Had a curry earlier getting a bit worried :flamed . On a serious note just finished my project, Fitted Garrett T04S, 1600 secondarys, blitz front mount etc....... I had the turbo rebuilt by ATS turbo\'s before fitting, just wondering whether to fit a blow off valve or not, I\'ll only be running 0.8-1.0 of boost so not overkill, There\'s mixed opinions on this but surley the turbo would be fine at the low boost level?
Cheers
I\'m also tempted to loose the dump valve, over on the GTR forums there was a similar thread and it was said that its fine to run without and that there were far too many other things that could fail before the turbo due to stalling. Personally I much prefer turbo stalling/flutter to a dump valve any day.
Agree 100%, I haven\'t had mine on the road yet but it\'s flutterin a gud un on the spot with a good rev, can\'t wait to see what it sounds like on the road!!!!!. It\'s the first car I\'ve driven with an external wastegate, think it\'s going to be a bit anti social... but who give\'s a ****!
Simple really,
If there was no need to have one then Manufacturers would not fit them as standard to production cars cos it would save them money.
I think that your investment should be looked after by having one as it does take the strain off the compressor when throttle is shut.
If you want it to be quieter then plumb it back into the system preturbo.
Regards
Carl
oh no , not this old chestnust again :rollin
I vote no to a dump valve as it hurts performance, do a search on previous threads on the fors and against dump valves
alot of manufaturers didnt actually fit any as standard originally. then they started fitting recirc valves to quiet things down as people want cars to be quiet. you wont have any problems - was running without one on my skyline for a while and no probs at all. infact the turbo was running better as wasnt loosing lots of compressed air! just dont do it if you have a roller-bearing turbo.
Been running without a dump valve for the last two years on a roller bearing turbo no problem at all with it
Quote from: BlitzBoyoh no , not this old chestnust again :rollin
I vote no to a dump valve as it hurts performance, do a search on previous threads on the fors and against dump valves
Hurts performance? Why do all the 8 sec car downunder use them then:Hammer
it does hurt performance, basically becasue you are blasting all the compressed air out of the system into the atmosphere - takes some power to create it using the turbos! :D
I seem to remember a huge thread fors and against dump valves on Ausrotary, also ive seen quite a few drag cars run without as well and they run 6s and 7s,8s, so this argument will never go away
Rally cars run without them as they do many gear changes so time iwould be lost repressurising the intercooler pipes at every gear change if they did run them.
Quote from: 12AHurts performance? Why do all the 8 sec car downunder use them then:Hammer
oooohhh what we have here yes its a 7 second Supra, whats with wrong with this picture?? thats right NO dump valve!
lol! there is no winning, you can run with and without.. wihtout sounds great! :D
for every Drag car that has a dump valve I can show you another that does not have one.
oooooh what we have here another 6 second drag car oooh and guess what NO dump valve
Quote from: BlitzBoyoooohhh what we have here yes its a 7 second Supra, whats with wrong with this picture?? thats right NO dump valve!
...but I bet that turbo has a ported shroud, which is a little like having a dump valve in any case.
Dump valve only releases the excess pressure between throttle and turbo compressor wheel, which prevents slowing down or stalling of the turbine. Without one the compressor wheel loses a lot of speed, so is no longer \'on boost\'.
As far as performance goes - it\'s the difference between spinning up the turbine again after it\'s been slowed/stalled or re pressurizing the pipework between throttle and compressor - there probably isn\'t a lot in it - but depends on pipe lengths and diameters, volume of air in the intercooler and so on.
Certainly for the smaller turbo\'s, the dump valve should be used as you will be causing bearing wear every time you \'let off\' and the turbo won\'t last anywhere near as long. Larger turbo\'s can probably take the punishment.
I think someone should do some tests on various factors with this - and post up the results so that we all know what the pros and cons are.
But are they missing because they "hurt performance"? or because they use extremely short inlet tracts. 468bhp and only 11.39 - i guess you know it all :rolleyes:
on out and out drag cars you don\'t need one cos the gearboxes change with the throttle staying wide open and not having to shut so obviously there is no need.
On road cars though the throttle is shutting all the time so it is better,although as Mark say\'s not essential to have one.
If I have invested in a fancy turbo on a road car,I would have one.On my drag car I would not with the right drag gearbox where the throttle stay\'s wide open between changes, whereasif it was a clutched manual that I have to shut the throttle on shifts then I would still have one.
