28* initial timing for a 318? How can that be?
Max torque on a 340 would likely be around 3000 and max hp would be around 5000, I would guess somewhere around 28-30 degrees at 3k and 34-36 degrees at 5k.
Not saying this will be the case every time but typically what I see is less than 2000 and and over 1000 rpm between peak torque and peak hp.
Most engines will have a window of timing degrees that doesn't change power at each rpm Increment. Some engines being more fussy than others.
Usually what an engine wants at peak torque is within the window of what it will want at peak horsepower. If not it will be very close.
Where I see the difference in the window that an engine wants for timing at a particular rpm is usually below peak torque and above peak horsepower at the ends of the rpm range.
These observations are at wide open throttle and full load.
Most ignition systems will retard some amount with 1000 rpm increase. Some worse than others. Most are not so bad that they affect the engine significantly unless you are at the ends of the curve not so much at peak torque and peak horsepower.
A combination of an ignition that has a lot of retard per 1000 rpm., a fussy engine with a narrow window of acceptable timing per rpm increment, a very long usable wide open throttle rpm range and a timing curve that stops advancing very early could get you close to having different timing requirements for peak torque and peak horsepower.
This is just my opinion. You should sort out your wide open throttle fully loaded engine timing requirements for the rpm range that the engine will be operated in first. This will be your base timing measured at a specific rpm and your mechanical curve if you are using one. This is tuned for max power if that is your goal or enough power if that is you goal. More importantly it should be safe for the engine. How far you are willing to push the safety factor to be determined by you.
Next is part throttle. Use the vac advance to add timing in a tolerated amount where the engine will increase in performance and or efficiency at different part throttle loads. Most likely compromises will have to be made here. How far you push the safety factor is determined by you. I think of this tuning as icing on the cake.
Last is the idle timing. If your motor wants or needs manifold vac along with the initial timing nows the time to figure it out. Keep in mind that altering your base timing at idle should not affect the numbers you have already established for the wide open throttle fully loaded rpm timing curve. You can go less and sacrifice power but not more and sacrifice safety. And if this affects your already determined part throttle curve (lower in rpm than the wot curve) then you will have to compromise somewhere again.
Same with the vac advance can at idle. If you need it and it is too little or too much and you change it. You will now have to compromise the part throttle vac curve.
When you look at how all the methods there are to manipulate the timing curve and how they affect each other it can seem overwhelming. It does to me anyway. Does every motor need to be tuned to the max using all methods available? Probably not. Work at it until your happy that it's doing the job it needs to do. If that means locking the distributor so be it. If that means going all out using everything at your disposal then knock yourself out.