[scarecrowX]

We'll kill this myth yet.

 

[scarecrowX]

There is definitely a reason why Toyota engineers decided to include the valve,

The problem is people assuming that reason is mechanical. The reason is to reduce noise, period. Mazda even comes right out and says it in the repair manual for the RX7.

ST185's were a rally homologation special that didn't need to be refined. The SW20 MR2 was a moderately high end (keep in mind how much they sold for new) GT sports car that, by definition, SHOULD be smooth and not make weird noises. Imagine the Road and Track review of the MR2 if it snickered every time they shifted it. Like MWPau was getting at, Toyota designed the MR2 for the masses. They designed the ST185 to comply with FIA rules.

I wouldn't even put a blowoff valve back on my car if someone paid me to do it. Drivability with the OEM valve in place is actually quite bad once you're used to driving without it.

 

[scarecrowX]

I already have in the other forum, they also have very little volume to fill, and don't run a whole lot of boost like us and most of us have a TMIC with lots of piping.

Here's the thing: Pressure is irrelevant. It seems a lot of people don't understand HOW a turbo actually generates pressure.

The compressor wheel NEVER sees PRESSURE.
A turbo compressor is not just a spinning wheel, the compressor also has a diffuser volute/scroll as well. The wheel does NOT generate the pressure. The wheel imparts massive VELOCITY to the air which the diffuser scroll THEN turns into higher pressure as it slows that air back down again (Bernoulli).

Now reverse the process. A diffuser with air moving backwards across it becomes a nozzle with pressure on the inlet and velocity on the outlet. There is no pressure at the outlet, thus the compressor wheel NEVER sees pressure, only air velocity. That air simply pushes against the air coming off the wheel, causing airflow across the compressor to stagnate and some air to leak back past in the gap between the wheel and the housing.

Here are some MYTHS:
1. ZOMG! the compressor wheel spins backwards! That's bad for ur turbo hurr durr.

Reality- The turbine requires a steady flow of super-heated exhaust to drive the compressor. If it takes, say, 200hp worth of fuel (ENERGY) to do that, how is a stream of comparatively cool, fuel-less air going to have enough energy to stop, then reverse the direction of a wheel that's not even designed to harness energy in that direction? The ONLY thing that slows down the turbo is shutting off the turbine side. Or sticking your hand in. I recommend the former.

2. That ch-ch-ch sound is your turbo speeding up and slowing down!

Reality- That ch-ch-ch sound has nothing to do with the speed of the turbo. Seriously, think about this using what you learned in high school physics for a minute. If we've switched off the driving force for the turbo and it slows down, how is it going to magically speed back up again? It's not. In reality, the sound is related to the airflow equalizing across the compressor in both directions. The wheel is spinning with the energy of your engine's flywheel near redline. It really couldn't give two sh*its which direction less than a lb of air is moving across it.

3. I don't want to ruin my expensive BB turbo!

Reality- ball bearing turbos are even less affected by these conditions than journal bearing turbos are.

4. Garrett says I need a blowoff valve! They make turbos, so they should know!

Reality- Garrett is a business partner of TiAL. TiAL sells blowoff valves. Advice from someone telling you that you should buy something when they have a vested interest in selling you that thing should always be taken with a grain of salt.

5. Drag racers and Time attack cars use blowoff valves!

Reality- That's because they're not real race cars. REAL race cars don't use them. Champ cars, Turbo-era F1 cars, IMSA GTP cars, LeMans cars- None of them use blowoff valves. The Porsche 956 (which won LeMans several times) used a pair of K27 journal bearing turbos producing upwards of 700hp without blowoff valves. Why did they run without blowoff valves? Because keeping the induction system sealed was worth whole seconds per lap. Blowoff valves make the car slower.

6. Those cars didn't need to care about turbo damage because they were race cars and they changed out the turbos all the time!

Reality- 1 race at LeMans is equivalent to the abuse an average street turbo would take over the course of about 200,000 miles. Porsche and Mercedes have both won LeMans with turbo cars. Toyota, Nissan, and Porsche have all won the 24 Hours of Daytona with blowoff valve-less Turbo cars as well.


Seriously, if you can find a documented failure of a turbocharger that can be directly attributed to not running a blowoff valve, I would love to see it. In the 7 years I've been searching for such evidence, I've come up dry.

 

[scarecrowX]

Sure you might have a little more pressure left in the system but you will have a turbine spinning backwards too.