Regards
Carl
Quote from: 12ABut are they missing because they "hurt performance"? or because they use extremely short inlet tracts. 468bhp and only 11.39 - i guess you know it all :rolleyes:
who said I know it all????, I am just presenting evidence for and against the use of dumpvalves, I believe they hurt performance thats my opnion as I believe time is lost in repressurizing the pipes and its an opnion shared by some pro drag racers but I didnt say all tsccch.
BTW Im sorry my daily street driven FD is slow in your eyes, please share with us your car spec and results attained as it seems by the way you speak you seem to be an expert in the field of Rotaries
But... surely even a manual road can safley run without a dump valve. It would have to take a ton of punishment before the turbo finally gives up. I\'d be intrested to see a comparison of figures with/without.
Quote from: Prof.
Dump valve only releases the excess pressure between throttle and turbo compressor wheel, which prevents slowing down or stalling of the turbine. Without one the compressor wheel loses a lot of speed, so is no longer \'on boost\'.
.
hmmm sounds like a description of a pop off valve, I thought a dump valve releases what ever pressure there was in the pipes on every gear change when on boost
Quote from: Initial-DBut... surely even a manual road can safley run without a dump valve. It would have to take a ton of punishment before the turbo finally gives up. I\'d be intrested to see a comparison of figures with/without.
well the only time I was able to test this when I run with the old Street Port setup and To4R (0.85 BAR) it had a blitz blow off valve installed, went to POD running consitant 12.8s when I disconnected the valve I was running 12.6s and picked up a couple more mph over the line
i just realised, the title of this thread would make a good porn vid name ;)
I remember about 6-7 years ago it was actually COOL to have a dump valve. I had one and I loved it. Now it seems every chav has got one and its a sign that a toss pot is driving down the street. I must admit I have 2 on my FD, any noticeable difference? Not really enough to be sure, I just have it to help prolong turbo life by reducing the chance of compressor stall.
fwiw my opinion..
dump valves whether recirc or vta are designed for 2 reasons
one is to prolong life of turbo(how many people keep a perf car longer than a couple of years and manufactures give 3 year warranty on new cars so do not want claims)
all production cars come with some kind of relief valve mostly recirc
they do prolong life of turbo and only racers will notice any kind of perf gain
second is sound some prefer ppttssshhh some prefer flutter
but just understand that ppttsshh is air leaving the system safely and flutter is approx 15psi upwards of air flowing back over a turbine that is spinning at a trillion times a second too many years of that will create problems
Understand that drag/rally cars etc all have regular strip downs and maintenance unlike your average non sponsored road car
you pays ur money and makes ur choice but i would hesitate buying a non dump valved turbo car for this reason
Ptsssuuuuuuuuuuuuuuuuu Innnnnnnnnnnniiiiiitttttttttttttt M8
By the way I have never discounted the reliabilty aims of recirc and dump valves.
I wouldnt run one purely on performance terms plus as I run a big shaft turbo so its not prone to shaft damage as a small turbo would be.
Anyway the Rotary engine is most likely to pop first then the turbo :rollin
Quote from: rico2k_uki just realised, the title of this thread would make a good porn vid name ;)
:spank :spank :spank :eek:
Quote from: BlitzBoyhmmm sounds like a description of a pop off valve, I thought a dump valve releases what ever pressure there was in the pipes on every gear change when on boost
I`m pretty sure a pop off valve prevents overboosting ie, It senses too much boost so opens releaving the pressure.
The dump valve is as the guy says, stops the pressurised air from bouncing back off a closed throttle butterfly and stalling the turbo by opening and venting the air in the pipes.
On a side note I have 2 brand new SSQV for sale, http://www.mazdarotaryclub.com/forums/showthread.php?t=42450 (http://www.mazdarotaryclub.com/forums/showthread.php?t=42450) :)
I know Ben, Prof described it as venting excess pressure which sounds the same as relieving excess boost pressure as a pop off would do
My Janspeed turbo has an old skool style \'pop off valve\' I dont think you get them on modern cars though, there are far better ways to control boost.
Quote from: benRX7I`m pretty sure a pop off valve prevents overboosting ie, It senses too much boost so opens releaving the pressure.
The dump valve is as the guy says, stops the pressurised air from bouncing back off a closed throttle butterfly and stalling the turbo by opening and venting the air in the pipes.
