Compression ratio help

[Timmy]

I’m starting my 390 build and have a question that I should have gotten answered before now.

What do I need to do to get to 10:1 compression with this combo. I thought I would be fine but the more I read the more I think I’m going to come up short. This is my first FE and first build and I guess I’m just getting nervous. I’m also wondering what head gasket to use.

390 block .030 over
Stock bottom end
Federal Mogul SpeedPro forged (TRW-L2291F)
CraneCam Part# 343801 Grind# H-278-2
Edelbrock RPM 72cc heads

[GREENSNAKE]

Hi Tim! have you did your math on the Compression Calculator web site thats where i go to build the right compression engine. Let me know if you need help. Lonny

[whitey94]

Hi Tim,
Remember for every cc in the head you will need 10 in the cylinder to get your 10:1 ratio. Thickness of the head gaskets add to the head size also. Top of piston can increase or decrease ratio--dish or dome. Hope this helps, Whitey

[Joe Prochazka]

I was going through this a couple of years ago.....edelbrock told me that for every CC of chamber volumn, you need to remove .006 of material from the head. My engine builder said the to get to 10.25 CR we needed a 68 CC chamber. We actually ended up removing close to .030 to get 10.25 ( I think that Edelbrocks numbers were off a little)
I think that I used the same pistons, too. I can check my builders invoice to see the Felpro P/N for the head gasket.
I think that those heads out-of -the box would get you 9.6 CR with those pistons.

[Timmy]

Thanks for the help guys. I love this board, no BS just good info.

The only thing I’m not clear on is the deck clearance/volume of the block I’ll be getting. It will be a used truck block and I don’t have access to it yet. Steve Christ’s book has two different deck volumes listed (.008 and .112). Is that correct?

With a .008 deck and 72cc heads, I get 9.786:1

With a .112 deck and 72cc heads, I get 8.08:1

With a “zero” deck and 72cc heads, I get a 9.935:1

With a “zero” deck and 71 cc heads, I get 10.034:1

So right now I’m looking at taking .006 of material from the head and running a zero deck. Are there any issues running a “zero” deck volume on a 390?