~17 In HG During Idle
 

http://i840.photobucket.com/albums/z...6/P1000775.jpg

is it normal to have the vacuum this "low" during idle? i've noticed the change ever i switched from my Blitz SS BOV to the current Greddy Type S BOV.

i swapped from the Blitz because it'd be stuck sometimes causing compressor surge. but for some reason, i felt that it held better because vacuum would be at 15 In HG prior to swapping the Greddy BOV.

notes:

• none of the BOV's were recirculating air back into the TID but i'm considering doing it with the Greddy BOV when i get my hands on that adapter.
• when cruising then letting go the throttle, the gauge would read between ~25 In HG. I don't recall the vacuum reading that low when i had the Blitz BOV a while back... :scratch:

ultimately, i just want to know if this is normal or not. and if not, what may be the reason why it reads low? vacuum leak perhaps?

and if somebody could let me know what the diameter of the nipple (correct me if i'm wrong) to recirculate the air from the BOV please? :)

thanks. :icon_tup:

17"Hg isn't low.

hell, if you claim to get anything over 18" i'd say your gauge is broken.

17 is pretty much what you should get.
when letting go of the accelerator you are suppose to get 25inhg+, unless you have a massive vac leak in the manifold.
A fresh rebuilt broken-in 13b will pull 16-18inhg at idle.

Ive heard also that porting will lower the vacuum to 12-15inhg at idle.
hell my engine is idling at 12inhg and its not even ported, compression just sucks is all LOL

Btw, higher the number, means more vacuum is being pulled.
15inhg with the Blitz SS BOV compared to the 17inhg with your Greddy BOV, the Greddy BOV is the better choice.
It seems like the blitz SS Bov is leaking.

my full bridges bounce around 5"..

BOVs shouldn't affect vacuum anyways, so something got unplugged while doing the swap.

Vacuum will fluctuate with the amount of load on the engine at idle, as well as the idle speed. A very very healthy stock port engine will idle at over 18+ inches depending on the aforementioned factors. Here is a video of a brand new FD engine (not reman) from Mazda idling at about 475mm Hg, which is around 19 inches vacuum.

http://www.youtube.com/watch?v=PkgeYeYdMo4

It does have to do with porting and compression though. A lot of non-performance piston engines will do 20+ inches of vacuum at idle. Stock Civic engines (D16Y8 for example) idle around 800prm and will pull 20 inches easily.

i see. thanks for the replies everyone. :)

i forgot to add in that i have a rebuilt street ported motor that has about 24,XXX miles already too. :icon16: also only running the BAC. other emissions stuff are gone (not that it matters... maybe?). as for the Blitz BOV, i have read a lot of negative feedback about it back then. good thing i got rid of it.

i honestly just didn't know what readings from a boost gauge is right or wrong as far as vacuum goes. but now i do. *whew*


just gotta fix that stupid vacuum leak i have... i think it's from the vacuum cap on the TID since it's cracked when i inspected the engine bay. engine dies sometimes when i throw the car into neutral. :facepalm: i'll get that fixed ASAP by capping it for the time being until i recirculate the air from the BOV.

mine idles at 8 HG(big bridgeport)but when cruising then letting go the throttle, the gauge would read between ~25 In HG like yours.For me is kinda scary 2 see that i only pull that little vacuum but like most of the guys here posted already is all about the porting and compression,my brakes do suck a that vacuum level,17HG in your motor is awesome,that is a pretty healthy motor and i bet you that feels really strong.Have fun with it.