Math
The diagram above breaks down most of the important engine measurements. The picture below shows the major measurements on the piston. Believe it or not pistons are tapered!
From these pictures, you can calculate displacement and compression. This will give you a starting point, and a rough idea of what its all about. The rest apparently comes from experience. There are min/max specs on almost everything. Tolerances are with thousands of an inch, barely visible with the eye. The following is how to measure displacement:
calculating deck clearance :
The complete compression formula :
So the game is to maximize everything for max power. Ie, the next step is to know what to buy from what manufacturer. Other factors will affect compression, like camshaft timing etc., and I guess thats where experience comes in. But everyone has an opinion about everything, and who knows what to believe. Do you go with flashy advertising, or the opinion of so and so. I dunno. But research is the best way to go. Looooots of web surfing.
According to KB pistons, quench is another important factor. But ive seen manufacturors not even consider it, like Diamond. Active uses KB pistons, and they are supposed to be the best, so im leading towards them. Quench is the flat part of the head shown in the diagram. The idea is that when the piston comes up it squishes air rapidly sending a sharp shockwave outwards that acts to disturb the mixture in the chamber. This is supposed to aid combustion and reduce detonation. Basically you just make the head dome circumference less than the cylinder bore, easy. This is what they call a closed chamber head. Chevy has been doing it since the begnning. Chrysler, on the other hand, never did it. They instead use a smog type chamber, which has the same circumference as the bore i.e. open chamber head. Then again Chrysler BBs typically dont have high compression and so it doesnt matter.
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| open chamber chrysler head | closed chamber chevy head |
Specs of my 440...
Crankshaft |
I have a stock forged steel Chrysler crank, with 3.750" stroke and a 2.750" main bearing diameter. The main bearings are 0.097" thick. | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Deck Height |
I removed the mains and the bearings, and took a steel corner and put it accross 3 mains and up to through a bore. This was square from the main bore up the side of the cylinder. Wall height + bearing thickness + 1/2 main diameter = 10.722" | According to Wiseco, the official Chryser deck height = 10.725" | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Cylinder Bores |
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The 440 in 69 had a bore = 4.320", with the ability to over bore the block by a maximum of 0.06". With the wear I have in my block, I can overbore by 0.01" and clean up all the cylinders. So I am looking to bore between 0.010 - 0.060, depending on the pistons I plan to use. | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Pistons |
The casting numbers on my pistons are 2863109 and 2863108. They are stock B/RB cast aluminum, steel reinforced flat top pistons. Unfortunately, I couldnt get the pins out because they are pressed in there tight, so all my measurements are from an assembled unit. Anyhow, the width of the piston, measured from the bottom of the skirt, is 4.318", and the width measured at the top is 4.295", which gives me a tapered piston with wall clearance of 0.002". From inside pin to top of piston = 1.660. Pin thickness is 0.173", and pin outside diameter is 1.094". For compression height, I got 1.656 + (1.094/2 - 0.173) = 2.030". dome = 0. For 1st ringland height I measured 0.391" | According to KB, these pistons should be Comp Ht = 1.970, Pin Dia.=1.094 Offset. Why am I off? thats wierd... | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Connecting Rods |
I have a stock 1851535 forged steel I-beam chrysler rod. After measuring different things I got 1.094/2 + 4.975 + 0.063 + 2.377/2 = 6.774" | According to the book the RB rod height = 6.768" | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Head Gasket |
Standard steel chrysler gasket. Measured 0.018" | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Camshaft |
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The closest cam I could find to this is the MP P4286675 which has 221*@0.05". Its rated for 1000-5300 RPM, and Mild comp. & performance RV. | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Cylinder Heads |
Standard cast iron "906" Chrysler heads - 2843906, intake valve = 2.082", exhaust valve = 1.738" | According to Active, the stock heads are 85cc. |
So....
...now to the most important part. Using the above numbers, and my brilliant equations, my stock 440 has the following stats :
| PI | 3.142 |
| DECK | 10.725 |
| STROKE | 3.750 |
| BORE | 4.320 |
| GASKET | 0.018 |
| ROD | 6.768 |
| PISTON | 2.030 |
| HEAD | 85.000 |
| DOME | 0.000 |
| PIS_WID_TOP | 4.295 |
| RINGLAND | 0.391 |
| Dome vol (in inches) | 0.000 |
| Head vol (in inches) | 5.187 |
| Ring vol (calculated) | 0.265 |
| Swept vol | 54.972 |
| Displacement | 439.779 |
| Deck Clearance | 0.052 |
| Compression | 9.486 |
For those of you who are unix savvy, you can save time and download my tiny perl script calculator : calc.pl
So there are a few more issues remaining. The first is about valve lift. How do you know weather the valves are going to hit the pistons at TDC? Is it carefully meaured such that the combination you are using will have good clearance? I made this drawing :
I used a straight edge and used the heads to measure height1=0.208" and height2=0.709". The only thing is I cant pinpoint where on the piston surface this edge would fall. We know that the intake valve diameter=2.082" and that the max exhaust lift is at #7 cyl =(1.596-1.309)=0.287". Since I have 1.5:1 mechanical advantage at my rockers, the lift at the valve=1.5*0.287=0.4305". Anyhow using the intake valve diameter, and some highschool trig, I came up with : h3 = 0.210" and valve angle = 76 degr ees from horizontal.
Now, with a gasket thinkess of 0.018", the valve will enter the cylinder by 0.192". I calculated my clearance to be 0.052", so with my flat-top pistons, and everything going wrong, my valves should leave a small crater the depth of 0.14" during total catastrophic failure!! Hmmmmm.... OK so the explanation is in the timing of the valves. The cam times it so well that you will never get 100% lift at TDC. Examining the power cycle :
I stole the picture above from http://www.howstuffworks.com/engine1.htm"
Anyways....
... The valves are safely withdrawn inside the head deep enough so that at the risky times there is no contact. There must be a way to calculate exactly the lift at certain degrees. There is a big gear on the cam and a little gear at the crank. If you count the teeth, then you can figure out the ratio of cam spins to engine spins. It should be like 4:1, so 1440 degrees of cam spin for every 360 degrees of crank spin. There has to be a f(t) for this at every degree at the crank, you should be able to calculate the lift at either valve, that way you can max out your lift and duration without guesswork. Anyhow, Im going to assume that there will not be a problem with colliding pistons and valves. I cant really do much about it now at this stage anyhow, so Ill turn my attention to camshafts. Accordingt to http://www.dodgecharger.net, they have a cam selection guide as follows :
