The point here is that if you have a low vacuum engine, you need a lower number power valve, not vice versa, as commonly believed.  Once the power valve is figured out (and this takes some experimenting sometimes, especially if you don’t know what cam is in the engine) you can fool with the main jets to get the right mixture out of the engine.  Generally factory specs on jets for the engine are pretty much what one will need to follow, but if you have just bought a performance.aftermarket carb, chances are you’ll have to do some messing around to determine just what the engine likes.

That brings us to the firing order. Now all things being equal, the most efficient firing order is that of F1 cars more or less – which is 1-5-3-7-4-8-2-6, with some slight variations on that.  The important thing is that no two adjacent cylinders fire sequentially; i.e. no, 1-2. 7-8. 6-7. or so forth as with most major automakers. (Note: all firing order references are to one bank numbered 1-4 and the other 5-8.)  Now, the theory behind this is that when one cylinder fires, it will heat up the cylinder wall, and expand the cylinder; albeit a minuscule amount, but it expands nonetheless.  This produces a problem in reference to the cylinder next to it when it fires.  First is the fact that now it has to squeeze through a smaller bore due to the expansion caused by the other cylinder.  Secondly, it will be dealing with a heated charge of air due to the rise in overall temperature due to the common wall/combustion chamber areas.  Thirdly there is the matter of undue stress on the cylinder wall as it is rapidly forced one way and then must change direction to push 180 degrees opposite.   This is why the firing order of an engine is important in the makings of a race motor, and some things that were taken into consideration by the high rpm crowd of F1 guys.  It is also something that is of interest when trying to understand just what a motor does.  There is also a lot of involvement with intake runners and fuel charges when dealing with firing orders, though a lot of that is only a carburetor discussion; mass quantities of it can be ommitted for the Sequential Port Fuel Injection crowd.

This is why in some performance operations people opt for a cam that “swaps” a couple of cylinders on the firing order, such as a 4-7 swap on some Chevy’s.  It has to do with the increase in power garnered from the correct usage of the available fuel charge and the increased efficiency of the engine overall.

First off we will look into hoe to calulate engine displacement, which is actually a bit of simple math.  First one needs to know the bore of a certain cylinder – say 4.00″ – and the stroke of the crankshaft on that cylinder – say 4.00″ .  If we take the bore of the cylinder and multiply it into the formula for the area of a circle, which is πr^2, (π being equal to 3.1416 for all intensive purposes) then we get 3.1416 x 2.0^2 which is to say 3.1416 x 4, which is equal to 12.5664 this then is simply the area of the circular portion of the cylinder, which then must be multiplied by the stroke of the cylinder to get the diisplaced volume of th ecylinder. When we do this we get 12.5664 x 4.00 which is eaual to 50.2656.  If we multiply that by eight, which is getting slightly ahead of ourselves and our involvement here, we get 402.1248 – for all intensive purposes a 400 cubic inch engine.

Now that is just the swept volume of the cylinder, which really doesn’t tell you a whole lot unless you are looking to calculate compression ratios.  To do this accurately you need to first convert the swept volume to cubic centimeters (cc’s) seeing as that is how most combustion chambers are measured.  The conversion factor for inches to cemtimeters is one inch to 2.54 centimeters.  So to be absolutely accurate we will convert the bore to centimeters – 10.16 – the stroke then is also 10.16 cm; so now we divide 10.16 by 2 to get 5.08, or ‘r’.  We insert that into our equation, getting 3.1416 x 5.08^2 or 81.0732.  If we multiply that by the stroke, we get 823.7036.  Now, if we decide to install a 70 cc combustion chamber over this cylinder, we take the swept volume – 823.7036 and add the 70 cc’s to it to get the overall cylinder volume (as a side note, the head gasket needs to be taken into account as well, and those vary quite a bit, so we will take one of .050″ and calculate that) which results in 893.7036.  Now we must calculate the aforementioned gasket area, so we’ll take a gasket that is .030″ over bore – normally they are more, but this is an example after all – so we get our bore of 4.030″ or 10.2362 cm and an area of 82.2938 cm, multiplied by our .050″ (or .127 cm) to get 10.4513 cc’s.  Add that to our 893.7036 and we get 904.1549.  What is all this, this is the total volume of the cylinder including the head gasket and combustion chamber. It does not include the slight amount of “squish” around the cylinder before you get to the first compression ring. Be that as it may, if we take this volume and divide it by the size of our combustion chamber, we get 904.1549/70.00 which comes out to 12.91:1.  Bear in mind that this is a fairly thin head gasket and the combustion chamber size is fairly small as far as that goes.  This is a stout compression to say the least, and it would require the running of some seriously high octane gas.

Now that we know that little bit of engine math, we shall look into the efficiency of combustion between cylinders in the next installment.

First off we will look at the points style, simply because if you understand how that works, the others kind of fall into place.  There is a point gap that needs to be set, and the factory gives a specification (heretofore referenced as ’spec’) for the particular engine/vehicle combination in relation to a dwell angle.  Now the point gap is simplhy how far the points open at the high point of the cam on the distributor shaft.  The dwell angle is the amount of time the points are closed, allowing the coil to “recharge” as it were for the next discharge. The dwell angle is more important for tuning than the points gap, but both should be set in conjunction with each other.  To set the dwell necessitates the use of a dwell meter, and it helps to have a tach handy, which is usually part of the dwell meter.

Now that we know that little tidbit, point gaps are usually set around 15-20 degrees and the dwell angle varies upon engines, but for a V8, look for around 30; as I said, the factory has specs for the particular set up.

Once you have stabbed your distributor – that is installed it in relation to the #1 cylinder on top center with the rotot lined up on the #1 firing position – you will need to set the points and dwell; as long as you are not too far off on the overall engine timing.  Once you get those set you can set the overall engine timing specifically where you want it to be, or where the factory says it should be, whichever the case.  That needs to be done with a timing light and tach, just for reference on the latter.  Now, to figure how soon the timing comes in on the power/rpm band, one really needs to fool with the mechanical advance on the distributor, assuming that is the set up. On a lot of the older Fords, the process is slightly more difficult than some of the newer aftermarket models, but the overall concept is the same; in order to bring the timing in later one needs to add heavier springs, in order to move it in sooner one should add lighter springs.  However, a troublesome problem will arise if one fails to have tension on the springs in the first place, so make sure the spring attach points are adjusted outward enough to fully engage the springs and put a little initial tension on them.

That said, the total timing of the engine is the initial timing plus the advance timing, which should run you somewhere in teh neighborhood of 28-34 degrees or so, depending on the initial and where the stops are for the advance.  The Vaccuum is actually there just as a fuel economy thing, and may be capable of being adjusted, however, at Wid Open Throttle (WOT) it is doing nothing, seeing as the engine produces virtually no vacuum there, so for tuning it can be all but omitted.

Once you figure where you want the timing to be, you can go about the rest of the tuning of the engine; i.e. carb settings and mixture.