[skyline69_uk]

Only the mugs :chairshot .

It's there for a reason, they appeared in the turbo racing world in the very early 70's to improve lap times and life of the turbos and there is no reason whatsoever to remove even today as they still do the same job. Some rally cars etc can do without them as can any car that has an open throttle shifter which isn't the GT-R.

This question is asked everywhere lol...

http://www.dsmtalk.com/forums/showthread.php?t=159821

 

[skyline69_uk]

Careful mate, someone on the internet might call you a mug cause of stuff theyve heard but never tried

Glad someone else can back me up here, as id tried it many many maaaany times, but as ever on here, I expected the internet backlash, lol...

I'm only going by what half a dozen professional auto engineering books and a friend who spent 3 months with the Renault F1 team say but maybe they're all mistaken.

I know none of this from experience unfortunately just from what the text books and auto engineers say (I was going to be one but ended in computers instead (I'm the mug this time) and work with several people who did it at Uni etc).

I'm sure there are many situations when they are not needed or indeed cause more issues than they fix but I have never seen an AE textbook that ever stated those conditions - only pictures of the damage caused due to the lack of them Steve. The problem is surge causes other failures to happen first that mask the real cause and it appears like something else e.g. inbalance is the cause etc when the surge caused the metal on metal contact over time that in turn caused the inbalance. Only a professional test environment shows the real cause and AEs will look to see what caused the inbalance while everyone else just put it done to "wear" or a "dodgy turbo".

 

[skyline69_uk]

Yeah, cause TURBOS are such a top subject on a modern F1 car

And for what its worth, when F1 cars were turbod in the 80s, did they run dumpvalves? Not on any ive seen, and I know someone who builds historic turbo F1 engines for a living...
Neither do any LeMans/GT cars ive seen actually...

Must be mugs

Like I said in "certain situations" there may be reasons for not using them but on F1 cars they changed the engine every race but I don't have that sort of money :bawling: . From everything I've read and been taught on turbos they do have a very good reason for being there e.g. for the life limit of the turbos but it all depends on 100s of factors whether or not it will effect your ownership of the car - this much is known, most turbos last longer with them on.

They originally were used for racing reasons especially in endurance racing and not for normal passenger cars etc so they didn't appear as a noise suppression devices but a proven race aid in performance and endurance type races.

Unless you are doing something special and have the money to spare because of it then it makes sense to just leave them on the car or replace them if they're knackered.

I'll see if I can dig out the info on them over the weekend but most AE books I have are over 1000 pages or so just about engines and finding the damn info again is a nightmare!

 

[skyline69_uk]

If they did ANYTHING worthwhile in performance reasons, why wouldnt they run them in 80s F1 and current GT/LM?
10th of seconds count in them races, so im sure theyd fit one if they did anything at all...
They didnt have ALS systems in 80s F1, and you cant imagine instant response when you got a 1.5litre engine running 1400bhp turbos...
Granted, they run dog boxes so gearchanges are almost instant, but a 10th of a second is an instant...

The damage running a full F1 or GT or LM race at anything up to 4bar boost with no dumpvalve will be more than youd ever give a turbo car in a lifetime of ownership...

I guarantee you there will be a good reason that none but AEs would know about totally.

DVs are only needed where the throttle plate shuts and therefore where the pressure difference either side of the wheel causes stress on the bearings enough to break the oil film and make metal/metal contact or where the blades are weak enough to bend but you can NEVER in auto-engineering take anything for granted especially the old "it's good enough for them then it must be OK" as the number of factors are too great.

For decades I read tuning and fairly basic books on car technology and then decided to read the Uni and professional stuff as the other books where not answering my questions (ones like "why do you need a DV in the first place").

It was a right f'ing eye opener, a bit like the difference between secondary school physics and quantum mechanics. There is a great benefit to be had if you can change the parts before the damage is done or if you can find a better method to avoid surge (keeping the Tplate open on seq shifter etc) but without the full knowledge of the engine/turbo and it's design remit then it is VERY dangerous and a mug game to assume anything other than that the manufacturer had a good reason to use them. Maybe it simply is for noise suppression on the GT-Rs and the DVs can be removed - I don't know, but neither do you so we have to assume they are needed maybe for some other reason.

If you seen a proper AE book on engines (Engine Fundmentals is a good one) than your whole view on the subject would change I would guarantee it as I had much the same naive approach until my eyes were opened .

 

[skyline69_uk]

No, i TOTALLY understand the theory behind it, if you look at it purely from books etc, they are vital.

But NOTHING beats practical testing.

And testing proved to me they not half as vital as they seem on paper.

