360 Tune Up

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Basics are this.
You can set the initial at X rpm.
If the engine will idle at 650 rpm at 16*, that's a pretty good place to establish as a baseline.
The problem, or potential problem is what happens as rpm increases.
For a street, road race or circle track using vacuum advance equiped distributor, its very easy to have too much advance below 3000 rpm.
A timing curve that looks something like the Mopar Performance shown in this post is the ballpark for a factory hi performance or hot rodded 340 or 360.
Your distributor is advancing way to quickly to be using a vacuum advance.
Begin with the guidelines and make small changes based on performance.
40* at 2200 rpm on up can do serious damage at wide open throttle under full load.
Full load is somehting like pulling a boat out of water, a 1/4 mile run - particularly the top gears of a 1/4 mile run.
 
Thanks Mattax. I appreciate your input and have enjoyed it in the past. I obviously need to dig some more. I do have another distributor I can mess around with possibly limiting the full advance after I understand my baseline testing.
Care to take a stab at why my timing is coming in so fast so I know where to start? As far as I know my current distributor is stock.
 
JoePole1 said:
Thanks Mattax. I appreciate your input and have enjoyed it in the past. I obviously need to dig some more. I do have another distributor I can mess around with possibly limiting the full advance after I understand my baseline testing.
Care to take a stab at why my timing is coming in so fast so I know where to start? As far as I know my current distributor is stock.
Click to expand...
It's all in the springs under the point plate.
 
Joe, I will bet the engine idled better going from 16* initial to 25*.
 
JoePole1 said:
Care to take a stab at why my timing is coming in so fast so I know where to start? As far as I know my current distributor is stock.
Click to expand...

I've not seen a factroy magnum timing specs.
Stabbing:
A. 5.9 Magnum distributor would be emissions era, and although helped by catalytic converters, may have still used a relatively retarded initial to reduce CO at idle and maybe also to insure less leftover HC. Cats are damaged by 'raw gasoline.'
B. Cylinder head and maybe the cam and intake distribution is more efficient than the older LA, therefore the flame development and pressure rise is probably a little different.

The effect of the idle emisions game on timing is pretty apparent when comparing two exact same engines with and without an early CAP.
Take a look at the acceptable 1967 timing curves shown at the bottom in this post: Timing Marks on the 273 [66 Barracuda]

See how similar they are for the driving range even though one distributor begins 5* ATDC and the other at 10 BTDC?
 
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If you have a spare dizzy you should read up on setting your curve by means of springs and plate slots. JMO
Mattax is far more knowledgeable than me though. By far.
 
Edited my previous post to clarify the timing plots are at the bottom of that post.

Looking at the DC/MP instructions for their distributor, at least in the mid to upper rpms, my interpretation is the magnum engines create faster developing flame fronts. This is suggested because instead of targeting 35* at 2800 rpm, they suggest 32* at 2800 rpm.
How To Limit and Adjust Chrysler Vacuum Advance Cans

aside:
They aren't providing an initial because it they are offering a 'one size fits all' distributor. They can't predict what sort of cam etc has been put in, but they know the users are most concerned about hih and mid rpm performance. Also getting the timing close in the higher rpm ranges is more critical than the low. Worst case with low rpm is poorer milage, less torque, maybe some pinging or "gurgling sound' at par throttle. Worst case at high rpm, high load, is melted piston or similar.

Returning to the example using the MP distributor and setting the timing as they suggest, the timing curve would like this.
upload_2022-8-10_8-29-27.png

Most of the Chrysler engines we are dealing with like a fairly quick rise in timing going from idle to around 1700 rpm.
Then slow the increase in timing is reduced greatly because the combustion itself is getting faster. That's why it doesn't need continued rapid increases in lead time. It only needs more lead time when we reduce the density of fuel and air which is dealt with by the vacuum advance.
 
Overlaying your measurements for that distributor timing the advance looks very linear.

upload_2022-8-10_8-47-21.png


Were springs changed? Is that what the factroy wanted for some reason on that engine and vehicle? I don't know.
 
Lots of good infomation. Thank you. I do not believe the springs were changed but can't say for sure. Oddly enough I purchased lighter springs prior to testing believing I would need them. I will be doing some trial and error today and report back.
 
Hey Guys. Did some more testing and I have to say that she seems to run better with the higher initial timing but the numbers scare me. By better I mean Idle quality, higher vacuum and more seat of the pants power. No pinging or nocking.
730 RPM. 28' 45' w/vac can
1000. 28' 45'
1500. 36' 53
2000. 43' 60 max
2500. 45' max

When I set the initial timing back to "normal" the idle drops and I had to adjust it back up. Still has good power and fires right up with twist of the key, no gas in either case. Car runs at 190 deg as well.

700 RPM. 16 deg
1000. 16'
1500. 26'
2000. 30'
2500. 32'
3000. 35'
3400. 37' max

Pretty much textbook with maybe slightly too much total timing which I can limit however something doesn't make sense with the numbers. I am going to leave it this way for now because we are road tripping in it tomorrow for a few days and about 400 miles.
I'll try switching to my spare distributor and more testing when I get back.
 
If you are getting 45° at idle with the vacuum hooked up you have it hooked to the wrong port on the carb. You don't need that much advance at idle.
 
Joe,
Was expecting the answer that idle was better with 25* init. My engine engine idles with 48* [ yes, 48* ! ]. So much BS with this topic.
The 'one size fits' all dist doesn't exist. If you want the best, you have to dial in your own curve & be prepared for some trial & error work.
The engine speed & vacuum increased with 25* because the engine is making more HP. It likes the extra timing at idle; it may like even more.
Get the highest idle rpm you can by toggling the dist with the engine idling. More cam needs more timing. Once you have that, you have to decide how to get it permanently. If it likes 35* initial, the starter probably doesn't.....
The fix here is to lower the initial to where the starter is happy [ 25*? ] & add the rest using vac adv hooked to manifold vacuum. In the example, you would need to limit the travel of the VA plunger so that it only adds 10*. You should also use an adj VA unit with the Allen Key fully CW to start with.
The curve in the dist will have to be modified [ shortened in this case ] to provide the total timing under load [ VA goes to zero under WOT load ].
Engine will run cooler/smoother at idle & have better tip in response.
 
Yes the defination of horsepower is that higher rpm makes more horsepower.
The point of strong idle is to make the most power at a low rpm.
If the engine is slipped into gear at 650 rpm and the truck marches away that's good power for idle.
Increasing rpm and vacuum in neutral proves nothing. Because the rpm isn't the same as before and there is no external load.
 
"Was expecting the answer that idle was better with 25* init. My engine engine idles with 48* [ yes, 48* ! ]. So much BS with this topic.
The 'one size fits' all dist doesn't exist. If you want the best, you have to dial in your own curve & be prepared for some trial & error work. "

Yes. This appears to be the case.
 
Mattax said:
Yes the defination of horsepower is that higher rpm makes more horsepower.
The point of strong idle is to make the most power at a low rpm.
If the engine is slipped into gear at 650 rpm and the truck marches away that's good power for idle.
Increasing rpm and vacuum in neutral proves nothing. Because the rpm isn't the same as before and there is no external load.
Click to expand...

So my initial goal for this build was lots of low end power as opposed to HP. My car is a 72 B body so it's pretty heavy.
My current testing and adjustment has been mostly from a stop and a couple of low speed "passing gear" performance.
I have my initial set at 16 now mostly because I am concerned about my total timing numbers even though I am not hearing any detonation or pinging with 28 initial. I will be doing a combination of highway, twisties, hills and around town on my trip so this a pretty good test. I will also be running my AC at times. I'll mess with it some more next week.
 
JoePole1 said:
So my initial goal for this build was lots of low end power as opposed to HP. My car is a 72 B body so it's pretty heavy.
My current testing and adjustment has been mostly from a stop and a couple of low speed "passing gear" performance.
I have my initial set at 16 now mostly because I am concerned about my total timing numbers even though I am not hearing any detonation or pinging with 28 initial. I will be doing a combination of highway, twisties, hills and around town on my trip so this a pretty good test. I will also be running my AC at times. I'll mess with it some more next week.
Click to expand...

If it's happy with more timing and there are no signs of detonation I'd leave it there. Maybe pull a few plugs to verify. What does taking 9 degrees of curb idle timing out leave you with all in?
 
JoePole1 said:
So my initial goal for this build was lots of low end power as opposed to HP. My car is a 72 B body so it's pretty heavy.
My current testing and adjustment has been mostly from a stop and a couple of low speed "passing gear" performance.
I have my initial set at 16 now mostly because I am concerned about my total timing numbers even though I am not hearing any detonation or pinging with 28 initial. I will be doing a combination of highway, twisties, hills and around town on my trip so this a pretty good test. I will also be running my AC at times. I'll mess with it some more next week.
Click to expand...
Fair enough.
You will refine your testing program the more you do it.

Lets break this down:
72 B-body with a/c. automatic transmission, 5.9 magnum with the distributor from original application. Goal street use mainly or only?
>> It would certainly be helpful to find out the initial and advance specs from the original application. Additionally if the original application used a A/C switch actived solenoid to increase idle rpm with the A/C on. This would provide a baseline. (Your 72 B-body may have had an throttle solenoid tied to A/C - its not a new idea).
>> If the engine was originally a 2 bbl or standard performance, note if you've made changes that would effect combustion. Typically we see increase in efficiency at high mid to high rpm, wide open throttle, with things like going from a 2 bbl to a 4 bbl.
Above is for establishing a baseline off of all the engineering and testing done by the factory - unless you think they're a bunch of dummies and didn't know what they were doing.

Testing
>> Do steady state testing first, transitions afterwords. Steady state tests make it easier to isolate and change one variable. Transistions will often take require nothing if the steady conditions are tuned in.
>> Accelerating at part throttle, especially from low rpm, is an example of a transitory test. The throttle opening is changing at the same time the rpm is changing, and the load is changing. If you have a dash mounted vacuum gage you will see the changing load reflected in the changing vacuum. It is possible to do a part throttle acceleration where one 'crowds' or holds the vacuum stready. The throttle will not be steady when crowding, but needs to be squeezed further open to maintain the crowd. I've posted a data log of that.
>> Steady state tests that you can do.
a. Idle in drive. The least drop in rpm and/or manifold vacuum when going from neutral into gear will be the strongest. This is a good foundation and will also be immediately useful for at least driving around town.
b. Idle in drive with A/C on. This will be a higher load test. It will give you an idea as to whether a solenoid that bumps up idle rpm may be needed. I would test with a/c on only after the battery is recharged (as shown on the ammeter) so as not to also have a high alternator load on the engine.
c. Full load tests at higher rpm. Ideally this is a 1/4 mile drag strip run so the engine is at wide open throttle (max power) in third gear (max gearing load) under highest resistance from air etc. in the power band.
c1. If no access to a drag strip, or your not ready for that yet, then pick a place you can consistantly do a heavy load full throttle test. If you hear gurgling at full or near full throttle, back off!!! The test has to been done with so much load that the vacuum advance is out of the picture, and the power valve or step up circuits are enrichening the mixture. In other words at or near full throttle.
c2. Judgement of performance on max load will be higher mph through the lights (drag strip) as an indicator of top end timing, and lower rpm timing curve can be judged by e/t, 60' and so forth for engine acceleration.
c3. An indicator of too much advance will be any sounds of pinging (back off throttle !!!) and specs of aluminum on the spark plug porcelain.

Vacuum advance
Set so the vacuum advance on moderate to intestate highway cruising is close to factory recommendations. See the MP instructions linked earlier. If its pings on part throttle or light acceleration, make a small adjustment to reduce the advance at that vacuum or limit the toal which ever is applicable for that condition. (A little gurgle under light throttle is not the highly destructive condition that it will be under full or near full throttle.)

This is in the ball park.
upload_2022-8-11_10-23-31.png


make small changes to tune.
For example.
Do the in gear at idle tests. Then adjust timing 2* and fiddle with idle speed and mix to get back to the same rpm (700 if thats what it is) and retest. Write down the resutls and compare.

You know how to adjust initial.
Earlier in the thread there are instructions on how to get the advance to being at lower or higher rpm. Similarly you can get the secondary spring to engage at a little lower rpm. The latter may be useful with this engine.

Performance tuning is the opposite of plug and play.
Its low dollar and high on time.
Good luck.
 
^^ Good write-up, have not read the entire thread... hopped on at the end. What kind of fuel was in use when the MP timing spec was made? When I was in CA I found more timing all in early worked better with the crap gas... especially the "summer blend".
 
74Scooter said:
^^ Good write-up, have not read the entire thread... hopped on at the end. What kind of fuel was in use when the MP timing spec was made? When I was in CA I found more timing all in early worked better with the crap gas... especially the "summer blend".
Click to expand...
I'd have to dig out my old notes. The timing was measured on my 340 with Comp cams 280 around 1995 - so NE reformulated gas, but maybe after MTBE was thankfully banned.
The timing shown above in blue for joepole is that advance curve shifted so the timing at 2800 rpm is 32*. That's the big circle and comes from the MP recommendation for that distributor when used with a later LA engine. I thought that might be another useful baseline.
 
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