Hot Rods Offenhauser 375 Heads Question

I have a set of Offenhauser 375 heads. I am not sure of the difference between the 375 and the 400 or 440. My 59AB is stock but I would like to increase the horsepower a little. Are these heads going to give me more compression or should I have something done to them for that?

ClubJoe
Sunny Brandon, FL

 

The 425 heads are the lowest compression ratio (around 8.5 to 1). I used to have a chart for each of the available ratios but can't find it. As the numbers go down the ratio goes up. Example: a 400 head is probably about 9 to 1. I have a set of 325's which if I remember right was about 10-1/2 to 1. Hope this helps. Make sure you check valve clearance before you install them.

 

The numbers refer to allowable valve lift.
A .375 head would allow a cam with .375" lift or less.
If you run an Isky 400jr, a .400" head would be required.
The head gasket gives you additional clearance.

 

This will get you started. There are more comprehensive charts out there.

 

If these are new heads, you are probably good to go. If they are used from some unknown source, you're better off checking out everything because they may have been surfaced or who knows what.

 

Thanks everyone that replied but I still would like to know if these heads will increase my horsepower at all?

ClubJoe
Sunny Brandon, FL

 

42merc is correct, the number on Offenhauser heads correlate to the valve lift of the camshaft. It is important to note that the compression ratio chart Kiwi 4d posted from the Offenhauser catalog is based on stock valve diameter, non-relieved blocks, and factory pistons. Enlarging your valve diameter will decrease the camshaft valve lift allowed. Relieving the block will decrease compression ratio. Pop up pistons will increase your compression ratio. To put it simply (as far as increasing your horsepower) if all factors on your engine remain the same, a higher compression ratio will increase horsepower.