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Corvairs That Are Draw Through Do Not Need a Blow Off Valve?
Posted by: Phil Dally ()
Date: November 27, 2020 06:31AM

Rather than clutter up the picture thread I started a new post.

I won't poison the well with my opinion because I'm no expert.

What say turbocharger experts here...plenty of gurus on hand.




Edited 1 time(s). Last edit at 11/27/2020 08:12AM by MattNall.

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Re: Corvairs That Are Draw Through Do Not Need a Blow Off Valve
Posted by: Phil Dally ()
Date: November 27, 2020 06:48AM

BTW: Not trolling the person I'm quoting...just looking for more information.

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Re: Corvairs That Are Draw Through Do Not Need a Blow Off Valve
Posted by: jjohnsonjo ()
Date: November 27, 2020 07:05AM

You not only don't them, you want them, if they blow off you would be blowing an atomized fuel mixture into the engine compartment of a running engine.

J.O.

65 Corsa Turbo Vert
79 Honda XL 500S
69 Honda CL 160 D
2010 BMW F 650 GS
2003 Bounder 36D
2013 KIA Optima SX turbo-AKA ZIPPY (wife,s car)
69 Newport Holiday Sailboat
Baja 150 dune buggy cart
Coleman HS 500 UTV
2016 KIA Sorento SXL Turbo

Bethlehem,Pa


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Re: Corvairs That Are Draw Through Do Not Need a Blow Off Valve
Posted by: Phil Dally ()
Date: November 27, 2020 07:07AM

Not if a waste gate and/or blow off is installed in the exhaust system before the turbo.

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Re: Corvairs That Are Draw Through Do Not Need a Blow Off Valve
Posted by: 63turbo ()
Date: November 27, 2020 07:41AM

Yes Phil, you are absolutely correct... not needed on a draw through. Blow off valves, compressor bypass valves are used on blow throughs to help mitigate surge/partial stalling when the throttle is suddenly closed. Surging is a rapid intermittent stall, and is caused by too much resistance for the tip speed. When the throttle is closed, after being into boost, the airflow through the turbo slows way down, but the turbo is still spinning really fast. At some point, this low airflow high tip speed condition causes airflow instabilities between the blades, and this causes the turbo to loose its grip on the air, leading to a big loss of airflow and pressure. Now the engine slows down. If the throttle is then snapped open, what can happen, and what surge is all about, is this: Throttle goes open, engine tries to take off, then the turbo tries to feed this demand, boost comes up way too quick for the engine rpm and goes into stall again, airflow slows down, a few nanoseconds later the engine consumes the boost spike and tries to take off, but since the turbo just stalled, the boost went away, engine airflow slows down then the turbo takes off, going into boost again but goes into stall (because the engine cant consume it all fast enough) and the cycle repeats over and over. Blow off valves can greatly reduce this phenomenon by inducing airflow through the turbo, but they are venting to the atmosphere. A bypass valve merely sends this airflow back to the intake. On a draw through, this low speed surging is literally impossible to have happen, although I've seen "slight" momentary surge at high rpms and higher boost levels. The evidence is a rapid wiggling of the needle on the boost gauge. You dont really want a blow off valve on a draw through anyways, if it is carbed as gas will be vented to the atmosphere, possibly causing a fire!

------------------------------------

Kevin Nash
Friday Harbor Washington
63 Spyder, Daily driver, EFI read about my project here: [corvaircenter.com]
first test start on EFI here:[www.youtube.com]
first official EFI boost test here:[www.youtube.com]
My new fan! [corvaircenter.com]
engine less 62 Spyder
Canadian 64 Monza Parts car






Edited 1 time(s). Last edit at 11/27/2020 07:44AM by 63turbo.

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Re: Corvairs That Are Draw Through Do Not Need a Blow Off Valve
Posted by: Phil Dally ()
Date: November 27, 2020 07:48AM

What is the difference between Blow Off Valve and Waste Gate?

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Re: Corvairs That Are Draw Through Do Not Need a Blow Off Valve
Posted by: thewolfe ()
Date: November 27, 2020 07:56AM

Blow off valve on intake, waste gate on exhaust. They are not interchangeable. One is made for intake air, the other for hot exhaust gases.

Nate Wolfe
Portland OR
65 Corsa 180

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Re: Corvairs That Are Draw Through Do Not Need a Blow Off Valve?
Posted by: Phil Dally ()
Date: November 27, 2020 08:19AM

That is my confusion...to me they were the same.

Our turbo cars came from the factory with none.

So then why not run with none in today's world?

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Re: Corvairs That Are Draw Through Do Not Need a Blow Off Valve?
Posted by: MattNall ()
Date: November 27, 2020 08:28AM

Phil Dally Wrote:
-------------------------------------------------------
> That is my confusion...to me they were the same.
>
> Our turbo cars came from the factory with none.
>
> So then why not run with none in today's world?


=======================================================

No need on Stock setups. Plain and simple.

MODERATOR
Sea Mountain, between Charleston Harbor and Coos Bay! SW Oregon Coast
Click HERE for My Website...Click HERE for My TechPages!
..............................110-PG.................................................Webered-Turbo

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Re: Corvairs That Are Draw Through Do Not Need a Blow Off Valve?
Posted by: American Mel ()
Date: November 27, 2020 08:31AM

Phil Dally Wrote:
-------------------------------------------------------
> That is my confusion...to me they were the same.
>
> Our turbo cars came from the factory with none.
>
> So then why not run with none in today's world?


