Discussion
marcevo1 said:
anyone got any experience of to dump to atmo oposed to re circ type?
want a quick open close at low preasure for the charger (so will need a light spring?) - any ideas - its got a bosch style recirc plastic type on it at the moment.
marc
want a quick open close at low preasure for the charger (so will need a light spring?) - any ideas - its got a bosch style recirc plastic type on it at the moment.
marc
Best way to detune a turbo / supercharged engine is to fit a dump valve. Not used on competition engines despite ads for 'Group A Dump Valves' (Rally cars use total recirculation with 'pop-off' valves to get rid of excess pressure, the 'flutter' you hear from circuit engines often called 'wastegate chatter' is in fact the compressor stalling, the noise is the air bouncing off the blades after its bounced off a closed butterfly. This is the noise Max power types try to recreate with dump valves), stick to your OE recirculation system.
Edited by Paul-C on Friday 6th October 00:28
Paul-C said:
the 'flutter' you hear from circuit engines often called 'wastegate chatter' is in fact the compressor stalling, the noise is the air bouncing off the blades after its bounced off a closed butterfly.
I saw this posted the other day, and didn't entirely agree then - now i see the same answer again.
I agree that the sound you hear, that everyone calls the "wastegate chatter" is incorrect, but then again the reason for a dump valve (be it atmos or recirc) is to relieve the pressure between compressor and the throttle plate TO PREVENT compressor stall - which slows it down and in certain cases damage it.
eliot said:
Paul-C said:
the 'flutter' you hear from circuit engines often called 'wastegate chatter' is in fact the compressor stalling, the noise is the air bouncing off the blades after its bounced off a closed butterfly.
I saw this posted the other day, and didn't entirely agree then - now i see the same answer again.
I agree that the sound you hear, that everyone calls the "wastegate chatter" is incorrect, but then again the reason for a dump valve (be it atmos or recirc) is to relieve the pressure between compressor and the throttle plate TO PREVENT compressor stall - which slows it down and in certain cases damage it.
An emergency 'pop-off' or vent valve in a recirculation system, full recirculation or partial, is used to bleed off excess pressure which would cause cause damage or excessive stalling. A degree of stalling occurs prior to this being vented off, hence the noise.
Edited by Paul-C on Friday 6th October 15:52
most comp cars have a really strong spring/piston in the re circ dump valve - which causes the stalling of the turbine.
obviously comp cars require as much boost to remain - a weak spring allows leakage over prolonged use. But obviously rally cars turbos are throw away items (ever tried an anti lag system on a road car! - expensive rebuilds!) This happened with my old 'grale when the piston stuck - great noise but unchecked could have ripped the turbo apart! 10,000 rpm to 0 in a fraction of a second :-(
reason for original question was i had heard that a dump to atmo may be faster to respond to low pressures?
what does all the other charger owners have?
obviously comp cars require as much boost to remain - a weak spring allows leakage over prolonged use. But obviously rally cars turbos are throw away items (ever tried an anti lag system on a road car! - expensive rebuilds!) This happened with my old 'grale when the piston stuck - great noise but unchecked could have ripped the turbo apart! 10,000 rpm to 0 in a fraction of a second :-(
reason for original question was i had heard that a dump to atmo may be faster to respond to low pressures?
what does all the other charger owners have?
I think you need to elaborate on what you are using it for.....
And if its a MAF based system, dumping to atmos is not reccomended, as it will mess with the airflow meter readings. Wont do any real harm though.
As Paul says, the flutter noise you hear is air backing up in the system. Although I wouldnt agree that its quite as damaging to the turbo as he might make out.
Ive run both setups over the years, and never had any turbo issues I would put down to lack of a dump valve.
But generally, if a DV is fitted, the car can run smoother and better at part throttle, on/off throttle etc.
As for spring tension...different setups will need different amounts. If you have excessive pressure, then you will hear a flutter, and a whoosh, depending on how fast ( or how much air it cah shift ) the DV operates.
Design also comes into it.
I use 2 Greddy BOV's on mine, venting to atmos. But in a SC car, having the ability to vent sufficient air on closed throttle is vital, as turbo stall cannot happen. The blower will continue to pump air regardless of what your right foot is doing..
And if its a MAF based system, dumping to atmos is not reccomended, as it will mess with the airflow meter readings. Wont do any real harm though.
As Paul says, the flutter noise you hear is air backing up in the system. Although I wouldnt agree that its quite as damaging to the turbo as he might make out.
Ive run both setups over the years, and never had any turbo issues I would put down to lack of a dump valve.
But generally, if a DV is fitted, the car can run smoother and better at part throttle, on/off throttle etc.
As for spring tension...different setups will need different amounts. If you have excessive pressure, then you will hear a flutter, and a whoosh, depending on how fast ( or how much air it cah shift ) the DV operates.
Design also comes into it.
I use 2 Greddy BOV's on mine, venting to atmos. But in a SC car, having the ability to vent sufficient air on closed throttle is vital, as turbo stall cannot happen. The blower will continue to pump air regardless of what your right foot is doing..
V8HSV said:
I only hear air being dumped when I come off the throttle voilently or full bore gear changes
If you hear a fluttering noise....you need to sort it out. That air needs somewhere to escape !!!!!
Otherwise its putting a lot of strain on the supercharger, and its belt drive setup.
stevieturbo said:
V8HSV said:
I only hear air being dumped when I come off the throttle voilently or full bore gear changes
If you hear a fluttering noise....you need to sort it out. That air needs somewhere to escape !!!!!
Otherwise its putting a lot of strain on the supercharger, and its belt drive setup.
Belt drive currently, no fluttering sounds, just a release of air, could not be heard normally as the valves had a metre of tubing from them to quiten the release. belt drive & 12-15 psi being considered currently.
Boost pressure in the inlet manifold means nothing.
Blower size and rpm are everything.
If you shut the throttle at 6000rpm. Doesnt matter one bit what boost you were seeing in the intake manifold, but now have xxxx cfm of air, and it needs somewhere to go. Immediately.
The engine is still rotation, albeit slowing down, but the blower is still pumping a serious amount of air.
If the air doesnt have somewhere to go ( ie out the DV/BOV ) then it will try and go back out through the blower, putting obvious strain on it, and its drive.
If you dont hear any strange fluttering noises, then you should be fine.
Might be worth sticking a boost guage on the intake pipe before the TB, just to see what sort of boost spikes occur on a closed throttle
Blower size and rpm are everything.
If you shut the throttle at 6000rpm. Doesnt matter one bit what boost you were seeing in the intake manifold, but now have xxxx cfm of air, and it needs somewhere to go. Immediately.
The engine is still rotation, albeit slowing down, but the blower is still pumping a serious amount of air.
If the air doesnt have somewhere to go ( ie out the DV/BOV ) then it will try and go back out through the blower, putting obvious strain on it, and its drive.
If you dont hear any strange fluttering noises, then you should be fine.
Might be worth sticking a boost guage on the intake pipe before the TB, just to see what sort of boost spikes occur on a closed throttle
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