356A-B DISTIBUTOR: Static Idle vs Full Advance Timing issue

[Chip Flor]

Questions:
1) If you set the static timing at 5* BTDC and your BR18 or 022 has a spec 30* full advance.
Then... if you do the math your full advance will be at 35*BTDC.
If you correct full advance to 33*BTDC you will then end up with an idle timing of 3* BTDC (2 degrees off static setting 5* BTDC)

Also (for example)
If you follow Harry Pellow's .050 set up with static timing at 5* BTDC, then with a spec full advance at just under 27 degrees, you would end up with a full advance of 32*
Which sounds around just right.

Is it perfectly OK to run idle timing at 3-5 degress BTDC similar to a 912?

2) Should full advance for modern gas be around 33*?
3) Can you re-spring/adjust any distributor to get the correct idle (5*BTDC and full advance timing 33* ATDC)?

Any help here would be well appreciated.

[Chuck Allard]

Do the math again. As a distributor spins, it advances the timing from static. If the distributor adds 30 degrees of advance and you set the initial static at 5 degrees, you get 35 degrees at around 2800 RPM. If you set the static at 5 degrees after TDC you will then have 25 degrees of total advance around 2800 RPM.

[Chip Flor]

I believe the factory spec is 5 Degrees (BEFORE top dead center). I was retarding not advancing my numbers.
Thanks for pointing this out ... my bad.

[Chip Flor]

Here is from Harry's .050 distributor swap instructions:

"5. With OT Timing mark notch on crank pulley 1/4" to the LEFT of the timing mark on the Third Piece, (that's about 5 degrees) rotate 050 until points jusssst begin to open.
6. Snug down clamp bolt.
7. Hook up wires in cap, knowing that the firing order is 1-4-3-2 and you're at #1.
8. Hook up wires to coil. Fire up and adjust high speed timing at 33 degrees. Idle should be at 5-6 degrees. The pre-gapped points are at .016-.018"."

So... from what I gather (according to Harry) it is OK to set your timing at 5-6* BTDC

Does this sound correct to everyone?

[Ron LaDow]

Chip,
No.
Since the crank pulley rotates clockwise, the timing mark on the pulley to the left of the one on the timing cover is BEFORE TDC
You want ~5* BTDC, static, which will give you ~35* BTDC, all in. Any static timing ATDC will make the engine reluctant to come off idle.
("on the pulley" and "timing cover" added by edit)

[Bruce Smith]

Here are some curves I plotted and posted for common Bosch distributors, including the BR18. The max. mechanical advance spec. for a BR18 is 30° +/-3° at the crankshaft starting at about 3000 RPM, not including a 2-5° initial (static) advance. The total advance should be about 32-33° and no greater than 35°, a bit lower than original factory specs with today's gasoline. The best way to set timing is at max RPMs (i.e. at 3000+). If (and only if) you've got the measured advance curve of a particular distributor, you can set static at idle and add it to max to get total.

http://www.sparkingplugs.com/8.html

[Chip Flor]

356 pointer.jpg (14.34 KiB) Viewed 2401 times

Ron,
Thank you for helping me solve my problem.
Your timing pointer is a work of art. I think every 356 should have one. Timing from the pulley (instead of the case) is brilliant.
Many Kudos to your ingenuity!!!!!

The point of my post is...Harry states (.050) the static timing mark is: "5. With OT Timing mark notch on crank pulley 1/4" to the LEFT of the timing mark on the Third Piece, (that's about 5 degrees). I somehow mistook this for "After" top dead center. my mistake.

I am a huge fan of your all your (machined masterpieces )parts and all the expertice you have provided the 356 community over the years.
Many thanks.

[Chip Flor]

Bruce,
Thank you for the total full advance (32-33* no more than 35*) for today's gas (suggestion).
I appreciate all the work you have done with this issue. Many thanks..

So that begs me to ask...
If a .022 or BR18 has 30 degrees (full advance) and you set it at 5 (BTDC) you would be right at or over the modern gas limit at 35* (total advance).
So if you ended up setting the static at 3 degrees (as per SC or 912 engine timing spec) to get total timing at 33*... What affect would that have on cold or hot start up?

Is the ideal idle timing still 5 degrees (BTDC) or is this minutia?

Inquiring minds?

[Chip Flor]

Bruce,
From what I can see the .050 does not advance well as the 022 and the BR18.
Thank you for making these advance curve graphs showing the substantial difference between the stock cast iron dizzy's and the Maestro's favorite.

[David Jones]

Chip, I cannot argue with Bruce on the correct timing for a 356 engine but keep in mind that these are carbureted engines with lots of variables and the gas we run today is very different from the gas used in 1960. Each engine to operate at it's most efficient will require it's own settings because there will be small variations likely with every component. I run 87 octane gas in all my engines and I set my timing to 35 degrees at 3K rpm. If I were to detect any pinging on hard acceleration I would either go up on octane or back off the timing. Factory spec was 35 +/- 2 degrees so you do have some latitude. A long time ago when tuning engines but not having access to modern tuning equipment we used to run down a straight piece of road at 3K rpm in 3rd gear then at a predetermined point like a telephone pole slam the right foot to the floor and time how long it took to get to another point down the road. Repeat this maneuver with slightly different settings until you got the fastest time then leave it there. Nowadays I rely on my IR gun, synchrometer and variable timing light and experience and of course I am not so concerned about getting the last dregs of power out of my cars as I am not racing anything but father time.
A variation of 2 degrees should not make any discernible difference to cold or hot starting.

