Sounds low to me. For comparison, I have a 302 Mustang with a larger cam than that and it pulls around 8-10lbs at idle. My brakes are ok after the car has been running for a minute, but it's only good for one panic stop before the booster runs dry. If I need to hit the brakes hard twice in a short period of time I will most likely be wrecking. heh...

Might want to look for vacuum leaks or double check the gauge. You could also have an issue with how the gauge is plumbed, or location of the vacuum source. Are you running a vacuum reserve canister, or having any issues with the power brakes?

Chad

 

Not really having any issues that I can tell with the brakes yet. Well considering I have used both electronic and mechanical gauges and they are both reading 7.5 I am going to assume that not the issue. I am going to mess around with my mechanical gauge on different ports and see if its all the same. I guess the best question is am I compromising horsepower/torque with a low vacuum running engine?

 

Here is a very poor picture of how I have my catch can hooked up with guidance from Mighty Mouse. I have the hose running from the pass. side valve cover to the intake of the can. The exit (PCV) side enters into a vacuum port beside the old PCV valve. The old PCV valve location has an orifice and a hose that now runs to the non pressurized side of my supercharger. I capped the port on the TB where the old hose went from the pass. side valve cover. Does this look/sound right?? The can obviously has a filter on the top not sure if this would cause a vacuum/boost leak though?

 

I wouldn't really worry about low idle vacuum unless you are chasing down some other gremlins. ie...Trouble tuning a MAF car due to vacuum leaks, power accessories losing vacuum during normal driving/idle, or oil/blow by issues.

Not sure if I asked before, but is your vacuum source for the gauge directly off the manifold? Some times people tap/tee five things in some funny places and get strange readings. heh..

Lot's of application specific things that can affect your readings as well depending on if it's a MAF car, (blow or draw through), are you running a blow off or bypass system, are check valves in the proper places and proper orientation...

Chad

 

I have it t'd into the drivers side intake manifold that runs to a solenoid. I also have my Bypass valve T'd into that as well. Im going to put my mechanical gauge directly on the intake outlet and see what it shows there.

I have the red race bypass valve if that is what you mean! is that what you mean with check valves or are you talking about the PCV system? As far as I know there is a check valve in the might mouse catch can.

 

Just to give you an idea. My old setup 388ci. 8.8:1cr, CC306 cam, F1, ebay intercooler etc...new motor I had 19" of vac. When I washed the rings out due to my lack of tuning skills I had 7-10" of vac. This was on a motor with less than 1K miles total and when it did finally die, I did a compression test and had less than single digits on 5 cylinders and the remaining had 0! That's how much air the F1 was pushing just at idle...enough to start an engine alone.

Not sure if you got it sorted out since you last post but as others have said you may need to find another way to tap for vac or check you cylinder pressures. just for giggles. I would think 15-20" would be the norm with a healthy engine but I'm no expert on the subject.

 

Yeah for a 112lsa cam that's extremely low. Weird how you haven't experienced any issue with brakes? Did they suck to begin with? I'm at 11" now and can definitely tell a difference between normal stopping and when the engine is decelerating while applying the brakes.

 

If I recall correctly, I've got around 15-16" of vacuum with the CC503 at idle.

 

My heep makes 17-19in at idle pending temps, cam is very close to yours, but I am 383ci

I would double check that your BOV is functioning correctly.