6 cyl casting

[Dude68]

I am getting conflicting info researching casting number 3921968. It looks like an exchange motor that was put in this truck. In a 1968 C10. I have it pulled out, pistons removed. Looking for a head. If it was original motor it is 1968, but since it is not it could be a 230. Any suggestions.

[dmjlambert]

As I have found from researching my 6 cylinder engine 230 and 250 use many of the same parts including block. Are you interested in knowing if it is a 230 or 250? The shape of the top of the pistons is how you tell, dished for 250 and 4 dimples for 230. I have not looked at mine yet, I can't really see much through the spark plug hole. But since you have your pistons out do you still have them to look at? The factory made 230s and 250s in the same years, and put those into different vehicles depending on year and model, there were overlapping years like that.

[RustyPile]

I'm relying on my 60 year old memory of my racing days.. I raced a 250 cid engine only one year, 1972.. If I remember correctly, the 250 and 230 heads are interchangeable.. The 250 pistons are dished to cancel the increased compression ratio of the longer stroke 250 into the same sized combustion chamber. We ran flat top pistons, but I don't remember if they were 230 pistons or aftermarket pieces.

Just a bit of advice: -- don't bother with the integrated head.. It's a very poor design that is prone to cracking..