Blowoff valve

[86Nick]

They use blowoff valves on Rice Burner cars. Does anyone use one on a turbo buick? Is it needed?

 

[DailyDrifter]

Yes, Some people say there only for stick cars.............their idiots. When you close the TB the air rushes back towards the compressor, and bends the fins, you can however get away without having one, but you need to roll out of the throttle everytime.

 

[ttypewhite]

No blow offs here. Never had any issues with any of the turbos that have been on the car. I tried one back in the 90's and it bleed the boost in WOT. I took out the spring and filled it with pennies to test it out, and sure enough it started haulling ass. So I took it off and never looked back. Over rated IMO. My car has been running mid 10's since 94 and driven heavily out of the winter season.

 

[GNVYUS 1]

There are tons of threads on this to form an opinion on if your GN needs one.

DailyDrifter, before you start calling people idiots for not running a blow off you should get your facts straight, "and bends the fins".

I don't recall any bent fins on my turbo comp wheels, are you sure you know what compressor surge hurts??

 

[kraus]

i have one on mine right now, better safe then sorry I don't have 1300 bucks to waste if my turbo gets some bent fins..weather or not its needed i'm not going to argue...

 

[BlackMetal]

Been discussed before. I have one on my Buick. Will you destroy your turbo without one? Probably not. But there are benefits. It's as simple as that. Not NEEDED but also not completely useless.

 

[meaclez]

i dont have one...YET..lol but oh trust me im getting one..i just got my turbo back form rebuild...lol a bov woulda of saved me ALOT of money.

 

[Red C5]

Yes, Some people say there only for stick cars.............their idiots.

It's "they're idiots".

BTW, no BOV here

 

[BlackMetal]

Compressor surge is damaging to the bearings, it's not about the risk of bending fins. Can't imagine what type of air pressure it would take to do that!

A BOV is more useful on a stick shift car because you release the throttle when shifting gears, and you don't want all your pressurized air backing up in the intake, slamming back off the throttle plate, and making your turbo work harder when you shift into the next gear and start to accelerate again. It's better in this case to vent the air out of the intake while you shift, and then when the turbo spools up again, there's no pressurized air coming the wrong way back towards the turbo.

This is not a concern with an automatic transmission. You spool the turbo at the line and go - go - go, shifts are not a problem. BUT, you do have the exact same situation as a manual transmission any time you end a run and abruptly let up the gas pedal. The throttle blade slams shut, any boost/air headed for the intake plenum slams into the throttle blade, gets forced back the other way, and slams into the turbo. The turbo is forced to spin in the wrong direction and that's when you get the "turbo sneeze" sound out of your intake.

This is clearly not ideal for the life of your turbo. Sure, some GN guys have beat on their car for years and years without a BOV and the turbo hasn't exploded, BUT you do often hear about shaft play and oil leaks in used turbos. Could be because of the constant abuse the bearings are taking. Your turbo doesn't want to spin backwards, especially when it has momentum spinning in the correct direction.

So it's not a matter of "no BOV and your turbo explodes", the results are not that sudden, BUT having that backwards air movement hitting your turbo day after day after day will eventually wear it down.

Does your transmission like being shifted into reverse while the car is rolling foward? Would your engine bearings enjoy it if the crank suddenly came to a dead stop and started spinning backwards? Your turbo doesn't like it either.

Hey, a lot of guys say they are nonsense. But I'm not rich. I can't afford to waste $900 turbos. A BOV is $50-100, why not? Oh, because you're scared of being a "ricer"

 

[notacarlo]

A slow lift of the "gas foot" is free.

Here's a general question:

Does anyone have proof that the shaft actually comes to a stop? I realize the stress it puts on the shaft, and a BOV would almost eliminate that, but never had one fail because of it.

I just removed my stock 150K mile turbo last year.

If you want a BOV, get one. It won't hurt to have it. If you don't want one, don't get one.

Money can be spent in a whole slew of places on these cars. Choose wisely.

 

[Turbo1dr]

Compressor surge is damaging to the bearings, it's not about the risk of bending fins. Can't imagine what type of air pressure it would take to do that!

A BOV is more useful on a stick shift car because you release the throttle when shifting gears, and you don't want all your pressurized air backing up in the intake, slamming back off the throttle plate, and making your turbo work harder when you shift into the next gear and start to accelerate again. It's better in this case to vent the air out of the intake while you shift, and then when the turbo spools up again, there's no pressurized air coming the wrong way back towards the turbo.

