5.4l vs 4.6l compression math.

Silver95bird

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okay, so I'm using the compression calculator here:

http://www.csgnetwork.com/compcalc.html

Starting with 4.6L numbers as a guess, I'm using these for numbers:

bore 3.55
stroke 3.54
hg bore 3.58
deck height 0.012
hg thickness 0.039
npi chamber 52cc
npi piston 10.5cc
pi chamber 44cc

for a 4.6L npi stock setup, I get about 9.1:1 . Sounds about right.
for a PI headswap, I get 10.1:1 . I Always heard 10.5, but it's still close enough not to worry.

Now I change the stroke to 5.4L stroke, and the deck height to 0.120 (that's what I've heard it is), and I get:

5.4l npi stock CR: 8.63:1 . I knew they'd be different, but this is pretty low. So then I ran the same for a PI headswap, 44cc chambers just like the 4.6L and I get:
5.4l pi head swap: 9.39:1

Not only does the added deck height drop a ton of compression, it also blunts the pi headswap to under .8 of a cr boost, as opposed to a full point.

I read that the .120 isn't always fully .120, so I ran the numbers for it with .112, and it only increased from 9.39 to 9.53, so I'm not seeing enough to make a huge difference.

Either my numbers are wrong, or Ford's advertised 9.0:1 for the 5.4L engine in 97-99 is bunk.
Anyone?
 

96blak54

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Yeah, either a longer rod or taller compression height of the piston to make a zero deck.
 

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