O.k. whats the difference???

[Guest LIghtningZ]

Never learned how to properly adjust timing... all I knew is Start, it point the gun at it see where it's at and advance it till it YELLS UNCLE (Read, DETONATION!) back it off a hair, and call it good. I know there are tricks, (To me)and adjustments to make it run better/more power. and im still in the dark about timing curves and adjustment

[Guest bastaad525]

As I understand it that is the best method of tuning for power. Advance it as much as possible until you hear that first ping under load or hard acceleration than back it off a degree or two. May not be the best method for engine life though, causes it to run a bit warmer, increases the chance for a random ping here and there if you ever get a lean spot for whatever reason, and is probably hell on your spark plugs. Oh also being too advanced can sometimes cause your car to not want to start in the morning. *shrug* I just tune to the stock recommendation.

[DAW]

It helps to know the distributor specs as to how much advance is available in it because you don't want to go too high on total advance, nor put in too much initial timing (which can cause the starting problems, light load ping, etc). There are a lot of variables as to what's right for a particular engine, and a lot of opinions and experiences. For an engine with at least some mild mods like increased compression, initial (static) timing of 12-15 degrees is a reasonable place to start. Add the distributor's contribution from its specs and make sure your initial plus distributor (make sure you convert distributor degrees, if given in specs, to crankshaft degrees (and rpm) or they will be off by a factor of 2) totalled together isn't much over 38 degrees. In many cases, by increasing the initial advance over stock you will also put the total where it will benefit performance over stock and you have shifted the curve of advance to the left across the entire rpm range. Still, that may not be optimum yet and increasing the distributor's rate of advance may provide further benefit (switching to lighter advance mechanism springs or heavier weights so that it is all in by about 3500 engine rpm). If 38 degrees total advance is reached with only a few degrees of initial advance, then you need to somehow limit the distributor's advance contribution so you can run more static timing without going too high on the total.

 

The timing with the ping method can work well especially for trying to get all you can out of a stock distributor. One approach would be to set timing at 12 degrees and listen for a ping on the road. Mid range acceleration on an uphill is a good situation. If it pings on good quality and octane fuel there then I'd look to the fuel delivery instead of backing off the timing. Richen it up to get rid of the ping then try advancing a few degrees more until it pings again and then split the difference, backing it off towards the point it initially pinged, before enrichment. With a higher than stock compression engine the overall performance can be significantly improved, especially the throttle response, and the fuel tuning will also protect the engine from damaging detonation.

 

Once you set the initial timing, scribe a mark at the distributor base as a reference point so you can make changes at the side of the road without needing a timing light. Once it's sorted out you can measure the result with a timing light and note for future tune-ups. DAW

[DAW]

Addendum: BTW, when I recommended "richenning it up" above, I mean by changing jets, etc (Webers), needles change or reshape (SUs), or sensor/CPU changes (EFI); not just trying to richen the idle circuit. Also, with a lot of ECCS and OBD-II type systems most of the above doesn't apply because the computer manipulates the parameters and eliminates the middle-man (the tuner). DAW

[Guest Anonymous]

Its been my experience that if you advance it till it pings and back off, you may just find it hard to start, I know with the low compression I have I'd have to really get crazy with the ignition timing to induce pinging and for sure it would start just like it was heat soaked. Just something to think about.

 

Regards,

 

Lone

[Mike C]

You can "map" the ignition curve if you have a remote tachometer and a dial-back light or timing tape. I bought a Mallory dual point because I want a distributor that is un-worn and has an adjustable advance curve beyond just setting initial timing. I also wanted one WITHOUT vac advance for my triple Del"Lortos because I have heard the triple manifolds don't provide enough vac signal for full advance. I will get my L28 running with the dual points then switch to just one set of the points triggering a Crane HI6 I have lying around. If the point trigger proves unreliable or maintenance intensive I'm going to put a Pertronix Ignitor in the Mallory. I have single points on mine now. I burned up my Ignitor while doing a compression check and it was out of warranty. I had good luck with the Ignitor on my last 240, over 7 years of use when I sold the car.

[pparaska]

I've read recently (I have the link at home) that the "til it pings then back it off a few degrees" method of setting initial timing is not always the best power.

 

Of course finding the right mechanical advance curve for an engine is not easy either. Again, I can't remember where, I saw a method for finding the optimum mechanical advance curve. It entailed locking down the mechanical advance system, disabling any vacuum advance system, and driving the car with different initial timing settings. You start with your guess at an idle initial timing setting, test the acceleration of the car (I think a Road Dyno or Gtek would be great for this) and home in on the optimal idle initial timing.

 

Then move up several hundred rpm as you test rpm, put the initial timing (and therefore total timing, since you've temporarily locked out the mechanical and vacuum advance) at a somewhat higher amount, test acceleration and keep testing different amounts of advance by doing acceleration tests starting at that test rpm, and home in on the amount of timing for best WOT acceleration starting at that rpm (or maybe a bit lower?).

 

Repeat for other higher rpms at several hundred rpm intervals. You'll probably be all done by 2500 rpm.

 

Anyway, that's a ton of work, but you'd then know what the optimal power timing curve for the car is. Trying to get a simple device like weights and springs to give that exact curve will probably be futile, but you should be able to approximate it. Of course, you'll need to use the first idle advance number for your initial timing and look at the total change from that number to your highest advance as the change the mechanical advance will need to give, along with it's rpm dependence.

 

From there, you'd play with the vacuum advance for part throttle acceleration in a similiar way, changing the initial timing a known amount and trying part throttle acceleration at different rpms to come up with the vacuum advance curve you'd need. For that you'd need to also note the amount of vacuum. With an adjustable vacuum cannister, you can then try to get close to the optimal vac advance curve.

 

I'd guess it'd take a long day or two to do this, but you'd have tweaked it pretty good.

 

Of course, your carb / FI had better be ballparked pretty good, because leanness might make you artificially have to retard some of the timing curve segments falsely.

 

Wow, EFI with a knock sensor and WB O2 feedback and an intelligent closed loop optimizing function for all that would be a lot easier to deal with!

 

If anyone has a good reference to these kinds of perfomance timing and carb tuning methods, I'd love to see them.

[DAW]

Pete, the method you describe has got to be the more effective way as it is tuning for power, using empirical results. It is a much larger project though. The ping-parameter method is just a ball-park means of roughing it in (and usually big improvement over stock or random trials). I think the ping-parameter or endpoint is more of an engine protection measure than a power tuning method but ultimately it is a selection towards optimum stoichiometry for a given rpm and load. Measuring acceleration changes is far more direct and accurate than muddling around with teasing the engine with ping parameters. An A/F monitor would be a good thing with either method and would provide a common denominator when correlated with a specific rpm and timing setting. DAW