100% completely false. The turbine DOES NOT EVER SPIN BACKWARDS.

 

[scarecrowX]

Even if it just slows it down it's still lost inertia that needs to be made back up.

Have you monitored RPM to confirm how much it slows down or that it doesn't stop?

I don't need to. I took physics in 10th grade. Google "Law of conservation of energy."

If it takes hundreds of HP worth of energy through a very efficient turbine to 120krpm, what makes you think that pushing a small fraction of that energy backwards through a compressor wheel would be able to even remotely affect its speed?

 

[scarecrowX]

Well if everyone is so confident it does no damage. I'll run my GT35R with no bov, videotape it, and datalog the whole run on 26 psi. However if it does so happen that the turbo makes funny noises/go boom, I need a list of people who are willing to donate me some funds. $100 bucks minimum.

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:thumbup

Seriously? I've been putting my money where my mouth is for several years now. And I'm not asking anyone else to foot the bill.

 

[scarecrowX]

It doesn't take hundreds of hp worth of exhaust to spin the turbine. The hp it takes it proportional to the amount of boost you are trying to make.

It takes hundreds of HP to get the shaft to 125,000rpm. 140HP won't do it. Try driving full throttle with the wastegate open sometime. Airflow alone through the turbine isn't enough to spin it to those speeds. It takes pressure and heat. Keep in mind that the turbine side is a purpose-designed nozzle, and the turbine wheel is shaped to take advantage of flow in that direction as efficiently as possible. The opposite is true of the compressor side. There is no heat (comparatively), there is less pressure and there is air coming in the other direction. There's just no way there is anywhere NEAR as much energy acting on the compressor wheel during flow reversion. The imbalance is huge.

With a BOV valve you would release pressure on the compressor side at the same time as the turbine side allowing the turbine to freewheel. With a recirc valve especially if it were designed right it would be introducing a pressure wave before the turbo helping (to however small of a degree) it stay spooled and the air traveling in the right direction.

Here's the other point that people don't realize- let's say for a minute that you're right and the turbo slows measurably while shifting. When you open the throttle again with a BOV, you start from zero. You still don't have full turbine speed because of the loss of drive, but boost builds from zero as quickly as it can.

When you do not have a BOV, you open the throttle again and there's still 10psi or whatever in the pipes. Keep in mind that a turbocharger is a positive feedback device. The more boost you have, the more boost you make. Next time you're out driving, hold the car at 0psi at 4000rpm, then floor it. Note how quickly the turbo spools. Then hold the car at 10psi under the same conditions and note how much (exponentially) quicker the turbo spools. One will hit quite a bit harder than the other, I assure you. That's the advantage of keeping the system sealed between shifts- when it's time to re-spool the turbo, you're starting with SIGNIFICANT boost to help drive the turbine, even if it were spinning a little bit slower.

I've never driven a CT26 car without a BOV, only my TD06 car. The difference when shifted quickly is the difference between being able to chirp the tires at will and not being able to. It's not a "hmm, I think it might be a bit faster but I'm not sure" difference, it's an "I can now do something I couldn't do before" difference. I'm not trusting my butt dyno, I'm trusting the black ribbons of star spec rubber on the pavement behind me.

I would agree with this but I do think it's funny that after pages of swearing there are no negative effects you say that a ball bearing turbo is less effected by the conditions that should have no effect on any turbo.

I never stated that it had no effect, only that the effect doesn't damage the turbo the way people think it does. The turbo will die of some other cause long before off-throttle surge kills it.

I'm also not telling people to remove them or trying to belittle people who decide they'd rather use one. I'm only trying to help undo the myths and hype that BOV manufacturers and magazines have managed to turn into "common knowledge."

 

[scarecrowX]

When a turbo goes into surge, and that is what you hear without a BOV it can and does snap the blades off the compressor wheel. It may not do this on low power road car but will on a high power race car.

Bob, can you point to any specific examples of this? We know that turbo-era F1 cars didn't use them even with 75+psi of boost (granted, that was in qualifying). We know that the 1000+hp GTP and Group C cars didn't use them (or Group B, for that matter). Turbo failures weren't a very common cause for those cars to retire from races. It happened, sure, but it was more the exception than the rule. A few of those cars used BB turbos, but most used normal journal bearing units. Porsche Toyota and Nissan had both single and bi-turbo systems. Find footage on Youtube of the Audi Quattro GTO cars. The lift-off surge is VERY audible. Those were 600-700hp cars. Search "porsche 962" on Youtube and you'll find an on-board of a 962 at LeMans with plenty of surge every time the driver shifts.

