The 3836848 is the good 235 head and the 3836850 is the good 261 head. They both have the same port and valve size and flow the same amount, but the 848 head increases compression ratio about 0.5 when used on a 261. The 850 261 head has some extra water passage holes that need to be added to the 235 head if it is used on a 261. Other heads don't have as good of flow capacity (none of them could be called great) and are not really desirable but do work if you need something to get you going.


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