Optimal Ignition Timing??

[Huicho417]

Car is a 1967 Coronet 440 with 318, automatic 727 Torqueflite. I have been having a lot of fun with it after chasing a rear main seal leak and bad distributor gasket/clamp. I have upgraded the engine with hooker headers, flow master dual exhaust, Edelbrock intake and four barrel carb. The distributor has also been converted to electronic and switched to a double roller timing change. When I get on the highway I get the feeling that it just lacks power when pushing past 60. It will do it, just felt forced. After reading several articles on timing I decided on tuning this to see if it makes any changes. When I checked it this weekend with my timing light showed 11 btdc, I cannot recall why I tuned it to this. Possibly because the service manual suggest 10, but for the stock engine. Which it no longer is. I changed it to 15 btdc and noticed a very positive change when I drove it this morning. It accelerated much quicker from light to light and it seemed to get up to 75 with little effort.

Question is: How much more timing should I add and what can I look for before it starts having a bad effect on the engine? One article I read mentioned you can add until you start hearing pinging from the engine. Which in their case was to about 18 btdc. TIA.

 

[pnora]

Lot depends on fuel and how it starts when hot. If it does not detonate and cranks easy you most likely are ok. My experience is to much timing can cause hard starting and a lot of times a lope or surge at light throttle esp. if the vacuum advance is used.

 

[Huicho417]

I agree pnora. I do have a fuel return line back to tank that I added to avoid vapor lock. We had a brutal summer in Texas this year and that helped a lot. When hot it starts back up right away with just the key. If it sits for several hours I pump the pedal twice, wait about 10 second for the fuel to atomize then starts right away with the key. I will keep adding timing gradually while watching for the sings you mention.

 

[Doorkicker]

So there's base timing (what the engine is at idle... aka 15deg.), advanced timing (timing at RPM like 3000, aka 20deg.), and together that makes for total timing (in this example, 35deg.). Do you know your advance and/or total timing?

Even though the dist. is electronic, it may have one or more forms of timing management.. commonly mechanical and may have vacuum advance as well.

Mechanical is your primary timing curve management. Vacuum is for addition advancement in certain conditions - specifically running down the highway at 65-70. Note that at hwy speed the throttle position is low and RPM is high making for high vacuum manifold, which will typically require more timing, usually a handful of degrees.

If you're controlling your timing with an ignition box... then you need to check those numbers and program them... a good starting point is 13 on ignition, 15 base, 20 advance, and if the 440 isn't stroked or running high compression, I would set the max advance around 3000-3500 rpm... again, starting point. It's worth noting there are several types of distributors that have essentially an ignition box inside, like a ready to run, but still may have advancement springs and vacuum. There are other distributors where you set dipswitches inside the distributor to set timing curves. In all cases the initial timing is set manually.

If you're not running an ignition box, check a few things...
- If you have it, make sure that the weights in the distributor are working correctly and note the color of the springs (signifying rate of the curve).
- If you have it, make sure you have the vac advance line/tube connected and connected to the correct vacuum port on the carb... there are two basic types: manifold and throttle. Which one depends on your distributor's vac advance type.

 

[diesel_lv]

I'm going to "assume" you are using electronic ignition w a vacuum advance on it. You need a vacuum gauge to see what vacuum you are pulling at your cruising speed. Then, w car in park, put a vacuum pump on vacuum advance on distributor and pull a vacuum to your cars cruise vacuum and have rpm at the same rpm as your cruise. Then check timing. Many cars like over 40° at cruise. Initial, mechanical plus vacuum. Some as high as 50° at cruise. Some vacuum advance pots have an adjustable Allen head inside to adjust when vacuum advance comes on.

 

[Geoff 2]

Read my comments in Ign & Fuel section.

Increasing idle timing from factory/generic 8-12* ALWAYS livens up modified engines & even stock engines.

The lack of 'go' at/after 60 mph could be the centri curve in the dist frozen up [ not advancing as it should as rpm increases ]. That should be checked first & fixed if needed.

 

[Huicho417]

Read my comments in Ign & Fuel section.

Increasing idle timing from factory/generic 8-12* ALWAYS livens up modified engines & even stock engines.

The lack of 'go' at/after 60 mph could be the centri curve in the dist frozen up [ not advancing as it should as rpm increases ]. That should be checked first & fixed if needed.

Will do thank you. I did change the springs in the distributor to recurve.

 

[diesel_lv]

Will do thank you. I did change the springs in the distributor to recurve.

You put in new springs. So did you disconnect your vacuum and plug it, then bring rpms up and see what your total mechanical timing was and at what rpm it comes in?

 

[Huicho417]

You put in new springs. So did you disconnect your vacuum and plug it, then bring rpms up and see what your total mechanical timing was and at what rpm it comes in?

I have not done that but plan on doing it this weekend. To what RPM's do bring it up to read total mechanical timing?

 

[diesel_lv]

I have not done that but plan on doing it this weekend. To what RPM's do bring it up to read total mechanical timing?

That depends on cam, gearing etc. You have to decide at what rpm you want all timing in by. Part of replacing springs. Softer springs, timing in quick, firm springs, timing in later.

 

[diesel_lv]

@Charlie71rt please expound on why you disagree. If i am incorrect, i would like to know and correct it. If you do not know, then please refrain. But if you are going to disagree w someone's post, you should always explain yourself.

