blowoff valves: anyone have experience with negative effects from not using?

[GN noslo6]

Hi all,

I am the owner of a 1987 Buick Grand National and recently wondered why almost no one with GNs, including some very highly modified cars, runs blow off valves. Given that my inquiries in our forums have gotten little interesting feedback, I thought I'd try the tech gurus for my next favorite cars!

So has anyone ever seen bearing failure or compressor fin damage that they attribute to a malfunctioning or non-existant blow-off valve? Any opinions on whether this is more than a *technical* concern?

Forcing the charge back through the compressor seems like a very real concern to me, but again no one in our camp seems to use them and there seem to be no problems (at least detectable ones...). Maybe the larger reason you don't see any on the GNs is that we're all autos so there is no performance gain, but I'm still interested in the potential damaging effects.

many thanks,
Scott

[BatmanGSX]

Originally posted by GN noslo6
Maybe the larger reason you don't see any on the GNs is that we're all autos so there is no performance gain

Yup, that's why, you aren't closing your throttle under load as often. As you stated, a BOV won't be beneficial for performance to you. I'm sure there are some times when you will be completely lifting under load/during boost... Just not very often. I do know that the Cyclone and Typhoons are equiped with them from the factory, they are all autos as well. I would say if nobody else is using them and having no problems then you will be fine.

[Rdy2race]

Well I am A X GN oner and I suffered from bearing failer. I was running a TE-34 and after it failed I went to a TE-44. The biggest problem I saw was even on light boost I would get compreeor surge, Now if i knew then what I know know the FIRST thing i would have done was a BOV ( by pass valve if you want to be picky about the name ) now with the huge imvestment in the car I would think thart many other would be doing this also. part throtal and having it open is not a prob if you know the inner working of a BOV but that is not the Q at hand. I feel even STOCK it would be a good idea and allow the turbo to live a longer life and have tighter clearances. it's a simplke install with the location of the upper IC pipe and the air intake. A solid pipe will be needed for the intake and not the factory pipe. The reason this is not factory is B/C they feel it's a Auto trany and will not experance any problems. But then again many things were over looked in the GN's like rear body mounts!!!

Trust me I had the horror 11 sec GN that ate $25K in 2 years so I do know a good amount about them. Run one.A factory 1G BOV from a DSM is about $50 and works well and with very little mods can be fitted to the GN with no probs in driveability.

so in a rush no spell check :D
Good Luck
BM-

[GN noslo6]

Yep, even at part throttle I get compressor surge as well.

A $25,000 11 sec GN? Even if that was 11.000, you must have had some incredibly bad luck. My condolences- hope you're having more fun with the DSM's!

Thanks for the reply and the tip on the 1G unit-- that may be my next purchase,

Scott

[Cooter]

sy-ty's don't have bov's....

Cooter
http://www.sound-performance.com

[Rdy2race]

the SUPER short list

3 motors
3 turbo's
2 level 10 tranys
2 converters.
2 fuel pumps
some cash on junk chips ( all of them are junk IMHO to general and just time bombs )
7th inj from ATR. Never ran the way I wanted it to.
2 rear air bags
a few sets of tires
1 heater core
crank angle sensor
a few o2's
a few welding jobs for the driver side manifold.
saw how far I could throw the POS VDO EGT, got another one greddy

I could keep going but you have a idea

[ForestTalonAWD]

Even on an automatic, A compressor by-pass valve (or BOV) is still something you don't want to leave off. The reason Sy-Ty's don't have BOV's either is that they all auto's, like the GN/T-Types.

Rdy2Race, I agree - after dropping the cash for a large turbo, I'd want to protect my investment from compressor surge. Especially considering how cheaply a BOV could be installed. Fitting a BOV to a GN shouldn't really be that big of a deal, either, as long as you had a source for manifold pressure.

[Rdy2race]

ya a pressure source would be cake. the G's have a Vac block on the top of the intake just past the TB. if I remember right it has 6 taskoff's on it so pleanty of room for one tap.

