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Yadkin
04-11-2016, 09:17 PM
I am experiencing rough running under load and recently, some knocking at about 3000 rpm. My newly rebuilt engine has about 9.7:1 compression ratio with the stock iron cylinder heads.

Cam is a Comp Roller 33-000-9. This is one step up from an OE or "towing" cam. Idle quality is good, 650 RPM. I measured valve lift and they are all identical.

I did a dry compression test and found 7 cylinders at 170psi, 1 at 180. Wet compression all at 180.

Initial timing is 10 degrees BTDC. Using that as my zero, I measure centrifugal timing to be as follows:

RPM OE Rec'd This setup
800 .5-1.5 2
1000 3.5-4.5 8
1600 5.75-7 19
2800 8.25-9.5 24
4000 10.75-12.75 24(max)

Vacuum advance at 1000 RPM

In Hg OE Rec'd This setup
8 2-5 0
10 4-7 3
15 5.5-8.5 4
20 5.5-8.5 4

Yadkin
04-11-2016, 09:29 PM
I run 93 Octane pump gas, E10. I have a FAST 1.0 fuel injection kit.

I did nothing to my mechanical advance from it's factory setup, except of course for putting 90,000 miles on it. It's obviously putting in too much advance, and too soon. The vacuum advance is adjustable so that's not a big deal, except no reason to adjust it until I have the mechanical dialed in.

Fordmuscle.com suggests using a total advance of 38-40 for peak power. Mustang 360 recommends no more than 34-36. I have 10+24=34.

Yadkin
04-11-2016, 09:33 PM
I also have a Crane XR-i points conversion module in the distributor. I marked my crankshaft damper at 45 degree increments, tested each plug wire with my timing light and am within a degree at each.

Do I just need to re-curve the distributor to be more like factory specs? If so, how much lower should I make the total advance?

Yadkin
04-11-2016, 10:15 PM
I'm going to set my initial at 8 and see what happens.

simplyconnected
04-12-2016, 12:32 AM
...Cam is a Comp Roller 33-000-9...Steve, this is a race roller cam core. It is a custom grind into whatever duration you choose.

Consequently, I have no idea what cam you actually have. It could very well be that your duration will produce a lumpy idle. Let's see the cam card.

Your compression spread looks ok. Your compression ratio demands premium fuel (93 is good but don't go lower).

You can always dial back ignition timing and it will work to a degree, depending on your cam timing. I've discussed my way of timing the cam but yours is quite different.

At what rpm is your cam timing 'all in'? - Dave

Yadkin
04-12-2016, 10:08 AM
Thanks for your input Dave.

Here is a photo of the cam card.

Yadkin
04-12-2016, 10:11 AM
I found out last night that I had my vacuum advance plugged in too low on the throttle body- oops. I was getting a signal below the throttle plates instead of on top. It's a rain day so I can't test it out.

scumdog
04-12-2016, 03:18 PM
I found out last night that I had my vacuum advance plugged in too low on the throttle body- oops. I was getting a signal below the throttle plates instead of on top. It's a rain day so I can't test it out.

The vacuum advance SHOULD be hooked up to manifold vacuum, i.e. Below the throttle plates.

Yadkin
04-12-2016, 03:56 PM
The vacuum advance SHOULD be hooked up to manifold vacuum, i.e. Below the throttle plates.

That's not what I read yesterday. And it makes sense to me; here's why.

Under the plate(s): At idle, manifold vacuum is high, so the vacuum advance would increase to it's maximum then decrease under load.

Over the plate(s): At idle, vacuum is zero, then increases with increased throttle opening.

I've been taught to disconnect the vacuum advance and plug it temporarily while setting initial (at idle) timing. If you then add in advance with vacuum, you lost that setting at idle.

Yadkin
04-12-2016, 04:51 PM
I just came back from a 30 minute test drive. She's definitely running better. No matter how hard I mashed the throttle, no knocking. Idle quality is better; so is top end power. I couldn't even see any smoke while full throttle, where as before there was a big blue cloud back there. Still, though, not as smooth as I expect while cruising.

Could it be the cam? I figured for a bit of "lope" at low engine speed, but not cruising speed.

scumdog
04-13-2016, 03:53 PM
That's not what I read yesterday. And it makes sense to me; here's why.

Under the plate(s): At idle, manifold vacuum is high, so the vacuum advance would increase to it's maximum then decrease under load.

Over the plate(s): At idle, vacuum is zero, then increases with increased throttle opening.

I've been taught to disconnect the vacuum advance and plug it temporarily while setting initial (at idle) timing. If you then add in advance with vacuum, you lost that setting at idle.

Your call BUT with manifold vacuum you get the following: lots of advance when manifold vacuum is high i.e. at light throttle setting/light load on engine and you get best economy, engine efficiency.

