Blowoff valve

[Turbo1dr]

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???

Ah, I thought I'd choke you up on my last post. You're the one that said air doesn't rush back out the turbo. All I want to know is where all the pressurized air goes if it doesn't rush back out the air cleaner? I'll be waiting for your magical answer to that one.

 

[TurboDave]

Ah, I thought I'd choke you up on my last post. You're the one that said air doesn't rush back out the turbo. All I want to know is where all the pressurized air goes if it doesn't rush back out the air cleaner? I'll be waiting for your magical answer to that one.

You didn't choke anybody up. I told you I'm done argueing. You can believe what you like about fluid/air dynamics, it's neither here nor there.
The BOV guys will continue to brag-up the virtues of BOV's no matter what. Personally I no longer care.

For everybody that thinks they need one. My advice? BUY IT!!

Happy now?

 

[Tony Shoaff]

Blow-off valve

Out of all the 3 GN's I have owned including my race GN. I have never had a blow-off valve. I am not sure who said the turbo spins backwards when you let up but they started a bad rumor. Because that is false,wrong, no way and totally not true! The Turkey gobble sound it makes is what people wonder what the Hell was that? I have never backed out slowly after a run either because of the stopping distance we have. I have never had a issue with the turbos on these cars without the blow-off valve so I think they are a waste of money. Just my 2 cents.

 

[87natl]

Apparently the gentlemen at GM that designed our cars didn't feel we needed one. I think I'll trust that judgement.

 

[GNBRETT]

Apparently the gentlemen at GM that designed our cars didn't feel we needed one. I think I'll trust that judgement.

True I would suppose to a degree. But are cars did not come with alky kits either from the factory but they sure seem to make our cars run better and safer. Alky kits have been around a lot longer then our cars have.

Obviously there are many that have never used a BOV and have never had a proplem or will have a problem. I think there are too many variables when determining if a Turbo lasted longer due to a BOV. But those who have used them don't seem to have too many Turbo issues. I'm sure some have tho.

They do look kool tho... I just can't see it doing anything but a good thing but that dosen't make it necessary tho.

 

[Underboost]

I've never ran one either but then again I'm still running an internal wastegate. :smile:

 

[turbojimmy]

I know the turbine doesn't spin backwards, but I do wonder where the air goes when you slam the throttle shut. I had always assumed the fluttering sound was air rushing back out the air cleaner (since that's where the noise is coming from) but I never cared enough to investigate.

I 'cured' my part-throttle compressor surge with a BOV. I used a BOV that has a port on both sides of the diaphragm in conjunction with a pop-off valve (to control when the BOV sees boost). It's not perfect, but I finally got it set to where it will bleed that excess boost away from the intake tract at part throttle. This way I can keep it out of the surge zone but while feeding it only the amount of air the engine can ingest. It was a balancing act between the pop-off valve and the tension on the BOV spring but I finally found a good balance. If I go WOT it slams shut immediately. The real irony with this arrangement is that it is less effective when I let off the throttle (which is what a BOV is supposed to do) - I still get a 'sneeze' for a split second before the BOV opens and vents.

I haven't had time to move my Tornado to see if that does any good (for those following the Tornado thread).

I had thought about ditching the BB T70 and getting one that was more appropriately sized since that's the proper way to cure surge. BUT, I was driving my brother's GT3255-equipped car over the weekend and that thing was surging too!

Last, I think the BOV sounds neat. Much better than the turbo flutter. But that should be on the bottom of the list of reasons to get one.

Jim

 

[SloGN]

well a blow-off valve or aka recirculation valve does more than one would think of just dumping the pressure off when the throttle is closed under boost.


okay here is a scenario. your crusiing down the road @ say 60mph . while your cruising @ 2300-2400 rpms there about right. since your just cruising there is no real pressure on the throttle so maintain those speeds. you at about 10-12% percent throttle. so that means the butterfly is barely open but the engine rpms is @ 23-2400 rpms so that means the turbo is spooled up per say due to the amount of exhaust gas is flowing thru the turbine. so since the turbo is spooled up is tring to compress air against the abck og the butterfly all the time. If one had a BOV/recircualtion valve the turbo would not have to be compressing air against a almost shut butterfly. When allowing the BOV to be open and the turbo not compressing air the turbo would simply run @ a higher idle rpm while at cruising. this would allow less energy to be used to get eh exhaust out of the engine and would help fuel mileage. since there is really no work to be done by the exhaust. The jap car have been doing for awhile now.

IF you have a mass air car all one would have to do is hook the BOV back into the intake side of the turbo inlet and it would simply recirculate the air until the BOV is shut by boost pressure and then it's on

also since the turbo would be running in a vac per say with a BOV. the idle rpms on the turbo would be higher and that alone would help some lag.


ok the turbo is spinning @ 50,000 rpms with a none BOV @ 23-2400 rpms with the turbo tring to compress air with the butterfly open @ 10-12 %.

ok with a BOV allowing the turbo to dump off that air it's tring to compress @ 23-2400 rpms the turbo would then not be having to compress air so the idle speed of the turbo could be in around say 75,000 rpms. as you can see if would help on lag/fuel mileage.


any of you guys ever have your car running with the I/c pipes off and see how much air the turbo is flowing @ idle (8-900 rpms) well then imagine that @ cruising speeds/engine rpm)



but what the hell do i know.