( BTW this spot is also the place that the 7th injector is mounted. If you look on the dash of a GN look at the lights that light up when you turn the key on. On the left side on the top or middle was it is a light for "power Injection" The orginal plain from GM was to install Alch Injection but the idea didn't fly when they thought that it would be to hard for the end user to find Alch for the cars. This makes the 7th inj a bolt on to the intake!! )

BM-

[TheHondaKiller]

I would reccomend a bigger BOV than the 1g for a GN. I run into surge problems at 15+psi on my t3/t4 because it flows too much air for the 1" valve to vent before surge, it a a single surge but still bad enough to merit the purchase of a large valve (Godzilla anyone? :-) I would reccomend the Godzilla for two reasons:
1- it has a 1.5" diameter valve that can flow 2x a 1g BOV (which is good for 350-400hp)
2- it is dual port; push and pull type, for the fastest response possible

[Cooter]

if you want big the only way to go is the old hks type R or the greddy type r.. absolutely huge... will flow more air than a 14b... btw.. i've seen the godzilla bov's from turbonetics.. (i'm assuming this is the godzilla your talking about) and i wasn't impressed.. the build quality wasn't even close to the greddy or the hks.. and they are both set up for dual port.. i personally wouldn't hook it up that way, but thats me...

Cooter
http://www.sound-performance.com

[TheHondaKiller]

Please explain the build quality problems with the Godzilla. I have checked all aftermarket BOV's including the Greddy type R and the Tial and by far the best I have seen was the Turbonetics Godzilla valve. I have even used a Godzilla on an old car with success, the dual port setup is amazing. I imagine the Godzilla would work to 800+ hp due to its severe flow capacity. Also using dual port allows you to pull the BOV from the intake manifold vacuum source after the throttle is lifted and the push from the compressor housing that will hold the valve open as long as boost exists the piping. There is absolutely no negative to running this way, only positive with extra fast response. Back up your claim...

[Cooter]

well...
1. the valve that i looked at was brand new in the box... the plunger stuck wide open when i pushed on it...

2. somehow during assembly they managed to scrape the coating off in three places....

3. we put a miti-vac on it and it leaked!

4. the one we got had a v-band mount that did NOT seal properly..

i have NEVER seen a greddy or hks come out of the box with ANY problem.. in fact the ONLY problem i have EVER had with a greddy or hks is after a few years of use the diaphrams may dry rot...


as for dual port setups... if your using any type of aftermarket bov the spring pressure can be backed off to a point where the thing will hang open at idle (with the exception of hks sequential and new type 2 racing).. now you tell me how your dual port setup will react faster if it opens at 20in Hg with no pressure on the i/c pipe side... most of the time on a dsm ppl have the bov spring cranked down so it stays closed at idle so they can vent it atmostphere and keep their car idling... dual port setups just create another potential vaccum leak... i'm not saying its wrong to do it this way.. it's just not the way i install them... EVER... besides.. did you also think about the fact that there is a pressure difference in the i/c pipe compared to the manifold... all it takes is 2-3 psi difference and guess whats goanna happen.... the pressure in the bottom side is goanna force the bov open and holy shit a boost leak.. if i EVER see a car come into the shop that has boost leak problems and the bov is set up this way... this is the first thing i change... and you know what? i've cured boost leak problems on TWO cars like this... they were both modded mildly and both had stock intercoolers and the bottom port was tapped on the pre-i/c side and the pressure drop across the intercooler caused enough of a difference to make it open slightly at big boost levels... besides.. as long as there is pressure in the i/c pipe there is force being exerted on the plunger, therefore holding it open, it may close slightly as pressure drops in the pipe, but it will stay open as long as there is some positive pressure in the piping..

Cooter
http://www.sound-performance.com



[Edited by Cooter on 08-02-2001 at 02:15 AM]

[TheHondaKiller]

Sounds like you got to play with a defective Godzilla valve. That's too bad you had such a bad experience with it. As far as stock intercooling systems go with high inefficiency (say 3psi of pressure drop) I think that this could cause a boost leak. But on highly efficient setups with 1psi or less this shouldn't pose any sort of problem, besides, use of a small restictor on the side port would be wise to compensate for any sort of pressure drop in the system and would fix all problems associated with a dual port setup. You would still see the fast response benefit as well.

[TheHondaKiller]

Foot in my mouth update!!!
I just put on my Godzilla and the fucker leaks like none other. I shimmed the spring, lapped the valve and valve seat and changed how it saw pressure and it still leaks like a civ... at 10psi! I really need a BOV and my last Godzilla was good but this one sucks. What high hp BOV can I get that won't leak but will flow and react quick enoungh to prevent any surge on my beloved Garret???
Help me out here, I endorse someone's supposedly good product only to get screwed by their poor quality! Ideas... please

[shabby]

You cant beat the hk$ bov, the turboxs type H is right up there too.

[Cooter]

like i said before if you can find an old hks type r or a greddy type r they are both huge and react fast as hell and can be set up for dual port operation...

Cooter

p.s. I've never had any problems with these type of valves...