However when you stab the gas pedal and the manifold vacuum drops your timing retards so you don't get pinging/detonation, ease off on the gas pedal and you're back to optimum timing for smooth running and economy.

BTW: Ported vacuum control of timing was introduced by the car manufacturers as a 'crutch' to get through emission issues when smog control arrived.

Yadkin
04-14-2016, 09:18 AM
Interesting perspective. Connected to the manifold directly, vacuum advance would be highest at idle. You'd have to keep that conected to set initial advance? Wouldn't you then get a decrease in advance at cruising? It seems to me that the mechanical and vacuum advance curves would be working against each other.

OX1
04-14-2016, 09:50 AM
Interesting perspective. Connected to the manifold directly, vacuum advance would be highest at idle. You'd have to keep that conected to set initial advance? Wouldn't you then get a decrease in advance at cruising? It seems to me that the mechanical and vacuum advance curves would be working against each other.

Would think you have to either bump static up considerably or re-curve distr to get the total timing you had before (unless the theory is to have less total timing at high load, higher RPM).

Yadkin
04-14-2016, 01:23 PM
Would think you have to either bump static up considerably or re-curve distr to get the total timing you had before (unless the theory is to have less total timing at high load, higher RPM).

By connecting to manifold vacuum you'd have to reduce static timing to get the factory recommended 8 to 10 degrees BTDC at idle speed.

Maybe I'm looking at this the wrong way but everything I've read is that ignition timing should be increased with RPM. There is a certain amount of time between spark and enough pressure building where it begins to push on the piston.

I look at it like pushing a child on a swing. If you push to late, that is while the swing is going away from you, you won't get power into it. If you push to early, that is the swing seat coming at you, there's going to be a shock, or impact. If the spark is too late you lose efficiency and power, too early and the engine knocks.

The time required to achieve pressure should be (I'm guessing here) a constant. So the RPM/ advance curve should be linear. But in a mechanical advance, the force resisted by springs is a linear function and the force developed by centrifugal weights is a squared function. I thought the vacuum added to that is to make the curve more linear.

simplyconnected
04-14-2016, 02:13 PM
I'm not taking sides here but you need to consider air-to-fuel mixtures. I grew up with GM cars that use manifold vacuum. Yes, I know this is a Ford but hear this out:

For initial timing, GM pulls the distributor hose off and plugs it. Then they time at ~6 degrees BTDC. What does this do... When your engine is stopped there is no vacuum so timing is at 6 degrees. As soon as it starts, vacuum advance.

If you punch it at a light vacuum immediately drops off and so does the advance. As rpms increase the distributor weights advance timing even at WOT (wide open throttle). Ease off the pedal and the vacuum adds more advance, as it should.

Punch it again at high speed and vacuum immediately drops off and so does vacuum advance, as it should. Mechanical weights still control HS advance. Lifting the pedal again advances more with vacuum. There is no lag.

Remember, when vacuum is high, air is choked off. In affect, this makes your engine displacement smaller because the air is thin and fuel is reduced. This is where the air/fuel mixture tries to maintain 14.7:1 for the best economy. When vacuum is low, air is more dense and the mixture is rich. This is the time to back off on spark advance. - Dave

Yadkin
04-14-2016, 09:23 PM
Dave, you know as well as I that a Ford relies on a different Periodic Table than a Chevy does. ;)

Back to reality for a minute, what you state makes sense. Referring to my curves in Post 1, I should adjust my vacuum advance to obtain 7 degrees advance at 15 in Hg, connect it to manifold vacuum (under the throttle plates) then set total timing at idle to 10 degrees BTDC (7 vacuum plus 3 mechanical).

That way punching the throttle at idle will set the timing to 3 degrees BTDC (0 vacuum and 3 mechanical), and as the engine speeds up both the vacuum and mechanical advances will increase, so at cruising condition, 2000 RPM, advance will be about 26 to 28 (5 to 7 vacuum plus 21 mechanical).

scumdog
04-15-2016, 08:07 AM
I'm not taking sides here but you need to consider air-to-fuel mixtures. I grew up with GM cars that use manifold vacuum. Yes, I know this is a Ford but hear this out:

For initial timing, GM pulls the distributor hose off and plugs it. Then they time at ~6 degrees BTDC. What does this do... When your engine is stopped there is no vacuum so timing is at 6 degrees. As soon as it starts, vacuum advance.

If you punch it at a light vacuum immediately drops off and so does the advance. As rpms increase the distributor weights advance timing even at WOT (wide open throttle). Ease off the pedal and the vacuum adds more advance, as it should.

Punch it again at high speed and vacuum immediately drops off and so does vacuum advance, as it should. Mechanical weights still control HS advance. Lifting the pedal again advances more with vacuum. There is no lag.

