Hey fellas- just a quick question for those versed a bit more in BOOST than I am-

I have recently installed a boost gauge on my s/c vert, and not having one before, was unaware of vacuum readings during normal operation. At cruise, I am pulling ~15 lbs of vacuum, and during decel it spikes up to 25 psi of vac. Are these ranges normal? Just want to get a barometer reading of how healthy my motor is. Thanks in advance.

 

wow- 6 days, no response? Gurus? Anyone?

 

sounds normal. the more important thing to notice is how much vacuum it is pulling at idle (fully warm) with no accessories, as it is one indicator of engine health. but even that number depends on engine porting.

 

Ah, I see. More variables are needed.

So , 15lbs at idle, stock ports, fully warm.

 

sounds ok to me, although many stockport motors do pull a bit more than that. But it's going to vary some based on idle RPM, if you have any leaks at all, and how much compression the motor is making. I wouldn't worry about it unless you are having unusual hot start problems.

 

Thanks very much- my idle is a bit low with the supercharger at ~600 rpm (gotta play with that). No hot start issues (knock on wood) either.

 

if you still have a stock ECU (or like an rtek) with BAC valve you should do the idle set procedure in the Fuel and Emissions section of the FSM.

 

You mean in inHg, not psi. But yeah...

 

Uh, IDK about your setup, but my boost/vac gauge measures in psi

 

I was just wondering, considering that 15 psi of vacuum with respect to atmospheric is...impossible.

 

I stand corrected. The gauge is not marked in units, but upon some basic internet research, the units of vacuum are indeed measured in inches of mercury. My bad.

Physics>me