distributor advance

[Sweet_Johnny]

thanks all i have been doing a lot of reading
im going to keep my hei dist when my kit comes in i will put the new weight bushings in with my original weights i;m unsure of what spring to install any insight of what rpm the total advance should max out not including vacuum advanse as for the end play i have 42 thousands i will check when installed to make sure i have a little play i have a 350 engine 8.5 compression ratio mild cam peak torque is probably around 300 lb at 3000 rpm and a auto trans i have a new timming light with didital advance and tach built in and am ready to play the nice thing about retirement is i got the time thanks for all your help

For springs, start light and move up until the pinging goes away, and a combination of different springs is very common (probably 1 silver, 1 gold). The perfect amount of distributor shaft endplay is 0.040 (you're fine at 0.042) and the gap between it and the oil pump driveshaft should be 0.050. The aforementioned 34-36 degrees of total timing (base + mechanical) is typically a good target area to aim for.

 

[jcelk]

thanks johnny good to know my end play is ok i have a vacuum can that is fully deployed at 8 inches is that to low of a vacuum for a mild 350 that idles at 18 inches of vacuum ?

 

[Sweet_Johnny]

thanks johnny good to know my end play is ok i have a vacuum can that is fully deployed at 8 inches is that to low of a vacuum for a mild 350 that idles at 18 inches of vacuum ?

If I recall correctly the canister should be all in at 2 inches less vacuum than you have in gear. So you have 18 in park, maybe somewhere around 12 when in gear, and that's a good cushion to ensure you have solid vacuum providing a steady advance with no fluctuation. A canister that's all in by 8" of vacuum is fine for many, many engines though it comes in a bit too soon for some high performance setups.

 

[jcelk]

thanks i will get an adjustable vacuum can and i guess Ill try to get the weights all in at 2500 rpm.. going to try building a distributor tester

 

[Ernest]

Typical oem, even aftermarket vacuum advance cans pulls to 10(20 crank degrees), which was fine back in the day when factory low compression emmision engines were timed 4-6 BTDC on the balancer with varied mechanical advance up to 22degrees. When all in during acceleration with ported vacuum and cruising where its needed, the total advance was still safe up to 51degrees or under, either way, the more initial advance the better, up to a point for low compression engines.

Instead of messing around with the adjustable vacuum advance can and guessing, may i suggest getting a fixed unit that pulls to 5(10 crank degrees), of which gives you the opportunity to use more initial advance, again, up to a point with a higher compression engine, the NAPA ECH 1703, it starts @ 4hg and all in @ 8hg, which would be better IMO. When i used to run with a mechnical HEI distributor(aftermarket), came with the car when i got i, i swapped out the vacuum advance can for the napa one, just for my ZZ4 crate engine and used the full manifold vacuum instead of ported source on my Holley 770SA metering block. I basically set the initial at 5 BTDC, much easier to start when hot, with the engine idleing, it was at 15 BTDC, ran well without issue,

When using the adjustable or fixed type, its a good idea to use a hand held vacuum pump w/guage that typically comes with a brake bleeding kit if you can find one for sale alone, along with a few inches of 1/4"ID vacuum hose to check the start/stop setting on the adjustable or for diagnosing a possible leaking or damaged diaphram for either one.

 

[78Delta88]

If you find the 1/4" ID line is too large to make the hook up, just use the step down adapters that come with the kit. You will be fine.

 

[Ernest]

Perhaps a 3/16" ID vacuum hose might be a better idea.

I just measured a vacuum advance can nipple OD and its 3/16" in size, just so happens to be the same sized used on the ported vacuum tube on the holley primary metering block.

 

[64nailhead]

Vacuum advance has only one real purpose - fuel economy - lean out the motor and give it as much timing as it will take without detonating and still have enough power to cruise with in light throttle situations.

For what you're attempting to do, unhook the vacuum advance and plug the port for the time being. Once you have starting, idling and WOT performance dialed in, then hookup the vacuum advance cannister and work on increasing fuel economy.

 

[melloelky]

I'm late to the game on this one but big bushing, light Springs.10 or so degrees under the cap rest on the crank.

 

[jcelk]

i have a mity vac and a timing light with digital advance and tach built in .. I;m not sure what rpm the mechanical advance should be all in i guess put in light springs if it pings under load go a little stiffer on the springs i have read about advance limiting bushings going on a stud under the advance plate mine has no stud ..10 deg mechanical that sounds low i don;t know how much base timing i can go before hard starting to get total timing up to 34 deg on crank ..as for the vac can it's a good idea to mess with that after i get everything else done thanks all for your input