Blow Off Valves Fact vs. Fiction

it seems to me there are two theories of thought on this.

Every Turbocharged car needs one

or

Completely unnecessary in the world of ball bearing turbos.


Anyone have any real world actual knowledge on this?

---

-Tom
DemonRallyTeam | Fine Tuning | CTS Turbo & RP Turbos | RalleyTuned | JRM | Meister Autowerks
Spitfire EFI | Product Apparel | JVAB Imports | NLS | AP Tuning | USRT

Add us on Facebook | Next Event: 2013 Olympus Rally June 22-23 Olympia, WA

Option 2 For real race cars, and BB turbos. Crawford performance has 100's of turbo kits on the streets, maybe 1% have BOV's rest do not. We hear nothing of the customers complaining about blown turbos. Ive driven the setup with no bov, drives fine, decided to go the same route on my own car. None of the car KB raped in his videos had a BOV.

Interesting. I thought compressor surge was compressor surge. If I don't need a BOV that's one less item to worry about. More research is needed obviously...

---

Jay Woodward
Snohomish, WA
'90 Mazdog Frankenprotege
Chronologically, 46...

Supposedly there is good compressor surge (off throttle) and bad compressor surge (on throttle).

Here is a video I found of BAD compressor surge





Here is a video I found of Good compressor surge (ALA John Lane's Volvo)





I still am lost on this BS though, I already have a couple of blow off valves, I'd rather sell them and race or buy a tire or something though....if my turbo ain't going to suffer because of it.

---

-Tom
DemonRallyTeam | Fine Tuning | CTS Turbo & RP Turbos | RalleyTuned | JRM | Meister Autowerks
Spitfire EFI | Product Apparel | JVAB Imports | NLS | AP Tuning | USRT

Add us on Facebook | Next Event: 2013 Olympus Rally June 22-23 Olympia, WA

You can hear it in car really well with this video. 35r Turbo 500+ whp NO BOV

Good video for that chirping sound.

What would the benefit to be for not running one other than cost?

I mean it probably can't hurt (unless it's defective) to have it installed right?

---

-Jason

BOV will bleed 100% or damn near 100% of your built up boost between shifts so your system has to go from 0 PSI or vacuume to given positive boost pressure. No BOV the system cant really get down that low since there is no place for the air to go so your after shift spool time is quicker. Plus yeah it would suck for one to get stuck open on a stage for any reason NA car hello!

I know Senior Lane doesn't run one, but Senior Jardeval does. I read about how when you close the throttle, you get big pressure spikes that if there's no BOV, go back to your coldside, slowing, stopping, or maybe even making it go backwards (although how you confirm this, I don't know). I reckon if you're roadracing and almost never slamming the gas closed, that you might not get too many spikes but it seems like every now and again I find myself lifting off the throttle for some reason or another, mostly having to do with an awareness of personal mortality and impending trees or somesuch. So do you run a BOV to maintain reliability and avoid spikes that might damage your throttle plate or bust a hose or break a turbo, along with maintaining spool between shifts, or go without and lose one subsystem to break, and don't worry cuz it won't hurt your turbo, and either get worse performance or better between shifts depending on which story you buy?
I'm thinking once my car's back on the road, I'll try running it with the bov line plugged and see how it goes. I don't know that I wanna do that to my street car, but maybe.
One other thing, it looks like vent to atmosphere BOV's should oughtta run an airfilter one 'em in rall

---

Jay Woodward
Snohomish, WA
'90 Mazdog Frankenprotege
Chronologically, 46...



Edited 2 time(s). Last edit at 02/24/2010 11:27AM by Jay.

Whats with all the senior prefaces lately?

---

Welcome to the cult of JVL drink the koolaid or be banned.

Tom B Wrote:
-------------------------------------------------------
> Supposedly there is good compressor surge (off
> throttle) and bad compressor surge (on throttle).
>
> Here is a video I found of BAD compressor surge
>
>
>
> Here is a video I found of Good compressor surge
> (ALA John Lane's Volvo)
>

John Lane's car, all 500+hp of it, has never had a blow off valve, btw, and he's never blown a turbo. We put one on at the very beginning but it was a piece of crap and leaked boost so I shimmed it so it would never open. We needed something to plug the hole in the intake hose therefore it looked like it had a blow off valve.

Just copy what they do on Ken Block's Fiesta...

http://www.motoiq.com/MagazineArticles/tabid/59/articleType/ArticleView/articleId/1289/PageID/1441/Inside-the-800-hp-Olsbergs-Fiestas--update-1.aspx

What's it have for a turbo?

---

Grant Hughes

Coleman in the "subaru boost tube" thread made this comment:

"Pete,

The damage caused by compressor surge is typically to the thrust bearing. When that huge spike in charge pressure pushes back on the compressor wheel, its acting on the full surface area of the wheel. Conventional sleeve-bearing thrust bearings are pretty weak and will eventually fail if repeatedly subjected to this kind of abuse. Ball bearing turbos, though, have virtually indestructible thrust bearings (ie. they are no longer the weakest link), so you can get away with shenanigans like anti-lag, boost tubes, and such without guaranteeing turbo failure.

-Dave"


http://www.rallyanarchy.com/phorum/read.php?5,34529,36958#msg-36958

And that relates to John Lane's Volvo how? Or are you assuming it's a ball bearing turbo. I was more asking specific. Like, "that sweet Tiburon uses the Garret GT3071 turbocharger" or something similar to that.

---

Grant Hughes