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The tendency for most of us with up-sized street-cams is to ram the timing into the engine as hard and fast as possible. You will hear things like time to the highest vacuum, or crank it in til the starter kicks back.While there's no denying that this can work, I don't subscribe to this ideology for streeters with less than 240*ish cams, and stockish TCs.
I subscribe to getting the T-port sync set up, and let the idle timing fall where it may.
-To get a nice idle, is a little trickier this way, but it eliminates a few harder to overcome issues,later.And granted, getting a custom timing curve is trickier as well.
To me a streeter needs a well-tuned Vcan. And with a very-fast, single-pattern curve, getting the Vcan to be of proper use, is a real challenge.
-Getting a fast mechanical curve to work with a stockish TC and sub-optimum gears is an exercise in frustration.Unless your Dynamic C/R is in the basement.
With a 2800TC and minimum 3.23s, or a stick car with 3.55s or better, the ram-it method can work if you are not much concerned with fuel-economy.
-So here's my philosophy. Ram-it is for race-cars. Streeters are gonna have to spend some time choreographing all 3 or 4 timing systems. 3 or 4? yes.
You know about Centrifugal advance, and you know about Vacuum advance.
The C-timing is used to compensate for the decreasing amount of time available to light the fire as rpm goes up, and
The V-timing is used to compensate for engine loading/cylinder inefficiency's at lower rpms and part throttle.
So what else; Well, additionally we have the rate of mechanical advance and the rate of vacuum advance and the amount of vacuum advance, and the vacuum advance cut-in point.And one of the most important is the rpm at which the centrifugal starts.
As far as I can tell a street engine has at least 5 timing requirements. They are full power, idle, part throttle, hiway, and PT-cruise.The only one the dyno can figure out is the power-timing, and sometimes they are not even the best at that.
It is on you to figure out the rest.And I gotta warn you, it can take thousands of miles and many months to get a sweet program.But take heart, you can get close enough to start driving in a couple of hours or so. After 2 or 3 days, you will begin to understand how all these systems interplay. And when the summer is almost over, you will have had the dizzy out so many times you will wish you hadda just rammed it.
So you wanna start with the idle timing, cuz if the engine won't idle reasonably well, it is very frustrating, and all other timing adjustments are relative to the idle set-up and the power set-up. The latter of which is generally fixed over a very narrow range.
So where to begin with idle timing?
Well the engine will idle with anywhere from about 5 to 25 degrees; the only compensations being throttle opening and idle mixture.
Problem #1), the more advance you give it, the less throttle it will want to control idle speed. This leads to
Problem #2),the further closed the throttle is, the less transfer is exposed. This can be compensated for, to a degree, with the mixture screws, but this leads to
Problem #3), hesitation at throttle tip-in.
-Now comes a a personal street preference; for power and economy, you need a big engine with a small cam and in-the basement gears. Since this philosophy is at odds with reason, some sacrifices have to be made to whit; rear gears,camming and engine size. Most of us have found that SBMs work pretty good with 3.55s,and sub 228* cams as DDs or sub 240*cams and as much as 4.30s(for the adventurous)as weekenders.And 5 gears trumps everything.
But what has this got to do with timing? Well if your stuck with 2.76s and 1400TC, your SBM will have completely different timing limitations than the guy with a 2800 and 4.30s; completely different. So if you subscribe to the ram-it theory, be prepared to change your rod bearings frequently, and eventually your skirts may fall into the pan.
Then we have
Problem #4). At hiway speed. In considering fuel economy, the engine will want a ton of advance, and as minuscule a throttle opening as possible. Here comes the T-port sync again. Yes it is entirely possible to have the engine wanting to be very low on the transfers to get the best economy possible.
-Back to the beginning; where to start with timing.
Having now an idea of what timing is needed under whatever your application might be, Just follow the outline below, and the engine will tell you what idle-timing it wants. How easy is that?
I guess I could have told you that on line 1. but would you have believed me? Probably not; it's too simple.
The truth is; Every combo is different. Any number a guy can ballpark is just that.
Your engine will tell you what it wants. Learning to listen, and being able to answer it, will make all the difference.
So why did I go there in post#63?
Well glad you asked. Retarded timing leads to overheat, and so does lean running.
Now I believe that excessively retarded timing leads to excessive throttle opening, and that coupled with overheat, usually leads to run-on after the ignition is killed. You didn't mention that. So Ima thinkin your engine is not excessively retarded.
I believe that excessive advance leads to very small low-speed throttle openings, which leads to lean-running.
So I wanna say; T-port sync.
But hey, until thr IR gun results are in , I could be pissing in the wind.....
