Why so little advance?

[65CrewCabPW]

I've been busy with life and whatnot, but the first hot day this spring, I had to make a quick trip in the truck and it started pinging badly. This is after some disassembly and reassembly, and I had moved my ignition timing some (moved the sensor / wheel relationship. I use a Megajolt Lite Jr for ignition, no distributor.

Anyway, after re-doing my timing curves and resetting the wheel properly again, I noticed that I'm running very little advance. It runs good at 22 degrees at WOT and 3000 rpm ( no pinging there). This seems wrong. The engine should like a lot more on gasoline. Of course, I have much higher compression than stock ( true 8 or so, to 10.5).

I always figured that because it ran good where it was, I should avoid backing off. Really, I can go another 2 degrees retard and it still run quite good. It seems to like more like 10 to 14 initial, but not a lot of full load advance at higher rpm.

This just seems wrong, but perhaps it isn't. Any thoughts?

[franz]

A little refresh on the application would be helpful. An engine that suddenly starts pinging or detonating usually indicates a problem with combustion pressure, and if it is occurring at the correct period. Mechanically, it can be caused by combustion buildup (not that common on LP engines) or oil carbon buildup. Dynamically, it can be caused by the combustion sequence beginning before it is ready, during the compression stroke. Since LP has a static octane rating of around 104, convention wisdom would indicate it is tolerant of wild ignition timing advances.

I still have to buck the odd backyard tuner that wants to crank the timing until it pings but in reality, all an engine needs is enough timing to increase torque, before detonation. Any more and there is no more realized benefit. On the dyno, we call it MBT, or "Mean Best Torque" and lock it in. Added timing will increase combustion pressure which can actually decrease torque if it occurs too soon, and can cause piston damage and increased emissions with no real gain.

If your sensor is triggered by a balancer mounted wheel, did it slip?

For what its worth, on the Roush LPPFI truck, they added about 3 degrees to base timing and retarded it about 5 degrees at max load from gasoline with a little more curve at low to mid range loads.

Franz

[Steptoe]

I still have to buck the odd backyard tuner that wants to crank the timing until it pings but in reality

That was an old 50s 60s seat of the pants lucking if had a timing light home tune ..thats was what they did to make do with what they had on very forgiving engines of the day...
And the myth persists in places that suprised one when it pops up every now and then...
There is a point retarding where within afew degrees everything sorta drops off fast, power torque economy...
The 'sweet area is a couple degree above that.... from there performance drops off slower as it becomes over advanced...even detonating ...And as the engine is advanced above that sweet piont, in tends to sound bit more freer grunty...Within a car its like an optical illusion.

For what its worth, on the Roush LPPFI truck, they added about 3 degrees to base timing and retarded it about 5 degrees at max load from gasoline with a little more curve at low to mid range loads

That also sort of describes the graph illustraed in the IMPCO manuals
IMPCO also mention that with VA dont go over 42 degs all up.

[65CrewCabPW]

If your sensor is triggered by a balancer mounted wheel, did it slip?

For what its worth, on the Roush LPPFI truck, they added about 3 degrees to base timing and retarded it about 5 degrees at max load from gasoline with a little more curve at low to mid range loads.

Franz

No, it didn't slip, but I realized I had changed quite a bit of stuff since last time it was hot. Ran richer at higher rpm, was breathing hot air from under the hood, and a few other things.

It also blew a head gasket. Not sure the two were related.

In any case, I have found that the lesser advance performs better, gets a smidgeon better fuel economy, etc.

The truck's gonna get a bunch of towing this summer, after I change gears from 3.55 to 4.56.

I'll try to update on how it tows and how it runs heavily loaded.

