Cylinder Head Comparison

[Webster]

Picked up a '79 FJ40 2F cylinder head to replace my cracked '84 FJ60 head. Everyingthing seems to match up except that the combustion chamber is larger and round shaped whereas my newer head is a egg shaped chamber. Both heads use the same gasket so I think I am OK.

My question is;

The larger combustion area leads me to believe that I will now have a larger compression ratio than stock. What are the negatives as a result of this and what adjustments to timing and fuel can I make to compensate?

Or am I screwed with this head?

Thanks,

CW

 

[Roswell Rat]

I hope you aren't going to be disappointed when I tell you this, but larger combustion chamber = LOWER compression.
Good luck with the head.

Jayson

 

[Doc]

Lower compression is going to be the case here, also lower power numbers.

But you'll be set up for boost nicely!

To regain some of the lost compression you can use a thinner headgasket, but it might not be enough. To establish exactly how much you are loosing you need to determine the volume of the combustion chamber of each head.

Then you can determine if you can gain some of it back with a thinner headgasket.

There's not much you can do other than that to compensate for it withough installing new pistons, or major head work.

You can get the head milled down some, but that is expensive.