Ignition Timing Settings

[srrodder]

I have reviewed all of the threads I could find on this website and others on what ignition timing settings should be for the M code 351C in my Mustang and conclude that the best recommendation is for around 10º-18º initial advance and a maximum initial plus centrifugal advance of 32º-38º all in between 2800 and 3500 rpm, with the centrifugal advance beginning at 1200 rpm, and with ported vacuum advance of between 6º and 10º. An acceptable idle would be around 800-1000 rpm. My engine is recently rebuilt to OEM specs but with a Lunati cam equivalent to a D1ZZ-6250-A cam which is a 1971 CJ cam. The cam specs are:

Valve Advertised Duration 0.050 Duration Lift

Intake 269º 206º 0.481 in.

Exhaust 283º 221º 0.488 in.

The carb is a Holley 600 CFM with mechanical secondaries. I want to set the timing to the best setting that provides the most power without drivability problems and pinging. I am concerned that the initial advance recommendations would be too much for today’s oxygenated gas and would result in strong detonation (pinging) on light cruise.

Has anyone tried settings in these ranges with good results on a 1971 M Code 351C-4V with advertised compression ratio of 10.7:1 and closed chamber heads and using 91-93 octane pump gas?

For reference, the shop that sent the engine out for rebuild set the initial timing at 2º ATDC (to avoid pinging they said) and total advance (initial + centrifugal) at 32º BTDC. Vacuum advance is connected to ported vacuum and the vacuum retard is plugged.

*1971 Mach 1, Light Pewter Metallic, M Code 351C-4V, C6, Ram Air, A/C, PS, PB, Convenience Group, Rim Blow Steering Wheel, Tilt Steering Wheel, Tachometer Instrumentation Group, a rust free body and chassis with original paint & interior.

 

[73pony]

That initial they set it at is crazy. I think the stock on an emmissions 73 351 is 6 degrees BTDC. I think the most common recommendation is about 12 to 14 initial. Maybe Barnett will chime in here, he seems to have a lot of knowledge on setting the timing on the Cleveland motors. Keep in mind thought that every engine reacts differently to timing and it is a trial and error process to get the timing for your engine correct.

 

[Stanglover]

I have reviewed all of the threads I could find on this website and others on what ignition timing settings should be for the M code 351C in my Mustang and conclude that the best recommendation is for around 10º-18º initial advance and a maximum initial plus centrifugal advance of 32º-38º all in between 2800 and 3500 rpm, with the centrifugal advance beginning at 1200 rpm, and with ported vacuum advance of between 6º and 10º. An acceptable idle would be around 800-1000 rpm. My engine is recently rebuilt to OEM specs but with a Lunati cam equivalent to a D1ZZ-6250-A cam which is a 1971 CJ cam. The cam specs are:

Valve Advertised Duration 0.050 Duration Lift

Intake 269º 206º 0.481 in.

Exhaust 283º 221º 0.488 in.

The carb is a Holley 600 CFM with mechanical secondaries. I want to set the timing to the best setting that provides the most power without drivability problems and pinging. I am concerned that the initial advance recommendations would be too much for today’s oxygenated gas and would result in strong detonation (pinging) on light cruise.

Has anyone tried settings in these ranges with good results on a 1971 M Code 351C-4V with advertised compression ratio of 10.7:1 and closed chamber heads and using 91-93 octane pump gas?

For reference, the shop that sent the engine out for rebuild set the initial timing at 2º ATDC (to avoid pinging they said) and total advance (initial + centrifugal) at 32º BTDC. Vacuum advance is connected to ported vacuum and the vacuum retard is plugged.

*1971 Mach 1, Light Pewter Metallic, M Code 351C-4V, C6, Ram Air, A/C, PS, PB, Convenience Group, Rim Blow Steering Wheel, Tilt Steering Wheel, Tachometer Instrumentation Group, a rust free body and chassis with original paint & interior.

While I'm NO expert on this, my settings may be of interest. I too have a 71 351C 4V M code, but with a manual trans. My engine rebuild also was close to stock with just a small increase on the cam.

You didn't say what distributor you have, so I'll assume it's a stock Motorcraft as is mine. I run a Holley 670 Street Avenger carb with vacuum secondary's and I also use the timed port. Others will disagree! I do not have the temp vac switch connected so my manifold vac ports are plugged.

On the distributor, I bought an original reman. , but I found that these are built to a generic spec and for the M code, it has way too much mechanical advance. I welded the smallest limit slot and recut it to a 10L or about .400" . This is equivalent to 20 deg. on the crank. Not forgetting I have a manual trans, my setting may be different. Once this was done, I set my initial to 14 deg. or 34 deg. total and all in by 3000. I also purchased a new adjustable vacuum canister and at present it is set at only 4 deg. vac advance, so I have a total of 38 deg. all in. My set-up does still need a bit of tweaking as I'm still not quite there. I do seem to get minor spark ping when it's warm weather, but not when colder (??). With these numbers, my car has never run better in the 8 years I've owned it.

