MrGokster

Hi everyone,
I have been rebuilding 5.4l 3v engine with new forged crankshaft and rods, 020 oversized flat top pistons and comp cams 127100. Since piston size is bigger the compression ratio increased. I found a website that calculates CR. I am trying to bring my CR back to standart which is 9.81 because I wanna use 87 pump gas. So I found that value 0.051" for the head gasket thickness from the calculation.
chamber volume: 49.6
deck height clearance: 0.115
bore size: 3.572
head gasket bore diameter 3.62
Stroke 4.165
http://www.csgnetwork.com/compcalc.html
After the calculation I found this head gasket below. I have no idea with compressed volume 8.611 cc in head gasket' spec. What is it? Shoul I take it into account while calculating CR. The CR calculation website I found is not asking this value. Do I miss something?
Thanks

https://www.summitracing.com/parts/cgt-c5119-051/make/ford

Screwed05

What ever your cylinder head chamber cc volume is, add 8.611 to it compensate for the head gasket. Example if cylinder head chamber volume is 49.6 + 8.6 = 58.2 chamber volume.

Head gaskets have 2 thicknesses compressed and un compressed. The compressed thickness is how thick when the heads are torqued down to spec. Example, the gasket may measure 0.051 out of the package. Now after installing and torquing the heads down the the gasket may measure something like 0.033.

The higher the chamber cc volume the lower your compression will be. I hope this answers your question. If not please clarify your question. FYI your link isn't working.

MrGokster

Added 8.611 to the chamber volume and put the total value in the calculation. But this time CR turned 16.53:1
http://www.csgnetwork.com/compcalc.html
It doesnt look right to me. I will try to find the stock head gasket compressed volume.

Screwed05

Yeah that's not right, seems something is missing.

ZSK

The Summit Racing head gasket lists its compressed thickness at .051"

Using the linked calculator enter these values:

Bore/Stroke in Inches = 1
Bore Size = 3.572
Stroke Length = 4.165
Head Gasket Bore Diameter = 3.62
Head Gasket Thickness = .051
Chamber Volume in CC = 49.6
Piston Dome Volume = 0
Piston Deck Clearance = .115

Calculated Compression Ratio = 9.87:1
Total Displacement Volume = 77.1cc

The calculator figures out your volume from the head gasket, no need to add it in. Your combustion chamber volume is 49.6 + 18.88 + 8.61 = 77.1

18.88cc is the volume of the cylinder when the piston is at the top of the stroke. Head Volume + Block Volume + Head gasket Volume = Total Combustion Chamber Volume

MrGokster

Thank you ZSK. When I added gasket volume in CR value was like crazy. Now it make sense. So If I install this head gasket 0.051 is it safe to use 87 octane pump gas without detonation. And why is this after market gasket so expensive?

ZSK

You'll be fine at 9.87:1 on regular gas assuming you are not running a bunch of extra timing. The gasket seems expensive but it's also one of the thickest one I've seen, and from a very reputable company.

MrGokster

If you mean extra timing by after market cams oh yes I am going with comp cams. Do they affect my low octane gas choice? I wouldnt like to deal with the detonation problem.
https://www.jegs.com/i/COMP-Cams/249/127100/10002/-1

Screwed05

To clarify, you are doing all this work plus cams. But, you are going to run on 87 octane? Or, you just want to know it's 87 safe incase you had too?

MrGokster

Mostly I am planning to use 87 sometimes 93. I wanna know if its safe if I go with 87