Ignition Timing

http://www.automotiveu.com/tuningperformance.htm

Edited by toolmanxiii - Jan/19/2013 at 12:42pm

Like it or not, a 40 year old cast iron engine designed to run on yesterdays premium gasoline, leaded and approaching a level of what was called 101 octane back in the day, will not run on todays 87 octane no matter how wishful your thinking is. When the 390 in my Javelin was built it was designed to run on premium gas and back in the day that was typically 100 octane leaded gas. And you tuned the engine to maximize the performance at the time.
WHY?
Because that was how it worked.
If for some reason you refused to do that you had to DE-tune the engine to run on a mid grade gasoline. In general, retarded the timing, setting it late. The side effect, h.p. was reduced, engine temperatures increased and exhaust manifold temperatures were up. That little thing caused exhaust manifold gaskets to blow.

Fast forward to today those same cast iron wonders of yesteryear still do not run on low octane gasoline if your compression ratio is close to or exceeding the factory 10.5:1. And they still run the same way today as they did the. It is you who has to detune them to get them to do it and complete with the engine heat and exhaust manifold heat And the decreased HP output.
Buy your new V8 what ever (or 6 or 4 or 10 or whateve) has a full electronic engine manigement system that detects knock which is an indication the gasoline is too low an octane for the compression AND what ever the current tune state is and detunes things.
As to your cast iron wonder from yesterday either load it up on Octane Boost or detune it so it will run.
Of course doing that puts you back into engine heat and exhaust manifold gasket failure to to increased exhaust heat caused by late timing.

Building a high compression engine requires high test gasoline with an appropriate octane rating to get them to run well.
For those of you living were 94 and 93 octane is available at the corner gas pump. That stuff is very close to old school 100 octane premium or maybe even better.
For those who live where the best it gets is 91 octane? If your compression ratio is greater than 9:1 or so you are going to have problems detonating and breaking pistons. Either load it up with octane boost or detune it.
I blew 2 engines up before I got smart enough to stop building anything over 9:1.
For those who insist that they are using 87 octane with an 11:1 compression engine? And tune it to put out maximum HP?
No I don't believe it.
Tokyo, Stuttgart and Detroit could not do it or they would have and I really don't think Open Pants Montana is going to pull it off.
But to each there own I guess. But I  have been building 9:1 engines now since some where in the 1980's and they run hard, don't run hot and don't break pistons. I am just building another one and it should be running by summer and I have 2 more to go and then I quit.
As to timing? Depending on the engine I run as much maximum timing that I can get away with, a vacuum advance canister and try to find what the curve is as a function of vacuum, run manifold vacuum to it and pick static timing setting to match the components I use all on premium (in this state 91 octane) gasoline. And I can tell the difference in how the engine runs when I go through NM with a 90 Octane premium and then hit some were south of Chicago where 93 and 94 can be found. And there? The engine sings like it used to when Sunoco 260 was actually 101  leaded gas.

 

I only use what we call premium. 98 octane in everything I own . most of my friends do also . $ for $ they go farther on premium fuel than regular 75 , that yes your car will run with but not go 100,000 miles on . my 72 232 still runs great on it . mind you I still add the lead additive to keep the top end working . and just started adding zinc to the oil thanks to the wealth of information here .

Edited by toolmanxiii - Jan/19/2013 at 6:40pm

JonnyB wrote: So you ported a pair of 304 heads? I hope you're wanting 1.74" ex and not 1.94... Anyways...What initial timing are you running?  Whats total advance and when does it all come in? You should be able to change the springs to get it to come in quicker and change the bushing to get more mechanical advance...

I am guessing your compression is way high or your damper has slipped and you are not timed where you think you are.