Hope this helps,

Geoff.

 

[Don C]

I agree with Jason, their initial timing doesn't make sense. The shop must not understand how closed chamber Cleveland heads work, nor must they understand the effect of camshaft on dynamic compression ratio.

The ranges you are talking about are correct. You shouldn't have any problems using pump gas.

I'm sure you also found the posts on how to modify your distributor to adjust the maximum advance, you'll likely have to after you get your initial advance up to where it should be. It'll take some experimentation to find the optimal settings for your particular build.

Your engine will like having a larger carburetor sitting on the intake manifold.

 

[jpaz]

Here is what I did. I had a lot of help from Barnett. My car is running great!

I have a 72 Q Code rebuilt with a little larger than stock cam, Blue Thunder intake w/a Holley 770 & C6 auto trans. http://www.7173mustangs.com/thread-distributor-curve

 

[Mikes73]

Beetlejuice, Beetlejuice, Beetlejuice. Just kidding, 12 to 14* seems to be the happy point for initial timing on these engines, just make sure the total timing isn't to high after bumping it up.

 

[will e]

What distributor do you have and how adjustable is it?

The best bet is to get a vacuum gauge. Set timing to highest vacuum at idle (in drive). Adjust RPM to be around 600 or so, what ever feels right. If the vacuum dropped try giving it a bit more advance on the timing. If the car is idling pretty smooth go for a test drive. Does it ping?

If the answer is yes, it pings, you have two choices. Try to adjust the timing curve or retard the initial timing a bit. Most people choose the latter (it is easier). By adjusting the initial timing you don't really change the timing curve, just how much advance you get at each point on the curve including total advance. You can do this till it no longer pings. Re-adjust the idle RPM and then adjust the idle screws on the carb to best vacuum. This will get you pretty close. You will most likely give up a litte horse power compared to doing a distributor curve adjustment.

If it doesn't ping you can always try advancing the initial timing until it does ping and then back off the initial a bit. In some cases this means you don't have the best vacuum at idle. That's okay if the engine is idling the way you like. Again adjust the idle screws to best vacuum.

In either case if you can get the engine a bit more smooth at idle adjusting the idle screws in or out a bit but at a point you don't have 'best vacuum' then go with that. You are looking for a smooth ride.

If you have an adjustable distributor where you can limit total mechanical advance and adjust the advance curve then again set the intial timing to best vacuum. Use a timing light to check total mechanical advance. You want to be around 36. Now play with the advance springs. Find a setup that avoids pinging. (Keep in mind that vacuum advance is not a factor when putting a load on the engine). If you get a good spring advance that avoids pinging you can try to advance the initial timing a bit. See if it pings, if it does, turn it back and try adjusting just the total advance and check for pinging. If after adjusting the initial timing a bit advanced it doesn't ping then you are probably about the best spot you can be. Check total advance again with timing light (just to be sure). You can always try a bit more total advance and if it pings bring it back down a bit.

The good news is you don't own one of the many engines where the distributor is in the BACK! There is a lot of trial and error to get the setting where it works 'best'.

 

[Stanglover]

What distributor do you have and how adjustable is it?

Mike, that is one of the best timing descriptions I've read. Even I can understand it!! I'm sure our friend will too.

Geoff.

 

[Stanglover]

*1971 Mach 1, Light Pewter Metallic, M Code 351C-4V, C6, Ram Air, A/C, PS, PB, Convenience Group, Rim Blow Steering Wheel, Tilt Steering Wheel, Tachometer Instrumentation Group, a rust free body and chassis with original paint & interior.

We need pictures!!! You have a great sounding car there, lots of option (I'm jealous!) so we'd love to see it.

Geoff.

 

[Mister 4x4]

Beetlejuice, Beetlejuice, Beetlejuice.

HEY!! :yeahthat: :nono:

I see what you did there. rofl

Sorry... :threadjacked:

 

[Mikes73]

I was watching a movie when I posted that, musta been on the brain

 

[Mister 4x4]

Uh-huh... :whistling:

 

[Mikes73]

Backhanded compliments good, movie lines bad, got it. Here we go again derailing a thread.

Anyways it is my experience lower compression engines seem to like quite a bit of advance at idle with a total ignition timing of 36 - 38 degrees all in at 2500 to 2800 rpm depending on the rest of the combo like gear ratio, cam profile, stall speed, compression, etc.

 

[jbojo]

This is what I have found to work best for me.

