XR6-T Torque Limiter (Actual Workings) - Ford Forums - Mustang Forum, Ford Trucks, Ford Focus and Ford Cars

XR_Strider_GuY · 05-18-2003, 19:07

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.

Aussie Pete · 05-18-2003, 20:13

It's called a wastegate Strider. Come on, surely you know about this stuff?

XR_Strider_GuY · 05-18-2003, 20:28

Quote:

Originally posted by Aussie Pete
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.

PURSUTE · 05-19-2003, 15:00

Quote:

Originally posted by XR_Strider_GuY
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).

Aussie Pete · 05-19-2003, 16:45

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?

PURSUTE · 05-19-2003, 17:21

Quote:

....Ford engine running 48psi boost....

Holy C**P!!!! You could pump your tyres up with that!

FordTech65 · 05-19-2003, 17:29

Quote:

Originally posted by XR_Strider_GuY

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.

Unigroup · 05-19-2003, 22:20

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.

FordTech65 · 05-20-2003, 01:30

Quote:

Originally posted by Unigroup
Good theory but in practice the turbo engine holds 5psi from boost up till engine cut out .

So what stops the boost going higher than this??

EATURBO · 05-20-2003, 05:44

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