 

[Huicho417]

New findings in this matter. In the process of trying to determine total timing this weekend, I noticed that the initial timing went back to 12 BTDC after I had set it to 18 last week. When pointing the timing gun at it the ignition timing mark also jumps around about 1/4” side to side. The car ran great, just wondering what may be causing this before I continue to readjust timing. When I worked on the motor last year I did install a double roller timing chain and made sure it was lined up properly. The distributor clamp was tight and I don’t think it moved around.

 

[Geoff 2]

Front driven dists are not 'loaded' like rear mounted dists where the valve springs acting on the cam acts as somewhat of a damper.

Depending on how much slop you have in the dist drive, you can get a few degrees variation.

Dist drive wear areas:
- dist shaft tongue
- timing chain
- cam/oil pump drive gear wear/mesh

 

[diesel_lv]

New findings in this matter. In the process of trying to determine total timing this weekend, I noticed that the initial timing went back to 12 BTDC after I had set it to 18 last week. When pointing the timing gun at it the ignition timing mark also jumps around about 1/4” side to side. The car ran great, just wondering what may be causing this before I continue to readjust timing. When I worked on the motor last year I did install a double roller timing chain and made sure it was lined up properly. The distributor clamp was tight and I don’t think it moved around.

Are you setting timing w engine warm? Vacuum disconnected from distributor and plugged? At a set RPM? Vacuum leak can cause erratic timing. Different RPM can cause different timing. Just suggestions. Cold/warm, if you have a choke will also cause different RPM causing different timing.

 

[Huicho417]

Are you setting timing w engine warm? Vacuum disconnected from distributor and plugged? At a set RPM? Vacuum leak can cause erratic timing. Different RPM can cause different timing. Just suggestions. Cold/warm, if you have a choke will also cause different RPM causing different timing.

Engine temp when I am setting it is at about 165-170. I do disconnect the vacuum line and plug it at the carb and line. RPM's at at about 650-700. I don't think i have any vacuum leaks, when I plug in my vacuum gauge it is at a steady 17-18" of vacuum. I do have an electric choke on the carburetor. Should I deactivate the choke by forcing open the blade?

 

[toolmanmike]

Front driven dists are not 'loaded' like rear mounted dists where the valve springs acting on the cam acts as somewhat of a damper.

Depending on how much slop you have in the dist drive, you can get a few degrees variation.

Dist drive wear areas:
- dist shaft tongue
- timing chain
- cam/oil pump drive gear wear/mesh

Loaded? As soon as the play is taken up in the gear teeth, the distributor is "loaded' regardless of which direction it turns.

 

[old guys rule]

Car is a 1967 Coronet 440 with 318, automatic 727 Torqueflite. I have been having a lot of fun with it after chasing a rear main seal leak and bad distributor gasket/clamp. I have upgraded the engine with hooker headers, flow master dual exhaust, Edelbrock intake and four barrel carb. The distributor has also been converted to electronic and switched to a double roller timing change. When I get on the highway I get the feeling that it just lacks power when pushing past 60. It will do it, just felt forced. After reading several articles on timing I decided on tuning this to see if it makes any changes. When I checked it this weekend with my timing light showed 11 btdc, I cannot recall why I tuned it to this. Possibly because the service manual suggest 10, but for the stock engine. Which it no longer is. I changed it to 15 btdc and noticed a very positive change when I drove it this morning. It accelerated much quicker from light to light and it seemed to get up to 75 with little effort.

Question is: How much more timing should I add and what can I look for before it starts having a bad effect on the engine? One article I read mentioned you can add until you start hearing pinging from the engine. Which in their case was to about 18 btdc. TIA.

Destination occurs before you can hear it and is a motor killer.

 

[toolmanmike]

I like to start out at 10° before and go from there but just remember, advancing the initial timing too far also ads to the total which may get you into starting issues and detonation. Way more is involved in timing than just the initial timing. There's the mechanical with it's curve and the total limits (which are changeable but not easily adjustable) and of course the vacuum advance which is somewhat adjustable with the right vacuum pot. Then there's always the discussion between members whether the vacuum should be provided from a ported or constant vacuum source. That's a whole series of threads in itself.

 

[diesel_lv]

Engine temp when I am setting it is at about 165-170. I do disconnect the vacuum line and plug it at the carb and line. RPM's at at about 650-700. I don't think i have any vacuum leaks, when I plug in my vacuum gauge it is at a steady 17-18" of vacuum. I do have an electric choke on the carburetor. Should I deactivate the choke by forcing open the blade?

I haven't dealt w any type of choke in many yrs. I honestly couldn't tell you. But you do want engine at operating temp and choke completely open when setting initial timing.

 

[Orig69]

New findings in this matter. In the process of trying to determine total timing this weekend, I noticed that the initial timing went back to 12 BTDC after I had set it to 18 last week. When pointing the timing gun at it the ignition timing mark also jumps around about 1/4” side to side. The car ran great, just wondering what may be causing this before I continue to readjust timing. When I worked on the motor last year I did install a double roller timing chain and made sure it was lined up properly. The distributor clamp was tight and I don’t think it moved around.

If the timing is moving by itself then check to see if the distributor is loose (with the engine off)