On a side note I have 2 brand new SSQV for sale, http://www.mazdarotaryclub.com/forums/showthread.php?t=42450 (http://www.mazdarotaryclub.com/forums/showthread.php?t=42450) :)
great plug my man
colum
I run one and still get the turbo stall?? go figure??:Tongue1
Quote from: mx1311great plug my man
colum
Yeah you cant miss these opertunities, lol
Blitzboy, I thought you would have known the difference, just checking
Quote from: BlitzBoyhmmm sounds like a description of a pop off valve, I thought a dump valve releases what ever pressure there was in the pipes on every gear change when on boost
Yeh - bad description wasn\'t it.
I meant to say when throttle plates are closed, and obviously the \'excess\' is whatever the spring in the dump valve allows - so a softer spring would allow more air to be dumped before closing up the valve again. Dump valve is operated by vacuum from the manifold side of the throttle plate - whereas the other valve just lets off excess air.
Actually most dump valves will begin to leak at higher boost pressures in any case - hence the need for a harder spring !
Quote from: G@NDYI run one and still get the turbo stall?? go figure??:Tongue1
What one are you running? If it\'s not got the capacity to get rid of all the compressed air, the remainder of it will still stall the turbo.
just to remind people - turbo stall phrase isnt the classic stall of something stopping - its an aerodynamic term for the air that passes the fins of the turbine becoming more turbulant and pealing off the fins unevenly. the rotation spin of the blades isnt effected as much as you would expect. the sound of the flutter is the air becoming unstable, then stable, then unstable a little bit less, then stable, etc etc.
Ive got the box somewhere, i\'ll have a look. I think it was a FSE one. The descritption said that it can handle 30psi?? might need to change the spring, it did have another one with it.
Quote from: rico2k_ukit does hurt performance, basically becasue you are blasting all the compressed air out of the system into the atmosphere - takes some power to create it using the turbos! :D
But venting to atmosphere reduces turbo stall, in turn when you get back on the gas the turbo has to do less to spool back up to full boost. Just fitted an HKS copy to mine which not only sound excellent but has made the car even less laggy than it was (T78 single) :3gears-rh
no, its the other way around, they work harder to recompress all the air in the system, without the bov, the air is still compressed in teh system when needed so less work is needed.. :)
doesnt matter,you get a big turbo, a little lag difference from bov or no bov wont be noticable! :D
Quote from: rico2k_ukno, its the other way around, they work harder to recompress all the air in the system, without the bov, the air is still compressed in teh system when needed so less work is needed.. :)
doesnt matter,you get a big turbo, a little lag difference from bov or no bov wont be noticable! :D
But all that compressed air is heading back towards your turbo because your throttle is shut, forcing pressure on the turbo to send that air back towards the inlet :Hammer . Anyway no blow off or dump valve is going to vent all the air in the system so so its not going to take long to re-compress.
Quote from: BlitzBoyoh no , not this old chestnust again :rollin
I vote no to a dump valve as it hurts performance, do a search on previous threads on the fors and against dump valves
On the other side of the coin not stakking the compressor means less spool time between shifts. May or may not be a problem depending on rev range, target boost and general laggyness of your setup though.
I quite like the noise of no dump valve - reminds me of WRC cars but I do notice the laggyness if I\'m not fizzing along at higher rpm.
Got any links to the previous discussions on this?
Heres a link for you
http://www.mazdarotaryclub.com/forums/showthread.php?t=19689&page=2&pp=15&highlight=bov
Scroll down to my post and read away!
Regards
Jon
oh god i cant be naffed talking about this anymore :rollin, there is a massive thread on Ausrotary. The turbo still rotates and does not stall when you snap shut the throttle plates, some air gets force back over the blades causing the flutter sound but does not stall the wheel. My own personal experiances has shown less lag between shifts without a BOV but hey thats just mine.
Ask you yourself this question why do WRC cars run without BOVs if it creates lag? and they do thousands of shifts per rally.
Since that old thread I changed my mind and decided not to run one :D
here is another good read, which a lot of skyline owners listened to:
http://www.skylineowners.com/forum/showthread.php?t=63478
Nice find Rico, quoting Nisfan excellant post
"so it does put more stress on the turbo?
Not really. (Here is the medium version, I\'ll leave out the heavy stuff)
Please remember that boost is a consequence of the engine not being able to flow as much air as the turbo, therefore the pressure rises. As it rises the engine can take in more air, as the engine is volume dependant not air mass dependant.
