vacuum

[blackthunder1970]

hi guys
this might be a stupid question
can vacuum at idle be changed with timing
my timing is set at 8 degree intial on my cammer and vacuum is between 4 and 6 at idle would like to get it to at least 10
 so by advancing intial timing will that help vacuum
cheers
barry

[jayb]

I think it can, but to be honest I've never actually monitored it.  I usually run a lot more initial timing than that, at least 15 degrees.  Of course that will increase the idle speed, and your vacuum signal will increase.  So when you back it down to the same idle, I guess I don't know what will happen to the vacuum, whether it will stay higher or return to the original level.  I'd just give it a try; let us know what you find out...

[66FAIRLANE]

Gee Barry thats not much initial. Should be able to pick up some vacuum as stated. More timing, same idle speed, less throttle opening = more vacuum, not sure how much though. Make sure you check your total too. I just stick a protractor on the rotor button with double sided tape and then make up pointer. Twist the rotor, see how many degrees it moves, double it of course and you know whats in the dizzy.

[66FAIRLANE]

Stuff up, double post

[blackthunder1970]

thanks guys
will check it out
cheers
barry

[machoneman]

2X to the above and yes, virtually all engines pickup more vacuum with more initial timing advance. If running the OEM cammer's stock pistons, you should be at a nominal 12:1 and require high octane gas, 93 here in the states at least or race fuel.  Adding a lot more initial advance, as noted above, should be your goal for better performance. But it still begs the question: why do you desire more vacuum...power brakes?   

[My427stang]

More initial will bring you some vacuum, but for significant changes, advancing the cams or a cam change will make the more drastic difference.

You may get to 10, but I would guess 8

[bmalone]

On my Cammer, I set initial at 10 degrees.  That yielded 4.5" of vacuum.  I mention this is a reference for you since you are at eight.  In other words, you may not pick up "much" by increasing the initial timing.

I was 12:1 and Crower custom-ground cams with .557 lift at .050 and the duration was quite a bit - forget the exact figure.

[lovehamr]

Bill, you're so full of crap, you don't even have a cammer!   

[blackthunder1970]

hi
what would you guys set intial timing at
and what total timing in by when
looking at using fast efi carb kit and it needs 8 inches of vacuum to operate
i am running a vacuum pump to operate power brakes
cheers
barry

[66FAIRLANE]

Hi Barry

Thought somone would have jumped in by now but Jay is having a mega thrash for drag week so you may have to wait until thats over to hear from him. I have no canmmer experience and know nothing about the efficiency of those combustion chambers but I would be thinking somewhere around 16 initial give or take a couple with no idea what the optimum total is for those heads. How many cubes ya got again?

How do you like the vacuum pump? I just bought one for my brakes and hopefully will be fitting it this weekend.

[amdscooter]

So how does everyone adjust "total mechanical advance"? I get recurving by adjusting spring strength and such. But my stock distributor has only 2 options, 14 and 18 for a total of 28 or 36 degrees total mechanical advance. I've been told 36 degrees mechanical is about the max for my 390fe so I use 28 degrees mechanical plus 8 degrees initial to get 36 total. I'd love to start at 12 degrees initial for better throttle response but that puts me over my 36 total mechanical advance maximum budget. Are there distributors with more mechanical advance options? I've been unable to locate a replacement distributor cam with numbers in the range I'm looking for. 

[jmlay]

I would experiment with the initial to understand what your combination likes before modifying to limit the total.

I know this is not exactly what you are looking for but it may still be helpfull. As the instructions below indicate you may weld the braker plate & file to meet your total advance requirements.:

http://www.reincarnation-automotive.com/Duraspark_distributor_recurve_instructions_index.html

"Decide which slot you want to use and if necessary remove the upper advance shaft retaining clip and springs so you can lift and rotate the shaft in to the proper position."  "If you have a distributor with the larger numbered slots limit rotation via welding the slot smaller or placing a bushing around the pin to limit total shaft roatation."

http://www.gofastforless.com/ignition/advance.htm

[amdscooter]

^^^ I've read a lot of that material already.. I'm just thinking there has to be an easier way. You'd think the bushing around the pin idea would be easy but it adds to the initial mechanical advance as well as limiting the total. I tried that a little while back by putting a small piece of vacuum hose over the pin. The results were kind of wonky. I'll be giving it a go again when I get my motor put back together, post back with results/ideas. 

[rockhouse66]

Ideally, you will find a reluctor with the 10 degree slot, but they seem to be hard to find and hit/miss as I haven't been able to figure out which distributors had them originally so it is a shot in the dark.  On the 14/18 ones like you have, I have been bending up a small piece of metal and silver soldering it to the 18 side to limit the travel.  I guesstimate the location based on the difference in slot between the 14 and 18 (assuming the difference equals 4 degrees) and then place it to get, for example, an 8 degree reduction in travel to get 10 mechanical.  It looks sort of crude, but I have been running two of these modified in this way for about a year and they are still there and working.

Sorry, I didn't take a picture of the finished product or I would post it as I'm sure my description is lacking.