Block Filler Olds
Thomas Bush, Winnebago, WI: I had my Olds 455 block rebuilt from 462 to 472 ci when the nitrous roasted a piston. In the redo process, the Olds mavin wrencher (Greg's Olds Performance) used some amount of block filler and sleeved the cylinder. It retained its street/strip applications-using an aluminum radiator, electric fan, and electric water pump with Evans coolant in a '65 Cutlass 4-4-2. Completing the drivetrain is a G-Force four-speed, a 4.11:1 gear, and a Detroit Locker in a Moser 9-inch. I've measured the rear-wheel power at 435 hp at 5,400 rpm and 461 lb-ft at 4,100 rpm on the motor and 522 hp at 5,500 rpm and 602 lb-ft at 3,600 rpm on a 125hp nitrous shot.
Is the practice of using block filler in a primarily street-driven 455 Olds still applicable in today's rebuilds? I presume this was done for durability. Is it overkill for a car that seldom uses its slicks? I seldom hear about block fillers used anymore in automotive performance publications. In fact, my 572ci aluminum-block Hemi motor with Indy Cylinder heads in my Challenger has no filler and produces considerably more grunt that the Olds. Was the filler needed or simply a precautionary measure? Is there any downside to using it?
Jeff Smith: The use of block filler is basically intended for thin-wall blocks that suffer from unstable cylinder walls, especially when pushed to their limits in terms of horsepower. The combination of high rpm and very high cylinder pressures can and does force thin cylinder walls to move around, reducing ring seal. The most common material is a specifically designed product called Hard Blok. This is a cement-based material that has the same thermal coefficient as cast iron, so it grows at a similar rate as an iron block. Once this material is mixed, poured into the block's water jacket, and allowed to harden (usually in less than 24 hours), it cannot be removed. For race engines, the general procedure is to perform what is called a tall fill in which Hard Blok is added almost to the top of the water jacket. A short fill pours roughly half the depth of the cooling system jacket to allow for better cooling. Drag race-specific engines generally go with the tall fill, while circle track engines prefer the short fill. Summit sells the Hard Blok in a 14-pound container for $89.95 or a short fill with 12.5 pounds for a little less. You can buy two, 61/4-pound bags for $79.95. Moroso also sells a 1-gallon jug of engine block filler for $13.75 through Summit Racing. Keep in mind that this material is not a sealer. It is porous and will not seal a leak that originates from the water jacket.
The obvious disadvantage to using this material for a street engine is that engine cooling will be restricted. While that's of questionable benefit for a street car, what is less obvious is that the oil temperature will also rise dramatically because the inherent cooling effect of the water at the bottom of the cylinder walls also pulls heat out of the oil. With the jacket filled with Hard Blok, the oil temperature also spikes. For these reasons, I would not recommend this procedure for a street engine since it would require adding a large external engine oil cooler just to keep the engine oil temperature within reason. By stabilizing the cylinder wall with Hard Blok, you should see a small return in terms of better ring seal. To quickly address the other engine with the aluminum cylinder block, this Indy block is an aftermarket piece that was built specifically to handle a large dose of power. The cylinder walls are certainly thicker and structurally enhanced to improve ring seal, making Hard Blok unnecessary.
Hard Blok; Brentwood, TN; 865/457-0509; hardblok.com
OK, this photo is pointless except to remind you about the Car Craft Summer Nats, July 16-18, 2010, in St. Paul, Minnesota.