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Discussion Starter #1
How many people run without a BOV or Recirc?
Any running issues, failures etc etc.
 

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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
 

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Er, I don't use a BOV or re-circ. I use 2 overboost valves venting to atmosphere.
 

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skyline69_uk said:
It's there for a reason
Purely noise suppresion reasons on 99% of standard cars fitted with em ;)

IMO they not ANYWHERE near as vital as most people think.
But most people who know that still fit them in a "better safe than sorry" manor.

Can usually find a lot more people with proof its had no noticable effect than people who can prove running with one has helped them.

Lot of AFM equipped cars NEED them as airflow going backwards past the AFM messes the fueling up tho.

Performance reasons are generally laughable and despite a lot of searching, seems to have never been proven. Just tons of internet/book/tv rumour and myth, like "wastegate chatter" and other such bollocks.

Turbo reliablility reasons are genuine depending on boost level and turbo strength.

Some turbos are fine without one, I ran 30psi held boost for over 12k miles with no DV at all with no ill effects, hell, I ran agressive ALS at the same time just to make it worse, lol.
Did the same at 23psi on another car, and know countless people doing the same.

Theory has it that they do something, reality is what they do is far more often than not not even slightly noticable.
 

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Discussion Starter #5
The reason I ask is my car came with BOV's (not recirc ones) and all my recirc tubing has gone so no chance to retrofit to recirc.
BOV's mess up the AFM's but also leak and only hold boost to the spring rate of the BOV. Stronger springs can hold more boost but then BOV pressure release has increased also, same effect as not having a BOV at all?
Remove them and the leakage has gone, no more pressure relief but at a measily 1 bar does it really matter.

So do I invest in some new BOV's (as mine are past there best) or blank them off and run BOV-less.

Thats my choice but was wondering what the Skyline population has tried.
 

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I doubt anyone in the UK skyline world has tried with none, its not the most daring scene ever!

I dunno how well the ceramic turbos will take it, but otherwise id have a go personally as never done me anything but good in the past.

But id never advise someone tho, as tried it on tons of cars, just never a GTR.
 

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it depends more on your ecu runs anything else, if you have a MAP sensor then who gives a shit but if you have metered air then you could over fuel and stall from time to time
 

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i've been "temporarily" running with blocked-off recircs for about a year now. had a bad one that wouldn't shut even at idle. figured blocking the outlet was a quick and easy fix till i got a replacement. haven't had any real problems.
 

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tyndago said:
The Super Taikyu N1 race cars didn't have them. Not the 2 cars we have.

I am not that much of a fan of them. Most of my old experiences of them have been leaking under high boost. The leak does more damage by over spinning the turbo.
Careful mate, someone on the internet might call you a mug cause of stuff theyve heard but never tried :p

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...
 

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BoVs do not rely on the spring pressure to hold them shut against boost, they have boost pressure applied to the rear of the diaphram via the actuation pipe. The spring is only there to define the opening point in relation to manifold vacuum and to hold them shut during spool when there is a delay between pressure on either side of diaphram......
 

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

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".
 

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Indeed - you will not achieve 160 000km durability without a dump valve. Does this concern the average GTR owner / tuner, probably not. It does not change the reason for the component being used!
 

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skyline69_uk said:
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.
Yeah, cause TURBOS are such a top subject on a modern F1 car :p

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
 

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SteveN said:
Yeah, cause TURBOS are such a top subject on a modern F1 car :p

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!
 

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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...
 

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SteveN said:
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 :cool: .
 

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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...
 

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Discussion Starter #20
As I see it if you run with a recirc valve everyone is happy and the engine works perfectly (up to 500+BHP on standard ones too) so stock is best.
However, I can not return to stock as the car came with BOV's and no stock piping.
AFM's get all confused when dumping air (or leaky valves) and the engine runs lean = bad and blows up.
Theory says that Turbos need a relief valve of some kind to protect them from boost back pressure when off the accelerator or gear changes.
No relief vales = poor turbo life.

Since my BOV's seized shut during winter last year the car ran better, I have recond the BOV's this summer and the car has run not as good. Blitz valves run on zero lubrication and are exposed to all the crap that our roads can chuck at it (GTR valves are located by the drivers side front wheel). Mine do-luck (sorry do look) worn and pitted and the certantly do leak.
I think I am going to take the bleeders off and run with out them. If something goes :popcorn: it will give me an excuse to upgrade.......


ps If you drive hard I notice you dont get a BOV discharge between gear changes anyway as the engine holds good revs keeping some sort of pressure in the system. Anyone else noticed this?
 
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