engine builders , please calculate my compression ratio

[Stegs]

ok guys, for you engine builders. Im wondering if you can help me out to calculate my compression ratio of my 440

I will list all the specs that i know of my motor, hopefully you guys can chime in and see. I just came from a engine shop, I gave him this exact info, and he came up with something totally different than what i was told in the past

Here is a list of the parts, maybe you can help me out

69 440 block bored 30 over
pistons - part number 1263 1966-1971 dodge pistons flat tops federal mogol fm350Np (taller version / 9.5:1 pistons
cam elgin
valve lift .431
lift ex .429
duraton 282 intake, 296 exhaust
lobe center line 222
lsa 111 spread

stock 906 iron heads with stock valve, heads were shaved .005

stock bore and stroke

engine shop says total chamber cc is 104
chamber cc in head is 87 (88 from factory, minus the .005 resurface)
piston dome cc is 0
gasket thickness is .039
gasket bore 4.4
deck height (guessed at .03) as mopar hung them low

Let me know what you think!!

 

[69Bee]

69 440 block bored 30 over
pistons - part number 1263 1966-1971 dodge pistons flat tops federal mogol fm350Np (taller version / 9.5:1 pistons [https://www.summitracing.com/parts/slp-350np30/overview/make/dodge (for piston specs)]
stock 906 iron heads with stock valve, heads were shaved .005
stock bore and stroke [Bore is not stock, but stroke is]
engine shop says total chamber cc is 104 [Don't really understand this statement]
chamber cc in head is 87 (88 from factory, minus the .005 resurface) [Need to CC the heads, you can not guess or assume they started at 88 (they didn't)]
piston dome cc is 0
gasket thickness is .039
gasket bore 4.4
deck height (guessed at .03) as mopar hung them low [Cannot guess, you need to measure]

You need the actual chamber size in CC's and the correct deck height in inches. When you have that info, use this formula:
CR=(C+P+D+G+V)/(C+P+D+G) for a valve notch piston
CR=(C-P+D+G+V)/(C-P+D+G) for a domed piston

Below is my worksheet for your example, but you will NEED to adjust the correct chamber and deck height numbers to be correct.

 

[65-440]

This

 

[65-440]

Input your own numbers obviously !

 

[Hemirunner]

Based on the information given.... assuming the block has been decked .025 and is 10.700 and assuming the top ring is down .300, I get 8.99:1. If the block is taller, it will be less.

http://www.diamondracing.net/tools/

CH is 1.99 on the piston and the piston is down in the hole .067 at 10.700

 

[dieseldazzle]

Just had a 67 block decked that was at 10.716 down to 10.70 for one of the strokers I put together.

 

[451Mopar]

engine shop says total chamber cc is 104

I believe this 104cc takes into account the gasket volume and piston to deck clearance, so all you need the the swept piston volume
4.350" bore (0.030" over stock) and 3.75" stroke.
Piston displacement (single cylinder = pi()/4 * bore^2 * stroke) = 55.7314 cubic Inches. Multiply by 16.3871 to Cubic Centimeters = 913.275

Add the total volumes of piston swept, and the volume above the piston at TDC (104cc?) = 1017.275 cc
Divide the total cylinder volume by the volume above the piston at TDC = 1017.275/104 = 9.781:1 compression ratio.

If I have time later, I can run the numbers to calculate the gasket volume and piston height to deck.

Reason, it the 0.030" deck clearance does not sound correct for the Z350 piston?
The Z350 piston is a 1.990" compression height piston that normally sits about 0.090" below the block deck? Maybe the ZH143 piston?
When I looked up the UEM-1263 piston, it shows a shorter compression height of 1.969"? So the compression height numbers look suspect?

 

[451Mopar]

Here are some of the numbers to use as a baseline for calculating the distance the piston is below the deck at TDC for the 440 RB engine.
The Blocks deck height from center of crankshaft to the deck surface the head bolts to is specified to be 10.725". Some blocks might even be slightly taller, and milled blocks can be low, but it is a good starting point for the calculations.
The stock connection rods are about 6.768" long from center of rod bearing to center of pin hole. Again this can vary a bit, and if using non-stock rods, the length is easy to change.
The Crank stroke (stock) is 3.75", and we only want the stroke offset length from crank centerline to the center of the rod pin, so 1/2 Stroke = 1.875.
The last part is the piston compression height. The distance from the piston pin center to the top of the piston (flat top piston.)

