1g BOV on a 2g, vacum leak?

[WSU99GSX]

I remembering reading some where that with the 1g BOV on a 2g it will leak alittle at idle, like my vacum at idle is about 18 or so, in park it goes up to 19. So does the 1g BOV on a 2g leak at idle?

 

[steve]

An uncrushed 1G BOV is open at idle on either generation DSM. It opens anytime the lower section is 7.7psi higher in pressure than the upper section. Since that's about 16 in hg vacuum and your intake pressure will be close to atmospheric at idle the BOV will be open.

Thats one reason why venting a 1G BOV isn't a very good idea. The air that enters via the open BOV is unfiltered and unmetered.

Steve

 

[WSU99GSX]

Thanks, that is true, with the BOV at idle I do read about 16 vac. Just making sure that is normal. Oh and I don't vent, nor do I plan on it.

An uncrushed 1G BOV is open at idle on either generation DSM. It opens anytime the lower section is 7.7psi higher in pressure than the upper section. Since that's about 16 in hg vacuum and your intake pressure will be close to atmospheric at idle the BOV will be open.

Thats one reason why venting a 1G BOV isn't a very good idea. The air that enters via the open BOV is unfiltered and unmetered.

Steve

 

[Defiant]

I remembering reading some where that with the 1g BOV on a 2g it will leak alittle at idle, like my vacum at idle is about 18 or so, in park it goes up to 19. So does the 1g BOV on a 2g leak at idle?

Apparently you're an automatic transmission (which you really should mention in your profile tag). When in gear, the engine has to open the throttle to maintain idle speed against the drag of the torque convertor. When the throttle opens, vacuum goes down- because "vacuum" is only the pistons sucking against the closed (or restricted) throttle. The very best normally-aspirated engines can get vacuum as low as about 3"hg, that value caused merely by intake air friction against the tubing of the intakes.

 

[WSU99GSX]

So is it normal then when in drive for a 1g BOV to cause a leak that may cause a vacum reading of 16 on a 2g?

 

[steve]

You seem to be confused. The BOV doesn't have any effect on the engine vacuum.
Please reread what Defiant wrote. Pay close attention to "When in gear, the engine has to open the throttle to maintain idle speed against the drag of the torque convertor. When the throttle opens, vacuum goes down- because "vacuum" is only the pistons sucking against the closed (or restricted) throttle."

Steve

 

[WSU99GSX]

You seem to be confused. The BOV doesn't have any effect on the engine vacuum.
Please reread what Defiant wrote. Pay close attention to "When in gear, the engine has to open the throttle to maintain idle speed against the drag of the torque convertor. When the throttle opens, vacuum goes down- because "vacuum" is only the pistons sucking against the closed (or restricted) throttle."

Steve

Okay, wow I must sound stupid, I get what he was saying now, so because I have an auto I have higher vacum, so unlike a manual for me to run vac. higher then 20, say 16, that is normal.

 

[Defiant]

It sounds more like you have an efficient engine- high idle vacuum (in park or drive, either one) is a sign of a healty engine.

The BOV being open at idle -or, any other time not under boost- is only allowing some air to bypass the turbo, intercooler and all that drag and distance. Since it's already been metered, this is a good thing.

Stop thinking about it. You're fine.

 

[WSU99GSX]

It sounds more like you have an efficient engine- high idle vacuum (in park or drive, either one) is a sign of a healty engine.

The BOV being open at idle -or, any other time not under boost- is only allowing some air to bypass the turbo, intercooler and all that drag and distance. Since it's already been metered, this is a good thing.

Stop thinking about it. You're fine.

Okay thanks, I was just wondering since I read some where that a heathy 4g63 should have 20 vac. Thanks though!