Slacker7

iTrader: (2)

Sorry I missed this.... Err.. the Exhaust wheel and the compressor wheels are both different materials. The Exhaust has to be some sort of material that can withstand really high temperatures, so it would be something like cast iron? while the compressor can be made of aluminum for weight savings. From a fatique standpoint, if the turbine is made with a material that doesn't have an endurance limit like cast iron and is designed within the endurance limit, it theoretically will not fail in fatigue. Aluminum on the otherhand, doesn't have an endurance limit so it will eventually fail in time.

S2-13BT

Factory items are plumb back aren't they (i'm not really sure)? In which case there won't be any BOV noise, so it's there to prevent the surge noise that joe public definitely doesn't want to hear on every gear change. Let's face it, anyone who isn't an enthusiast isn't going to want any wierd noises.

That's pretty conclusive if you ask me. A BOV that passes air back into the inlet doesn't make the whoosh noise that ricers like. So it's obviously to stop surge noises. Which it does.

I didn't say Mazda engineers know best. I was just wondering if anyone wanted to argue with them! As far as I'm aware, it's been stated in other manufacturers service manuals as well.

Nah. It's entirely by the ol' seat of the pants dyno! Although if you flick through that thread I linked to Rice Racing has logged data on his previous car which showed no gains.

I should also point out my engine is a Jap import motor with god only knows how many kms on it and the turbo, and it still runs strong.

S2-13BT

Sorry for posting again.

IMO, it's really a personal preference thing. That thread I linked to has 13 pages of discussion and there was no easy yes/no answer.

I say if people like the noise, use one. If you believe it will prevent damage to your turbo, then use one, if you don't like either, then don't use one!! It's really that simple.

It's an interesting topic that's for sure.

White_FC

Slacker7, I'm not going to argue with you about the properties of metals, aluminium of course has a lower coefficient of restitution when acted on by a force than say cast iron.

My original point about exhaust pulses on the exhaust wheel was that there would be sideloading in the bearing due to that aswell.

The exhaust pulse would, at least in my humble understanding, put MORE load on the bearings than compressor surge.

And the main reason blades fail is from touching the compressor housing. Not due to compressor surge. This is actually the first time i've hear of compressor blades shearing off due to compressor surge.

Slacker7

iTrader: (2)

hmm.. Can't argue with that. I'm going to unhook my BOV and see if it's any noisier... but I couldn't tell the difference before

Slacker7

iTrader: (2)

I don't think the sideloading will be that great when you don't have compressor surge, that's because the wheels are allowed to spin freely. When you have compressor surge, you have the exhaust pulses trying to spin the turbine one way and the surging air in the intake tract trying to spin the compressor the other way thus causing a side load.

White_FC

See thats just it, you DON'T have exhaust pulses (effectivly) when you back off.

It doesn't spin freely when its not surging. The exhaust pulses are trynig their best to compress air. Not all of the pulse can therefor be converted into rotational motion of the shaft.

Slacker7

iTrader: (2)

Why not? the engine is still running ain't it?

White_FC

Thats why I put 'effectivly' in brackets next to it.

The exhaust pulse is negligable when backing off compared to when your under full power.

Fairly obvious, no?

Slacker7

iTrader: (2)

Okay... I don't think it's negligible. If that's the case, then you won't have a problem with compressor surge, the compressor would just end up going backwards.

RotaryWeaponSE7EN

iTrader: (6)

I wasn't arguing that it didnt have to do w/ noise. And a bov has nothing to do w/ performance. I was arguing the fact that the turbo will be in better shape longer w/ a bov than w/o. Thats all. Also I pretty sure the faster rotary powered vechicle is Albels 6.84 @ 191. Thats a little more impressive. Finally someone to whoop those toyotas. Now only if he stays consistant.

S2-13BT

No... That's the quickest, not the fastest!! There is a difference. I vaguely remember a thread on here sometime that was essentially an argument about what the terms meant!!

Abel hasn't done 200+mph yet, but we haven't done a 6 yet! So Abel is the quickest down a quarter, we are the fastest!

Anyway...

RotaryWeaponSE7EN

iTrader: (6)

Ok, sry quickest is what I meant.


P.S. 1111.....<retard

adamlewis

Just wanted to say that venting metered air results in a RICH condition. Also, this only effects cars with metered air systems. Cars that run off a speed/density EMS ( like mine or pretty much anyone with an aftermarket ECU ) wont have this problem.

adamlewis

And I love it when people comapre race cars to everyday cars.

Hey White FC, you ever watch WRC races? You know that popping you here whenever theyre going around turns and arent on the gas all the way? Got any clue what that is?
Well, lemme educate you. They have an anti-lag device to keep the turbo spoolied when theyre off the gas. It does so by igniting fuel around the turbine. This absoulutely KILLS a turbocharger. They replace them after every event anyways.
Point is, just because thats the way the race teams do it doesnt mean we should to.


