heads 240 cs 300
New User
Joined: May 2003
Posts: 11
Likes: 0
From: Stockton, CA
So, if the combustion chanber on the 300 head is larger than the one on the 240, putting a 300 head on a 240 block will lower the CR? My '66 has the 240 with a VERY sick head-cracked in two places and badly worn valve seats and guides thanks to unleaded gas and 300k miles. I've got a 300 out of a '76 with a nearly perfect head, but everything else needs to be rebuilt. I'd like to put the head on the 240 until I can rebuild the 300 (budget delays) since I need the truck running. I have to run 91 octane (california gas sucks) in order to keep it running as it is. Lowering the CR should mean I can run a lower octane, right? I'd have to check the new CR of course, but I know where to look to find that procedure although I haven't done it in, gad, nearly 20 years.
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Posting Guru
Joined: Feb 2005
Posts: 2,499
Likes: 1
From: Missoula, MT.
that is correct, but i dont think a 240 head has enough compression to make you have to run high octane but your right, lower compression should make it run on lower octane fuel, one thing you may wanna check if your pinging, is your timing.
New User
Joined: May 2003
Posts: 11
Likes: 0
From: Stockton, CA
I don't have a pinging problem (that I can hear, anyway) but the truck suuuuure doean't like 87 octane. The performance drops noticeably, and it's a lot hard to start. After I put the 300 head on, I'll certainly keep my ears open and play with the timing to get the best performance out of the old guy.
