Ignition timingg or curve.

Ol' Ron

Ol' Ron

Well-known member
This discussion goes on and on. I know Jim has to deal with a multitude of engines and has come up with a worlable value. Unfortunately this doesn't coner all our engines. For those of you that find the timing problem a little confusing, I can simplfy it by sayind it depends on cylinder pressure and fuel quality. Cylinder pressure is determined by compression ratio, which is affected by cam timing. Don't leave yet. There are two types of CR static and dynamic. The latter is what the engine sees. In a 276ci 8.5cr engine with a long cam (Long duratin) The Dynamic CR is closer to 7:1, but with a stock camshaft closer to static.
When driving the car, asuming it's carburetion is properly tuned. WOT (Wide open throttle) builds the maximum cylinder pressur.
MY and others have found that 17-20 degrees total advance produces max torque. Under WOT the fuel mixture is rich because the power valve is opemn.
Under cruise conditions it's closed and you have a lean mixture which takes longer to burn, thus it need more advance.
Well what are the ansers?
Well I don't know about your engine, but mine works well with 20degs total @2000 and 28 at cruise.
BUT! we haven't tried other combinations, untill then we won't have the optimum timing cruve. Just because it SEEMS to run all right doesn't mean it is.
Having fun yet
Ol' Ron
 
Ron, I love the manual lever on my Model A,I often think that it would be great to have one on my 33 and 34,
Lawrie
 
Good post Ron,I am running a little less advance than you are, 16º at 2200 WOT and a little less at cruising but the cam is advanced a little so a little more dynamic compression, going to change it to straight up on the cam this winter. Running two av8's with 8ba's and both have different advance curves. Both could be inproved on a dyno but not going to happen so will continue playing with them.

Vergil
 
JWL uses an MSD timing computer, I tried one on my friends 276, but couldn't get it to work as advertized. I will use it on my sons 280ci engine if things work out I'll post the results.
 
Good post Ron ,its what I have always thought ,its not that predictable because it needs to be set to your particle r engine this lines up with what Ford suggested in there tune up shop book .That is to advance it until it pinks then back it of ,on the road .
 
Ol Ron,

How about vacuum advance distributors as opposed to these centrifugal advance ones Speedway is selling as the "best thing you can do for your flathead"? I've run both a cutdown Chevrolet single point distributor in my 8BA and a Mallory dual point full centrifugal. Maybe it's my imagination, but it seems I can run more initial advance without pinging on the Chevy distributor. It seems to run cooler with more advance - even sounds better. The Mallory is probably alright for people coming from the original 8BA venturi vacuum distributor. But with dual Strombergs on mine the original would barely run. It was hooked up to manifold vacuum (wrong!) I'm running the Mallory now. I have a compromise timing setting to run well. I just can't lug it too much or it pings bad. Going to go back to the Chevy soon, trying to find a dual point Corvette with tach drive to cut down. My car is 6 volt. Am I on the right track? Please clear this up for me.

Thanks, Rich
 
Up date from richard
Well-made converted GM points distributors WITH vacuum advance are
perhaps the most economical approach to really flexible flathead
ignition. Set up right, they give you the sought-after combination of
"ideal" WOT advance of about 20 degrees BTDC AND a cooler and
higher-mileage cruising advance of 26 or 28 degrees. These are numbers
we've found to work well in the engines we've experimented with, but
you can easily vary them to suit your engine.

The simple springs and weights centrifugal advance system is easy and
inexpensive to experiment with, and by using an adjustable vacuum
advance canister connected to MANIFOLD vacuum you can just as easily
tune your cruise timing to perfection. You can make changes to both
systems without removing the distributor.

The converted GM points distributor also has the advantage of being
usable on both 6-volt and 12-volt cars. The HEI versions of these
distributor work with 12 volts only, but the centrifugal and vacuum
advance systems are the exact same as in the points versions.

