Timing suggestions for 360?

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billytuffnuts

billytuffnuts

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I have a magnum 360 that I'm going to be firing up tomorrow and looking for some ideas on where to start for setting the timing.

Its very similar to the MP 380hp crate 360 magnum with a slightly smaller cam

-Stock heads, internals
-Holley 650 CFM 4bbl vacuum secondaries
-MP Electronic Distributor w/Vacuum Advance
-Air Gap Intake manifold
-Intake .487" lift 231* dur @.050 Exhaust - .497" Lift 234* dur @.050
-Dynomax full length headers
-2800 stall
-3.91 gears

Also, how do I go about setting the total advance with a vacuum advance distributor? Is that possible? thanks
 
Yup, it's adjustable. That's a nice unit. There's an allen screw inside where the vacuum hose attaches. I think clockwise is advancing and counter clockwise is retarding, but I'mnot 100% sure. Just mess with it, you'll see.
 
I have an LA 360 with magnum heads and a cam with a little more lift and a little less duration than yours with a lot more compression (I am assuming your is stock). I am running 17 degrees initial timing and 33 degrees total with springs that have the mechnical all in at 2500 rpm. Vacuum advance only works at light load cruising which with my car is about 15" Hg of manifold vacuum. I used a MightyVac hand pump to set up my vacuum advance so it was all in at 14" Hg vacuum.

If the MP distributor you have was made after 2002 it has both an adjustable vacuum advance and an adjustable mechanical advance. They come set for 24 degrees of advance and I believe brown springs which is close to the 2500 rpm point, this is going to be too much (initial + mechanica l = total). Magnum heads have a more efficient chambers and do not need as much mechanical advance so the typical 34-36 you hear is too much for a mgnum headed engine, 32-34 is where you want to be.

The MP distributor is made by Mallory and uses the Mallory advance mechanism. Mallory #29014 advance tuning kit comes with a bunch of spacers for setting up the mechanical advance with a selection of springs to tune the rate. The instructions include a bunch of graphs so you can select the proper color springs for tha advance rate you want. The $30 investment makes getting the distributor set up or changed very easy.
 
One thing needs cleared up here. The vacuum advance may be adjustable but not the amount of degrees it advances. That allen adjuster only affect when it advances. The amount of vacuum that's needed to pull it in if you will. Like DGC said he has his set to get full vacuum advance at 14 inches of vacuum. If the vacuum can has 10 degrees of advance it'll always put in 10 degrees of advance no matter what the allen screw is set at. Also consider this, double the vacuum advance's rating to get the amount of degrees of advance at the crank so a 10 degree can will produce 20 degrees of advance at the crank.
 
fishy68 said:
One thing needs cleared up here. The vacuum advance may be adjustable but not the amount of degrees it advances. That allen adjuster only affect when it advances. The amount of vacuum that's needed to pull it in if you will. Like DGC said he has his set to get full vacuum advance at 14 inches of vacuum. If the vacuum can has 10 degrees of advance it'll always put in 10 degrees of advance no matter what the allen screw is set at. Also consider this, double the vacuum advance's rating to get the amount of degrees of advance at the crank so a 10 degree can will produce 20 degrees of advance at the crank.
Click to expand...


I was taking for granted everybody already knew that.
 
I have a couple of caveats to add;

The vacuum advance pod has a number stamped on the arm (usually on the bottom side so you can't see it when it's installed) that lists the total possible advance you can get. The number is expressed in cam degrees (don't know why they did that when all discussions of timing are in crank degrees) so you need to double the number to relate it to timing at the crank.

The adjustment changes the preload on the spring that pushes the arm back to the zero position. Making an adjustment changes the vacuum level at which the advance starts to move and consequently the total amount of vacuum required for full stroke. So you could add enough preload that it will take more vacuum to get full stoke than the engine generates effectively limiting the amount of advance. If you need to need to limit the timing the advance can add you are going to better off getting a pod with less advance built in.
 
dgc333 said:
I have a couple of caveats to add;

The vacuum advance pod has a number stamped on the arm (usually on the bottom side so you can't see it when it's installed) that lists the total possible advance you can get. The number is expressed in cam degrees (don't know why they did that when all discussions of timing are in crank degrees) so you need to double the number to relate it to timing at the crank.

The adjustment changes the preload on the spring that pushes the arm back to the zero position. Making an adjustment changes the vacuum level at which the advance starts to move and consequently the total amount of vacuum required for full stroke. So you could add enough preload that it will take more vacuum to get full stoke than the engine generates effectively limiting the amount of advance. If you need to need to limit the timing the advance can add you are going to better off getting a pod with less advance built in.
Click to expand...

Dave, I couldn't agree more with your posts. I've always tried to stress the importance of a vacuum advance on the street. It just makes sense. A couple o fnotes on my responses.....i take a lot for granted when I spew about a subject. Such as most people know the basics....and when I talk about timing on a Mopar, i am 99.9% of the time talking about the Mopar electronic ignition. It just slap is the best ignition to run, IMO. It's almost always right on the mark right out of the box for a street car. I've always been impressed with how close they are.
 
fishy68 said:
I have ran across a lot of people that don't realize how the adjustment actually works so that's why I mentioned it.
Click to expand...

...and you were dead right for doing so. Like I said, sometimes when I'm spewin, I get caught up and forget not everybody can read my mind. LOL
 
and what about a cam,,that doesnt produce enough vacuum to make the advance work ???? i recently read that some place,,,,

gonna try a vacuum advance dizzy again,,on my blower motor see if i can pick up some mileage,,
 
You are kind of stuck in that situation. The factory style distributors never used a vacuum pod that was designed to work on real low manifold vacuum levels.

You may want to look at one of the distributors that have a digitally controlled timing curve. I do recall seeing an artical on one that you connected the manifold vacuum source to it and you adjusted the vacuum advance with a poteniometer like the adjustment for total and rate.
 
i have never seen a cam that made your engine not make enough vac... only move the higher vac at a higher rpm. hope that makes sense but if your cam pushes the vac that high in the rpm i hope your useing gears to match
 
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