This is not a concern with an automatic transmission. You spool the turbo at the line and go - go - go, shifts are not a problem. BUT, you do have the exact same situation as a manual transmission any time you end a run and abruptly let up the gas pedal. The throttle blade slams shut, any boost/air headed for the intake plenum slams into the throttle blade, gets forced back the other way, and slams into the turbo. The turbo is forced to spin in the wrong direction and that's when you get the "turbo sneeze" sound out of your intake.

This is clearly not ideal for the life of your turbo. Sure, some GN guys have beat on their car for years and years without a BOV and the turbo hasn't exploded, BUT you do often hear about shaft play and oil leaks in used turbos. Could be because of the constant abuse the bearings are taking. Your turbo doesn't want to spin backwards, especially when it has momentum spinning in the correct direction.

So it's not a matter of "no BOV and your turbo explodes", the results are not that sudden, BUT having that backwards air movement hitting your turbo day after day after day will eventually wear it down.

Does your transmission like being shifted into reverse while the car is rolling foward? Would your engine bearings enjoy it if the crank suddenly came to a dead stop and started spinning backwards? Your turbo doesn't like it either.

Hey, a lot of guys say they are nonsense. But I'm not rich. I can't afford to waste $900 turbos. A BOV is $50-100, why not? Oh, because you're scared of being a "ricer"

Very well said!

 

[DailyDrifter]

See what you started 86Nick, now i look like the d-bag .

Dr. Boost when i bought my t-type with a fairly new turbo on it the fins were straight, then after a couple thousand miles when i went to take it off i noticed the fins actually did bend alittle, no they do not fold in half, but they do bend.

And to Red C5 did you notice i didn't capitalize "i" the entire time for this thread

I'm only joking guys its all 86Nick's fault Look under DailyDrifter...what does it say

 

[Blazer406]

The turbo is forced to spin in the wrong direction and that's when you get the "turbo sneeze" sound out of your intake.

I would like to see proof that the blade in fact stops... and turns backwards.

I hear the sneeze.... but I (as a mechanical engineer) have a hard time grasping the concept of a spinning pair of wheels... and a shaft.... with some measureable mass.....spinning in excess of 100,000 RPM's.... comes to a complete stop, reverses direction, and then starts back up forward again.....

I say no way.

I will say the high pressure air hitting the spinning compressor wheel is likley a form of cavitation..... boat propellers do that sometimes...... fluid pumps can experience it...... it is a bad thing.... I'm not arguing that....I just don't think the compressor wheel stops and turns backwards.

This cavitation if it were in an incompressible fluid... like water... would destroy the turbo in a relatively short order....but IMHO... since it is air.....the air since it is compressible... acts like a shock absorber.....and dampens the slamming considerably.


This is my opinion.... FWIW....

 

[Dreamcar86]

I would like to see proof that the blade in fact stops... and turns backwards.

I hear the sneeze.... but I (as a mechanical engineer) have a hard time grasping the concept of a spinning pair of wheels... and a shaft.... with some measureable mass.....spinning in excess of 100,000 RPM's.... comes to a complete stop, reverses direction, and then starts back up forward again.....

I say no way.

I will say the high pressure air hitting the spinning compressor wheel is likley a form of cavitation..... boat propellers do that sometimes...... fluid pumps can experience it...... it is a bad thing.... I'm not arguing that....I just don't think the compressor wheel stops and turns backwards.

This cavitation if it were in an incompressible fluid... like water... would destroy the turbo in a relatively short order....but IMHO... since it is air.....the air since it is compressible... acts like a shock absorber.....and dampens the slamming considerably.


This is my opinion.... FWIW....

100% agree. I cannot in my wildest imagination see the compressor wheel getting hit with so much force of air that it would rotate in the opposite direction.

 

[grocerygetter]

I watched through the inlet on a drag car that was a DSM (500+ horse) on a dyno...when he dead lifted (no BOV at the time)you could see it radically slow the wheel down when it sneezed at 31 psi but heck, he killed the car and the turbo was still spinning the right direction...just for a second...ball bearing.