Initial timing 12 to 14 degrees

34 to 36 degrees total at 2500 to 2800 rpm

Ported with 10 degrees vacuum advance.

As mentioned cam, rear axle ratio, CR with affect these settings but these should get you into the ballpark.

 

[4Vforever]

That initial timing set up is terrible, so it's obvious they have no idea what so ever about tuning a Cleveland. They obviously don't understand canted valve shallow chambers and it doesn't matter if closed or open chamber heads. The biggest misconception about closed chamber heads is they were designed to provide more compression, not quench. There's nothing in early literature about them being quench. In fact quench is important to wedge type chambers, not shallow canted valve type. People say about the big block chev heads, but the canted valves are about the only thing they have in common with a Cleveland head.

First thing, make sure your distributor only allows 20* total advance, once that is established then start 10* initial with a total of 30* then take for a drive. After that then advance it 2* at a time until you're not happy with it, then go to the timing that impressed you most, but usually 14*-18* initial and 34*-38* total by 2800-3200 RPM is the sweet spot for a Cleveland. Also a spring kit maybe needed to give you the right curve you need for your application. As has been said previously, all engines react differently, so what may be great for one of similar specs, may not be for yours. Also carb tuning may be of help too, but a 600 on a 4V is a performance killer, I know Ford ran a 605 CFM Autolite on the closed chamber 4V, but as someone said to me years ago, he was sure Ford did this instead of putting on rev limiters on all CC 4V engines as they'd be out of breath by 5800 RPM if that. I don't know as I've never driven a totally stock 4V flat out.

Anyway give it a go and plenty of people on here to help you get it right. Just start basic and tune from there until your happy. Good luck with it and let us know how you go with it.

 

[Stanglover]

Our friend srrodder, has not yet responded to the suggestions made as of this time. We can't all be on the computer day in and day out, but it would be nice if he (and others who post questions) would at least acknowledge that the efforts by members, is appreciated.

Between will e and 4vforever and the info with regards to reworking the slot plate to equal an L10 or 20*, I think there is enough info to reset or recurve any Cleveland distributor. I have certainly learned more from the responses given here. Thanks guys.

The only other suggestion I can make is spring rates and from my own efforts, the possible need to play with them to get the best balance. As of now, I have 1 Mr.Gasket spring (can't remember the number) and the original heavy spring on the left side. I found this combo to work quite well, but as stated, I'm still not quite there yet. Tweaking the spring pressure may be in order, but till Spring hits it's too cold to play anymore!!

Geoff.

 

[Mister 4x4]

Backhanded compliments good, movie lines bad, got it. Here we go again derailing a thread.

Nothin' there, Man. Just pickin' on ya. Doesn't anybody read "smiley" anymore? :shootself:

Anyways it is my experience lower compression engines seem to like quite a bit of advance at idle with a total ignition timing of 36 - 38 degrees all in at 2500 to 2800 rpm depending on the rest of the combo like gear ratio, cam profile, stall speed, compression, etc.

Agreed. My initial settings were 6* BTDC, as I was told/learned. After some research and discussion (primarily here with all these guys who've forgotten more about Clevelands than I'll ever know), I got mine sorted out with the dizzy running 20* advance, with an idle setting of 16* BTDC.

You're right as well, Geoff. I hate it when we don't quickly hear back from folks when they ask advice. I want to know how it went! I think it's very cool and exciting when someone has a problem, asks a question, then we get to find out we were able actually help them out, or need to troubleshoot further.

 

[Stanglover]

Agreed. My initial settings were 6* BTDC, as I was told/learned. After some research and discussion (primarily here with all these guys who've forgotten more about Clevelands than I'll ever know), I got mine sorted out with the dizzy running 20* advance, with an idle setting of 16* BTDC.

You're right as well, Geoff. I hate it when we don't quickly hear back from folks when they ask advice. I want to know how it went! I think it's very cool and exciting when someone has a problem, asks a question, then we get to find out we were able actually help them out, or need to troubleshoot further.

Yes Eric, when we get to hear back that what has been suggested helped sort out a problem, that's where the reward is. Not only that I/we learn too. I know nothing compared to most of our members, so I'm always keen to pick up tips and tricks and at times, pass then along.

My engine too was base timed at 6 degrees from the factory (always wondered what the L 6* meant on my engine code sticker!!) I learned that here and how 'wrong' it really was.

 

[srrodder]

Many thanks to all who posted replies. The info should be very helpful in setting up the ignition system (and carb). In response to questions - the distributor is stock, but I will soon be installing a Pertronix Plug n Play distributor with an Ignitor III system and with an adjustable vacuum can so I can tune all the timing settings. The differential is a 3.25:1 TractionLok. Pictures of my car are posted on this website in the Garage and Registry areas under srrodder.