blow off or dump?

[TonyN]

as fun as this, you're missing some important facts.

Basics...

Wastegates control boost pressure, BOV's control turbo lag and turbo wear.

On to the topic

1/ Surfs have a throttle plate, to make the EGR work, so shutting the throttle will produce compressor surge so a BOV should 'work' (ie make farty noises) IN THEORY. but still not much intake vacuum.

BUT......

2/ At a Surfs boost pressure you'll never notice it

FINALLY...

3/ try and increase boost pressure and turbine speeds to justify a BOV and the ECU will laugh at you and throw fault lights.

Leave it for the boy racers.

I'd guess ditching the throttle butterflys and EGR gives far more performance

[Calos]

Truth of the matter is, you can go for longer with out a blow off than you can with out a dump.

Even if you think you need the former more.

peace
cal

[Albannach]

And do you know how much 10 PSI actually feels? thats a lot of pressure to be pushing on a turbo at 200,000 RPMs.

Oh! Oh! I know this one...

[surfenstein]

And do you know how much 10 PSI actually feels? thats a lot of pressure to be pushing on a turbo at 200,000 RPMs.

youve completly lost me there,how does the pressure PUSH on the turbo.?


Blow-off valves are also known as pressure release valves. They are found in turbocharged engines. They are pressure release devices that emit turbo pressure after their throttle plate has been closed. At that time, the turbo continues spinning and keeps up the pressure. The air is forced, and then reaches the throttle plate. Then, the air returns to its original place.
When a blow-off valve detects a vacuum from either the inlet or intake manifold (engine component that provides air/fuel blend to the cylinders), it results in either the valve becoming softer or opening up. This allows the pressure to leave the opening. For proper functioning, the air must return to the intake before the turbo does, because the engine's Air Flow Meter is then aware of its existence. If this does not happen, the engine will have a brief condition of richness that will slightly bother the idle. However, this situation can be avoided with proper and frequent tuning. If the blow-off valve has any tiny holes or vents, it will result in the air creating a high, loud sound in many cases.
The blow-off valve basically is a device that is based around a vacuum. It is created to emit pressure in a turbocharged car engine's intake system (when the throttle is either closed up or lifted). Then, the air pressure goes into a circle and moves back into the part of the intake (before the turbo does) that isn't undergoing any pressure. However, it returns after the mass airflow sensor device does. This sensor is used for stopping compressor surge.
Compressor surge occurs when a throttle (of a turbocharged vehicle) has been lifted. Then, when the plate of the throttle closes up, the intake system's increased pressure doesn't have anywhere to move to. It is then forced to go back to the turbocharger as a wave of pressure. This causes the wheel to quickly slow down and ultimately, stall. An erratic airy sound will then be audible in the vehicle.

[surfenstein]

A dump valve,also commonly referred to as a blow-off valve, diverter valve or compressor bypass,is a pressure release valve that allows air to escape from the equipment that connects the turbocharger on a vehicle to the throttle
The purpose of installing a dump valve can be one, or a few, of many things. The primary functions that dump valves accomplish are making an often desired noise,unique to turbocharged vehicles as air releases, allowing air to escape without backtracking through the airflow chambers, eliminating rattling in the turbocharger caused by backward airflow, increased fuel economy and lowered emissions.
Research has not been conclusive as to whether dump valves increase the life of a turbocharger, but many believe that the elimination of rattling caused by backward airflow can prolong the life of equipment.
Dump valves are actuated piston valves that rely on vacuum and pressure signals to open and close. When an engine is idling or cruising, there is equal pressure on both sides of the valve, meaning there is no need for pressure to be released. To ensure the piston keeps the valve closed at idle, a spring applies pressure to the mechanism.
The amount of pressure necessary can vary slightly with elevation and the specifications of the dump valve, so it is important that it is calibrated so just enough pressure is applied to keep the valve closed at idle. If the valve is open unnecessarily, the car will be subject to stalling and flooding.
When the throttle is opened to accelerate, boost pressure is created, which flows over both sides of the valve. When the throttle is once again closed, however, a vacuum is created, which opens the valve and rapidly releases the pressure before it closes again.

[Ptarmigan]

Hi guys,

If I can sidestep the humerous and hissy fit bits of this thread I was really interested to find out that the diesel surfs could/do have a throttle butterfly. I had often pondered (during those all important post-barbeque ice-cold beer moments) if there was any point in having a recirculating dump valve on a diesel to reduce turbo lag, as I had fitted an uprated one once to my turbo petrol car.

After much steak and beer I had concluded that probably, as a diesel runs at full open throttle (I always thought my 3L diesel had no butterfly valve), there would be no need for a dump valve since inlet presure should be a function of turbo boost and engine RPM, not of accelerator position. I assumed a wastegate would still be required since it performs an equally important but different task.

So now, given that my 3L engine has an aftermarket turbo, no ECU and actually I have no idea what boost the wastegate is set to, should I entertain the notion of adding a dump valve (i.e could it actually have some small advantage, even if it is rather too small to care about really).

Cheers,
Jon
=====================

as fun as this, you're missing some important facts.

Basics...

Wastegates control boost pressure, BOV's control turbo lag and turbo wear.

On to the topic

1/ Surfs have a throttle plate, to make the EGR work, so shutting the throttle will produce compressor surge so a BOV should 'work' (ie make farty noises) IN THEORY. but still not much intake vacuum.

BUT......

2/ At a Surfs boost pressure you'll never notice it

FINALLY...

3/ try and increase boost pressure and turbine speeds to justify a BOV and the ECU will laugh at you and throw fault lights.

Leave it for the boy racers.

I'd guess ditching the throttle butterflys and EGR gives far more performance

[TonyN]

I think only Jap Surfs have a throttle butterfly, UK 4Runners and pickups don't, cos they didn't have a EGR system, I'd assume the rest of the world is the same.

The throttle was fitted to make the EGR system work, so you will be getting some intake vacuum when its shut, so in theory a working BOV is feasable, but really not sure its worth it, or noticable TBH.