I know champ cars used titanium compressor wheels, but that was partly due to the shaft speeds for such a large wheel and I'm guessing partly due to the 4 massive fuel injectors spraying into the mouth of the turbo.

 

[scarecrowX]

I'm sure that a few of you have boobs.

Guilty. Sorry.

 

[scarecrowX]

so if on throttle surge kills turbos and the compressor never sees pressure how does the turbo get damaged?

When the compressor is spinning, it's generating a thrust load axially in the direction outward from the turbo inlet. Basic Newtonian physics, actually- for every action (suction) there is an equal and opposite reaction (thrust loading). The turbine generates thrust loading in the same direction. (that's why there's only one thrust bearing)

There's a pulsation generated against the thrust bearing as the compressor wheel slips/grabs the air. It's not a huge deal when there's small load on the thrust bearing with a closed throttle, but when you've got full power going through the turbine it just hammers the thrust bearing. On-throttle surge happens at full throttle and high shaft speeds (therefore, high thrust loads). The oil film on the bearing surface has a harder time dealing with the hammering load when it's happening with full force already on the bearing.

Some turbos have stronger thrust bearings than others too. Holsets probably have the best thrust bearing design out there. MHI turbos can be upgraded to holset-style thrust bearings.

 

[scarecrowX]

Yeah, above 20psi it pretty much just makes a whoosh sound.

 

[scarecrowX]

where is the flutter coming from?What causes it?

It is the sound of the compressor wheel operating left of the surge line.

Ive read here that the wheel never ever feels pressure but i didnt understand that.How then its ever possibe to pressurize a system?
Except there is an explanation that has something to do with velocity happening after the compressor wheel?I dont get it.

Bernoulli's principle- pressure and velocity are inversely related. The compressor wheel draws air in and flings it out at extremely high velocity. The diffuser (there are two- there is a double wall diffuser at the very exit of the compressor wheel, and there is the scroll of the housing itself) then takes that very high velocity air and slows it down. Velocity is converted to pressure by the housing. This happens away from the compressor wheel itself.

The compressor wheel's job is to introduce the energy necessary for converting velocity to pressure. The housing's job is to actually DO the conversion.

and why does the new EFR turbos COME with included/Special designed BlowOffValve?

Good question. Marketing? I think a better question would be whether any of the race cars (who still lift to shift) actually use the BOV or if they block it off.

 

[scarecrowX]

Its true, with the advent of flatshift there is no reason to close the throttle plate through shifts... Most modern standalones have flatshift capabilities, so it stands to be reasoned that there is even less of a reason to have a bov on race setups...

I know you know this, but anyone else wondering about this relative to my previous examples of race use, flat shifting didn't start happening in F1 until AFTER the turbo era. Flat shifting didn't start happening in Indycars/CART until 1993 (penske), 1994 (everyone else). GTP and Group C cars never had sequential gearboxes so they ALL lifted to shift.

Has anyone logged a turbo's speed (RPM) comparing with BOV versus no BOV?

Simon Gishus of Nizpro in Australia did an article for autospeed where he referenced actual turbo tachometer data.

The fact that people think that they keep the turbo spinning is a problem. The people that suggest this have never had an engine on the dyno and never had a turbo tacho in their hands. What people don't realise is, when you shut off the throttle, you shut off the air supply to the engine - this shuts off the exhaust gasses coming out of the engine. When there is no exhaust flow, there is no energy to keep the turbine spinning - the turbo slows down at an alarming rate.

He also states that on a 1:40 course, they LOST 2 seconds per lap with a BOV installed. I've posted this in every BOV thread in the past 3 years: http://autospeed.com/cms/title_Nizpros-Simon-Gishus-Part-2/A_1457/article.html

That article was what originally got me interested in the principle of running without one. Lots of research followed. I found no legitimate examples of turbos damaged by it and a whole lot of race cars that didn't use them. That's when I took mine off.

 

[scarecrowX]

On-throttle surge happens when the turbo can't move enough air at a given pressure ratio at full throttle

For example, my TVIS was stuck closed for a while and when I'd spool my 20g to 18psi at 4000rpm, it would begin to surge (make the same sound as without a BOV), only at full throttle. You could see the boost gauge flutter. It's because the secondary butterflies were a huge restriction in flow. The charge starts to back up in the intake even though the throttle is open.