 

[DailyDrifter]

I knew you would start to see it our way


And where the hell is 86Nick that started this mess............thanks Nick, start a fire and walk away

 

[T-Type85David]

really late but, anyone needs a good BOV or whatnot try out frozenboost.com just my 2 cents

 

[GNVYUS 1]

Wow, frozenboost has Tial knockoffs for dirt, that's hard to pass up if you are on the fence with this issue.

My take on the blow off is this with automatics, rebuilds are around $400 on most journal bearing turbos, blow offs are generally $300 after install etc. I would take my chance with the rebuilds, especially since most of us always upgrade our turbos every couple of years anyways. :biggrin:

But if the Frozenboost knock offs function like the real deal, not much of a loss on that one.

 

[T-Type85David]

Yeah i mean why not try them out and see if it works out, i mean the price is low enough to test it out. 50mm tail why not right????? anyway i really would like to see a 86/87 Gn use 1 of the water to air IC kits and see how it works out for them. On an other note, since nobody is helping me out with my other post, where do i hook up my AIR/fuel gauge????

 

[nuclearxp]

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.

A BOV that is setup properly and sized correctly does NOT bleed boost. The manifold pressure that goes to the BOV should keep it closed under boost. If you're losing boost you either: don't have a good line going to the BOV, don't have the correct spring tension to keep the valve closed, or you have too big of a BOV for your application.

In regards to the automatic vs. manual discussion, yes a BOV makes more sense because you're letting off the throttle more. But regardless with either type of transmission, snapping the throttle shut forces pressure back into the turbo. Regardless of whether the turbo is getting "spun backwards" or not is irrelavent. Any abrut changes in rotational velocity for something spinning at ~100,000 rpm is NOT good for it. I don't know why you would ever not want to invest in a $200 piece of hardware to ensure the longevity and proper functionality of your turbo.

 

[Blazer406]

nuclearxp.... I don't think anyone disagrees this high pressure pulse of air is not a good thing. I think the jury is still out if it does any measureable amount of damage. Most people I know that have run turbos without blow off valves have not noticed their turbo "going out". I got 159k miles out of my stocker... and the only reason it took a dump is because I spun a mean bearing.... and two rod bearings... and put all that metal in the oil... .that ended up going thru the turbo bearings...

Just an opinion...

I'm not going to run one... because it adds more complexity....and just another failure point during a run...

 

[nuclearxp]

Well I disagree. I don't think all the time and effort to develop BOVs was spent because they don't prevent damage but just make noise.

And I personally had a stock (rebuilt) turbo die on me from a bad BOV. Let's also keep in mind that those running boost controllers, and therefore higher boost will most likely see significantly more stress put on their turbos from the higher backpressure.

And as another point of failure, I look at it is a safeguard. If your BOV fails, worst case scenario is you get no boost. If it locks shut, then you're right back where you started without one.

Also killing your turbo from spinning a rod bearing and getting oil in the turbo, thats what they make turbo saver oil filters for.

 

[Underboost]

Call me dumb but I think a BOV's are best fit for stick-shift cars.

 

[jhanson1750]

okay here is a scenario. your crusiing down the road @ say 60mph . while your cruising @ 2300-2400 rpms there about right. since your just cruising there is no real pressure on the throttle so maintain those speeds. you at about 10-12% percent throttle. so that means the butterfly is barely open but the engine rpms is @ 23-2400 rpms so that means the turbo is spooled up per say due to the amount of exhaust gas is flowing thru the turbine. so since the turbo is spooled up is tring to compress air against the abck og the butterfly all the time.

This only works using your assumption as stated. At partial throttle there is insufficient exhaust energy to produce boost. Turbos work on ENERGY NOT JUST FLOW!!! There is an easy proof test. Move the line to the boost gauge to a PRE-throttle blade point. You will see a reduction in vacume but until you input enough energy to overcome the A/R ratio (+or - a slight paracitic loss) of the turbo you will not start to build pressure. There will show a rise in pressure due to the compression of the mass of the column of air colliding with an obstruction (throttle blade) and a corrisponding "pressure revision wave" reverbirating backwards in the column.

So I agree with EVERYONE, they work perfectly on NEITHER a stick or auto. So If you want to use one do so! :biggrin: Jon Hanson

 

[eightBALL]

It's only "rice" if you run around with your BOV going off *see: SRT4's everywhere. Some do make a good amount of noise, but I must admit, they do sound friggin cool.

As for them not being useful and just making noise ... I'm not real sure about that. I do see them serving a purpose. Also, there are many BOV's that make hardly any noise at all, just the sound of escaping air that's barely audible.

 

[GNVYUS 1]

Blow Offs are only good for hunting ducks.

YouTube - blow off valve duck call

 

[kingots2004]

i know the is old but i had a cpt66 turbo not sure of the age that looks like it twisted the exhaust wheel off the shaft. something broke it! and to say they are just for noise i dont see to many outlaw 10.5 cars running without blowoff valves do you? i guess those 6 and 7 sec quarter mile cars just like the ricer noise lol. call turbonetics (the people who make the turbos not the blowoff valve) and they will absolutely tell you to run one.mines in the shop right now getting one installed. as for buick designers not putting one on the car lets see: they didnt put 6776 turbos or front mounts or 9 inch converters or fast xfi or 60 pound injectors or the most needed thing for the buick motor to live a ROLLER CAM so why do we do it?