Inboard options 6.0 vs 5.7 vs Diesel

[Bushwacker]

Originally Posted by pelican

i'm not a huge fan of the stroker motors - seen quite a few problems internally with those . . .

I have to concur . . . when you increase the stroke on an engine with fairly short rods like a small block Chevy, the resulting rod ratio is far from optimum and it increases side loads on the piston. (To visualize this, draw a right triangle depicting the crank pin at 90 degrees to the CL of the cylinder, with the rod as the hypotenuse. Now move the crank pin further out to simulate the longer stroke and watch the angle between the rod and cylinder increase!)

An engineering colleague of mine learned first hand about what happens when you increase the stroke on a short rod engine! Jeff ordered a new 27' Seamaster in 1967 with a large custom fuel tank for Bahama trips and a 350 Chevy/MerCruiser II I/O. Now Jeff likes to run fast, and he ended up putting a rod right through the block of the 350 in about 150 hrs! So he then installed a 400 CI small block Chevy, which is the same basic engine but with a much longer stroke. He said it was much better, as he got about 300 hrs out of it, at which point it was burning oil and blowing smoke! So he pulled the engine, tore it down, and found that every piston was cracked due to the higher side loads with the short rod/long stroke geometry!

At this point he installed a single 454 big block engine! He had no more durability problems after that, and concluded that the only thing better than that 454 was TWO of 'em! So he bought a 28' Bertram, with TWO 454's in it! (which he had to install himself, since Bertram would only sell it to him without engines, claiming that it was only designed for twin small block engines, and that big block engines would screw up the CG of the boat, making it unsafe!) Jeff said no problem, you just have to go down to your friendly Chevy dealer and order 2 pair of aluminum heads; with aluminum heads they weigh the same as a small block engine with iron heads! That was a 50 mph rig with those engines in it!