compression ??

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rcrobdog

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I need help. What is my compression ratio?
I have a 72hp 440 block, stock 3.75 stroke crank , 40 over pistons
440 source stealth heads with 80cc chamber.
 
Need more info on the pistons and head gaskets. I was in Elk Grove yesterday.
 
They are stock style flat top pistons. And they are victor reinz gaskets not sure how thick they are but i measured about 1mm
 
How far down are the pistons in the cylinder at the top of the stroke?
 
Everyone is correct, you do need some more information to get a accurate answer. However, if they were correct '72 style/pin placement pistons, even with the smaller cc heads, I doubt you will be much over 9 to 1. I think head bolts are 11/16" :)
 
Ok I cannot find specs on these victor reinz head gaskets they came in a 440 gasket kit part number is 95-3344vr. My head is going to explode. I cannot find specs on the web !!
 
So I pulled the head off and with the gasket in place I measure 3.969" to the bottom of the stroke and .204" to the top.
 
rcrobdog said:
Ok I cannot find specs on these victor reinz head gaskets they came in a 440 gasket kit part number is 95-3344vr. My head is going to explode. I cannot find specs on the web !!
Click to expand...


Go to the source, there are a lot of things to know to get the correct compression ratio. You can do this easily if you have a burret and the time.
 
Actually you measure from the deck without the gasket. The new gasket should have the thickness on the package. They're usually around .050. Let us know what you get for a C/R.
 
The gasket should run about .039" or so if it is the common composite gasket. With the piston at top dead center, how far is it from the blocks deck, to the piston top? I see .204" mentioned, but that is a number I have never even seen close to on any I have measured. How are you getting your measurement? The bore size you know is .040" over, and we know the stroke. A good piston-deck measurement and we can give you a close guesstimate, assuming the 80 cc head measurment is accurate.
 
I know this is not a good tool but its what I got!!
 

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Is that a crack I see right at the top of that cylinder, and one in the other a little further down?
 
It looks like 8.23 to 1, Thats from the numbers you gave. Normal stroke is 3.75, I think thats what you have.
I ran it again on KB's website. It came out to 8.26
.043 Gasket
4.360 bore (4.32+.040)
3.75 stroke
.146 piston depth
80cc chamber
4.40 gasket bore
0 piston volume (flat tops)
This sounds like a stock low compression 440 rebuild. Not too bad, think about a whiplash cam. I'm told they will make this run well!
 
Thats woefully low,even for a street rod..I dont think your cr is that low. Those pistons are flat tops with no valve relief's,so maybe they do sit pretty low.
 
I used .039" for a compressed gasket, which helps you out a bit. Compression still comes in at only 8.3 to 1. I hate to be the bearer of bad news, but unfortunately your pistons are really far down in the bore. At least you checked yours to find out what it actually has. Too many people just guess.
 
Tkank you all for the info!! I am trying see what the compression is so I can pick a cam/intake/lifters/carb ect. I would like to get the most HP out of this block without having to sell the farm buying new pistons and rebuilding the bottom end again is not going to happen. This is my first motor build so I'm not hip to all the build lingo but I am wanting to learn. Thanks Again for all the help!!!
 
With some thin head gaskets you can get it over 8.5:1. Kinda low with aluminum heads but hey, a 440 is the most forgiving engine ever made. Stay mildish on the cam. Spend your money on traction and you'll have a great street car.
 
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