chevy distributor

[1365keith]

I currently am running MS1 on fuel only. Will be upgrading to MS2 for fuel and spark. I am confused about the distributor situation. I have an aftermarket distributor that I can lock both mechanical and vacuum advance on. I am using a crank trigger since I could not get a good signal from the distributor and coil I am using now. Can I use the distributor and coil I have or do I need to switch to a computer controlled distributor such as off a TPI chevy motor? I am having some trouble how MS2 can alter the timing using a standard distributor with the advance locked out of it. Since MS2 fires the coil, the distributor will only fire when the rotor lines up with the cap, am I correct? It appears to me I will need to get a small cap HEI off a computer controlled car for this to work. The engine is a 350 chevy

[Matt Cramer]

If you're using a crank trigger now, MS2 should have no problem with your existing distributor. The width of the rotor can accomodate a bit of variation from pointed straight at the tower.

[bleoh]

With a crank trigger can't you leave the mechanical advance in place to help with rotor allignment (or is it the vacuum, I keep forgetting!!!)?

Brian

[1365keith]

The distributor is mechanical and vacuum currently. So, the width of the rotor is enough to cover all the advance needed? That would be sweet since the am very happy with my current ignition set up but want to switch to computer control. With a crank trigger, the initial timing is set at the crank trigger I presume and that becomes my start point for MS2. Is this correct thinking? Also, will the fuel set up for MS1 work for MS2? I know I will need new VE tables since it is a 12x12 but with the current setup remain the same?

[bleoh]

If the allignment is good then you might be okay. It will be important to check and adjust the allignment, which when using a trigger wheel and distributor is easy.

If they offer a larger cap and rotor that will fit your distibutor that would be best. With computer controlled distributors they generally spread out the posts and put a wide tip on the rotor. Here is a comparison between my ford large cap rotor and the stock rotor that came in my jeep (jeep used a ford distributor). You can see how much longer and wider the ford "tfi" rotor is on the left.



MS will get your rpm and piston TDC information from the wheel and missing tooth/teeth. Then using the spark table, map, etc.. MS will tell your coil (external module, CDI box, whaterver you are using) when to fire. Rotating your distributor will do nothing for timing BUT it will determine your allignment between the rotor and the post. You will want your rotor pointed directly at the post when your timing is in the middle of its range. So if your timing varies between 10* and 30* then make sure your rotor is pointing directly at the post at 20*. You can get close to this by putting the crank at the desired advance on the #1 power stroke and then rotate the distributer so the rotor points directly at the #1 post.

To do this with more accuracy, and to see it in action, you need a timing light, spare distributor cap and rotor and some paint or something to mark the rotor. Cut a window in the spare cap between the center post and the number 1 post. Put a mark on the center of the rotor that will show up on a timing light and be in the window you just cut in the cap. Install the cap and rotor on the distributor and put the timing light on the #1 wire. Put the light on the window in the cap and you will see exactly where your rotor is pointing with the engine running. You can also see what the impact is from leaving the mechanical advance in place (I am pretty sure this type of advance moves the rotor and the vacuum moves the pickup inside the distributor - at least on my duraspark 1 dizzy).

I've never converted from MS1 to 2 so I don't know much about that. But I think you can convert your older tables to the 12 X 12 and be fairly close to where you want to be, but I would guess you'll need to fine tune once you get it running.

Brian.

[MB_Custom]

I was also wondering about this. Would it be better to leave the Mechanical and Vacuum advance fully functioning, thereby reducing the amount of 'correction' MS would have to do / allow MS to be more precise since the correction range would be smaller?

Or would it be better to remove, say just the vacuum advance, thereby reducing the number of variables that cause variance and difficulty in reaching close to optimal tune?

[bleoh]

When using a crank trigger and MS to control timing the mechanical (weights) and vacuum advance don't impact timing. In my distributor the vacuum advance moves a plate that the VR pickup is attached to. This causes the trigger to happen sooner creating advance. The mechanical advance rotates the (not sure of technical name) part that the rotor and reluctor wheel are attached to. As the weights go out it rotates the reluctor teeth closer to the pickup (in rotation, the gap does not change between the two). So, since the pickup inside the distributor is not being used there is no impact. But, because the weights change the allignment of the rotor, it can help keep it alligned as RPM increases.

If you are using the sensor inside the distributor I would lock down both advances. Otherwise you will never really know how much advance the engine was getting in any given driving condition.

[1365keith]

So, in your opinion, leaving the mechanical advance functioning would help the alignment of the rotor and cap as MS2 advances the spark. Since I will be using the crank trigger rather than the pickup in the distributor, it would not effect the timing at all.

[bleoh]

Yes, but I would verify this for your distributor. All you need to do is cut a hole in an old cap and shine your timing light on the rotor. Change your timing map to all the same number (somewhere between 10 and 15* should work). As mechanical advance comes in you should see the allignment of the rotor change but your actual timing to the crank will not. With a typical timing map loaded and correct initial allignment this will help keep the rotor closer to the post.