# Need Blow Off Valve plan



## azroyhelmy (Apr 21, 2011)

Do any one have plan for blow off valve for turbo engine?


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## gbritnell (Apr 21, 2011)

I'm guessing you're talking about a full sized engine and not a model? I can't imagine a model with a turbo would make enough pressured to require a pop-off valve.
gbritnell


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## azroyhelmy (Apr 21, 2011)

ya...sorry not to mention..yes,it a full scale engine...


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## waynes world (Apr 21, 2011)

they are cheap to buy why would you waste your time machining one for. you can get them on ebay dime a dozen.

its basically a 40-50mm bore dia with a piston with a teflon seal each end and a spring on top of it to keep it closed until the vacuum sucks it open to relive manifold pressure off the turbo to free spool to keep it spinning at rpm between gear changes. 

if you know what you are looking at you will know exactly how it works.


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## pickstock (Apr 25, 2011)

waynes world  said:
			
		

> they are cheap to buy why would you waste your time machining one for. you can get them on ebay dime a dozen.
> 
> its basically a 40-50mm bore dia with a piston with a teflon seal each end and a spring on top of it to keep it closed until the *vacuum* sucks it open to relive manifold pressure off the turbo to free spool to keep it spinning at rpm between gear changes.
> 
> if you know what you are looking at you will know exactly how it works.



its pressure isnt it?
during a gear change the throttle is closed but the turbo is still spinning and the manifold is pressurised, the pressure looks for a way out adn the only way is through the turbo or blow off valve/waste gate


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## Chaffe (Apr 27, 2011)

as mentioned the vac on overun opens the valve against spring pressure, ive made several in the past. The important thing to remember is to keep the dia of the "seal" where the piston meets the neck on the boost side smaller than the piston dia, or it will leak when it comes on boost due to the force on the piston. Ill do a sketch of a rough design and post it if you are interested? what size dumpvalve pipe is it going onto? 1" dia or 30mm? also is the vehicle using a metered air system or is it map sensing? this will determine the need for a "twin piston valve" or simply a non return device in the valve.


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## azroyhelmy (Apr 28, 2011)

Chaffe  said:
			
		

> as mentioned the vac on overun opens the valve against spring pressure, ive made several in the past. The important thing to remember is to keep the dia of the "seal" where the piston meets the neck on the boost side smaller than the piston dia, or it will leak when it comes on boost due to the force on the piston. Ill do a sketch of a rough design and post it if you are interested? what size dumpvalve pipe is it going onto? 1" dia or 30mm? also is the vehicle using a metered air system or is it map sensing? this will determine the need for a "twin piston valve" or simply a non return device in the valve.



chaffe-the pipe size is 30mm and the system runs with map sensor


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## Chaffe (Apr 28, 2011)

ok, i will do a sketch and post it for you, i will ommit the "one way, or twin piston" as this will not be required with the map sensing management, thanks chaffe


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## azroyhelmy (Apr 29, 2011)

THANKS A LOT CHAFFE! I REALLY DO APPRECIATE IT...DO YOU KNOW HOW WE COULD CREAT A DIFFERENT SOUND FROM AFTERMARKET BLOW OFF VALVE?


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## Chaffe (Apr 29, 2011)

its all down to hole size, shape and position, trial and error will prevail with the perfect sound


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## azroyhelmy (May 1, 2011)

ohhh ok..i shall try it in different holes,sizes n etc as u said chaffe. Can't wait to look at your sketch. Aren't they complete yet?


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## Chaffe (May 1, 2011)

lol, ill be back at work tommorow, then i can get use of the scanner and all will be clear!


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## Chaffe (May 2, 2011)

Here is a rough sketch i drew up, i hope it conveys the idea of what needs to be achieved, thanks


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## NickG (May 2, 2011)

Chaffe, that's a great schematic for anybody wanting to attempt one for their car. I've always been intrigued to know how the 2 piston type work but never had 1 to take to bits or been able to find a sketch on the internet. Don't suppose you could enlighten us if you have time?

Cheers,

Nick


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## Chaffe (May 2, 2011)

NickG  said:
			
		

> Chaffe, that's a great schematic for anybody wanting to attempt one for their car. I've always been intrigued to know how the 2 piston type work but never had 1 to take to bits or been able to find a sketch on the internet. Don't suppose you could enlighten us if you have time?
> 
> Cheers,
> 
> Nick


Of course, the twin pistin is in fact merely a "non return valve" that also allows for some ammount of resistance before opening so a car running a metered air system does not leak metered air when on part throtle (causing running/fueling issues)


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## azroyhelmy (May 3, 2011)

chaffe,
That was a wonderfull design! i will try to produce it shortly, and when it works i probably engrave your name on it!


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## NickG (May 4, 2011)

Chaffe,

Many thanks for that. As I said, I could never envisage how the two pistons worked because the bodies always seem to look the same from the outside. Think I've got one somewhere, will have to take it apart to see whether it's twin or single piston! It was on an R5 turbo (carb) so I think single.

Nick


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