I decided to check the stroke length as I was changing plugs on my fe. Ive owned it for about three weeks now and it's running better all the time. I put a wood dowel down the hole and marked top and bottom and went about finishing up the plug change. After timing it and going for a drive I looked up the stroke length differences here on the forum (3.5 for 360 and 3.75 for 390). I got the dowel out and measured it. Wouldn't you know it came out to 3.65, so the funny angle to the piston combined with my sloppy marks add up to me still not knowing what size it is. The previous owner swore it was 390 but I was sure it was the original 352. That is until I cleaned some of the grease off and discovered a blue metallic paint. I doubt Ford used metallic paints on their engine blocks in the sixties so I know the engine has been out and probably rebuilt. So I just have to be happy not knowing for a while longer.

Ok. on to the timing question. I unhooked the vacuum and set the timing at 9 degrees of initial timing. I revved the motor and saw the line advance maybe 10 or more degrees. I hooked the advance and it advanced to about 34, right where I want it. But what caused it to advance without vacuum? Is it just centrifugal force? It runs great and I don't think I have a problem but I wanted to check with the experts. Also it's points, I haven't checked the gap or dwell yet.

 

Engines from 66 up were Ford Corporate blue. You should have got more advance with the vacuum disconnected, it's a centrifugal/mechanical system. Check it again at a higher rpm..

 

It probably advanced 20 degrees but I had marks at 10 before and 34 after so I was just estimating how much advance I got without the vacuum hooked up.

 

Yep, there is the initial "crank" timing advance most are familiar with, but there is also the mechanical distributor advance, and finally vacuum advance. If you were somehow able to use a timing light cruising down the highway there would be around 50 degrees of advance BTDC altogether. Determining the mechanical timing is easy but for my part don't care much for running engines up over 4K in neutral, that's basically the way to find out. For safety's sake stay out of the plane of the fan or remove the belt for a quick test.

A stock factory distributor/engine is set up for quite a bit of mechanical (centrifugal) advance, tho not much initial advance, 4 or 6 deg. say, and it won't tip all in until at a high RPM - maybe over 4000 RPM, this is because trucks are made for hauling gravel and other heavy loads.

Some definite performance gains can be had by limiting the amount of mechanical advance while at the same time increasing the initial crank timing to 12 or so. The total timing degrees hasn't changed - still 36 or 38 say. Lighter springs in the distributor weights bring the timing advance in much earlier than stock distributor curve, below 3000 RPM

 

I broke a crank in five places with too much advance. I raced a non Ford product on a half mile dirt track. I had spot welded the advance on the dual point distributor. I had it timed to about 36 degrees all in. When the spot weld broke it advanced further and all hell broke loose.

That engine had over 600 lift and I revved it to 5500+ rpm's. It lost power if I timed it over 36 degrees. Why would the FE benefit from more advance than 36? You say it goes to 50, sounds dangerous and unneeded.

 

50 degrees would be the total of both vacuum and mechanical, and I agree that is to much with today's fuel. Timing depends on many other things also like compression ratio, cam, carb, type of fuel etc. Every engine is going to require a different setting to get best performance and economy. On my street engines, both FE 390 and 292 Y I like to run conservative, I have to deal with Calif crap gas. I don't worry about the initial timing at idle, I set it to a max of 34 degrees when the mechanical advance is all in, then adjust my vacuum advance to allow another 10 degrees so total is 44 under load.

 

Too much advance on a high compression engine and crap fuel we have today, that's correct.

Not just saying 50 degrees for the hell of it this is a well known figure and basic part of engine tuning or planning. V8 engines - Brand X as well as FORD, are all basically in the sweet spot around 34 degrees BTDC crank + mechanical.

Factor in another 10 to 15 additional degrees of vacuum advance when at steady highway cruise (lightly loaded) and there it is Bob's yer Uncle. It only takes about 50 horsepower to cruise on level highway. Advance is greatest at this point. Pinging or detonation is remedied differently depending on whether it is evident at cruise or acceleration. Vacuum advance helps fuel efficiency and better all around driveability and part throttle acceleration. It is only utilized in lightly loaded conditions.

Racing is different too, because most engines are mostly running WOT (low vacuum) all the time and don't even have vacuum advance installed anyway.

 

The vacuum advance port shouldn't pull vacuum after you've opened the throttle a certain amount. Once the flow through the carb is high enough, there will be a slight increase again in vacuum advance, but the real "vacuum advance" port shouldn't be pulling vacuum when your cruising down the highway.

 

Sure it will. It's not pulling any at idle either. When should it, then? When the go pedal gets mashed - vacuum goes away - vacuum advance timing is retarded.

As the load decreases, speed levels off and the engine reaches a steady cruise the engine vacuum comes back up and so does the advance. A stock engine at idle, sea level will pull around 21" of vacuum. It may not be 21" at 65 MPH but it's going to be up there. Vacuum advance is completely unrelated and independent of mechanical or centrifugal advance.

 

I see where you're coming from, but if I recall, there shouldn't be a lot of vacuum at the vacuum advance port at highway cruise. Of course, my highboy's "highway cruise" was like 3000RPM at 60MPH. Throttle plates were open pretty far, and the vacuum advance port slot was definitely not getting manifold vacuum at that point.

If you're running without a lot of gearing, or overdrive, I can see where you'd get some vacuum advance...

 

A stock V8 will always have 15"- 20" of vacuum at steady highway cruise, enough to dial all of the advance that is engineered. Typically 10-15 degrees. Lumpy cams that rumpety-rump at "idle" don't have much vacuum at all at any speed.

 

I agree - MANIFOLD vacuum. Not ported vacuum for vacuum advance. But I've already hijacked this thread enough...

 

Manifold or ported makes NO difference at cruise. Only at idle. Measure it yourself and see.

 

Idling with the vacuum advance disconnected, (or connected to the port fitting) will generate a lot of heat compared to idling with manifold advance connected.


Just stand next to the vehicle with the engine idling. You can really notice the difference around the exhaust manifolds or headers from the heat rising towards your face.


I would recommend manifold vacuum for this reason alone as I don't like a lot of heat in the engine compartment when standing still.


You do have to be careful with timing. I set my timing incorrectly once. Wasn't that I did anything wrong, but the outer rim on the balancer had slipped throwing everything out of whack, and caused me to set the timing way too far advanced. Below is the result:

 

I put the igniter in along with new accel wires, it's running even better. I pulled the one and four plugs and measured the stroke. Whatta ya know, it's a 390.

The pistons looked kinda oily. The plugs were white as could be after two miles of driving and I bit of idling. I just had the carb rebuilt and it starts, runs, idles and drives like a new car. But it could be lean. I haven't touched the screws on the side of the holly yet.