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.
|open chamber chrysler head||closed chamber chevy head|
|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.|
|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"|
|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.|
|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...|
|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"|
|Standard steel chrysler gasket. Measured 0.018"|
|The closest cam I could find to this is the MP P4286675 which has email@example.com". Its rated for 1000-5300 RPM, and Mild comp. & performance RV.|
|Standard cast iron "906" Chrysler heads - 2843906, intake valve = 2.082", exhaust valve = 1.738"||According to Active, the stock heads are 85cc.|
|Dome vol (in inches)||0.000|
|Head vol (in inches)||5.187|
|Ring vol (calculated)||0.265|
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"
Advertised @.050 RPM
240 - 250* 200 - 210* idle - 4500
250 - 260* 210 - 220* idle - 5000
260 - 270* 220 - 230* 1300 - 5400
270 - 280* 230 - 240* 1500 - 5700
280 - 290* 240 - 250* 2200 - 6000
290 - 300* 250 - 260* 2700 - 6200
300 - 310* 260 - 270* 3000 - 6500
310 - 320* 270 - 280* 3500 - 7000+
centerline - this is the least understood aspect of cam design & to over simplify the higher the # of degrees the longer & flatter the power band becomes [eg 115*] & the lower the # the shorter & more peaked the power band becomes [eg 106*] for example a 115 cam may give you 300 hp from 3500 - 5500 rpm with a peak of 375 hp where a 106* cam would give you 275 hp from 3500 -5500 rpm & a peak of 395 hp [these figures are arbitrarily made up] I prefer the long flat power band , it works well with the long mopar rods & gives pull everywhere but if you have ideal gearing & 5 speeds in the trans to decrease the rpm drop between shifts the car should run faster with a lower centerline cam. Generally choosing a smaller cam will hurt you less than choosing a cam that is bigger than you need.Installed Centerline: This is the number of degrees of crankshaft rotation after TDC (Top Dead Center) where the centerline of the intake lobe (max lift) occurs. This is NOT a camshaft specification, but rather an installation parameter. Moving the installed centerline (advancing or retarding the cam relative to the crankshaft) can have a major affect on performance. This also affects the valve-to-piston clearance.
Lobe Separation - This is the PHYSICAL configuration of the cam in relation to the actual spacing of the intake and exhaust lobes from each other. Lobe separation is ground into the camshaft. You CANNOT change it (Unless you regrind the cam). You CAN change the Centerline by degreeing. These two terms are often confused with each other.
Here are a few magazine articles Malcolm found in a yard sale, they also document a rebuild, some good information. They are a bit big so you may have to save them to a file first and then view with some viewer... :
Anyhow Chuck suggests to first determine your needs and build accordingly.Here is the goal :
Now as far as advice goes, here is what I need to do
|Block||Install Main studs instead of bolts.
Increase stock oil passageways, and pump flow.
|Bottom end||Reuse stock crank.
Aftermarket lightweight aluminum pistons, floating pins.
Two of my rods are damaged, so maybe new steel rods.
Balance rotating assembly.Compression of 10.25 Maximum!
|Heads||I dunno, do I want to sacrifice my low end to gain power?|
If I dont, I can go with the stock heads, othrwise aftfermarket. ?????
|Camshaft||Same with the head idea. How crazy do I want to go?|
|Intake Manifold||Need to decide on single plane - High RPM or dual plane - Low RPM|
Does big horespower mean I necessarily need to give up low end RPM?
How badly an Idle and power do I really get at low RPM, with a high RPM/power setup?
Maybe I just cheap out and do the minimum to get her back on the road? Can I drill my heads for better flow?
If I go for all this shit am I really gaining anything after losing $$$?
8.5:1 - Quench head engine for tow service, motorhome and truck.
12.5:1- Is the highest compression ratio suggested with unrestricted race gas engines.
15.5:1- Is the highest compression ratio suggested for unrestricted alcohol fuel engines.