Posted By: dodgeboy11
vacuum advance - 09/29/14 07:49 AM
Anybody remember the size of the wrench and which way to turn it to give less advance at a given vacuum reading? Dual plane is giving more vacuum and it's rattling at cruise speeds.
Quote:the DP might be packing the cyls more which is upping the cyl psi. Might need to go to a slightly stiffer spring combo as opposed to the can. For spot on (just me) I would (1) find the initial it wants with the vac gauge method (2) shorten the slots to get the appropriate total for your eng type (35-SB/31 if mag heads) & this total is initial+slots/can plugged. (3) spring combo- staying just under the pinging point at WOT up thru the gears on your hottest/driest (most likely to ping) day and the adv starts no less than 100 RPM above your hot in gear idle speed which is what you will be at at the stoplight (4) plug/adj the can. Anytime the cyl psi changes from a part/tuning change the dist needs changed from head to toe (for spot on). Easy/short version, for a cruiser (as said) the can adj may take care of this in minutes
Dual plane is giving more vacuum and it's rattling at cruise speeds.
Quote:
3/32 allen wrench. turning the screw clockwise reduces the spring tension, counter clockwise increases tension. less tension means less vacuum to open the unit.
Quote:It sounds like a prime candidate for 2 or 3 turns CCW & retest. just me I would T into the vac adv line (or manifold port) & run a vac gauge out taped to the windsheld & note the in hg (& RPM) that it starts/stops pinging at just for a baseline reference.
Rattle goes away when throttle is pressed further or backed off.
Quote:put heavy spring back in there, that light throttle stumble will go away.
Open chamber, 440. 38 degrees total with welded slots, heavy spring removed. Rattle goes away when throttle is pressed further or backed off. It might make more power with more timing, but I'm not going to check, runs exceptionally well with 38.
Thanks for everyone's input, I appreciate it.
Quote:
38 is where it's supposed to be, vacuum advance off and plugged. That's the most referenced number for stock bigblocks.
R.
Quote:what i'm seeing here is no quench, and high cylinder pressure. I doubt juggling the timing is a cure if the intent is to run on pump gas. I don't agree that 38 degrees total is always the best. to many variables; such as combustion chamber design, plug location, quench vs no quench, rod ratio, etc.Quote:
38 is where it's supposed to be, vacuum advance off and plugged. That's the most referenced number for stock bigblocks.
R.
This one saw dyno time. KB flat tops, .007" out. Ported 452's, had a torker II, holley 750 hp'ish. 1.6 rockers and a tq50 erson cam. 485hp, 507 tq.
38 degrees timing was all I had time to test, had to pull off dyno due to a leaking rear main and no time to retest.