Hot Rods Eliminating Vacuum advance

So what set up is good for doing this? My multi-carb will only be 2 of the 6 for now. I knew I'd be asking for it, some of you guys blow me away with your knowledge to the smallest detail of some topics. For an average guy though, what does all this mean? Can it be done and make good horsepower through-out the rpm range. Can the intial timing be set so that it's easy to start hot and cold. Will it diffinetly have a dead spot at some point in excelleration because it's been eliminated?

Some of you are saying to start at 10-14 initial, then others say to leave it alone?? Is this a: 6 of one, half a dozen of another question to begin with? If I decide to try it without, do I waste my time putting on the curve kit? Or should I leave the factory weights and springs?? The motor is a completely rebuilt 62' Cadillac 390, stock cam, pertronix ignition, 6x2 Edelbrock with 2-Holley ECG's (primary carbs for now), 350TH transmission and a final weight of about 2200lbs.

 

Initial timing relates to a number of factors, and there is no computer program that I'm aware of that will let you enter engine parameters and spit out "the answer".
Internal factors include mechanical compression ratio, dynamic compression ratio, combustion chamber and quench, engine operating temp
and external factors like intake/exhaust flow and if it's an auto and what kind of slip is in the converter. Another external factor is the fuel and local atmospheric conditions, and the weight of the vehicle of course.
Add in ignition system variables, such as coil, ignition type, plug range and gap.

The old rule of thumb was to connect a vacuum gauge to manifold vacuum and let the engine idle. Adjust timing to highest vacuum reading, then retard so the vacuum dropped 2 inches (20" to 18" for example).
The guy that has a stock 390 FE in a T-bird with a smooth cam, lots of heat, a fairly tight converter and a heavy car can't/won't run as much initial timing as the guy with a 289 with high compression, a big cam, free flowing intake and exhaust, and a 4 speed in a stripped down Model A.

 

This thread has been a BIG help to me with my '36. I now have it running great, temps staying at around 190/195, and have determined my hot start problem is a starter/selonoid overheating issue, not the timing.

I now have the vac advance to manifold vacume, at idle it's 14 lbs vacume. It now runs like it seems like it should, idles nicely, doesn't overheat (at least it didn't tonight) so I'm happy.

Here's the specs: 472 Cad, 10:1 compression, MTS #10 cam with 275/280 duration, stock intake, Quadrajet, stock converter, 400 Turbo in a car that weights, I'm guessing, less than 2500lbs. Full hood, Mustang '66 V8 radiator, 14" elec fan, 180 degree thermostat on fan and 180 degree thermostat in the engine, new stock water pump. I now have the timing set at ? advance with 30 degrees of dwell.

I think I've got it licked.

 

I always had pinging issues with my 63 TBird 390. I read and read but nothing ever sounded "right" to me. I bought a rebuilt distributor from Advance Autoparts. Engine ran marginally better. I used ported and manifold vacuum and stuck with manifold. I had the engine rebuilt mostly because it was leaking from every gasket. The hardened valve seats were worth the effort.
After I got it running I really dug into the distributor. I bought a vacuum gauge and a vacuum pump. I found the vacuum advance covered 25 deg and the mechanical advance covered about 15 deg. WTF. I dug down to the bottom of the distributor and found the heavy spring was loose causing the short advance. It was already at 10 deg at idle. I bent the tab to pull the spring just to snug and got the full 26 deg (13T). Now I was getting somewhere. I left the vacuum off and set initial timing to 6 deg. It never ran so good. No pinging and strong acceleration.
I put the vacuum advance on and it pinged like a bastard. No wonder, the 25 deg vacuum advance caused the detonation. I limited the vacuum advance to 10 deg by drilling a hole through the mounting bracket inside the slot in the arm and inserted a nail. Runs sweet now on manifold vacuum. It also cured what I thought was a torque converter problem. I had to have an 1100 rpm idle in park to get a 650 rpm idle in gear. Not anymore. So:

1. the TBird shop manual says to only test a torque converter on a PROPERLY TUNED engine.
2. Advance Autoparts rebuilt Motorcraft distributors aren't tuned for anything.
3. Distributor curves don't make sense until you get it straight in your brain. Then they are easy as pie.
4. I should have sent my old distributor out to be rebuilt and curved by someone who knows what the hell they are doing. Sorry GMC BUBBA, I should have spent the $50 on you, I probably still will.

Rick

 

Got a Motors Manual that covers your engine?

Copy the stock specifications.

It'll run fine and after you get a few miles on it you'll have some experience with what the engine wants and can fool around with timing curves.

Drag racing timing curves (all-in real early) aren't always the best for street use.

 

Theres' some food for thought in this thread.
In the process of setting engine timing with manifold vacuum, is the distr connected to vacuum during this process?

 

No. If you look up how to set the timing, the first thing they say is to remove and plug the vacuum hose/tube. The car won't start unless you plug the tube. Then you set the timing to specs.