I've been thinking about replacing the stock grind cam in my 440 with something a little bigger to kick up the performance a bit. The rest of the engine is stock with no performance upgrades other than I added an electronic ignition. I don't really have much of an understanding of how cam size affects vacuum. What I would like to know is, at what point will increasing my cam size result in enough vacuum loss to influence how my power brakes will function?

hi
you want a cam that will have at least 12 in of vac at idle .
less than 12 and you will see brake issues !

mopar 280 / 474 cam is grate upgrade for this set up .

Agree PB work OK down to 12" or so vacuum. Typically stock is 18+".

The stock cam is probably around 205 degrees @ .050". I would guess you could go up to 220 degrees or so and still have enough vacuum with a stock 440.

Do you know your compression? Too much cam with lower compression can hurt performance so best to stray moderate.

With a bigger cam, re-tuning is needed to get best idle vacuum. Larger cams like more initial ignition advance. 15-20 degrees is common. With the increased initial, you may have to limit mechanical advance (ie weld the slots) to avoid excessive total advance.

Good luck!

Last winter I installed one of the repro Bendix tandem boosters from the Ram Man, and it works great. I pull 10.5" at idle and it throws me forward with almost no pedal effort. I really can't believe the difference from the single diaphragm Midland Ross unit that I ran before. I have disks up front and 10" drums out back, and those hadn't changed.

You can get a vacuum canister off of any 63-80 GM car out of the scrap yard for $5. No more issues with vacuum and a camshaft.

Here it is new. Easy to hide as you can put it anywhere you want.

http://www.classicindustries.com/product/truck/parts/ap7330.html