Paper and reality are two different things, regardless of how complex the books are.

Like said from the start, id never reccomend it as never tried it on GTRs, but tried it on plenty other cars at far higher boost than most GTRs to know that personally id take the risk to see what it was like, but if there no reason to on your car, then dont bother.

From a performance side, many dumpvalves that vent a lot of air can often make throttle response worse rather than better...

Agreed Steve .

DV valves are better than vent to air normally so the recir on the GT-R are a better bet and make a lot more sense. Unfortunately there is now a habit to put BOVs are hybrid valves that dump some air to atmos and recir the rest onto cars for "effect".

As you said you have noticed no problems so far but the damage is usually long term and can show up in differing failures than expected (exhaust side problems as the two sides are connected).

The type of turbo and boost levels etc are the main factors in whether you can get away with. If the turbo blades are strong enough and the pressure difference between each side is not enough to break the oil film with the unequal spiralling side forces, the shaft bending/rebound (all materials are like rubber (quoting Royce) i.e. all bend under stress) during this time etc then it will "probably" do no harm at all to remove it.

Also depending on throttle plate opening/closing during shift times etc and how much the DVs leak and energy lost during recir travel etc it may make little difference to the performance or may even help to remove them (less weight also) in some cases.

My problem is I can't see it being a good idea for normal Joe Public to do so, maybe for a tuner on a car that no longer is anywhere close to the original spec it would be of benefit to try it out but it can be a costly exercise in the long run (to the next owner normally) but may benefit in the short term if you are trying to get good 1/4 times etc.

 

[skyline69_uk]

What do you mean by vent to the non-pressure end Steve? I don't know the GT-R setup as I never looked.

The idea of a recir valve is to move the air to the other side of the compressor wheel to even the pressure as surge is caused by pressure difference i.e. the pressure on the throttle side is too great and stalls the blades while trying to get back to the entry side.

A small pressure difference will only slow the blades down and normally glently enough to not cause any problems so some turbo setups don't need a DV. With big pressure difference the recir valve is used to move some of the high pressure air to the other side to equalises it without going through the blades and therefore minimises/stops the stalling.

BOVs and recirs are a totally different ball games unless the GT-Rs are doing something a bit outside the norm?

BOVs were the early idea around 70/80s or so but had a very bad impact on effiency and therefore performance - pressuring air only to dump it to the atmos is a very bad thing while DVs (Diverter Valves) were the new way that avoided the surge and therefore kept the wheel spinning where prolonged throttle closed periods existed at high airflow.

I have a paragraph in an AE somewhere with figures for a test run showing pressure difference etc and graphs for stall points - I'll look it up if I can find it.

 

[skyline69_uk]

I think I know where you are coming from SteveN, when the recirc valve does its bit it basically dumps back to atmosphere pressure but keeps the volume of air constant (ie air mass is the same as the AFM's think it is) which helps the ECU fuel correctly.

And by moving the air back to entry of the compressor wheel also stops surge and helps keep the wheel spinning and effiency of the process high.

That's the theory anyhow, if the valve is leaking then that's a different matter lol.

When I get home if I have time (doubtful) I'll scan some of stuff and post it. AEs pro books are well above any mag article to be honest and. Engine Fundamentals is just full of calculus from page 1 to page 1000 :bawling: and the preface recommends having a degree in mathmatics before reading it .

 

[skyline69_uk]

I have had turbos fail for all different reasons, I can't put my finger on one that was because I didn't have a BOV.

And in there lies the rub :chairshot - as I have said earlier in the post it is well reported in AE books that surge causes failures that do NOT point directly at it - shaft inbalance failure being one of the main ones, problems also appear at the exhaust side too etc.

Turbos should not fail - period - if they do it is because of something amiss or someone being a muppet. They are built to a high standard and are built to last for the life time of the engine they are fitted to - as long as they are maintained and treated as expected.

 

[skyline69_uk]

A partially leaking DV, which is common and v.hard to spot, will overspeed the turbo and kill it far quicker than not running one.

That's assuming it is faulty Steve, I'm talking about a working one. How does the leaking DV overspeed the turbo? The turbo speed is defined by the wastegate setting / exhaust gas pressure, the pressure on the compressor/throttle only limits this. The DV's only purpose is to stop surge.

 

[skyline69_uk]

All the above is indeed in the books. Also running the incorrect air filter can cause big problems too as if the pressure on the back of filter is too high it starts to strip the material off the back of into the turbo!

They note that oil contamination is the most common reason.

Also said that turbos fitted to diesels last a hell of a lot longer then petrol as they don't have a throttle to cause stall among other reasons (EGT being another main one).