Remember, when vacuum is high, air is choked off. In affect, this makes your engine displacement smaller because the air is thin and fuel is reduced. This is where the air/fuel mixture tries to maintain 14.7:1 for the best economy. When vacuum is low, air is more dense and the mixture is rich. This is the time to back off on spark advance. - Dave

What Dave said,
I tried to explain the same thing but it seems that Dave has a better way of saying it!

Yadkin
04-15-2016, 04:24 PM
...adjust my vacuum advance to obtain 7 degrees advance at 15 in Hg, connect it to manifold vacuum (under the throttle plates) then set total timing at idle to 10 degrees BTDC (7 vacuum plus 3 mechanical).

I did exactly this and ran it around town than up and back I-40 one exit. I don't like the way it runs as much as before. There seems to be a bog when I mash the gas. Oddly, it also blows oil out the back while accelerating.

Remember I have EFI on this engine. At idle the air fuel target ratio is set to 13.6, WOT 12.5, cruise 14.1. Maybe it's getting too much gas during the transition??

Yadkin
04-16-2016, 09:20 PM
I'm working with two guys over at the FAST forum on his. One indicates that I should be running 16 degrees initial timing (the engine idles great at this setting) and a total advance of only 18, for a total of 34 at 3500 rpm. Mine totals at 24, and the curve is too steep. Here's the curve I have now:

Yadkin
04-16-2016, 09:23 PM
I can handle the curve issue easily by bending the spring mount tab on the smaller spring. I don't see an easy way to restrict the range though, without fabricating a part.

Yadkin
04-23-2016, 07:09 AM
I bought a new Pertronix distributor so I can adjusts the advance curves for modern fuels. It has three different spring pairs, three different limiter pairs, and the pairs can be mixed can be combined. I'll use one silver and one bronze spring (S+B on the chart), and combine limited to achieve 18 degrees total.

Yadkin
04-23-2016, 07:12 AM
Why would Pertonix use a larger shaft diameter that the drive gear rides on? I can't reuse my old one. Oh yeah, so you have to buy their bronze gear, spend another $60, and wait another few days for shipping. :mad:

At least I have Amazon Prime.

Yadkin
04-24-2016, 11:12 PM
I put the new bronze gear in and installed the distributor. I must be livin' right, because I didn't have to bump the engine to get the oil pump shaft to engage. It just dropped in.

I had a little clearance issue, which I sort of anticipated. The Pertronix is about an inch taller than the Autolite, so it contacted the underside of the air cleaner. My solution: "dish" the lower flange, effectively making the cleaner taller, "ding" the area right on top of the distributor, and lengthen the center attachment screw a bit. I have enough clearance to rotate the cleaner back and forth and the spark plug leads don't move.

And yes, the hood still closes.

Yadkin
04-26-2016, 08:15 AM
I started it up last night after some no-go cranking. The problem turned out to be the connector that I re-used to plug the distributor into my harness. It was one of those crimp or solder deals, then push into a holder where they snap in and don't back out. The problem is that the gauge of the metal used is so thin that they are easily deformed to the point where no electrical contact is being made. The pre-wired connectors are better, so I have some on order.

Once I got that replaced she started right up. I set the initial timing to 16 BTDC and the idle is nice and smooth. I hear a pleasant "whir" noise when the engine is running that I haven't heard before. Unfortunately, since I'm waiting for parts on my steering rebuild, I can't drive her and test the engine under load.

Working the throttle with vacuum disconnected, the advance retards while accelerating then advances at the higher RPM. Apparently the electronics does this?

I ran the engine through two cooling cycles and shut her down. No carbon deposits on the floor under the exhausts. Another good sign.

Yadkin
04-28-2016, 09:02 PM
I finally had time (and good weather) to test drive the car. Huge improvement. There is no knocking at any engine speed or load. My misfire is gone. No more black smoke and rich running condition at idle. I just drove about 50 miles, once up to 88 then later up to 94 mph, and the gas gauge barely moved. At 50 on a two lane the cabin is actually quiet.

That advance issue turned out to be my new timing light. Innova 5568. It allows you to delay the strobe in 1 degree increments. Set on 16 it can't figure out the changes in RPM fast enough to give an accurate flash. Set on 0 the strobe shows the advance operating correctly.

simplyconnected
04-28-2016, 11:18 PM
Glad you finally enjoyed success, Steve. I hope this is the last of your problems and you can enjoy the summer cruising in your classic. - Dave

Yadkin
04-29-2016, 08:18 AM
No kidding, and thanks. This one was a real bugger to diagnose. I had my old distributor checked out by a guy with a very good reputation, and the engine ran fine before my rebuild. I felt that it was an ignition problem, and replaced basically everything, least expensive on up, and nothing solved the problem.