controlled to achieve the de-boosting effect.
That is exactly how it works. There IS a maximum, but it is dynamic, not static, ie. the maximum boost level changes as the ECU senses differing conditions (RPM, temp etc).
 
#5 ·
The older turbo cars used a pneumatic controlled wastegate. It simply ran a diaphragm that had intake pressure air applied against it. As intake pressure (boost) rose, the diaphragm spring was compressed and the wastegate lever moved to open the wastegate. Whilst that was the theory the reality was that the wastegate opened gradually and in fact was often open before max boost was reached.

Years and years ago (I'm not THAT old) when many of us started playing with EFI Turbo cars we used heavier springs in the wastegate and adjustable wastegate rods to raise boost. This had the effect of raising boost but led to an engine with an on/off power delivery. The otehr option was pneumatic bleed valves to allow air out of the wastegate boost sense line making the wastegate think that the boost pressure was lower than it really was.

The other issue encountered with the above setups was was that boost came on so strong in the midrange that BMEP (cylinder pressures) were extreme and many engines blew up.

So we used a staged bleed system. In many cases up to four bleed solenoids were used that were set to open at varying rpm. This allowed the maximum torque range of the engine to be passed at low boost and then staging of boost pressures to increase as enegine volumetric efficiency decreased. What essentially happened was as revs rose, so did boost. Torque remained almost constant yet with revs rising power was raised dramatically. I saw one Ford engine running 48psi boost this way. I ran 24 in my VL Commodore.

Now of course the ECUs fitted to most cars allow this to happen by programming boost levels into the ECU map. Much simpler, more accurate, and as you see on XR6T it allows a flat torque curve and the ability to create an extremely civil and flexible engine.

Does that answer your question?
 
#7 ·
XR_Strider_GuY said:


What my question is how is the boost at the turbo lowered as the rpm increases?? I mean since the turbo itself is driven by exhaust gas's is there a mechanism that limits the exhaust gas's spinning the turbo, or is there a diaphram on the intake end that restricts air comming into the intake.

The PCM measures the boost pressure using the BP sensor and controls it in relationship to engine load,temperature & RPM.
The wastegate solenoid valve is located behind the battery and is PCM controlled to divert excess pressure as required.
 
#8 ·
Good theory but in practice the turbo engine holds 5psi from boost up till engine cut out as evidenced by many power runs on the dyno. Since boost is constant, the only other way you are going to close down the power is through ignition timing. Although for torque limiting I believe the electronic throttle closes momentarily and boost drops off for that instant, but not for extended periods eg. Over entire rev range.
 
#10 ·
you can control boost through throttle position, so as the boost drops off the throttle is being closed a little to achieve this.I run my car on 20psi but can vary the boost through throttle position.
I dont use this as a method of boost control, i have just noticed it when driving with different throttle openings
 
#11 ·
PURSUTE said:
Holy C**P!!!! You could pump your tyres up with that!
I believe that in qualifying the Sierra Cosworth Group A cars were running up to 60 psi. I know high 40s were a regular thing which was activated by a wheel mounted 'overtake' switch.

I had a very interesting time being a passenger around an industrial area one evening in just such a car. You can see why the rear tyres were always an issue!:hehe:
 
#12 ·
OK, heres a slightly off topic but related question that has always perplexed me.

How does a forced indiction vehicle build up and store vacume for the brakes etc? I assume that the maniforld would have vacume at certain points, but surely much less than a NA motor. Do turbo cars have a vacume tank or something? I have noticed in my ute that it seams to take a lot longer for the vacume that controls the vents inside the car to build up, yet when I put the blower on my AU, it had no effect on this. Weird.
 
#13 ·
They work the same way as normal.The booster supply hose has a one way valve at the booster end and it just scavenges as much vacuum as possible when it can.Also the BA's no longer use vacuum controlled heaters.It's now all electrically operated.
 
#14 ·
Re: Re: XR6-T Torque Limiter (Actual Workings)

FordTech65 said:
The PCM measures the boost pressure using the BP sensor and controls it in relationship to engine load,temperature & RPM.
The wastegate solenoid valve is located behind the battery and is PCM controlled to divert excess pressure as required.
Thanks for the detailed explaination and AP as well. So i think the first easy mod without destroying the engine is to bypass or trick the PCM measurement so the boost does not taper off, so one can get 6psi all the way to redline. After that then boosting to about 9-10psi should be nice for a daily driver.
 
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