Even with the stock cam I only saw 15 - 17" of vacuum at the 650 rpm idle. With the 224/236 cam 8" of vacuum at 850 rpm is what I see. Could it be altitude related? I'm at 3,500 feet and the altitude compensator device usually calls it 4,500 feet.

Had the GM Tech tool on the make sure the ABS box was opening its valves correctly so as to facilitate a proper bleeding. Still not satisfactory, so a vacuum can will be going on.

Hope that does it, or else that means there really is some air in there, somewhere deep inside, where only a GM dealer can exorcise it ...

LWM

 

LOL you need Pope Goodwrench to bring the air demons out. Anywho, I saw exactly 20 inches at idle with the stock cam. It's probably altitude related but I still think 14 inches is good for a cam of this size. I just need to adjust the rockers and bleed the coolant system some more, give it some miles then let er rip!

 

What kind of static compression are you guys running with this cam? Could the lower compression be causing less vacuum at idle? Just curious as I'm planning to put one in my car (stock bottom end, 10.4:1 compression) in the next few months but it has to have good brakes cause I drive it every day. I'm seeing between 18-20 inches at 1k idle now. Hopefully, I'll be able to keep using this cam when I punch it out to 383 CID in a year or two (hopefully 2).

 

Can went on, and no improvement

Can't say I wasn't expecting that, however, their is light at the end of the tunnel. It is now more apparent that there is indeed air in the system.

Bled the brakes down again to all 4 corners, now you can "pump up the pedal" at an idle. There is hope.

Just thought I'd give an update.

LWM

 

Up from the dead thread pile ...

Final update, problem is 99% solved.

Went to see Pope Good Wrench, they power bled the system and homed all the pistons in the ABS unit, turned the rotors, replaced the pads and then harmed my Visa card to the tune of $250.

No change ... went back to the boards and got into the adding timing idea ...

Set the idle up to 875 rpm in gear.
Added 5 degrees of timing on closed throttle.
Added 2 degrees of timing in the 400 - 4000 table up to 80 kpa.
Also a few more miles on the engine may have helped things a bit.

Now on deceleration I normally see 14 - 16" and the engine speed while decelerating is around 1,500 rpm. That gives enough vaccum for a good hard stop.

In short the above changes have given me around 2" of vaccum, just enough to tip the scales in my favor.

Now you know

LWM

 

good info. I have that cam in a new shortblock waiting to go in the car. we'll see just how useful this stuff is.

 

What did the additional timing do for the idle? Does it idle a bit smoother? I've got that cam in my turbo 383, and the cold start idle is lumpy, and the exhaust stinks a bit until it warms up.

 

Idle seems a bit smoother, definitely easier to get it going off a dead cold start. My cold start is an almost flood condition unless I give it 1/8th throttle. Something to do with the cold start enrichment and 42#SVO injectors. I also cut back the AF ratio in the cold parts of that table by a point, that also helped reduce the black smoke and rough idle when cold.

I think that the 875 rpm in gear idle value has more than a lot to do with idle smoothness. It also tends to "creep" a bit more than I like, but, WTF, did I get this thing this far to worry about excessive creep off idle?? Not me ...

I'm thinking that it could probably tolerate another 3 - 4 degrees of timing in the closed throttle table and another 2 - 3 degrees of timing in the 400 - 4000 rpm table, especially under part throttle conditions, that is less than 75 - 80 kpa map values.

I might try that, but for now, I can get the ABS to come into play before I get the dreaded "hard pedal".

It's all good

LWM