I am seeking input regarding spring selection for my distributor for the cent. advance.

The easy part, I finally settled back on the out of the box defaults for the MSD pn 8477 distributor.Which is BTW: 2 heavy silver springs and the blue bushing.

We are talking about an 82 f250 , 460, C6, x-cab, 4x4. It will only see fishing trails off road, but I have a 1500 mile one way highway trip coming up.

Is anyone WAY familiar with this distributor, and feel comfortable trying to explain it to a plumber, or feel like stating this is what I think the settings should be and here's why?



Thanks in advance

 

Each combo is different. But the rule is the same; Running the timing as far advanced as possible without pinging is going to give the best power and fuel mileage.

So you can start with the heaviest weights and the lightest springs. Since your truck is a heavy 4x4, it will probably ping when pulling a hill. If it does, put in lighter weights, or stiffer springs. Either one will reduce the amount of advance. You can play with the different combinations till you find the one that gives the most advance at the earliest rpms without pinging.

I would do all the above experiments with the vacuum advance line on the dist disconnected. When you get the springs and weights sorted out, then you can hook the vacuum advance up. It should be adjustable.

The vacuum advance advances the timing over and above the springs and weights. The springs and weights + your inital BTDC setting with the timing light may be around 38 degress total give or take above a certain rpm. The vacuum advance will actuallly advance this up to 50 degrees. The engine can take this at very light loads during cruising, and this gives even better fuel mileage. But when you step on the gas hard, the vacuum drops, and this extra advance is taken away, since the engine can't pull with that much timing without pinging.

 

You may have just made the whole MSD paperwork make way more sense to me.

I currently have the heaviest springs installed, so the advance is delayed in starting as much as the "kit parts" allow. Curve begins at approx 1900-2k rpm with these springs.

The bushing installed is a 21* bushing and the curve levels off at about 4k rpm, the only thing I am considering at this point is going with the 25* bushing which the charts indicate will level the curve at about 4750 rpm. Too high? For an all around daily driver and lots of highway, would I not want the advance curve to be as gradual as possible? Rather than "Steep" such as the example given of light springs causing the curve to start early and level off at a lower rpm?

heheheh, I am trying.... bear with me if you can

 

link to the MSD charts I am referring to


http://i93.photobucket.com/albums/l7...MSD_curves.jpg

 

I would try to have all the advance in at cruising rpm on the highway. This I am pretty sure will not be up around 4000 rpm. It all depends on the gearing and the tire size, but I am assuming your cruising rpm (around 55mph) is going to be around 2000? You want it all in by that time, so the engine can be most efficient.

You also have to consider your initial. I am assuming you are staying with the factory setting, but this can be played with too. It's especially useful if you want to quickly experiment and move the whole curve up and down.

You do need to be careful experimenting with the initial. When the engine is hot, if the initial is too far advanced, then the engine can be hard to turn over. When it cools off it will turn over normally. If you run into this, turn the initial back a little bit till the starter turns the engine over easily. Also if you get the initial up too far, it can mess with you carb settings. You might end up running out of travel on you idle screw and the idle rpm will be too high.

 

Could you explain the difference between light springs and heavy weight versus heavy spring and light weight as it applies to powerband rpm of the engine?
I think I have a pretty good idea but it would be nice to see it in layman terms.
Thanks

 

If you move the weights out manually, you can see how they rotate the dist, advancing the timing. They work on centrifgual force. The more rpm inside the dist, the more force. It's like taking a weight on the end of a string and swing it around above your head. The faster you swing the string, the further out the weight and the string will stretch.

So if you have very light springs with heavy weights, when the dist is turning, it doesn't take much rpm before the weights are flung out full travel. When the weights are out all the way, that's full timing advance. Stronger springs will hold the weights in longer, so it requires the dist to turn faster for more centrifugal force before the weights will move out.

If the weights are lighter, then there is less centrifugal force. Swinging the string above your head with hardly any weight on the end, and the string doesn't want to stretch out. Put more weight on the end of the string, and it will stretch out tighter. Same with the weights in the dist. Heavier weights will fling out earlier with less rpm. Light weights will require more rpm before they will fling out and overcome the springs.

This is how the timing curve is moved in relation to the rpm of the dist, which is directly geared to the engine. It turns 1/2 the rpm of the engine.