I have a 352 with 600 cfm edel and perf RPM, headers, pertronix ignition backed by a C-6. I just installed a 268H comp cam kit, and wanting to know if it is still going to run fine at 6 degrees BTDC.

 

I'm sure one of the more knowledgeable regulars will be along shortly, but in the meantime, I'll share my experience...

I think you will want to run a lot more advance than that. I have a new crank with just a little lope to it, and I run 20-25 degrees advance. Basically, you want to advance it until you get pinging or spark knock, and then back it off a little. I actually had to pull my distibutor and turn it one tooth so I could get enough advance.

Matt
'73 F100 360/C6

 

Yikes! The factory specs for your engine, I believe, are a lot closer to six degrees btc than they are to 25. You want to make sure that you're not advancing your timing so far that your engine is trying to run backwards on you (if it turns over hard, then speeds up and starts, that's a hint). You might get more power out of advancing the timing, and it might be beneficial if you havge a radical cam, but if you set it too far ahead, you're going to fry your motor in one of several spectacular ways. I set my '69 390 GT to six degrees btc so it will run good on pump gas (89 octane) and don't have any complaints about pinging or how it starts. The factory setting is ten, but I would rather have long engine life, good starting, and cheaper gas than a little more performance.
By the way, I get about 18-19 mpg on the highway with this engine.

Think about it: advancing the timing means you are supplying spark earlier during the ignition cycle. Giving the piston a little head start in the down direction before ignition is much, much easier on your piston surface and rod bearings than giving the combustion a head start on the power cycle ( I don't mean you should set it after tdc, just start from factory settings or maybe a few degrees less). Yes, you are getting more power, but you are also creating more resistance from the piston to the ignition of the fuel-air mixture and downward movement in the correct direction. Another thing to think about is if you advanced the cam when you built the engine. This may create the need to be a little conservative on timing.

If you really feel like advancing the timing, I say do it in small increments in 2-4 degrees until you are happy with power, startability and drivability. If you are getting pinging at a relatively conservative setting, adjust your carburetor's cruise and power circuits until it goes away. You can actually lower the engine's tendency to ping by enriching the fuel-air mixture. This will mess with your fuel economy but not enough to get overly concerned. Better safe than sorry.

 

Hmmm. Well, you make a good point. I'm not sure what the deal is. A friend of mine builds HOT Chebby motors, and he was the one that told me 20-30 degrees would be fine. I should know better than to take advice from his sort!

My engine spins free and consistently, and starts easy. If my memory serves properly, it wouldn't idle at 6 degrees. If I adjusted the idle speed up to keep it running, then it pulled through the brake when I was stopped. Now it purrs at a fairly low idle (although the lope is almost gone), and doesn't pull at all on the brake. I can even go through a drive through without shutting it off!

I'll double check my current timing and report back. Could be something else is off, or I am doing something stupid. If my points (dwell) is way off, could that affect my timing reading? I need to get the Pertonix unit -- maybe when I get my tax refund...

Thanks for the advice,
Matt

 

you want your total advance to be about 30-36 degrees. This is not your initial though. Total includes mechanical advance along with any vaccum, depending on how the vacuum is connected. I like manifold vacuum for my advance, which means at WOT the vacuum is adding nothing to the total advance. Then I can tune it by mechanical and initial. For you, I would start with 10 dress advance at initial, and see how it does.

 

I don't think you should be giving such pointed advice about ignition timing when we know so little about this fellow's engine. To my knowledge, I know of no FE motor that runs good on the street with that kind of advance set in accordance with shop manual directions, which tell you to unplug and cap the vacuum advance line, simulating a need for the engine to make max power/max advance. So the factory specs are the maximum advance that the engine in stock configuration is designed to have.

There is great variety in the FE family regarding ignition timing, due to various differences between engines. The length of the connecting rods, for example, can create a necessity to alter ignition timing.

My main point here is that we should err on the conservative side when we're dispensing advice. The best policy here, for the sake of engine longevity, is to start conservative and determine the best timing setting through a little trial and error. Also, if this is a freshly rebuilt engine, you're going to have a hard time getting it to start with any advance at all due to resistance from the piston rings.

If your timing is too slow, your motor runs like crap and has no power. If you set it too fast, though, you burn a hole in one or more of your pistons. Best to be reasonably conservative with timing.

 

Just my 2 cents, total advance refers to the maximum centrifugal plus the initial. So if you have 26 degrees max centrifugal at 3K rpm in the distributor plus 10 degrees initial, you have 36 degrees total. Vacuum advance is separate because it is high at part-throttle and low under load. It can pull an extra 20 – 25 degrees at 20 inches of vacuum. Sometimes the shop manuals give a combination of centrifugal and vacuum advance for a specific no-load rpm. Example: A ’68 F250 w/ 360 auto specs. at 33 – 42.5 degrees advance @ 2K rpm w/ vacuum hooked up, 13 – 17.5 degrees advance w/ vacuum plugged (that’s the centrifugal only, not including the initial). That may seem like a lot of advance but not at part throttle.

Barry

 

So what you and the other fellow are suggesting is that the timing adjustment that needs to be made might be a little more complicated than merely setting the advance at idle--that the cam may have changed the engine's needs at higher engine speeds significantly from stock. Sorry I missed this "point gap."

 

Thinking about it a little more, Pete is right that total advance is the combination of centrifugal plus vacuum advance at any particular rpm and load, at least for the distributor. The initial advance is always there and is added to the total. That's the textbook description.

I'm just used to thinking about total in terms of centrifugal plus initial. This is what you are concerned about under full power conditions. Vacuum advance does not come into play here, the diaphragm needs at least 5 inches of vacuum to start pulling advance.

Barry

 

Just another wrinkle to this issue. All of these engines are becoming of the vintage that one must consider other posabilities. For example, the rubber polimer that holds the metal ring on the harmonic balancer will deteriate with time. The result can be that the factory timing marks are no longer accurate as the TDC mark will no longer match up with the engine TDC. While this will not explain an initial advance setting of 20+ degrees, it can explain why some engines will seem to need a "different" initial advance.

As for an inital advance of 20+. I would suspect that the mechanical advance is not working on this engine. I have had Ford distributors where the weights have become frozen in place. If the weights cannot move, you have no centrifical advance and thus you end up putting in more initial advance to try to compensate. It is fairly simple to check by taking apart the top of the distributor and checking that the wieghts are able to move around.

Just my two bits worth. As I am in Canada, I guess that it make it about 2 cents US ;-).