 

[Big Turbo Scott]

Lets not forget that there still is exhaust gas exerting force on the turbine in the neighborhood of 2-2.5 times the pressure on the compressor side. IMO the shaft never comes to a stop when lifting abrutly because of this pressure differential. Oh, on a side note, the air does not change direction when it hits the throttle blade, rather it produces a pressure wave that travels back to the compresor wheel. Then travels back to the closed throttle blade and repeats the cycle. This wave produces the tis tis tis sound everytime it travels back and forth and "bounces" off the compressor wheel. This slows and bleeds off the volume of air trapped in between the blades and the throttle body. The same happens when the intake valve closes. Many people have tried to take advantage of this returning wave as a means of increasing the intake ramming effect relative to the timing of the intake valve opening . But thats another subject. So, my point is, a BOV cant hurt esp with a huge front mount and 15 feet(joke) of 3" piping like in my case. Thats a lot of volume in there under 28 psi trying to get out when you lift. I believe it is easier on the turbo. Thats my .03 cents

BTS

 

[TurboDave]

Yes, Some people say there only for stick cars.............their idiots. When you close the TB the air rushes back towards the compressor, and bends the fins, you can however get away without having one, but you need to roll out of the throttle everytime.

Ya, I'm one of those idiots. Blow off valves serve a great purpose on stick cars. Keeps the turbo up between gears.

Course, what would I know, I and many others like me have been doing this for well over 20 years now.

A few points for DailyDrifter:
1. The air doesn't "rush back" towards the compressor. It might seriously slow down or stop, but it isn't going to rush backward.
2. It doesn't bend the fins.
3. you don't have to "roll' out of the throttle.

You can believe anything you want, but after over 22 years now, I have not suffered a single turbo failure related to not running a BOV.
Haven't ever run one.
And trust me, I am not at all easy on my turbo systems.

Actually only ever suffered one turbo failure on either of my GN's, and that was due to injesting a piece of a pesky Champion spark plug that decided to come apart cruising down the highway.

Will a BOV save a turbo? Jury's still out on that, but the ricer's wont tell you that.
Will it help? Can't hurt.
Seems like a lot of money to spend on a screechy farty sounding device.


There are even those that are so dillusional to the point of believing that the compressor is actually spun backwards or stopped when the throttle is slammed shut. C'mon people!!! Think about it, from a 100,000++ rpm to stop/reverse. Good grief.
And yes, I've actually seen it NOT happening. Quite some number of years ago, at a fairly big meet in CA somewhere, I was in the pits watching of of the "heavy hitter" buicks getting warmed up/tuned up. They had it up on jack stands after some tranny work, I happened to be standing near the front fender basically looking into the turbo compressor (enjoying watching it scream).
Part of their testing was bringing the car up against the tranny brake (I assume to test a problem). The rpm was brought WAY UP, had to be well in excess of 4000rpm, then just slamed the throttle shut (didn't roll out).
Did the turbo stop? Ummm NO! Did it slow down? some, but not to the point of even running slow or stopping or "heavan forbid" reversing.

It's amazing the crazy stupid stuff than can be perpetuated about how the novices actually think turbo's operate. And because their pockets are deep enough to run a 10 second ricer, they're held up to be some kind of guru. Not speaking of anybody here, just generalizing.

 

[Turbo1dr]

Actually, the air does rush backward out of the turbo. Years ago, I had taken out the venturi piece of my MAF once for better airflow. The only result was it made the car idle like crap. I put the venturi back in place and drove the car again. I hit the turbo for about 4 seconds and lifted. When I come to the next stop sign the car was idling bad again. I pulled off the air cleaner and inside of it lay the venturi. How did that get in there...from the air rushing back out of the intercooler and pipes when the throttle blade closed shut.

If the air didn't rush backwards the venturi would have stayed in place.

 

[vader87]

Can debate all day about this but personally I will use whatever I can to save the life of my turbo. I only have $750 in my PT70 but I want it to last as long as possible. If the BOV only makes it last 1 week longer, the BOV served its purpose. Just my $.02!

 

[TurboDave]

Actually, the air does rush backward out of the turbo. Years ago, I had taken out the venturi piece of my MAF once for better airflow. The only result was it made the car idle like crap. I put the venturi back in place and drove the car again. I hit the turbo for about 4 seconds and lifted. When I come to the next stop sign the car was idling bad again. I pulled off the air cleaner and inside of it lay the venturi. How did that get in there...from the air rushing back out of the intercooler and pipes when the throttle blade closed shut.

If the air didn't rush backwards the venturi would have stayed in place.

Well I'm not going to debate you on this subject. I know what I've seen and what I haven't seen over the last 20+ years. I know what works, and what's a waste of hard earned $$. As a matter of fact my original 86 stock turbo is still going strong (on another car)(over 180,000 miles).
Ya suppose I screwed up not using a BOV????

My documentation tells me I have over 50,000 on my PTE44. My TA49 has even more than that!! Maybe I should worry???