Vintage Mustang Forums banner

1 - 5 of 5 Posts

·
Registered
Joined
·
204 Posts
Discussion Starter #1
I know this ? has been asked before. I used the search feature and didn't find anything. I need to know what to look for to identify the difference between a 390 block and a 428. Looking at a engine that is thought to be a 390 with 428 SCJ heads and would like to verify. All info would be appreciated.
 
G

·
Guest
Joined
·
0 Posts
Do NOT trust the block numbers. I believe all of the above block casting numbers could also be non-428. Most 428 blocks have no casting numbers (service blocks). The only way to know for certain is to measure & sonic check the bore which should be 4.13-4.17"). Note that a way overbored 390 would fall into this range also but would have paper thin cylinder walls. Check these sites for some hints on things to look for.

http://www.428cobrajet.com/id-block.html
http://www.network54.com/Forum/message?forumid=74182&messageid=983385091
 

·
Banned
Joined
·
4,577 Posts
Another simplier way to check, is to remove one of the center freeze plugs on the block. Just inside the hole will be a stamp "428", if it's a 428. All 428's were stamped like this. If it's a 390, there will be no stamp. Of course you will need to have the block out of the car to check this, as it will be quite hard I think to check in the car. As one of the poster above said, you can't trust the block numbers all the time.
 
1 - 5 of 5 Posts
Top