Right all the debate about dump valves and performance got me thinking (yes, be worried!). I've had them installed for nigh-on 6 years. the last time I drove a Z in anger with stock recircs was mine, when it was a poorly white automatic, 6 years ago.

 

this is my understanding of how a DV'd system works:

a) floor it

b) boost builds up - boost gauge shows max (whatever that may be - say 1 bar for now)

c) enjoy the rush

d) foot off - TISH - boost gauge starts to quickly drop to vacuum as the compressed air leaves the system

e) engage next gear while the above is happening

f) back on the gas - boost builds back up, and we're back to b) again.

 

now if you had recircs, how right or wrong am i about this:

a) floor it

b) boost builds up - boost gauge shows max

c) enjoy the rush

d) foot off - boost gauge stays at max(?) or is the 'held' compressed air not measured by the gauge(?)

e) engage next gear while the above is happening

f) back on the gas - instantly back to max boost with no lag (?)

 

I honestly can't remember how this works... :confused: during the hot weather we've been having, I've noticed a slight drop in performance, including 1-1.5psi lower max boost on same settings and slightly more lag and even after my comments in the other thread(s) about this I got to thinking how much difference in performance there really is...

Your charge temp will be higher and as the air is hot, it's less dense, so less air to build boost with. Not really anything else to it.

 

The hesitation that useless DVs introduce to the system could be amplified due to the heat maybe. But the above is what's really affecting you.

The recirc and atmos work exactly the same way - the only difference is that the vented air in a recirc is.. recirculated through the intake tract. It's an economy aid as much as anything, and also the car runs smoothly. Boost isn't held however. Atmos bov's shag the MAF readings after venting and can result in momentary overfuelling on release, as does removing the BOVs. Performance difference is negligable, if even recordable - but mpg goes down slightly.

Your charge temp will be higher and as the air is hot, it's less dense, so less air to build boost with. Not really anything else to it.

 

The hesitation that useless DVs introduce to the system could be amplified due to the heat maybe. But the above is what's really affecting you.

 

On a similar vein, my car has BOV's fitted (will have to check make, can't remember now) but are only audible in a bridge/tunnel where the sound can bounce back..

 

What I've noticed is the engine/boost levels react differently depending on your throttle inputs (yeah, yeah - big surprise). Let me explain

 

a) put foot down

b) boost builds

c) revs rise to 6k rpm

d) depress clutch, lift throttle

e) change gear

f) engage clutch, push throttle

g) hesitates, then boost comes back all at once, not increasing - just instant maximum boost

 

So for all intents and purposes it feels like turbo lag, except it doesn't do it all the time.. this is the other scenario:

 

a) push throttle

b) build revs

c) hit 6k rpm

d) lift throttle slightly

e) clutch in, drop throttle

f) shift

g) engage gear and back on throttle

h) now there's no noticeable lag, but you CAN feel boost building - not instant..

 

I'm sure that'll make sense to someone, but not me.. :detective: