Timing Curve on 360 in an RV

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OK if I am rading this right that is high teens s total AFTC advance? cAN BE A BAD PICKUP OR phasing kind of weird. Harder to start when hot?
 
I used asection of flexible 3" water heater duct and plumbed my air cleaner to the cowl plenum for fresh air to carb . I got the idea from 64/65 Nascar B-Bodies .
 
I also noticed that my temp never gets up veryhot unless its climbing in the heat . Which tells me the P.O may have removed the T Stat thinking it would cool better . Or the TStat is stuck open
 
What stall, rear gear, and tire roll-out? this will play an important roll in avoiding detonation on a long pull. Detonation and it's sometime partner pre-ignition, is the enemy of your engine, and has to be avoided at all costs. They break things like pistons and rings and hammer out bearings.
I'm trying figure out why you would chose all-in at 2200; and no vacuum advance. That is a race-car tune, with a lightweight car, a big engine, and race gears.

For you tho;
For fuel-economy reasons, as well as a bit of WOT power;
you will need to push the minimum cooling system temp up to at least 180*, Myself; I would try for 195. But your cooling system will have to be rock-steady without any hunting around. You will have to make it so. You cannot begin your tune until the cooling system is at a fixed and steady temperature; whether it be 195 or 180, or whatever it is; it has to remain stable for the tune. Later you can add temperature compensation.
And your engine will HAVE to have a source of fresh cold air. If the inlet air temp is bopping up and down, from 100* to 400*F you will have a big tuning headache.
Ok so, you should know that the more idle timing you give it, with no other changes, the higher the idle will climb. This is not necessarily a good thing. Your automatic transmission equipped engine will never be asked to pull at idle, so at the beginning of your tuning, it can be whatever. Later, much later, you can start to monkey with that. So, your engine doesn't much care about it's idle timing, as long as throttle response doesn't fall on it's face between idle and it's stallspeed. But beginning at the stall speed is where it starts to care. From there to ~3200 it is almost critical to not have too much, and after 3600 most engines fall to between 32* and 36*.
So,
Confirm your timing index mark.
reset the idle timing to 10 degrees advance.
reset your idle rpm to 600 in Neutral, or 550 in gear whichever is less.That stock engine should idle down to 600in gear, no problem.
Now increase your idle timing to 12/14* and leave it there.
Now program your computer with a linear power-curve to be 26* at 2800; and then change to a slower linear curve to be 34* all in at 3600. That is your starter POWER CURVE. It will only be near-correct at WOT. It will not be correct at any other throttle/load setting. I repeat; it will not be near-correct at any other throttle/load setting except WOT.
All other throttle settings and rpms are adjusted by the load sensor, AKA the vacuum advance. This timing is added to the power curve in direct proportion to manifold vacuum, which is 100%dependent on the load factor or throttle opening versus rpm, AKA speed-density.
So lets say you are cruising along at 50 mph in top gear at 2400 rpm. Your engine might like 56* of timing there; IDK, just saying. But if you give it any throttle there as in; you came to the bottom of a kill,then, at 56* and 2400rpm, it will only take a few seconds (15 seconds@2400rpm is 600 revolutions times 4 firings per revolution is 2400 hammer-blows, or 300 per piston)until the factory pistons may begin to fail; IDK how much they can take, but the rod bearings may fail first. Therefore,the "vacuum advance" will have to immediately start to decrease linearly with throttle opening (manifold vacuum), back to the power-timing,which might be 20/22*@2400( just guessing) which I purposely made weak for this reason. Once climbing up that hill, your "vacuum advance" will have to stay at zero, while the engine is stuck in top gear at 2400rpm, on the SAFE power-curve.
If you were to downshift,at this moment, with a 727, the Rs would jump from 2400 to ~4100, and the engine would be on the all-in timing of 34*@3600, and if you have sufficiently enough octane rating, it will pull itself along nicely. Perhaps nicely enough that manifold vacuum might rise high enough to again bring in some "vacuum advance". This might be a good thing but could just as easily be bad; that is for YOU the operator and tuner, to determine. To help you with this, your EFI may have a knock-sensor tune available, and I highly recommend that you use it.

So some of these things have already been mentioned, I just put them all in the same post, and added some reasons why, to help you understand.
Current thermostat is 185, keeps operating temp pretty steady on a hot day between 195-205, depending on if I'm in stop/go traffic or on the highway.

For the timing curve, the EFI system has the following parameters to set:
Idle timing - Sounds like I should set this to 15-16 degrees (aka initial timing)
Advance start (rpms) - Tells system when to begin the advance curve, currently at 1200 rpms
Total timing (degrees) - Sounds like I should set this to either 26 or 34 degrees (this will be max timing)
Total timing (rpms) - Sounds like I should set this to either 2800 or 3600 (this is the 'all in at' setting)
and Vacuum Advance - Not sure what to set this to, maybe 5 degrees (fyi - doesn't affect idle timing)

I didn't follow the "start with setting your curve at 26* at 2800, and then change it to be these other settings." Why do one and then the other?
 
I didn't follow the "start with setting your curve at 26* at 2800, and then change it to be these other settings." Why do one and then the other?
The info from AJ is to set TWO different slopes on the advance curve... one from idle to 2800 RPM and a slower slope from 2800 to 3400. But from your descriptions of the computer settings, you can only set one slope on the curve, from idle to the end RPM (Unless you can choose in an earlier menu to have 2 slopes in the curve).
 
The info from AJ is to set TWO different slopes on the advance curve... one from idle to 2800 RPM and a slower slope from 2800 to 3400. But from your descriptions of the computer settings, you can only set one slope on the curve, from idle to the end RPM (Unless you can choose in an earlier menu to have 2 slopes in the curve).
Correct. It's a single slope interface. Sounds like I should use the more conservative slope?
 
There is lots of good advice here, the only problem is most of it with the exception of the total and initial timing only apply if you’re running the factory distributor and vacuum can.

First off make sure you set the distributor per Edelbrocks instructions at 12* By locking the timing with the tablet And verify by timing light assuming you’re balancer is good. Then set your initial 16-20* and total in timing as suggested earlier to all in 32ish * at say 3600.
Adding vacuum advance with the Pro Flo 4 WILL affect idle timing slightly.

The most important takeaway here is to verify the 12* with the timing locked out because if this is off the computer has no was to know where the timing is And all other timing parameters will be off. The advice you received on the tech forum over there for 22* at 2200 was BS.

Report back with results but from my playing with this system it does not like anything more than 34-36* total without the backfire issues.
 
There is lots of good advice here, the only problem is most of it with the exception of the total and initial timing only apply if you’re running the factory distributor and vacuum can.

First off make sure you set the distributor per Edelbrocks instructions at 12* By locking the timing with the tablet And verify by timing light assuming you’re balancer is good. Then set your initial 16-20* and total in timing as suggested earlier to all in 32ish * at say 3600.
Adding vacuum advance with the Pro Flo 4 WILL affect idle timing slightly.

The most important takeaway here is to verify the 12* with the timing locked out because if this is off the computer has no was to know where the timing is And all other timing parameters will be off. The advice you received on the tech forum over there for 22* at 2200 was BS.

Report back with results but from my playing with this system it does not like anything more than 34-36* total without the backfire issues.
I've checked and locked in the base timing at 12 degrees via the "set base timing" workflow through the app. Timing light on wire #1 shows it right at 12, though the markings are a little hard to see. Worse case scenario I might be a degree or two off in one direction or the other, but that'd have little impact overall as I'm tuning.

When I set up an initial tune at 16 initial, 30 all-in at 3000 rpms with 5 degrees of vaccum advance, I was getting consistent backfiring anytime I was around 27 degrees of advance or higher, and acceleration was very rough. Anytime the engine was under load, things were not running smoothly. I could even get it to consistently backfire just by revving the engine up to 3000 rpms in park. This is the scenario that started my journey to the odd settings I currently have - an effort to tune out the backfiring and find a tune where I would get reliable, smooth accelerations.

That current tune is 16 initial, 21 total all-in at 2200 rpms. But that seems super-off from where I should be.
 
I would still verify your timing marks on your balancer to make sure they are correct. Is the firing order correct? I have the same backfire issue as you have but not until 34-36* so something sounds off on your setup. Have you tried a different coil?

I have mine currently set to have 32* all in at 4K RPM with initial at 18* and 10*vacuum which gives me an actual idle of about 24*. The vacuum numbers will drop some under acceleration depending upon the load on the engine as the ECU is reading the manifold vacuum and compensating accordingly.

I agree that you should be able to run more timing than you currently have without issue. I would raise the rpm for total in and try adding a few * at a time and see what happens. It seems to be all trial and error with this system and I’ll be the first to say I’m not really impressed by the timing control or lack thereof.
 
You ought to look up the factory advance, which is usually in the servvice manual.
The service manual will also have the initial timing and rpm it is to be set at.
All that initial advance is fine for engines that have slow flame and/or heavy exhaust dilution at idle.
I seriously doubt an RV engine would be set upo that way.

Yes some modifications were made for emissions, and they were altered over the years. So (a) I'm not going to guess what was done for a '78 RV. Find the specs and we can take an educated guess (b) the general chararacteristic of the advances didn't alter that much. All Chrysler engines used a 'two stage' advance in the era we're discussing.
 
Yes I forgot we were talking about an RV engine here. As suggested above you may want to curtail the initial timing to something closer to what the FSM says but you still should be able to run more than 21-22* total. The reason I suggested trying a higher all in number was to keep all timing from being in to early since you described the backfire issues. This has helped me avoid those issues.
 
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I am not home right now but I have the FSM for 78 Motorhomes and they do have 2 stage advances . Plus the vacuum advance.
My question about emmissions was because I wasnt sure if heavy vehicles fell under the laws at that time . I remember 3/4 and 1 ton trucks still ran leaded fuel into the 80s.
 
I am not home right now but I have the FSM for 78 Motorhomes and they do have 2 stage advances . Plus the vacuum advance.
My question about emmissions was because I wasnt sure if heavy vehicles fell under the laws at that time . I remember 3/4 and 1 ton trucks still ran leaded fuel into the 80s.
It's a totally legit question, and why I don't want to guess what tweaks were done.
It might have been cat exempt in '78 (like the pickups) but may have met some emmissions requirements - especially for idle and decel - in addition to vapor recovery and PCV.
 
It's a totally legit question, and why I don't want to guess what tweaks were done.
It might have been cat exempt in '78 (like the pickups) but may have met some emmissions requirements - especially for idle and decel - in addition to vapor recovery and PCV.

I am just wondering if there is room for improvement over the stock curve.
I will post the FSM curve data tomorrow.
Did OP mention his dist. # ?
 
I am not home right now but I have the FSM for 78 Motorhomes and they do have 2 stage advances . Plus the vacuum advance.
My question about emmissions was because I wasnt sure if heavy vehicles fell under the laws at that time . I remember 3/4 and 1 ton trucks still ran leaded fuel into the 80s.
They were catalytic exempt. I can recall being told this in a Ford dealership back in '76. I asked why the F150.... before that, they jumped from F100 to F200, and the 'new' F150 gave them the chance to make a high enough weight rating in a 1/2 ton chassis to not put in the catalytic converter. Sorta a 5/8 ton rating, I guess LOL
 
Anytime the engine was under load, things were not running smoothly. I could even get it to consistently backfire just by revving the engine up to 3000 rpms in park.
The backfiring in neutral (non engine load to speak of) does not suggest detonation. Detonation is a heavy load thing... when the throttle is open wide, cylinder filling is high, and consequently peak pressures are high.
 
If you have headers;
and an exhaust leak at the head,
this can cause the "backfires" you speak of which are actually after-fires, as a rich mixture leaving the combustion chamber continues to burn in the headers. Starting the fire earlier as you are doing, helps to alleviate the popping but is the wrong solution.
The better solution is to lean it out, and fix the exhaust leak, and put the timing back to where it belongs.

Log manifolds do not work like headers and do not cause this kind of problem. They are generally, under pressure almost all the time, more so if afterfire is occuring. But they can do a different thing. At the tail-end of the exhaust stroke the intake valve is already beginning to open, so they are both simultaneously open for several degrees; typically more than 30*, and less than 50* for an RV -type cam. If the log has a higher pressure than the intake, which it always will have in a rich-running engine, AND the cylinder also is at a higher pressure than the intake, which it always will be with logs;
then the pressure in the cylinder will go to where ever the lower pressure is. Often this is the intake manifold .... so now you have a pop in the intake, a genuine "backfire".
However this kind of problem goes away with increased rpm, as there is no longer enough time for the exhaust to behave this way. The cure for this is a free-flowing exhaust, a leaner mixture, and proper ignition timing.
 
The whole point of ignition timing is to light the fire at the right time to get the pressure in the cylinder to peak at the optimum crank position, to transfer the maximum amount of energy contained in the expanding gasses. This point does not vary much, but the burn time does, and that is why we have to lite the fire early at low rpm, very early, but that timing has to drop out rapidly with rpm and especially with load, and there are other factors such as altitude, inlet air temp, and cooling system temp( actually chamber temperature). And to some degree, the temperature in the exhaust .

If the pressure peak is too soon, then the crank is not rotated over far enough, and the rod-bearings take the hit.
If the pressure is too late, the rod bearings are happy, but the engine loses efficiency; that is too say, the expanding gas energy chases after the piston and does not push on it as hard as it could,if the pressure-peak had occurred a lil earlier.
Your job is not to throw timing at it in the hopes of accidentally lucking into the best place for this to happen.
Your job is to hit as close to it,but not too early, as often as is possible, from stall to ~3600rpm, to maximize your average peak pressure. But especially NOT to HAMMER the rodbearings to death, or break the piston skirts off.
So how do you do this?
Without a dyno, Ima thinking it is next to impossible.
So in the field, you have to sneak up on it. And since you are setting the POWER-TIMING, the best thing to do is to be conservative,so you don't break stuff. Furthermore, you gotta think about how often your engine is gonna be in the zone from stall to 3600 at WOT, and how heavily the engine will be loaded, that it will be missing the very few horsepower, that a slightly too-late ignition timing might cost you.
For example, going back to the previous combo that was 2400@50mph in top gear with a 727. Again assuming a 2400stall TC.
If you were to floor it at a dead stop, the rpm scoots up to 2400 right away, instantly bypassing all the timing below that. At this time, the engine doesn't care about any timing below the stallspeed. At this moment, all it cares about is to have the exact right timing for 2400@WOT; or LESS, not more.
At about 16 mph she will hit 3000rpm, and at 20 mph, she will hit ~3600rpm; where I am suggesting you max the timing at 34*.
So that is the first zone to be concerned about, namely stall to 3600 which is stall to ~20 mph ( remember I geared your can to be at 50MPH@2400@zero-slip. This assumes something like 4.30s and 28" tires.)
So already you have one data point of timing, namely 34* at 3600rpm, and some other number at stall; and I earlier suggested 26* at 2800. So lets figure that one out, and then correct it to 2400.
I'm gonna suggest that your idle timing be 14*, an arbitrary number I know your engine will like.
And I suggest you begin the advancing at 1000rpm, with an idle of no more than 750,in N.
Ok now, from 1000 to 2800 is 1800rpm which will be the working range of your advance, in this case.
And the amount will be 26 less 14=12*
So then; from 1000 to 2800, the advance will climb from 14 to 26, understand that? If that is true and the curve has to be linear, THEN; the rate of advance will be
12* per 1800rpm, which I will restate as .67 per 100rpm. and
Now we can calculate the timing for your engine, anywhere from idle to 3600rpm and beyond, simply be using the .67* per 100rpm.
So, at 2400 your timing will be 2400 less 1000 =1400 rpm, and 1400/100x.67=9.4* which we add to the initial of 14*, to total 23.4; at 3600 it will be 3600 less 1000=2600 rpm and 2600/100x.67=17.4* and add the initial of 14*, is 31.48..how cool is that.
Ok so now you have a built-in cushion of about 2.5 to 4.5 degrees to play with,to get to a theoretical 36* max timing; simply by changing the initial idle timing from 14* to, 14*plus 2.5 to 4.5
With a computer, you can also change the rate of advance to something other than .67* per 100rpm. In your case you can change the start point and end point, and the total number of degrees of change... right?
So you program the start point to 1000 and endpoint to 3600 and the amount to 34 less 14 suggested initial= 20*. Then you set your idle timing to 14* at anything less than 1000 rpm and you are all set.
This is a starter curve, and I think it's a pretty safe curve, so you don't kill your engine on the first trip. It may not make full power anywhere in the rpm band from stall to 3600, and it will, without "vacuum advance", make terrible fuel economy........ but at least it won't blow up.

Now, lets look at second gear.
Geared for 2400@50mph, then 2400rpm in second will be about 25mph at WOT. Will your engine ever be there?
Not if your Kickdown is working; she will downshift into first and shazzam away you motor.
How about at 3600rpm? This will be ~38mph in second, and if she downshifts, then this could go to more than 5500, so NO, the trans will not kickdown. In fact 5000 in first will be about 33 mph. If you are over 33 chances are the trans will not kickdown, so lets start at 33 mph.
In second,now at 33mph, your rpm will be ~2500 at zeroslip,so perhaps at 3200 with a slip-ratio of guessing 30% in the TC. So with my conservative tune, this is 29* timing, which should be safe. To this you can still add 2.5 to 4.5 on the initial, to get you up to 31.5 to 33.5 of Power-Timing; see how nice this is working?
Lets go to third gear. The 2-3 split is .69 compared to the 1-2 at .59 so it will be even better, so I won't bore you with more math.
so in conclusion; the curve I outlined is pretty safe, certainly within a handful of degrees.
What does 5* not enough timing cost you in horsepower, between 2400 and 3600 rpm, which is zero to 20mph?
IDK the answer to that; but I bet not a second of time.
What would 1* of too much timing cost you?
IDK the answer to that either, until the rod-bearings and/or the piston skirts end up in the pan... then I can estimate; a new engine.
So whatever you do, sneak up on it....................
 
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Now lets talk vacuum advance.
You have a program in your computer, that allows you to add timing to the base Power-Timing to compensate for OTHER THAN WOT throttle/load settings.
For example; while cruising , and still geared for 2400 at 50 mph, your engine might want a cruise timing of 48*/just guessing, to max the fuel-economy.
But your power timing, in the above example, is only allowing 23.4*.
The difference; 48 less 23.4=24.6, has to come from that program.
At 3200, your engine might like 54* of cruise-timing. Again the difference from the power-timing to what the engine wants, has to come from this "vacuum advance" program, whatever your computer calls it.
This also applies to Part Throttle operation.
Perhaps your engine in second gear,at 2800rpm, might want 50*/IDK, just guessing .The difference from the Power Curve to whatever it wants, has to come from this, adjusted for load, PT, timing program.
This increased low-load and PT timing, will allow you to lean the fuel out a bit, and simultaneously cause the engine to run cooler and make more PT torque.
I can't tell you how to program yours except to say 9* is a poke in the eye. Your engine will want something like 20 to 24* at cruise speed, whatever the manifold vacuum is at that time. And in first gear, it will want additional low-load timing beginning at about 1400 rpm, whatever the manifold vacuum is at that time.
Again, the operative phrase is; sneak up on it/ back it up if it detonates.
 
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How can you know what the engine wants for Low-load and PT timing.
That 's easy, with a distributor. AFTER the Power-Timing is getting close to finalized, AND the Idle-timing is fixed, THEN;here's what I do;
In Neutral, brakes applied,
I crank the engine up to ~1800rpm, and just start cranking in more timing, while simultaneously keeping the rpm at 1800. When I think I'm close, I begin being careful to only advance small amounts, always keeping the rpm at 1800. When I get really really close, more toiming will slow the rpm, and then I know I am too far, so now I check the timing with a light, read the number, and back it up 3*. That will be my cruise timing maximum starter target.
THen I move up to 2400 and repeat. Then 3200 and repeat. If a standard trans, then 1400 and repeat. Then I return the Idle-Timing to as I found it.
Now I have three or four data points which I can plot on a graph, and connect the dots, averaging as I do. From that line, I then subtract the Power-Timing, to arrive at what the Vacuum-advance program needs to approximate.
If you change the Power-Timing, You will then have to revisit the Vacuum advance because I only built in 3* of cushion.
Furthermore, the above was a MAXIMUM, NO-LOAD curve.If you were to install this curve you might find it pings mercilessly when switching from PT and going to the Power-Timing curve. Therefore, I recommend to take out 6* from the entire plotted line, and again
sneak up on it, little by little,
 
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I May have missed it in previous posts but did you lock up the mechanical advance in the dizzy as the ecu controls the spark except vacuum advance ?
 
I May have missed it in previous posts but did you lock up the mechanical advance in the dizzy as the ecu controls the spark except vacuum advance ?
A darned good question......

OP, you need to help us out and answer this. I cannot see this answered either. If you do not lock the mechanical advance in the distributor, then it will continue to add advance to the system and the electronic will add even more simulated mechanical advance.

But this possible issue assumes that the new system is measuring crank timing off of a pickup device in the distributor, and does not involve installing a new crank position sensor outside of the distributor.

And when you are driving along, are you monitoring the timing through some electronic device connected to the system?
 
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AJ, since no one else has said anything, thanks for the timing explanation. I’m sure it will help those who may not understand how timing effects the engine.

I don’t quite know how to explain this in a way others will understand so here goes, While I understand timing and have run some advance numbers in neutral that have been in the 40’s with a quick advance factory distributor and vacuum can, and with the vacuum can disconnected setting just the mechanical to 32* total by limiting the advance available to have a starting point around 20* this which ran great, this Edelbrock system takes all of this and throws it out the window. As you say there is a start point and an end point that are both adjustable. Vacuum advance is 0-15* adjustable in 1* increments. If you try and set this system up in the same fashion it will not tolerate timing advance numbers much over 30* without a backfire occurring around 3K rpm’s.

Obviously just cruising down the freeway at say 2500 rpm you would expect to And most likely want to have more than 26-27* of total timing and that is not possible without a limit on either total or vacuum advance or moving the all in number to say 4K rpm or higher. Anything over this 30*+ or - will result in backfire. I have been trying to get it to work In a similar fashion as a factory distributor timing curve unsuccessfully. I’m not as seen by this post the first one to have this issue.

Someone asked above about locking out the distributor, that is not an option as the Hall effect distributor is non adjustable. Timing is verified by locking timing At 12* and verifying with a timing light. After verifying, timing is unlocked and the computer takes over. I have discussed with tech support multiple times and that conversation is a waste of my time as I believe a lot of efficiency is left on the table with the limited timing with no explanation as to why this backfire occurs.
 
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