[Ron LaDow]

Chip, I cannot argue with Bruce on the correct timing for a 356 engine but keep in mind that these are carbureted engines with lots of variables and the gas we run today is very different from the gas used in 1960. Each engine to operate at it's most efficient will require it's own settings because there will be small variations likely with every component.

The factory had a selection of parts and a standard to which each assembler was directed and/or held. Dyno tests of those "standard" engines told the engineers that they required X ignition lead (+/- some amount); it is a discovered value, not a designed one.
Outside of random chance, none of our engines are now "standard", and the variables which affect that standard include compression ratio, chamber shape, quench clearance, cam selection and timing, second plugs (Cliff), and possibly more to a lesser degree. Unless you have access to a dyno, you have to use the factory specs or those who have dyno runs on similar engines.
There is power to be found by determining the optimal timing, but it can get spendy to find it, and if you haven't spent the time to optimize the numbers mentioned above, you'll probably gain more power by optimizing the throttle linkage to get WOT.
(added by edit) If you have been willing to take the time to optimize those values, all of your efforts to reduce the required 'all-in' ignition lead pays off in nearly all measured results.
And thanks for the kind words, Chip. Regardless of the timing scale, that tin sheet-metal distributor clamp is a monument to the bean-counters.

[C J Murray]

Always optimize the basics first. If everything is set standard on a relatively standard engine you are not going to gain much by small adjustments.

Some engines will ping and retarding the timing 2 or 3 degrees may correct that but retarding the timing too much will make the engine run hot. Modified engines(single plug) may want a lot less full advance timing if the builder is very clever.

The factory timing at idle is too little in my opinion and they idle better and cooler at a number closer to 10*. Over 10* is better but the starter may not like that as it kicks back. Modern cars crank at a low number and advance significantly as soon as they are running at idle.

Most of my iron distributor engines like around 8* at idle and 32-35* full advance with enough spring tension at rest to hold the idle timing securely.

For highly modified street engines the 123 Tune is the only way to go. Use your smart phone to set any curve instantly.

[Chip Flor]

Thank you all for your expertise. It is well appreciated.

In my case... my engine is a Maestro built engine. It started out as an '56 1600 normal.
But ended up an amalgamation parts.
Regrettably about a month after picking the engine in 2003 Harry passed.

He told me he did not like to "Hot Rod" these early engines because he did not like the "oiling system".
I think this was his way of telling me to be aware of things going horribly wrong.

Here is his parts selection for my "Hot Rod" 1600 '56 engine:
-912 pistons and cylinders
-912 heads
-B crank (why no counterweights? .. I think Harry told me it was lighter)
-"S" Zenith 32 DNIX carbs
-.050 distributor.
-newer styled fuel pump
-Maestro/Elgin cam

The problem is this engine sat for a decade or so and think the fuel has changed.
At around 4K RPM the engine notably seems to lean out and run hotter in 80* weather. It doesn't knock or hesitate it still runs great.
If I slow down to about 3000-3500 RPM it cools back down.

At the bottom of one of the spark plugs I noticed tiny little metal balls on the electrode. The exhaust J tubes and muffler tubes are bone white.
It seams I'm running on the "Hairy" edge of detonation.
I'm sure this will turn out to be a fuel starvation issue.
However, I wanted to start out with a "basic" standard of what people are doing.

The "Full Advance" timing with modern gas was always a burning question for me.
The correct timing and jetting/float bowl height was the first place I wanted to start.

Again thank you all for your help and support. It is well appreciated... I'm a huge fan of you all and what you have done for the 356 community.
Thanks again.
-chip

[David Jones]

Check the carb jets and see what you have then talk to carb rescue about what should be in there. I would surmise that you are running too lean just as you suspect from your description of the plugs and exhaust. With fuel starvation such as a low float level you would notice a lack of power not a tendency to run hotter. The 050 distributor is only going to have a slightly negative effect from idle to 3K rpm after that as long as it gets to 35* then it has no effect.

[Brian R Adams]

Check the carb jets and see what you have then talk to carb rescue about what should be in there. I would surmise that you are running too lean just as you suspect from your description of the plugs and exhaust. With fuel starvation such as a low float level you would notice a lack of power not a tendency to run hotter. The 050 distributor is only going to have a slightly negative effect from idle to 3K rpm after that as long as it gets to 35* then it has no effect.

Topic resurrection:

David, I am temporarily running an 050 distributor in my 'A' Super engine. It actually runs great setting it to 5-deg BDTC static advance. Is it best to set the static so that it maxes out at 30 or 35? (I live at 4700 ft ASL, and run mostly alcohol-free gas through Zeniths jetted for altitude.)

Brian