Higher pressure means more mass per cc of air, and that is how the engine gets to take more air fuel into the cylinders, when \'charged\'.
With this in mind, you will see that the turbo is always \'blowing\' against a backpressure, so nothing new there. It was built to handle this operation.
Here\'s a little scenario......
Lets imagine that the turbo was not connected to the inlet of the engine, only the exhaust side was connected, and the engine kept running at high enough revs to develop full boost. The air being pumped by the compressor is used to blow leaves off the lawn or something, and we have a small nozzle on the garden blower. We also have a boost controller to maintain say 2 bar in the blower.
If we were to block off our garden blower (compressor outlet), what would happen?
Airflow would come to a halt in the compressor housing, boost would remain constant although the turbines wastegate would open slightly to stop pressure rising any further. But, it would still need to pump reasonably hard just to maintain our set 2bar pressure.
(remember in this scenerio the engine is not slowing as it is not connected to the compressor, and is still running at the same revs as earlier)
Right, the airflow has now stopped in the compressor outlet. This is where surge comes in.
Surge is basically stall, this is an aerodynamic term. If the pumped medium were water, it would be called cavitation. Similar kind os thing.
Because the way the compressor works - air gets picked up by the blades and deposited at a higher speed the other side of them. It can no longer maintain this smooth operation because with the pipe blocked, the air the other side is not going anywhere. The air pressure builds up on the blades putting more load on them, and suddenly the normal laminar airflow breaks away from the blade in turbulant flow.
This is called stall.
Same happens on aircraft wings when the angle of attack becomes too great, or the wings are heavily loaded, like when a plane does a high G turn.
In this stalled condition, instead of the airflow running smoothly over the blades, it breaks away from the surface in a tumbling motion.
Lets get back to our compressor. During this stalled state (remember we are still powering the turbine in this little scenario, so no loss of speed as would occur on a closed loop feed back into the engine set up). What would happen if we kept like this?
When the compressor goes into surge (aerodynamically stalled) it no longer \'pumps\'. Because there is still 2 bar of pressure on the outlet side, and we are no longer pumping, the airflow reverses and spills back out the compressor. This happens until the pressure is low enough for flow to start up, and the stall or surge stops and the compressor is happilly pumping again. If the pipe remains blocked, it will just carry on riding through these surge / flow cycles.
Is this bad for the Turbo?
If you maintained a turbo in this continuous surge /flow cycle, there is a buildup of pressure on the blades, which would put the bearing mechanism under more load than normal, just before stall occurs. When stall occurs, there is turbulant buffeting around the blades, which would cause vibration. This vibration would be again be carried by the bearing system.
If we were to measure these additional loads, it would be a reasonalby small percentage of what the turbo sees day in day out.
Right, lets forget about the leaf blower above and get back to a normal car engine.
Unless you have a horribly mismatched turbo on your car, this constant surge thing never happens. (It can happen, especially on big twin turbo RB\'s when you get this chuffing sound, that is surge, but lets tal;k about normal sized turbos)
What does happen is this throttle off effect, when changing gears, or just when slowing down (foot off accel pedal).
Lets say the turbo is producing again 2 bar, foot flat. Turbine happily spinning at 120K revs.
We close the throttle flap to hook up the next gear. Immediately the exhaust gas energy drops massively, causing the turbine to slow down. We would have some inertial energy in the turbine that would keep it speed decay down a bit (opposite of turbo lag).
On the compressor side though, we would go into the same surge/ flow cycle as mentioned above.
Although this time the turbine is continuously slowing. The first surge would see the peak additional forces, and each surge cycle thereafter would be less and less, pretty soon even lower than the turbo would see in normal boosting operation.
Now we are back to our original question, is it bad for the turbo to not have a BOV?
Well, considering that even if you did have one, it would not react fast enough to eliminate the first surge cycle, remember this is the big daddy one.
It possibly would start to work by the second or third surge, but by that time the additional forces are likely to be lower than what would be normal under normal boost conditions. So how much help can that be.
In reality depending on the volume of air between compressor and throttle valve, the effect could be reasonalby good on a fast acting BOV, but these are the same ones that people avoid or tone down due to engine running issues.
If you really wanted to look after your turbo, you would fit an ECU with flat shift capability, and change gear with your foot flat on the throttle."
Great find BB. Thanks for that!
hey! i found it ;)
yeh Rico found it lol I just quoted it lol :D