Because we are MODIFYING our engines.
From the factory, they were so restricted, the boost was limited below the capacities of the engine.

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WA. state, 1 mile south of the Canadian border,
I am not at the end of the world, but you can see it from here.
Have; '66 Monza Coupe - 140, 4-spd. Daily driver beater
'67 Monza Vert. - 140, 4-spd. Daily driver beater
'67 A/C Moredoor Monza
Have had; '61 Monza coupe, 80hp, PG
'62 Monza Wagon, 4spd.
'63 Spyder,
'65 Corsa
.
non-vair
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Re: Corvairs That Are Draw Through Do Not Need a Blow Off Valve?
Posted by: Phil Dally ()
Date: November 27, 2020 08:35AM

Pretty sure the Rajay double E flow with aircraft impellers miniman82 built me for top end only (landspeed) needs a wastegate.

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Re: Corvairs That Are Draw Through Do Not Need a Blow Off Valve?
Posted by: American Mel ()
Date: November 27, 2020 08:38AM

Phil Dally Wrote:
-------------------------------------------------------
> Pretty sure the Rajay double E flow with aircraft impellers miniman82 built me for top end only (landspeed) needs a wastegate.


YES!

-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-
WA. state, 1 mile south of the Canadian border,
I am not at the end of the world, but you can see it from here.
Have; '66 Monza Coupe - 140, 4-spd. Daily driver beater
'67 Monza Vert. - 140, 4-spd. Daily driver beater
'67 A/C Moredoor Monza
Have had; '61 Monza coupe, 80hp, PG
'62 Monza Wagon, 4spd.
'63 Spyder,
'65 Corsa
.
non-vair
'04 Dodge Cummins Quad Dually, approaching 400K
'03 Honda Del Sol
17'Terry
[corvaircenter.com]

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Re: Corvairs That Are Draw Through Do Not Need a Blow Off Valve?
Posted by: MattNall ()
Date: November 27, 2020 08:44AM

Phil Dally Wrote:
-------------------------------------------------------
> Pretty sure the Rajay double E flow with aircraft impellers miniman82 built me for top end only (landspeed) needs a wastegate.
==============================================================

Sure it does... haven't blown a couple of engines at El Mirage? Too much Boost!

MODERATOR
Sea Mountain, between Charleston Harbor and Coos Bay! SW Oregon Coast
Click HERE for My Website...Click HERE for My TechPages!
..............................110-PG.................................................Webered-Turbo

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Re: Corvairs That Are Draw Through Do Not Need a Blow Off Valve?
Posted by: Phil Dally ()
Date: November 27, 2020 08:50AM

No never did it that way...mostly burned valves fron lean conditions.

New 650 CFM Holley cheater two barrel and intake pipe should fix that.

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Re: Corvairs That Are Draw Through Do Not Need a Blow Off Valve?
Posted by: Phil Dally ()
Date: November 27, 2020 09:03AM

Plus my new purty red Nash Super Fan will help it go faster too. smiling bouncing smileysmiling bouncing smileysmiling bouncing smiley

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Re: Corvairs That Are Draw Through Do Not Need a Blow Off Valve?
Posted by: MattNall ()
Date: November 27, 2020 10:48AM

Phil, what wastegate opening pressure have you run over the years?

MODERATOR
Sea Mountain, between Charleston Harbor and Coos Bay! SW Oregon Coast
Click HERE for My Website...Click HERE for My TechPages!
..............................110-PG.................................................Webered-Turbo

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Re: Corvairs That Are Draw Through Do Not Need a Blow Off Valve?
Posted by: Vairefast ()
Date: November 27, 2020 11:02AM

Like others have said, Blow off valve goes between the throttle blade and the turbo to let out intake back pressure when you let off the throttle. It also helps with keeping the turbo spooled up between shifting. It only works in Fi or blow thru carbs. If you are running an inter-cooler with blow thru I would highly recommend you try one. We have them on our drag cars and waste gates as well. 35-45psi boost. (Not a corvair) If you are running low boost it may not seem to make much difference. It will still save a turbo from surge, possible backfire that hurts them and should make it easier on the turbo between shifts. We have bent throttle plates from not using a BOV and ruined a lot of turbos.

Do not put a BOV on a stock suck thru system. You will be making a bomb.


The exhaust design on the stock corvair was the "wastegate" ie restriction. Anytime time you change to a larger or no exhaust(turbo only with 3-4" pipe no muffler) you cannot control how much boost the turbo can make. Then you need to add a wastegate. The good thing is a wastegate just doesn't dump all boost. You just control the max boost. It will hold boost psi to whatever you set it at. more or less.

Are you using a suck thru or blow thru set up phil?

Darrin
65 Crown
68 Monza convert

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Re: Corvairs That Are Draw Through Do Not Need a Blow Off Valve?
Posted by: Phil Dally ()
Date: November 27, 2020 11:04AM

10 psi...most I ever saw was 12.

New turbo should do around 25+.

That is per miniman82...we'll see.

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Re: Corvairs That Are Draw Through Do Not Need a Blow Off Valve?
Posted by: Phil Dally ()
Date: November 27, 2020 11:05AM

I Suck!!!

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Re: Corvairs That Are Draw Through Do Not Need a Blow Off Valve?
Posted by: Vairefast ()
Date: November 27, 2020 11:09AM

whens the next time you plan on running. I'll come to check it out.

Darrin
65 Crown
68 Monza convert

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