I've got a .557 cam and I'm trying to tune it on a 440 (with a six pack). The most I can get is 4" at idle. I've tried to tune it messing with the timing and mixture screws but no luck.

I'm just wondering if this normal for this cam - I don't have the specs for it.

My .509 could pull 11-12" inches this has me puzzled.

Sounds about right, how did you get 11-12" with a .509? I get get about 6" with my old school MP .509.

The 6-bbl is tought sometimes with a high-lift cam...And you can only bump the timing so far for the good vacuum...I'm in the single digits also with my hefty cam....

I get 9" @ 1k rpm with a .590 and a dominator.

i got around 7"-8" vacuum with a 440" a 509 cam and a 1200rpm idle.

that is a great cam. when you do the whole mopar performance bracket package suggestion, its makes the numbers it claims.

------ other vac readings to compare, will vary-----

i got 10" or so with the chevy sbc 350 Edelbrock RPM package.

12-14" with a xe268 sbc 350 at 900 rpm idle

19-20" with the 340 mp cam in 318"

The car runs good I'm just surprised how low the vacuum can go. I'm running rich but I may have a power valve issue - I'll have to look it may have a 6.5 pv., would a 2.5 be better consider the vacuum issue?

Mpg is bad - around 8mpg when I don't get on it maybe worse - hard to tell 'cause I can't keep my foot out of it.

Went thru 30 bucks of gas (4.39 a gallon) just testing it around the neighborhood maybe a total of 10 miles - not too good.

normal? nope. verify your vacuum gauge is accurate. if it is, then
start going over the carb settings again.

8-10Hg.
check the lash/timing/carb/engine sealing/ etc.

powervalves? vac(in gear)/2+.5=PV requirement. don't base it on the vac. you have now.

I've got no experience with 6 packs, but I would think you still should be pulling 9" maybe 10" of vacuum. Your power valve should generally be half of your idle vacuum.So, a 4.5 PV with 9" @idle.

Thanks guys - may have check the lash on this one...

Initial timing makes a BIG difference...make sure it is at least 14 degrees, if not more.

I was able to get ~11 inches with a MP .509 in a 340 with a tunnel ram + 2 4s.
What's your timing, and what's the idle speed?
Are you running the idle solenoid?