[gottago]

We have just recently torn down an engine that was running with 17-18 degrees advance without any pinging for a number of years. I know this is supposed to be too high and had assumed it was somehow related to installing the cam so far advanced. It wasn't just an illusion the engine liked that much timing, it really did pickup performance wise. This was an older 429 near 12:1 compression (static) , but running a single OHG mixer and x1 vapourizer. Ran quite lean most all the time. On inspection it was in remarkebly good shape considering the abuse it had taken. 80. 000 plus hard miles. It had a well balanced assembly and forged internal right from the start and the crank bearings were still near perfect. Valves had not burnt at all and seats had not recessed. Piston tops clean with no deposits or burning at all. Guides were real loose and rings worn but thats about it. Clean as a whistle, love that about rebuilding propane engines. Anyway, new cam etc goes in, installed straight up, dual 4 intake, dual mixers dual vapourizers. Ran it initial breakin at 12 advance, pipes almost glowed. Moved it out to 15 advance and ran way better. Just the other day moved the timing back out to 17 where it used to run best and still does, no illusion, smokes the tires in second gear huge 4x4 with 36 in tires. Won't quite do that at 14- 15 advance. It doesn't ping or knock. Has an msd dizzy running the lightest springs and lowest limiting weights, blaster coil, good plugs and wires with a 50 thou plug gap. Has my balancer slipped or do some engines just like a little more advance than others?

[Steptoe]

When we pulled my engine down a few yrs back after around 120K + miles... same thing...even negotiable wear on bores and rings... just worn valve guides and but of wear in the ring grooves
The guy who does our head work expected a lot more, in particular ressection....his big sunrise to him was less than what he would expect on a petrol engine.....he re built the heads some 15/ 20 yrs previously.

Has my balancer slipped

Difficult to tell from here....pull #1 plug, put your finger over the hole and bump start till u feel pressure...
Then manually turn the engine over (easier with no plugs in) with a screw driver of bit of mig wire in the spark plug hole... feel the piston come up....then mark the spot on the balance where the piston stops coming up
Keep turning and mark where the piston starts going down note the highlight of direction u are turning to mark these points.
1/2 way in between is TDC ... if that matches with your balancer....
I assume the balancer was not new on the last build and still the same now???
we replace parts like oil pumps , fan belts, even water pumps, yet we go miser on things like radiator flush, balancers and mounts... I dont get that logic.
Then u can use a tailors tape to measure the circumference of the balancer, divides by 36.. that gives circumference distance for 10 degs.....use a cold chisel and stamp the 10 deg marks out to 50 deg, and a center punch for the 5 deg points inbetween....and get even more fancy a number punch beside each 10 deg mark...20 30 40 50.
Clean up the surface, wipe area with a good quality marking crayon or white paint, then wipe off access leaving the white in the stamp marks.
THEN u can accurately set/ dial in timing curves.

[BigBlockMopar]

Headchamber design greatly dictates how efficient and quickly the engine can burn the fuel.
That's why newer 3rd gen Hemi's can get away with a lot less total advance.

On my daily driver 318, I can feel a difference in low rpm performance when setting initial timing at 10, 12 or 14 degrees advance.
It likes 12 best.
I recall having about 10 degrees mechanical in the distributor and not more than 6 in the vacuum advance.

[gottago]

These were the dove c high compression small chamber heads so maybe some difference with them than the newer.
re-

I assume the balancer was not new on the last build and still the same now???

Correct, (hang head) same one. it had been lined up and stamped previously and looks good but will check with a piston stop. I just didn't think I would be able to tell that way accurately if it were just off by only a couple of degrees.
\thnz

[Steptoe]

Tell u what do it with a piston stop and then do it with fewel and a bit of wire... see what the difference is using a fancy piston stop

[gottago]

OK done, borrowed a piston stop and tried it then again with a piece of wire. Same or very close results almost right on the tdc mark. So it just likes 17 advance for some reason. Power wise that is any way. That much advance will break the tires loose in second gear, any less not quite so torquey down low. The mixture seems pretty good although still fine tuning. Idle is 15.5 cruise about 16.3 under hard excel about 13.5. Its very responsive to tuning with dual vapourizers and mixers so I don't think I'm over compensating with timing for too lean. Definitely not an illusion. Is timing it just for the power gain at around 17 advance going to hurt anything in the long run? It has hardened seats and stainless valves and as said, no recession problems running on this advance on last cam . Just not sure why it likes that much advance. Thought the cam change and re degree to straight up would have altered that peculiarity.

[Steptoe]

So it just likes 17 advance for some reason. Power wise that is any way.

