June 27, 2022

Surgery Without Scars

Featured image for “Surgery Without Scars”

By Terry McGean from November 2019 issue of Muscle Machines

We’re finally getting close to firing up our Chevelle’s new 427 big-block crate engine, getting down to the final assembly, including the cooling system. Since this car has always had a big-block, we didn’t need to completely rethink the system—instead, we’re using factory-style parts with a few select upgrades.

As with most of this project, we didn’t want to rob parts off the Chevelle’s stock 396 engine, and we felt the new engine warranted a new radiator. Our desire to lean towards factory-style parts led us to retain a stock-style V-belt accessory drive system, as we covered back in the September 2018 issue (#181), though almost all of its components are new reproductions from Original Parts Group. The Chevrolet Performance ZZ427 engine ships with a water pump, but it’s an early short-style unit, so we swapped it to a long-style Milodon pump that looks like a GM unit but provides improved flow.

Since our Chevelle left the factory without air conditioning, it would have been fitted with a simple fixed four-blade fan, though ours had been changed to an aftermarket flex fan years ago. We opted instead to use a factory-type clutch fan, as would have been found on a car with A/C. OPGI had the fan and the clutch, and it seems to fit correctly with our original fan shroud. The seven-blade fan will be capable of moving lots of air, but the thermostatic clutch will allow it to slip when the airflow isn’t needed, just like GM intended for heavy-duty cooling applications.

Probably the slickest element of our revised cooling system is the radiator. We went to the crew at U.S. Radiator for a recommendation, and wound up with a unit that resembles a stock replacement big-block Chevelle radiator but offers significantly upgraded cooling capacity. U.S. Radiator builds its own units here in the United States, and even produces many of the new tank stampings.

Several choices of core type are offered for many applications, from a quality stock replacement to high-efficiency and on to aluminum construction. We opted for a traditional copper/brass unit with an Optima “Extreme-Efficiency” four-row core (our stocker used three rows), which on its own could have handled the new engine. However, the staff at U.S. Radiator recommended we try one of their Tripleflow designs, which use barriers concealed inside the radiator tanks to redirect coolant flow back through the core, and then back once more. The three-pass arrangement provides more cooling and enables the inlet and outlets to remain in the stock locations. The only downside is that this design can’t accommodate a stock-type integral transmission cooler, but we’re using an external unit anyway.

The new radiator fit right in place of the stock piece, though the fan shroud may need a little trimming to accommodate the wider core. We wrapped it up with reproduction radiator hoses, heater hoses, and tower-style clamps. We’re almost ready for fire.


Chevrolet Performance 800-222-1020

Milodon 805-577-5950

Original Parts Group Inc. 800-243-8355

U.S. Radiator 323-826-0965