Cam duration

Longest duration to still make enough vacuum for power brakes?

10.5/1, aluminum heads, forged crank, looking at roller cam kits.

I know, lots of particulars involved, just opinions/thoughts, please.

Displacement matters a lot. On a 496 with 243@.050 cam, 108 CL (not vacuum friendly) I get 13" at idle. Just enough vacuum for PB to work without noticeable issues and assist devices in my book. That's after tuning. Before it was under 10". Increasing initial advance to 20 degrees and tuning idle mixture helped a lot.

LSA plays a big role too. I had a 220/230 duration cam on a 114 LSA. pulled 14" of vacuum at idle in a 318, then a 222/228 cam on a 107 LSA in a 360, idles at 9"

with my stick shift transmission, the 9" at idle is not a problem for my power brakes. blip the throttle a little after starting the engine, and I get enough vacuum built up that I can manuver around in the driveway without having a hard pedal. downshifting the transmission while slowing down creates enough vacuum that I can get 3-4 full pumps of the master before vacuum is depleted.

with only 9" of vacuum in the last 4000 miles of driving, not once have I had a problem where my brake pedal was too stiff

Quote:

---

Displacement matters a lot. On a 496 with [Email]243@.050[/Email] cam, 108 CL (not vacuum friendly) I get 13" at idle. Just enough vacuum for PB to work without noticeable issues and assist devices in my book. That's after tuning. Before it was under 10". Increasing initial advance to 20 degrees and tuning idle mixture helped a lot.

---

I agree. I have a 417 stroker SB with a 242@.050 108 lsa cam and I get 14" of vacuum at idle and my PB work with no issues. As was stated above this was after some idle mixture tuning. My initial advance is at 18 degrees.

It all really depends on your setup.