Ignition advance
 

Over the past few years Richard and I have used his engine as a test bed for out economy tests. By using an A/F meter and a GM distributor, we tried numerious combinations of carburetor jetting and Ignition advance cueves. The explination I gave in another post was in error and richard was kind enough to make the following corrections. OK Dummy, here's the right way to do it.

"If you're running a converted Chevy distributor from Classic Ignition
or Bubba or some other source forget about setting engine-off static
advance with a light bulb. Both static and initial advance are
interesting to know but what's really important is maximum advance,
both mechanical and mechanical+vacuum if you're into vacuum... and
you should be.

This method works great with points, HEI, and MSD ignition. All you
need is a simple paper degree strip glued to your pulley and a timing
light with an inductive pickup. You can make the degree strip with
your computer.

Disconnect the vacuum and plug the rubber tube. Remove the
distributor springs so you don't need to rev the engine to get
maximum mechanical advance. With the engine at idle, set the maximum
mechanical advance where you want it when it's all in; 20-22° is a
good place to start. Let the initial fall where it may. You may want
to raise or lower your idle speed at the carburetor.

If you don't have vacuum advance, you're done. Replace the springs,
double-check everything with your timing light, and go for a ride.

To see or set the maximum mechanical+vacuum advance, reconnect the
vacuum with the springs still out. At idle, the engine is making high
vacuum, so it's like checking the vacuum advance at cruise. If you're
using an adjustable vacuum canister, you can set it where you want
it. 8° goes well with the 20-22° of mechanical, giving you a TOTAL
advance of 28-30°. Then put back the springs.

If for some reason you want to see what the initial (not static)
advance is (before any mechanical advance kicks in), disconnect the
vacuum, remove the weights then put back the springs. Now, at idle,
you can read the initial advance. Reinstall the weights, reconnect
the vacuum, double-check everything with your timing light, and go
for a ride.

You can increase or decrease the range between initial and maximum
advance by changing the advance-stop bushing in the distributor.
These bushings are easy to buy or make."

--------------------
We make changes to find the optium, so far we like this one. Just remember, these numbers work for his engine.

Re: Ignition advance
 

Re: Ignition advance
 

Okay, so what kind of advance curve works best; use light springs to have a quick advance rate, all in by say, 2,000 RPM? Or, use stronger springs for a delayed, slow or late advance, all in by say, 4,000 RPM?

Re: Ignition advance
 

Quote:

Originally Posted by 40 Deluxe (Post 326969) Okay, so what kind of advance curve works best; use light springs to have a quick advance rate, all in by say, 2,000 RPM? Or, use stronger springs for a delayed, slow or late advance, all in by say, 4,000 RPM?

All in by 1800 to 2000 rpm. This has produced the best response and power in our tests.

Incidentally, when you incorporate a vacuum advance canister, take the vacuum directly from the manifold, not from the carburetor.

Re: Ignition advance
 

THANKS FOR THIS POST, VERY GOOD INFORMATION !!!!!!!!!!!
Oh by the way I work for BUBBA one day a week and love working on old distributors.

Re: Ignition advance
 

Richard and/or Ron, are you having to use the adjustable vacuum advance cans to get the quick advance?

Re: Ignition advance
 

The quick advance comes from the weights and springs in the distributor, not the vacuum can.

Re: Ignition advance
 

Ol' Ron

How did you do with fuel economy tests?

Bill

Re: Ignition advance
 

Re: Ignition advance
 

I'll answer that since I ran the tests.

• 3300 lb '53 Victoria
• 276 flathead with L-100 cam
• Edelbrock 500 cfm four-barrel
• Edelbrock 8.5:1 heads
• Chevy-based magnetic trigger and HEI ignition
• NGK F4 plugs gapped at .025
• T5 transmission with a .72 5th gear
• 4.10 rear end

• 50-mile course, 2/3 town & country, 1/3 high-speed interstate

To make a long story short, the first run yielded 8.5 mpg. Pretty sad. The last run gave us 21.3 mpg. That was a happy day!

Since then, the ignition has been changed to a 15-year old MSD 6A. With everything else the same, the mileage was just about the same, too, but the engine performance is noticeably better. That's another story.

Re: Ignition advance
 

Quote:

Originally Posted by 36tbird (Post 327075) Richard and/or Ron, are you having to use the adjustable vacuum advance cans to get the quick advance?

The beauty of using the vacuum canister, especially an adjustable one, has to do with the nature of engine vacuum.

While your singing along a nice flat road at a steady speed, putting little load on the engine, the vacuum is high. This high vacuum activates the canister which then adds 8° (for example) to your 22° (for example) of mechanical advance. So in this cruise situation your engine is running at 30° of advance and is happy as a clam, getting great mileage.

When you accelerate hard as you would when passing, for example, suddenly there is very little vacuum available to operate the canister so it is no longer activated: so your advance drops back to the mechanical 22° where your engine makes it's best power.

If you tried to run without vacuum advance at 30° of mechanical advance, your engine would ping like crazy every time you tried to accelerate, and you could end up doing serious internal damage. That's the beauty of vacuum advance.

I've learned a lot from Ol' Ron.

Re: Ignition advance
 

Thanks for the info. I guess I am just asking why you need an adjustable canister versus a non-adjustable. Is the adjustment a matter of sensitivity so that it reacts quicker at a lower vacuum or what?

Re: Ignition advance
 

Re: Ignition advance
 

Yeah, I bought one so I know how they are adjusted but I have not installed it yet. I wrongly assumed that the adjustment had something to do with the sensitivity of the diaphragm. You are stating that the adjustment changes the length of throw to impact the amount of advance available. I know how mechanical and vacuum advances work in distributors but I did not know what the vacuum adjustment actually changed.

Re: Ignition advance
 

Re: Ignition advance
 

Great post and good job Ron and Richard, everyone needs to read this multiple times.
Lots of variables effecting manifold vacuum that you might not think about, i have a vacuum gauge on my street rod and watch it driving down the road quite a bit. Noticed on a rod run to west Va, that the gauge would drop off on a slight hill to 5-6 inches.Knowing that fuel delivery is controlled by vacuum i was concerned and had poor mpg !
As my car runs a quick change rear end i changed the rear end ratio from 3:08 to 3:68 and reran the same route later in the year, wow what a difference ! Now vacuum drops to 10-12 inches and mpg doubled !!!
Many car owners dont even know what the rear axle ratio is etc....:eek:

Re: Ignition advance
 

You are correct and so is Richard
From accel catalog:
These ACCEL adjustable vacuum advance canisters for GM points V8 are designed to give you instant horsepower and throttle response. ACCEL adjustable vacuum advance chambers for GM points V8 permit infinite adjustment to both the amount and rate of advance. The advance chambers include an adjustment wrench and an instruction guide. To optimize your engine's timing curve, you need ACCEL adjustable vacuum advance chambers for GM points V8.

The rate of advance and the amount is changed at the same time....

Re: Ignition advance
 

To Quote GE "Progress is our most important product" Use it it's free!
Ol Ron & Richard & Bubba.

Re: Ignition advance
 

Re: Ignition advance
 

Yo Bubba, I see that Accel, Crane and Moroso offer the adjustable cans. I read a report or two on different forums of one brand or the other going bad. Do you have experience with one brand being better quality?