Add the piston compression height, plus the rod length, plus 1/2 crank stroke. Subtract that number from the blocks deck height (10.725) and that will give the amount the piston is below the deck (or above.)

So for the UEM-1263 piston = 1.969", 10.725 - (1.969 + 6.768 + 1.875) = 0.113" below the theoretical deck surface.
The FM 350 piston compression height = 1.990", 10.725 - (1.990 + 6.768 + 1.875) = 0.092" below the theoretical deck surface.
NOTE: This still assumes the block height is 10.725"?

Next, you would want to calculate the volume of the space between the top of the piston to the top of the block surface (if it was capped, so we can add this to the head and gasket volumes.) The cylindrical volume is the same equation used for piston displacement, just stroke is replaced by the piston to deck clearance.
Volume = pi()/4 * bore^2 * Piston-to-deck clearance) = pi()/4 * (4.320"+0.030" overbore)^2 * 0.113 = 1.679 cubic Inches. Multiply by 16.3871 to Cubic Centimeters = 27.52cc. For the FM350 piston, 22.41cc. If the piston had a dish or valve relief cc volume you add it to this number, if a dome volume, subtract the dome volume.

The gasket volume is calculated the same way. 4.4" bore by 0.039" = 9.718cc? I usually use 4.41 x 0.040" bore = 10cc (10.012cc).

The cylinder head volume is measured (not calculated.) I believe you mentioned 87cc?

So total volume above the piston at TDC is... 87cc + 10cc + 27.5cc = 124.5cc (approx.) for the UEM piston number. 119.4 (aprox.) for the FM piston.

This is almost 20cc more that the 104 mentioned originally. To reduce the volume 20cc's by way of milling the block deck down, it would have to be cut almost 0.080"?
Cutting the block 0.080" would mess up the intake fitment and pushrod lengths would be too long, but would result in the piston being 0.033" below the block deck (assuming the UEM piston part number?)

Anyhow, we already calculated that compression ratio in an earlier reply.
Recalculation for the 0.113" piston to deck clearance would result in a compression ratio of (913.275 + 124.5)/124.5 = 8.336:1
The FM350 (0.092") is (913.275 + 119.4)/119.4 = 8.649:1

At this point, you may want to run a compression pressure check. Make sure the battery is fully charged, remove all the spark plugs, install the compression tester in the spark plug hole, and hold the carb throttle wide open while cranking the engine several revolutions until the pressure maxes out on the gauge. Record the pressure, then repeat for the other cylinders.

I will try to look up the cam you may have? It is possible to calculate a rough estimate of cranking cylinder pressure based off of the dynamic compression ratio, which is related to the static compression ratio and the intake valve closing point (as seen at the valve.)

 

[451Mopar]

I think I found the cam.
Elgin #E-327-S. Specs: 0.431"/0.429" valve lift, 283/296 Advertised duration, 208/210 @ 0.050" tappet lift duration, 64 degrees overlap, Intake CL 110, Exhaust CL 116.
To get the timing numbers they state, this cam would have a 113 Lobe Sepration angle. This cam appears to be a stock 350 HP 440 replacement cam?

With the low 8.35:1 compression, I'd expect maybe 120-130 cranking compression pressure?
With the 9.78:1 compression, I'd expect closer to 150-160 cranking compression pressure?

Note: This assumes the cam is installed on the 110 intake centerline?

 

[Stegs]

thanks for your help! i really appreciate it!. Looks like i need to bump my compression with some 75CC edelbrock e street heads.

If you took that info you had, and used the edelbrock 75CC aluminum heads, that should put me "around" 9.5:1 compression correct?

 

[451Mopar]

thanks for your help! i really appreciate it!. Looks like i need to bump my compression with some 75CC edelbrock e street heads.

If you took that info you had, and used the edelbrock 75CC aluminum heads, that should put me "around" 9.5:1 compression correct?

With the UEM piston at 0.113 below deck, the 75cc head is 9.13:1.
The FM350 at 0.092 and 75cc head is 9.52:1

 

[Stegs]

my piston is the fm350. I was told going with the eddy 75 cc heads i would be in the mid 9s for compression...exactly what you came up with.

Match that with a lunati 268/276 cam and new lifters.....should be a heck of a boost for that car!