Reply to "COBRA JET: Unleashing The Performance Capabilities Of 351 Cleveland Engines With Open Chamber 4V Heads (Q Code)"

Originally posted by Bosswrench:
John, in autocrossing (also known as parking-lot racing), I got a backfire on the starting grid with a friend's Pantera that wasn't sufficiently warmed up. The 351-C had been rebuilt with 11:1 c.r, bored 0.030" over, big solid lifter cam & Holley carb, and needed 102 octane fuel to run without detonation. Immediately after the little backfire, water was seen running out one exhaust pipe. A teardown showed a piece of cylinder wall about 1" x 1" had cracked and blown clear into the water jacket. The retrieved piece showed a cylinder wall thickness of only 0.050"! For performance use, cylinder walls need at least 0.150" and more is better! Chev guys like to see 0.200"- no 351-C ever had such thick walls when new!

Lesson #1 learned: do NOT bore a 351-C AT ALL unless you first run a cylinder wall thickness check. This block had a shifted casting core on that cylinder.

Lesson #2: As you found out, stock valves are made in two pieces and WILL separate at the head-to-stem weld if overstressed. And 'overstressing' is ridiculously easy on a completely stock 351-C. Air-cooled VW valves are made the same way. Use ONLY one-piece valves which require single-groove keepers.

Lesson #3: I also suggest a fully baffled 10-qt oil pan or you run the risk of wiping out crank bearings from cornering forces. A friend lost a connecting rod after only a dozen laps of open-track road racing with a stock pan full of oil. Good luck on your next 351-C engine build.

I’m definitely building a library of lessons gleaned from you guys here. And having great fun reading the various anecdotes of where things have gone wrong. I can’t imagine how it must have felt to find a chunk of cylinder like that.

I promise to have the block fully sonic tested before I overbore, I know I might be able to leave it stock with just a hone, but I’m tempted to get it done along with line honing and decking so that I’ve got everything nailed down and blueprinted as best I can.

Valves, I will definitely go with the single groove, whilst I have it apart it would be madness to avoid drawing the right lessons from Sick Cats experiences.

I was looking at a road race pan, from some guys called High Energy from Australia, which is an 8 litre similar to the moroso offering, and mating it with a pressurised oil reserve unit.

Also considering getting another bare block from Aus, (as they are scandalously cheap and my company has a great shipping partner there) to use for checking fitment and clearances.