Certainly possible, when you list all the factors;
Heavily loaded, hilly terrain,towing,lotsa frontal area pushing air, very high cylinder pressure, pumpgas, hot-running,automatic,
unknown rpm and timing.
There is nothing wrong with running a hi-Scr......... at part-throttle. Because your Ecr (Effective Compression Ratio) is usually still well below the detonation limit of the pumpgas you are using, and at the rpm and load settings being experienced. But as the load increases, you have to increase the throttle opening to maintain speed, which increases the Ecr, which might or might not still be below the detonation limit of the gas.Eventually tho, if the carb size is big enough, the detonation limit will be found.
This limit can vary with rpm and load, and timing.
It is possible for an engine to approach the limit several times throughout its rpm band. It is possible to ease the level of detonation with performance gearing, or to keep it in detonation with too low an rpm , or to put a bordeline engine into detonation with too-high a water temperature, or with a head that cannot shed heat fast enough, or with a poor chamber design, or too much timing.
So yes, before you bolt that head on, you probably want to recalculate the Scr, and more importantly, the Dcr which will require you to know the ICA (Intake Closing Angle).
Dcr is what the engine sees..... at WOT.
Scr is how we build the engine to achieve that Dcr.
Ecr is what the engine sees at any/all throttle settings other than WOT. It varies on a moment to moment basis with load,rpm,air density, and your bolt-ons.
That last one is very important. The root cause of Detonation is too high a temperature in the chamber. Remember that only about 1/3 of the energy in the combusted fuel makes it to the road. Another 1/3 goes out the tailpipe as heat, and the final 1/3 goes into the cooling system, and into the airstream as heat.
So you have several ways to deal with detonation, in a combo that is predisposed to it.
If you put a tiny carb on a hi-Dcr engine, the load might never get high enough to spawn detonation. Or if you put headers on it and a free-flowing exhaust perhaps that exhaust system will get rid of the heat fast enough to allow a bigger carb. And last is the cooling system; bigger is always better, and remember that the thermostat sets the MINIMUM water temp, and limits the coolant circulation by the size of the effective area around the pellet mechanism. And don't forget; tha automatic is pumping heat into the lower tank, sending it's heat straight into the waterpump.
And of course ignition timing. But this is a two-edged problem.Taking timing out reduces the power, and the engine has to work harder, creating more heat, possibly putting the engine into worse detonation. Sometimes more is less; more timing might create less heat.
____________________________________
I like as much cylinder pressure as I can get away with because it makes the engine much more responsive when transitioning from one output level to another, and because the engine is more efficient, burning less fuel at steadystate, and because it makes more power at part-throttle settings.
But the key is getting away with it.
I build my personal engines with what I always think is too much pressure, and am prepared to run an anti-detonant injection system. So far I haven't had to .
The cam's ICA for me, has been the pressure relief system, for the most part.Also; a lightweight car with a big engine and easy gearing, and a total lack of traction reduces the load drastically.Plus My engine operates at 930 ft plus/minus about 100 ft ; I live on the prairies. This makes the tune easy, and limits the load. The manual trans puts no additional heat into the cooling system. The easy gearing lets the engine spool up faster, reducing the chance of detonation. Twin full length 3" pipes take care of the exhaust heat. And the cooling system is Rock-solid. And the engine gets cool fresh air from outside the engine compartment.All these efforts plus aluminum heads allows my engine to live at 185psi and more, on 87E10.