 

[scarecrowX]

These bearings came out of a turbo run without a BOV for 2 years on my car at 20psi with spikes to 25psi, and a low oil pressure issue. This was a used turbo when it went on my car, and came from an OEM vehicle that came from the factory without a blowoff valve. This turbo probably only saw about 5k of blowoff valve use in its lifetime.

Compare them to the bearings Eric6 posted earlier. They're from the same frame turbo. Bear in mind these bearings are about 20 years old with probably 75k miles on them. I changed them out for a larger thrust bearing for better high boost durability. They're actually in very good shape for their age and lack of oil pressure (evidenced by the bluing).

 

[scarecrowX]

You have asked me to ignore it but its gone lean

Of course it has. He lifted off the throttle. ECU cuts fuel completely when you lift above idle. Its called decel fuel cutoff and is totally normal.

I understand what you're trying to say MANDALAY but there isn't an AFR sensor on earth with the response time to measure what you're seeking to measure.

Think of it this way: MAP sensors have response times of about 1mSec. That's significantly faster than you can open the throttle. And mass flow sensors account for every gram of air that goes through them.

 

[scarecrowX]

There really are two separate issues here...

In any case, limiting the discussion to a typical 3SGTE with a CT26 running a modest amount of boost, it seems unlikely that running without dump/recirc valve for few hours is going to cause an immediate failure.

It's unlikely to happen, period. Remember, the ST185 came with the same engine and electronics but without a blowoff valve from the factory.

For the transient response aspect, all those same factors are at play. It's probably going to vary for the different setups. One concern for people running a speed-density setup is that those oscillations in the intake could cause odd pressure oscillations at your MAP sensor during on-boost throttle transitions, possibly introducing some tuning issues.

Nope. As soon as the throttle opens, the surge goes away. The MAP sensor doesn't care anything about what's happening on the other side of the throttle plate.

The transient response thing is twofold:
1. Better boost response after a fast shift.

2. Better modulation of the throttle mid-corner. I'm sure many of us have felt that sudden loss of power while breathing the throttle for a faster corner where you don't intend to lift completely, but the BOV opens anyway and dumps all the boost in the pipes. You go from trying to use part throttle (which IS enough to build boost- maybe 80-90hp) to maintain speed around a longer corner like a freeway ramp, breathe the throttle ever so slightly and you suddenly have no power at all because the fast responding, "superior" OEM valve just dumped your charge when you least wanted it to. It's not only annoying, it affects your ability to balance the car with the throttle because the response is neither linear nor consistent.

On a roadcourse at least, this is (IMO) a bigger reason to do away with the BOV.

 

[scarecrowX]

Not exactly...
Consider a throttle being open at 1%. Pressure waves on one side will NOT be as strongly seen on one side vs. the other.

The throttle plate on a 3SGTE, when closed, is completely closed. Idle air comes from in front of the turbo through a separate line.

As for oscillations as the throttle opens, possibly. I'm trying to find a datalog with a MAP trace directly after a shift but there's a lot to sift through and I'm low on ambition and sleep these days..

For what it's worth though, the ECU on my car handled fueling just fine under full blown on-throttle surge, so if there are any oscillations they're of little concern to the ECU. The oscillations are well within the response time of the MAP sensor, so as long as those cells are tuned properly the ECU can deal with it just fine.

And as for surge going away when the throttle opens. That may be true in the steady state, but not necessarily in terms of transient response (depends on the input). Consider quickly closing the throttle from 100% to some lesser value still sufficient to maintain some boost.

Excellent point, very true. And after thinking about it, you're right that the surge doesn't go away immediately either. Whether it's a tuning issue though is down to the frequency of the oscillations versus the response time of the main load sensor. I suppose it's possible for some systems to have issues with it. For my ECU though, the frequency would have to be near the kHz range, and I can audibly tell it's nowhere near that.

 

[scarecrowX]

Pretty impressive results for no-BPV performance.
If anything the with BPV tests had an advantage as I was on a CT20B and was able to shift much faster in that test.

Thank you sir for posting your data.

People should keep in mind too that the advantage becomes even more pronounced with larger frame turbos that take more time to spool between shifts.

The performance advantage is on faster shifts, but there is definitely a driveability advantage with slower throttle transitions as well.

 

[scarecrowX]

C'mon guys, keep the chatter to a minimum. Threads don't stay open like this very often and it will get closed real quick if it turns into piddly bickering.