Richard
 
Looks like Ron and Richard ( from Fla) have played with these quite a bit. I built Richards unit and it seems to work well with the mechanical limited at 20 degrees and using the vacuum ( adjustable unit for tuning).
We just machined up a brass limit bushing for the chevrolet conversion and installed the accel adjustable advance unit.
Be more than happy to make up this set up for any "barner" that wishes one...the chevrolet is pretty flexable and can be adjusted to just about any spec a tuner could want for..
 
Deuce Man said:
Ol Ron,

How about vacuum advance distributors as opposed to these centrifugal advance ones Speedway is selling as the "best thing you can do for your flathead"? I've run both a cutdown Chevrolet single point distributor in my 8BA and a Mallory dual point full centrifugal. Maybe it's my imagination, but it seems I can run more initial advance without pinging on the Chevy distributor. It seems to run cooler with more advance - even sounds better. The Mallory is probably alright for people coming from the original 8BA venturi vacuum distributor. But with dual Strombergs on mine the original would barely run. It was hooked up to manifold vacuum (wrong!) I'm running the Mallory now. I have a compromise timing setting to run well. I just can't lug it too much or it pings bad. Going to go back to the Chevy soon, trying to find a dual point Corvette with tach drive to cut down. My car is 6 volt. Am I on the right track? Please clear this up for me.

Thanks, Rich
Click to expand...

I was just this weekend looking at some of the flathead advance specs on the vacuum ( ford called them pressure type) distributors. Most when converting to a latter chevrolet unit just rant and rave in regards to how much better it runs.
Looking over the specs it appears any mods at all would just throw off the curve so bad it would be un-tune-able for sure.

1949-1950 Advance specs ( dist degrees)

Vac test points are 0 vac, 0.4 In vac,1.7 in vac,2.85 in vac,and 3.7 in vac.

Cant imagine tuning to a spec of 1.7 in vac , that pretty low vac??
 
BUBBAS IGNITION said:
I was just this weekend looking at some of the flathead advance specs on the vacuum ( ford called them pressure type) distributors. Most when converting to a latter chevrolet unit just rant and rave in regards to how much better it runs.
Looking over the specs it appears any mods at all would just throw off the curve so bad it would be un-tune-able for sure.

1949-1950 Advance specs ( dist degrees)

Vac test points are 0 vac, 0.4 In vac,1.7 in vac,2.85 in vac,and 3.7 in vac.

Cant imagine tuning to a spec of 1.7 in vac , that pretty low vac??
Click to expand...


The '49-'53 flathead loadamatic distributors operate on very low vacuum signals that are a combination of venturi and manifold from the carburetors designed for them. Shop manuals for these engines will show 8-10 or so distributor degrees (16-20 crank) from about 4" Hg vacuum. That's why you don't connect these loadamatic diaphragms to manifold vacuum! :eek: Excess timing and damaged diaphragms will result! :o
 
The Ultra-flexible GM Conversion

Ol' Ron said:
Set up right, they give you the sought-after combination of
"ideal" WOT advance of about 20 degrees BTDC AND a cooler and
higher-mileage cruising advance of 26 or 28 degrees.
Click to expand...
I’m certainly not a seasoned flathead guru, but I like to share what I’ve learned over the past five years or so.

There’s no such thing as a “20-degree bushing” or a bushing that produces the same amount of mechanical advance in every distributor. Why? Because there are several different cam plates — the little plates with the advance limiting slot in them — and the slot in each one of them is a different length. Incidentally, we’re talking about CRANKSHAFT degrees here.

Therefore, a bushing that produces 20 degrees with one plate will not produce the same 20 degrees with other different plates. I found this out the hard way, pulling out my hair trying the figure out why one bushing was producing different advances with various plates... then I noticed the difference. So, you have to experiment with different diameter bushings to get the amount of advance you want.