That doesnt make sence....information that means nothing
the intial/idle (17) is the idle rpms... as the rpms increase (vechile moves off) so does the timiong, as to how much at a given rpm depends on the counterweight spring weights.....and what the total is...moving the intial up and down changes the total, and u are not tellinbg us what that is, or how many degrees u have in the cent.
And then we throw the VA ...does that 17 include VA on manifold vaccuum....which in that case makes the 17 made up of VA +intial....and the total is only intial + cent .. doesnt include VA.

could could very well drop intial way down, increase cent and/ or have lighter springs....both/ either can give the same results instead of messing up the idle timimg/ mixtures... if they have been set.
Idle timing/ mixtures have a big influnence on economy espec when driving around town... lot time sitting at interesections.

[gottago]

As per recommendations, its set at 17 initial with idle set at 700 rpm, no vacuum advance, and cent does not move advance numbers until 1000 rpm. MSD dizzy already uses the lightest springs and biggest weight stops available. Vacuum only adds 7 degrees max and cent 18. The curve is the last graph f on this msd page.
http://www.msdignition.com/instructions ... /85551.pdf

[Steptoe]

I strongly suggest that you graph what u have in your engine and not go off a theoretical graph
And quickly goinmg from the graphs (link) then u have about 25 degs in the cent .. the graphs show an intial about 5 deg... u have 17.. assuming not manifold vaccuum .. which gives a total about 37 degs.. then add about another 7 vac at cruise all up round 44 degs..
IMPCO recommend dont go over 42 degs all up.....detonation issues...
And a lpg curve has between 28 total (high compression engine to 32 degs all in about 2500 to 2800 rpm,

Timing has a very small window... as I repeat again... max explosion between about 12 and 18 degs AFTDC....and withing that window a tolerance of only a couple 2 deg at max off the best advance point... timing is not a hit and miss thing but a presion required amount of advance to hit that point at any load and rpms...for your engine.
Being off a couple degres at any given rpm and load can make huge differences to power, economy and even how well thwe engine lasts out without damage.... slow death.

[gottago]

No manifold vacuum, and we are using the 18 degree stop (the black one) not the red 25. I am just showing the msd spring and limit stop combination that is being used. I can map the curve but they are all about the same in an msd dizzy as is showing on the charts using their weights and springs. This is the fourth msd we have used and they all do seem to be quite close to the charts. They aren't theoretical, its supposed to be a precision made system with a predictable dependable curve. MSD has no lighter springs and does not have a lower stop than the 18 degree. The graph does not account for any initial advance. Its just the curve. So I have 17 initial and 18 cent and I can plug the vacuum for now giving a total of 35.

I understand what you are saying about hitting that timing window and would like to which is what puzzles me why this engine likes it with more initial advance. The power drops off rapidly and turns it into a dog with any less than 15 advance. The last build on that engine as said was run at the same advance numbers. No signs of any damage when torn down other than valve guides. Never pinged or detonated.

I will graph the curve though to make sure.
thnx

ps, I am questioning the opposite of this topic name, why so much advance but don't get me wrong. I am not trying to justify running that much advance, I am trying to understand and cure it.

[Steptoe]

me why this engine likes it with more initial advance.

because it is not the initial that is what is making the changes, it i you putting the curve far higher than what is being shown on those theoretical graphs...or... as I said above, in effect dropping very light springs in and in effect increasing the curve rate... but at the same time over advancing the total.
Now a thing on over advancing,,, doing so is like an optical illusion... over advance and the engine sounds far more powerful, so much so that if one is not aware of this one will actually think it is faster...Also once at peck timing the drop off is very slow over advancing further... but retarding from peck, the power drops off very quick.
End of the day, as mentioned so often before, either dyno or do actual road trials/ timing over given distances is the only way....basically start over advanced then drop back till suddenly power drops.

Also to dial in timing one NEEDS to have the idle, cruise and power circuits in the carburation at LEAST in ball park.....

There are many threads that describe the how tos etc of dialing in mixtures and timing... establishing , idle cruise , power advances independently of each other THEN configure the dizzy to met these tuning specs.

Anything less is simply banging around in the dark, hit and miss, get curve right, total goes out get that right idle goes out run around in perpetual circles