3400 with iron heads, whats the C/R?

[AutoTech]

I need to find out what the C/R will be if I use a 3400 roller cam-in-block engine with iron heads. Can anyone help me out or know any info on this?

[bszopi]

http://60degreev6.com/apps/crcalc.php

Hehhe... finally get a chance to put it to work. Use the default option to get info on the iron heads, and then again on the 3400, then use the "Use your own data" option and plug everything in and see what you get.

[bszopi]

Well, I did it for you (I was interested)... With the stock 3400 pistons and the iron heads and iron head gasket, I came up with 7.66:1.

[AutoTech]

That doesnt seem right. The calculator uses combustion chamber volumes, not cylinder head chamber volumes. Combustion chamber volume is the total volume above the piston when it's at TDC. In order for the calculator to be correct for my calculations, we would need to know the actual cylinder head chamber volume of the iron head 3.4, the compressed gasket thickness of the 3.4, the piston-to-deck clearance of the 3400 and the piston dome volume of the 3400.

[sharkey]

actualy 7.6 sounds right for that combo. this type of hybrid has been done before. in order to corret the compression ratio, the guy used 3.4l tdc pistons, and it ended up just over 9:1.

[bszopi]

That doesnt seem right. The calculator uses combustion chamber volumes, not cylinder head chamber volumes. Combustion chamber volume is the total volume above the piston when it's at TDC. In order for the calculator to be correct for my calculations, we would need to know the actual cylinder head chamber volume of the iron head 3.4, the compressed gasket thickness of the 3.4, the piston-to-deck clearance of the 3400 and the piston dome volume of the 3400.

I don't know where you are looking, but the calculator does use all of the values you mentioned. The combustion chamber volume is the volume of the CC on just the head (48.5cc for an iron head). If you would like to see the calculations that the calculator uses, I will be more than happy to provide them. Or, you can just take the numbers (or search for them in the forums) and plug it into any of the dozens of calcs on the web and get the exact same numbers.

[robby1870]

yeah, 7.6 something does seem right. You have a large piston dish with a 3400 block and large head chamber volume with an iron head. I think iron head chamber volume is like 2x aluminum head chamber volume.

[Guest]

From what I understand you can't use the iron head head gasket though because the piston will kiss the head. Thats what I have been told by people here who have tried to use it.

So you have to take the .040 iron head gasket thickness and go to the aluminum head gasket thickness which I always read as .060. This of course will lower it more,

CC of the iron heads is 52cc according to the GM power manual. Every head will differ though. Not sure what was used in your calcs.

I came up with around 7.3:1 when I calc'd it.

[AutoTech]

I don't know where you are looking, but the calculator does use all of the values you mentioned. The combustion chamber volume is the volume of the CC on just the head (48.5cc for an iron head). If you would like to see the calculations that the calculator uses, I will be more than happy to provide them. Or, you can just take the numbers (or search for them in the forums) and plug it into any of the dozens of calcs on the web and get the exact same numbers.

Combustion chamber volume is not the CC on just the head. Combustion chamber volume is the TOTAL volume above the piston when it's at TDC, to calculate combustion chamber volume we need to consider four things:

Cylinder head chamber volume
Compressed head gasket volume
Piston-to-deck clearance
Piston dish or dome

Combustion chamber volume is not the same as cylinder head chamber volume. Cylinder head chamber volume refers to the volume of only the head's combustion chamber area, measured with the valves closed.

Thats why I was confused with the calculator, because it is mis-labeled, stating combustion CC instead of head CC. So apparently the calculator is correct on the C/R, it's labeling just needs to be fixed.

Thanks guys

[bszopi]

Ok, I'll fix the labelling then.