Stock boost and recirc bov

[Davezj]

hi guys, got two questions.

Got late Dec 96 Legnum auto, boost gauge only goes to 0.5-0.55 bar (7-8psi) is this standard?

Is this correct operation for stock recirc bov. in Neutral no boost is generated when rev'ed. does the recirc valve open wide to stop boost when not in a drive gear. Normal boost generated when in drive gear.

What opens the recirc bov, is it the trapped boost pressure when the throttle valve is closed and the boost is cut to the inlet manifold but still resides in the pipework and intercooler all the way back to the turbos. Is it then the recirc valve lets go and dumps the excess pressure somewhere.

Technically thats three question but i am sure you won't mind.

cheers

Dave

[Kieran]

Your boost reading is correct for a stock, pre-facelift Auto VR-4.

No boost is generated in neutral because there's no load on the engine - so even though the revs are up, there's only a relatively small bang in each cylinder, meaning there's not much demand for air and not much exhaust with which to spin up the turbos to boost. At least I think that's how it works. You can rev and get a *bit* of pressure going on, but not as much. I think this is how it works anyway!:undecided


Our BOVs work like the one discussed in this article:

http://minimopar.knizefamily.net/perf/bov.html

Hope this helps!

[Kenneth]

Hi Dave,

Turbos are what is termed a 'load based device'. this means that it should only really work when needed, or the engine is under load.
When you rev the engine in neutral, there is no engine load to speak of, and therfore the turbos do not work hard.

If you hit the pedal from idle up to about 6k, then let off sharply you may produce boost as the speed the engine is trying to increase RPM does create some load.

A bypass valve is supposed to open when there is a difference of pressure between what is in the intake plenum and the intake pipe work before the throttle plate. so, when you take your foot off the pedal, the throttle plate closes and the plenum goes to vacuum while the turbos continue to push air into the pipework. this difference in pressure causes the bypass valve to open and eithier recirculate or dump the air.

Hope this helps you :)

[Davezj]

Thought that was about the size of but i like to have my theorys confirmed.

Thanks very much for both of you.

Nice link kieran

Cheers