How to determine best spark timing?

Many of the threads looking to cure overheating result in posts asking "Is your timing set to spec?". All the engine builders I've discussed ignition timing with, told me every engine is different. Even engines that rolled off the same assembly line built to the same specs. Most early Broncos were produced when gasoline had lead and could tolerate higher compression.More recently alcohol and other additives were added.To complicate things more,many of the engines we run are a unique combination of OEM and after market parts. The factory recommended timing and distributor curves are irrelevant. The traditional method used to find optimum timing is advance the spark until pre-ignition is heard and backing off a couple degrees. The same thing goes, through out the rpm range and various vacuum signals from the carb. This method gives the best HP and MPG but could strain the cooling system. Is there any way to set timing to minimize overheating other than trial end error? If so we could make seasonal changes allowing power and mileage to be the priority in cool weather and avoiding overheating in the summer.

Just my opinion...


If your cooling system is that marginal that a couple extra BTU into the cooling system because of an ignition timing change causes a problem, you need to be paying attention to the cooling system, not the ignition timing.

Since every engine is different is is trial and error. But usually right around 12 degrees BTDC is considered the sweet spot. factory specs are more for emissions than anything else.
If the engine is at the optimum timing then power will be at its optimum and you shouldnt overheat because the engine is not fighting itself to make power.
Nw overall jetting also affects heating issues as well you need to check the jetting just as much as the timing. as some timing settings will cause you to run lean. Just as a lean carb will not allow you to run the timing you need.

I had an 86 mustang EFI that loved 17 degrees, and a 92 that didn't like 17 but was happy around 15-16. I used vacuum to set my EB and I don't remember where we left it. I am one of those that do believe the factory timiing is a good starting point, and tune from there. I would expect any engine to run the right temp regardless of timing in such a small range.

Spark timing and cooling

I generally agree that if your cooling system is so marginal that timing adjustments are required to prevent overheating, you need to fix your cooling system. That being said, advanced timing will reduce cooling load(coolant temperature), within the timing range that produces acceptable engine performance. It's really no more complicated than that. Good luck!

Don't recall referring to any of my vehicles. I'm speaking in general terms. The issue of over heating in connection with spark advance, is because "how much spark advance are you running?"is one of the first questions asked on this forum when a thread is started by someone with over heating problems. Again the limiting factor in spark advance is preignition. A retarded spark would be more likely to cause over heating, but a review of threads dealing with over heating reveals many replies that site overly advanced timing as a contributing factor. The other question the comes up is 'Do you have your timing set to spec?". How can this have any meaning? Most small block Fords had a 6 degree advance specified through '72. After that, reduced compression,retarded cam timing,EGR and emission standards confused the issue. Many of the same engines had the advance increased to 14degrees by the '80s. The factory specs have little relation to the best running advance curve, so I doubt they are any better at curing over heating. It would seam more logical that an advance curve that produces the most efficient burning of the fuel would run the coolest. If this is not your experience, what have you found to be true?

While factory specs are generally not the best of perfromance they are best for the widest range of running. Yes most engines can run a little more advance and run even better. EFI engines are a bit different as the computer controls the advance.
but overall there's not much differance of the affects of over advanced or retarded timing. Yes to retarded tends to cause more heating issues than to advanced. Probably because if your to advanced your more likely to know it.
To advanced means the fuel mixture starts burning to soon before the piston reaches TDC and the combustion process impedes piston movement while trying to get to TDC. also incomplete combustion also results which creates more heat. Pretty much the same for retarded timing the mixture ignites after the piston has gone past TDC So the piston is already on its way down before this starts which leads to less power and again incomplete fuel burn so heat is generated in the exhuast because of that.

As for the advance curve well you generally want to run it so all the advance is in by 3000 RPM if its to fast then the engine will ping so you can retard the timing slightly until no more ping. For the best perfromance. yes stock advance curves are very slow but again they were that way for the widest range of running conditions Thats also where vacuum advance comes into play as it fills the gap in the factory's slow advance curve.
The best for any engine is just trial and error but usually if you at least start with factory specs you are within the correct range for the engine just may not be the best range performance wise.

I think you are saying the same thing I am. Since I own a Sun distributor machine I find it's fun to custom curve my distributors. My question mostly came up after doing a search of over heating problems on this forum. Many posts suggested that overly advanced ignition timing could be the cause. This idea contradicts my experience in tuning engines for 45 years. Not once in my search did I find a post that asked if the timing was retarded. If there is anything to this idea I'd like to know about it. I'm well aware that a lean mixture can cause overheating but a lean mixture can yield better gas mileage. Ideally a compromise that's lean but not too lean can be found but it's not easy.
In every engine I've tuned, the timing specs could improved on by advancing 3-6 degrees. Of course high compression engines from the '60s can't even take specified advance because they were designed for higher octane gas not the crap we get now.