(Edit...Remove insults....People, there are ways to disagree without calling each other names. If you can't figure this out, go to the Honda forums where you will be welcome).

White_FC

Thank you for all that information... as you might see in one of my earlier posts (obviously you didn't read them) I already know about WRC cars running anti lag systems.

Of course this kills turbos, wow big revelation there.


WRC is not the only form of motor racing. When I was talking about race cars, I was actualy refering to a class of racing called here in Australia as Improved production, as the name might imply they're quite closely related to normal production cars, this is an attempt to keep costs down.

I said it before and i'll say it again, you wouldn't NOT put a $50 part on your car if it saved a $1000 turbo.

Since you obviously understand the dynamics of air systems with respect to turbos much better than I, the idiot, perhaps you can enlighten me as to exactly how a BOV would prevent damage to a turbo?

RotaryWeaponSE7EN

iTrader: (6)

White_FC...
I said it before and i'll say it again, you wouldn't NOT put a $50 part on your car if it saved a $1000 turbo.

I would.

BlaCkPlaGUE

Yea so would I...

maybe I should just backoff since I havent been reading the 5 or so pages of whats been going on...

White_FC

Hmm sorry about the double negetive there.

I'll decipher that for ya.

'You would not kill the $1000 turbo for the sake of not spending $50 on a simple BOV'

This is what I was trying to convey, obviously these people with much more experience than I decided it wasn't worth the $50 to put a BOV on.

So would that not tell you that they would not help the turbo live longer?

scathcart

Racing is about winning, not engine/turbo longevity.
If adding a part that increases turbo longevity but severely dampers power between shifts, is any serious racing team going to do it? Of course not. No racing team will lose a race just to save $500.
The turbocharger only has to last the race and then it can be rebuilt.

scathcart

Problem is: Boost readings are taken at the intake manifold, post-throttle-body, in order to be able to get a reading of what the actual engine is receiving for boost levels, after the pressure drops have occured through the intercooler and its piping.
Now, without a blow-off valve connected to the intake plumbing, hook up a boost gauge so that it reads prior to the throttle body, and watch what happens when you let off the gas at 40 psi under WOT... the compressor wheel is still spinning, but now it is pressurizing a finite volume, which will cause a near-instantaneous pressure spike far exceeding the engine pressure of 40 psi.
I have watched this occur while monitoring dual boost gauges (to measure intake plumbing pressure drops on a Mitsubishi Conquest at 20 psi with no wastegate...

As for anyone claiming compressor surge does not kill turbochargers... well, I seriously question their personal experience in rebuilding turbochargers used in racing applications.

White_FC

I realise that scathcart... A guy earlier in this thread said he esperienced a 38psi pressure spike whilst running 20odd PSI.

What I was talking about with respect to the 40psi earlier was the all out race cars like the old group A Sierra RS 500s running 40psi with no BOV, would hate to think what sort of pressure spike that induced..
However they stood up to task fine. Winning the bathurst 24hr race quite a few times IIRC. Until they were banned.

Now racing for 24hr's running 40psi, countless gearchanges around the whole track, and your telling me that if they added a $50 BOV to their car they could have improved the reliability markedly? I'm not so sure of that...

But since you obviously do have alot of experience rebuilding turbos, what goes wrong with turbos that have undergone prolonged compressor surge?
bearing failure? wheel failure?

RXciting

Damn man you beat me to it.. i've neglected to read this thread for a while cause i figured all it would take to answer this persons question was 1 smart person..

it kinda sad that i've been messin with cars for only 4 years and only been readin into force induction since feb when i came across a set of turbochargers that would be perfect for what i want to do with my car.

Yet i understand why a BOV would be beneficial to a "street driven" turbocharger (specially a large turbo that tends to have alot of momentum) and y a race team wouldn't use it

also just to clear what someone said B4 a BOV does not vent excess pressure when you close the throttle plates, it is activated when the pressure on the turbocharger side is greater then the pressure in the intake manifold (even if your still registering vacume.. (i only grasped this when eViL Rotor explained it to me)

S2-13BT

I thought everyone was claiming that the BOV increases peformance between shifts by not letting the increase in pressure stop the compressor wheel by forcing air back against it.

By that reasoning, why would a race team doing endurance races at 40psi for 24hrs not use one? If they really did prolong reliability, and increase performance wouldn't the team put a $50 BOV on the car. $50 is irrelevant to them if it's going to give them a better car, as you and a few others have said.

Slacker7

iTrader: (2)

actually kinda think of it...performance bov's cost a little more than $50