The beauty of the converted GM distributor is that you can change bushings without removing the distributor each time. I like to use steel bushings because when you drop one down into the hinterlands — and you will — you can use your “magnet on a stick” to retrieve it. You can’t do that will brass or plastic.

Here’s a tip for adjusting a GM distributor in a flathead once you’ve set it up the way you want it. This works for both points and HEI versions.

1. Remove the cap and photograph the distributor you’re removing before you yank it out. The picture should show the positions of the housing and the rotor.

2. Remove the vacuum advance hose if there is one, and plug it.

3. Install the new distributor using the photo to get as close as possible to the right positions.

4. Remove the springs from the mechanical advance mechanism but leave the weights. This will make the distributor go to full mechanical advance at low RPM; no need to rev up the engine. Rough in the adjustment and let the engine warm up.

5. Now use your timing light to set the maximum mechanical advance to where you want it by rotating the distributor housing.

- - - - - - - - - -
NOTE: Using a 20-degree bushing doesn’t mean you will run or must run a maximum of 20 degrees mechanical advance! That 20 degrees you get from the bushing is simply the AMOUNT of mechanical advance that’s available. By rotating the distributor housing you can “place” that 20 degree amount anywhere in the crankshaft’s 360 degrees of rotation.

For example, with that 20-degree bushing, if you rotate the distributor in Step 5 above so your timing pointer is on the 30-degree mark on your crankshaft pulley, your MINIMUM advance will be 20 degrees LESS than that, or 10 degrees BTDC.
- - - - - - - - - -

6. Remove the weights and put in the springs. This will keep the distributor from producing any advance at all. At idle, use your light to show what is equivalent to static (not initial) advance. Now you have the two extremes of your mechanical advance system.

7. Put back the weights with the springs. Now you can using your timing light and a tachometer to chart your advance curve. See what the advance is at, say, 500, 1000, 1500, 2000, and 2500 rpm. Then go out and do a bunch of driving tests.

By changing bushings, springs, and distributor body rotation you can pretty easily arrive at an ideal setup for your engine in your car.

If you REALLY gets nuts about all this, you might want to try my idea of using a setscrew instead of changing the bushing a dozen times. I use it in my engine, and it works great.

I’ll tell you what I’ve learned about vacuum advance later.
 

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Credit Where Credit is Due

Ol' Ron said:
You should see the tuning and recording fixtures he's made
Click to expand...
Know where I learned probably 95% of what I know about flatheads? Ol' Ron!

In fact, I did dream up some useful shop toys I'd be happy to share.

The tuning fixture Ol' Ron referred to lets me pre-set both the mechanical and vacuum advances in a distributor before putting it into an engine. I can also find out what a bushing will do in any of the cam plates. It's very simple; anyone could make one.

The recording fixture he mentioned lets me drive around with a camcorder recording things like manifold vacuum or air/fuel ratio. Those are the two ways I've used it so far.

I'm just about finished with a little real-time ignition timing monitor that records the actual timing of the engine under any and all driving conditions. It consists of a plate that attaches to the timing cover with powerful magnets; on the plate is a multi-LED timing light and a tiny video camera watching the timing pointer and scale. The output of the camera is fed into a camcorder sitting on the passenger seat. During the test, I simply narrate what I'm doing. When the tape is played back, it's very easy to see what the distributor is doing throughout the entire test drive.

Should be extremely useful in our ongoing ignition experiments.
 
Once we get all this s--t figgered out we'll try EFI and an electronic advance curvd. Something to do on these co;d winter months. Ay my age I might get stuck in "Law& Order" reruns.
 
GM Distributor Advance Jig

Here's my GM distributor setup jig. Like I said, it ain't a Sun machine, but it works great!

394017916.jpg
 

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Richard-thanks for the info. I like the set screw tuning saves a lot time. I am saving all the info. I can get ,from BUBBA, Richard, and OL' Ron, GREAT STUFF. Harold central Ca.
 
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