HEI advance curve ?

[mikep]

I should state that I am running a late model delco gear reduction permanent magnet starter and I dont have any problem turning over my engine even with 9.5 :1 and loads of initial advance.

[MikeB]

Mikep -- that's an interesing subject you brought up. The engine's running at idle with initial mechanical and max vacuum advance. Then you stomp on it and all the vacuum advance goes away just when you need it. Sure, mechanical comes in, but not until the revs start to build a little. Where's an MSD engineer when we need one?

[Jesse 67 c-10]

This is where an electronicly controlled dist with a computer and knock sensors would be nice, runs max advance engine can take without detonation or pinging, adjusts in real time to suit the current conditions. But, who has the cash! a question though, I have an accel hei with an adjustable vac advance and a 1406 carb. should I hook the vac adv up to ported or full vacume? I have it on ported vac, seems ok but I don't want to be cutting myself short in milage or power or something. What are some advantages/dissadvantages of either? Another, when you guys are setting your timing, are you using a timing tape on the damper or some sort of special timing light?
Thanks!
Jesse

[crazy longhorn]

I use a timing tape on the balancer to set mine. as far as the advance , you will hear both ways......go for what the eng wants. With hotter cams,& fat carbs, I like to run on a full manifold source at the carb. some of the leaner setups seem to like ported spark better. try em both,& see what works best for your combo. good luck......Al

[mikep]

I use an advance timing light. Works great. I keep it in my tuneup bag along with a tachometer, a vacuum gauge, a dwell meter, an infrared pyrometer, assorted tools, and a fluke multimeter .

I dont use vacuum advance and I havent in years so cant help much there. In fact with lighter cars for hi performance use I dont use any at all . Get the advance in and get it in fast .

[robby]

this is great discussion. But lets say I was just a normal Joe who wanted the engine to run with some pep and soem decent gas mileage what would I do woth the curve on an HEI? Should I eye ball the stock springs and go with the ones that are close in strength? shoot for middle and call it good?

[robby]

man I gotta go to bed, ,I caint herdly spel no mo.

[Denny]

I run a timing tape and I use the full vacuum not the port. I have a vacuum gauge in the car that is connected to the same line as my vacuum advance. Port vacuum on the Holley and the Demon comes in when I don't want vacuum underload. Port vacuum is an emission thing for cars running not much advance.

[crazy longhorn]

Robby, if you pick up a Crane vac advance, they will have a good suggested starting point,with a chart on springs,& adjustments. I would try to start in the 2800 "all in" range(beaware that the lighter aftermarket weights will change the listed range). start by selecting springs,& setting the timing 2 degrees faster than stock setting. then make a full throttle run with out the vac advance. If it doesnt ping, bump the timing a little more,or go 1 step lighter on the spring. if it pings, go 1 step heavier on the spring. I would suggest about 10-12 BTDC as a starting point. Once you have the max timing,with no ping(full throttle run), then start on the vac advance. With a heavy truck,I would use the limiter plate set the the max amout of limitation(should give in the range of 12 degrees vac timing). now take it out for a part throttle run,pull a few hills,& check for spark rattle under lite throttle/ heavy load. if she rattles, adjust the screw in the port on the vac can CC 2 turns at a time till the rattle is eliminated. as far as hooking the vac advance, I like to run to a full manifold source at the carb,but you may find that your combo will respond better hooked to ported spark.........try em both, & use what the engine likes. good luck........Crazy Al