vacuum at idle/decel
 

how much vacuum do your cars pull at idle and on decel? mine is pulling 21-22 on idle and 25 on decel. seems high to me, i can't even find a BOV spring stiff enough to keep it closed (turbosmart only offers combos up to 21inHg). just wondering if something is wrong or this is normal...

You might have better luck trying this one in the forced induction section :)

why? i'm asking how much vacuum any other 86 pulls. I don't care if the car has FI on it or not.

Only FI guys are watching vacuum/boost. I see -20ish max on idle. I don't think I've seen higher.

agreed! i think im about the same

Ah yes, good call. How do I move it? Does a mod have to?

At idle, the cams are parked into what's most likely an "underlap" position for combustion stability. This produces high vacuum. Also, a healthy engine with good compression may produce more vacuum than one with poor sealing. Now When you have overlap at idle, like a traditional cammed pushrod v8, you get less vacuum and less stable combustion.

On decel, the engine is free spinning against the restriction of a closed throttle. This also creates a high vacuum. It's pumping air through a very narrow opening.

Basically, this is normal. Now any engine that uses aggressive dethrottling, like a BMW Valvetronic engine, will see very little vacuum at all under any normal conditions. This is because valve events control engine torque output rather than the throttle.

-20 to -21 at idle.