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Happiest when Tinkering
 
gsmith660's Avatar
 
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Do I need a blow off valve?

I need advise and opinions on blow off valves. I do have the PSSSSSTTTT sound when I shift so I suspect that is pressure spiking (but it sounds so cool) and will shorten the life of the turbo and what other problems can it cause? Did I mention it sounds so cool, oh well so what should I do? Since it is not CIS I can vent to atmosphere and I am thinking I can weld a flange on to the turbo outlet right below the intercooler it is stainless. Pic of motor to give ideas.

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Old 02-26-2010, 04:19 PM
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Nice looking engine layout!

You must already have a BOV on there somewhere - as any turbo charged car has - but I can't see it (probably mounted someplace on the back side of the IC). That's the psssstttt you're hearing when you let off the throttle to shift when on boost. A small vacuum line is opening the valve and venting the boost to atmosphere. You can do that with EFI (vent to atmosphere), but with CIS it causes havvoc with the fuel mixture. Getting rid of the boost, whether you recirculate it or not, is what's important so as not to stall the turbo compressor. I suspect you're already there....unless you did all the work yourself and did not install a BOV, in which case your location of choice should work just fine I would think.
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Old 02-26-2010, 06:02 PM
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Quote:
Originally Posted by mark houghton View Post
Nice looking engine layout!

You must already have a BOV on there somewhere - as any turbo charged car has - but I can't see it (probably mounted someplace on the back side of the IC). That's the psssstttt you're hearing when you let off the throttle to shift when on boost. A small vacuum line is opening the valve and venting the boost to atmosphere. You can do that with EFI (vent to atmosphere), but with CIS it causes havvoc with the fuel mixture. Getting rid of the boost, whether you recirculate it or not, is what's important so as not to stall the turbo compressor. I suspect you're already there....unless you did all the work yourself and did not install a BOV, in which case your location of choice should work just fine I would think.
Nope I dont have a BOV I was reading and the noise I am hearing is the pressure spike from the compressor when the trottle closes and is not good for the motor I am looking for opinions about this. Thanks that is the layout I concocted when I started laying out the parts.
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" Porsche there is no substitute" I always liked that saying. Air cooled is the only way to go!
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Old 02-26-2010, 06:14 PM
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Quote:
Originally Posted by gsmith660 View Post
I need advise and opinions on blow off valves. I do have the PSSSSSTTTT sound when I shift so I suspect that is pressure spiking (but it sounds so cool) and will shorten the life of the turbo and what other problems can it cause? Did I mention it sounds so cool, oh well so what should I do? Since it is not CIS I can vent to atmosphere and I am thinking I can weld a flange on to the turbo outlet right below the intercooler it is stainless. Pic of motor to give ideas.

[/img]
You will get as many different opinions on this one as there are contributors.
Cars were turbocharged for years before BOV were added to the intake duct and we saw very few turbocharger failures. It's my experience you are OK if you run street boost. BTW I like the sound also.
Old 02-26-2010, 06:30 PM
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Quote:
Originally Posted by copbait73 View Post
You will get as many different opinions on this one as there are contributors. Cars were turbocharged for years before BOV were added to the intake duct and we saw very few turbocharger failures. It's my experience you are OK if you run street boost. BTW I like the sound also.
Yeah Copbait, you're right about that for sure. But contributing is the fun part.

I guess I never realized that the backpressure "spike" as the turbo slows down can be heard as a pssssttt sound. To me, that's air escaping to atmosphere. Gsmith, that's one hell of a nice setup you've crafted. The only other thing I could offer would be that you might experience less turbo lag (and arguably less turbo wear) with a BOV installed.
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Old 02-26-2010, 06:56 PM
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It is pretty cool isn't it. I am running 7 lbs of boost so I would think I am ok I may install a BOV to reduce lag and keep the turbo spooled up but right now it is fun to drive and the sounds it makes reminds me of the old cart indycars and the sounds they made. I still am looking for all opinions though so let them fly.
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Old 02-26-2010, 07:01 PM
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My motor is already running at the ragged edge of what I think a mag case can take so I know not having a BOV adds wear to the turbo but does it stress the motor or does the press. and stress get stopped at the butterfly?
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" Porsche there is no substitute" I always liked that saying. Air cooled is the only way to go!
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76 Blazer also restored by me
Old 02-27-2010, 04:25 AM
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bov

my car is a modified efi car with a bov...i remember very well the time that i forgot to reconnect the vacuum line to the valve... building 14 psi in first and letting off to shift to second.....seals destroyed in a heartbeat as well as the rotor shaft...i did not realize that a car could generate so much smoke from the exhaust!!
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Old 02-27-2010, 05:21 AM
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I bought my car without one but quickly put one on because it slams the cartridge back and forth shortening the turbo life.
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Old 02-27-2010, 07:17 AM
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Quote:
Originally Posted by gsmith660 View Post
My motor is already running at the ragged edge of what I think a mag case can take so I know not having a BOV adds wear to the turbo but does it stress the motor or does the press. and stress get stopped at the butterfly?
No stress to the engine proper outside the intake system (hoses, o-rings, brackets). Right now you are deadheading the boost against a closed throttle and the turbo is going into surge (the aerodynamic area to the left of the diagonal line on a compressor map). This can cause the thrust bearing to fail or in turbos other than modern Garrett break the locking nut torque. There are many factors involved in predicting if or when a failure will occur, boost level being significant. I don't consider your mild boost to be significant.

All turbochargers pass a thrust bearing qualification test. In fact running in surge is required just to generate a compressor map. All turbocharger companies say regular OPERATION in surge will fail the bearing system. I would not expect any healthy turbo to fail the first time it surged however it’s common to get a sound like this when a turbo has a catastrophic failure.

All said, you will retain (a) sound if you just add the BOV and vent to atmosphere. It’s best you do this. This eliminates the risk of surge as your turbo will not see deadheading against the closed throttle. As for increased boost response by recycling air back into the compressor inlet? In street operation that stuff is mostly BS the factory used to hide the facts: 1) CIS demands it for proper operation, 2) MOST people are put off by unusual sounds......even turbo whine!

In my book a turbo engine should chirp or wheeze on shift plus whine up and down with boost.

Last edited by copbait73; 02-27-2010 at 04:15 PM..
Old 02-27-2010, 10:19 AM
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I just started it up after sitting for 2 and a half months balked a little smoked a little took a couple priming pulses and had to clear its throat very minor backfire and then nice even idle. Only hear the sound when driving and coming off boost. I think I will install a BOV before I get into the driving season just to be safe. I think I will get that new one everybody is talking about.
SYNAPSE ENGINEERING Synchronic Blow Off Valve SB001 : SB001A Blowoff / Bypass Valves Momentum GT
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" Porsche there is no substitute" I always liked that saying. Air cooled is the only way to go!
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76 Blazer also restored by me
Old 02-27-2010, 10:55 AM
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