Don Terrill’s Speed-Talk

I have the opportunity to pick up Gen 5 454 BBC 4 bolt main block for a good price. Are these good blocks for building a drag race application out of. Can you use 781 oval port heads with this block. Thanks Andrew

I happen to be partial to the Gen 4 block, but have built many Gen 5 with no problems.
The blocks are plenty strong, I just don't care for the one piece rear main seal.

blwilliams wrote:I happen to be partial to the Gen 4 block, but have built many Gen 5 with no problems.
The blocks are plenty strong, I just don't care for the one piece rear main seal.

I don't understand why you wouldn't like the 1 pc. rear main.
I've run a gen 6 502 (1 pc rear main) then upgraded it to a 548 (4.25 stroke W/ 2 pc rear main). The 1 pc rear main never leaked, the old style 2 pc, I could never get it to stay sealed up for any length of time.
BTW; I think the Gen 5 blocks must run a gen 5 head or some kind of water jacket adapter . You have to be careful which heads / gaskets you use.
Gen 6 resolved these issues (I run Gen 4 heads / gaskets on my Gen 6 block no problems).

cuslog wrote:

blwilliams wrote:I happen to be partial to the Gen 4 block, but have built many Gen 5 with no problems.
The blocks are plenty strong, I just don't care for the one piece rear main seal.

I don't understand why you wouldn't like the 1 pc. rear main.
I've run a gen 6 502 (1 pc rear main) then upgraded it to a 548 (4.25 stroke W/ 2 pc rear main). The 1 pc rear main never leaked, the old style 2 pc, I could never get it to stay sealed up for any length of time.
BTW; I think the Gen 5 blocks must run a gen 5 head or some kind of water jacket adapter . You have to be careful which heads / gaskets you use.
Gen 6 resolved these issues (I run Gen 4 heads / gaskets on my Gen 6 block no problems).

I have a gen 5 502 block ( now punched out to a 555 ) that has had both a brodix bb-1 and dart pro-1 cyl head put on it...No adapter needed with either head..I love the reliability of the one piece rear seal..And more good news about my block is that even goinig a .090 overbore, we still have roughly .300 wall thickness when sonic checked. Good Luck, Dan.