Help me with some math Please

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1930

1930

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CCd my heads, assuming I get the second head back and its like the first ( Im sure it will be now ) Ive got one chamber that reads 84 next 86 next 86 and last 84 so I average 85 CC.

If I remember right I have to take into account 440 head gasket thickness ( do you know what that is...standard head gasket bought from Napa unless Im told otherwise )

Also standard cylinder bore, Ive got an ultra low mileage 440 with a bore size of right around 4.325.

I want the engine to have 10.1 compression. Can someone help me with the math/explain to me how to figure out what piston I need to get.

Thanks
 
You need about 100cc of total combustion space to reach your goal. With 85cc in your heads, the rest will be your head gasket compression thickness and your piston deck height/valve relief volume. Assuming stock stroke and .035 or so head gaskets, a flattop piston down in the hole about .030 would get you close. There is a ton of info on here about figuring all this out. I use 3.14 for pi and 16.39cc per cubic inch. Pi x radius squared x stroke gets your cylinder volume, then cylinder volume + combustion space divided by the combustion space alone gets your compression ratio.
 
You are correct about needing to know head gasket thickness, and what they are referring to is "crushed" thickness........for a standard head gasket in a rebuilders gasket set, you will need to dig into the manufactures catalog, though truth be told, I'd look some place else for a gasket, not that they are bad, they are good gaskets for a standard rebuild, and it sound like that's not quite what you are doing. Fel=Pro, Victor Reinz, Mr. Gasket, Cometic, virtually a dozen manufactures have a gasket you are looking for, generally something thin......call their tech lines, talk to them, tell them what you are doing, it's their job.

You didn't say what year your 440 is....not that it makes a whole lot of difference, just nice to know where you're starting from. At around 4.325 inches bore diameter, you're around .005 inch O/S, standard bore is listed a 4.32 inches.....You might want to consider boring over size.

The following is an illustrative example:

From the Icon piston on line catalog, piston number IC822 has a compression height of 2.067 inches, rod length is 6.768 inches, one half stroke is 1.875 inches, add them all up and you get 10.710 inches, factory blue print deck height spec is 10.725 inches, that puts the piston down in the hole .015 inches at top dead center. Also from the Icon catalog, piston eye brow(valve relief) volume is 4.5 cc.

Compression ratio is total volume of cylinder with piston at bottom dead center divided by total volume of cylinder with piston at top dead center.

Cylinder volume is: pi times radius squared times height
pi: 3.14
r squared: (2.16 times 2.16)
height: 3.75
all of this equals 54.96 cubic inches, multiply by 16.39 and it equals 900.7 cc's

Head volume: already measured and averaged at 85cc's
Gasket volume ( Fel-Pro, from Summit racing catalog): 9.762 cc's
Piston volume: Icon catalog, 4.5 cc's
Deck volume: pi times radius squared times height
This is volume above piston when it is at top dead center, your height is how far the piston is down in the hole, don't forget to convert to cc's.

Now add: cylinder volume, plus head volume, plus gasket volume, plus piston volume, plus deck volume. Now divide what you just added by: Head volume, plus gasket volume, plus piston volume, plus deck volume.

The number you get is your compression ratio.

It's not that hard to do, I figured it out and if I had a dollar for every "F" and "D" I got in math in school, I'd have never had to go to work.

Hope this helps
 
The factory head gasket is .019-.021" compressed thickness . Fel-Pro blue gasket is .042" compressed . Cometic can be 2 layer or 3 layer and are a must for alloy heads . they are very good and they are very expensive . Reuseable too. The factory is good up to about 12.5:1 compression . think Max-wedge
 
At this point it has been reccomended to me an Icon 9953KTM030 and if noone has any objections I think Im going to roll the dice with that one, it will get me close to my 10.1 the way I figure it ( 9.6 or 7 or so ) adding the KTM gives me the rings ( hastings ) as well.

Thoughts??
 
9.6-9.7 c.r. is great for the street . go for it . Please make sure your mating surfaces are flat and have a good "tooth" for the gasket to seal . I have 9.6 c.r. and it sounds pissed off . Good luck
 
I'll add "blueprint deck height" is not "your deck height". I've yet to find a factory machined block that had a deck height within .020 of that. Normally it's more like +.040 and not flat or parallel. So if you are targeting a compression ratio make sure the machining you have done yields what you need too. parts are only so much of the equasion.
 
moper said:
I'll add "blueprint deck height" is not "your deck height". I've yet to find a factory machined block that had a deck height within .020 of that. Normally it's more like +.040 and not flat or parallel. So if you are targeting a compression ratio make sure the machining you have done yields what you need too. parts are only so much of the equasion.
Click to expand...

Thanks for the tip, I will be sure to measure the deck height
 
DO NOT average your chamber cc's, you are calculating for the least cc measured, 'cause that's the cyl.(s) that will detonate first. When power timing your eng., 6 cyls. out-
weigh 2cyls., for instance. In other words, if you have 6 at 86, & 2 at 84, the eng. output will continue to improve as you bump the timing even tho' 2 cyls. have reached or
crossed the detonation threshold. I cc'd a set of 906's for a 6bbl.440 job, the chambers for positions 3&6 on both heads were shallow, enough that I corrected them B4 I
proceeded. Examining the pistons showed Me, #3 definitely showed the telltale pitting of det., #6 not as bad but.......
 
It amazes me how much some of you guys know and this forum is lucky to have some of you participate.
 
1930 said:
CCd my heads, assuming I get the second head back and its like the first ( Im sure it will be now ) Ive got one chamber that reads 84 next 86 next 86 and last 84 so I average 85 CC.

If I remember right I have to take into account 440 head gasket thickness ( do you know what that is...standard head gasket bought from Napa unless Im told otherwise )

Also standard cylinder bore, Ive got an ultra low mileage 440 with a bore size of right around 4.325.

I want the engine to have 10.1 compression. Can someone help me with the math/explain to me how to figure out what piston I need to get.

Thanks
Click to expand...
Most composite gaskets aren't less than .030" compressed, felpros usually are .039"-.042" compressed, OE embossed shim gaskets are .017". For reference, I put an OE set
of open chamber 10:1 slugs in a '76 440 w/452 heads, all untouched & stock. It cc'd at 9.98:1 w/shim gaskets, so.........
 
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