360 Crate Engine Buildup & Dyno - Crate Expectations

We still had the change to synthetic oil, so the sump was drained and we put in a fresh fill and filter. Several pulls later, we were still at 401 hp and a little puzzled. We checked the dyno readout carefully and noted that the oil pressure peaked at 70 psi at 5,500 rpm, and actually dropped to 68.5 psi by the end of the pull. This could have been caused by a slight aeration of the oil. A check of the stick showed the oil was slightly overfilled, and 1/2 quart was drained. The next pull showed 439.5 ft-lb at 4,100 rpm and 409 hp at 5,400 rpm. That 1/2 quart of oil was costing 8 hp! Windage was no doubt a factor, but the fluctuation in oil pressure, though slight at only a couple psi, makes us suspect that some slight aeration had occurred, which hurts performance with hydraulic lifters. We've seen it before-in some cases more obvious and dramatic.

With that, we felt that we had taken this package to its full potential. The Magnum 380 (409?) crate, with a high-end carb, tuning, and oil, was making 29 hp over its base rating. To us, that's impressive. It's no wonder those crate-equipped A-Bodies move as hard as they do. We had some time left and tried to further tune the combo with a spacer under the Demon carb. First, a 1-inch open spacer was installed, and after a few runs it was clear that it was not going to add to the combo. Power was no better anywhere in the curve, the peaks were down, and low-end took a hit. Next we substituted a four-hole 1-inch spacer, and there was a hair more torque at the bottom of the curve, but it cost power up top to the tune of 5 hp. Neither spacer complemented the combo, suggesting that the plenum volume and layout of the M-1 is well matched as-is to the rest of the combo.

We had a good time testing the 380-horse crate. The engine did what it was supposed to, delivering the power promised and then some. Open the box, bolt on a decent carb and a set of headers, and rest assured, it will make its rating or more with only a little tuning. Dial it in and there can be 400-plus horsepower on tap.

That's enough to show 'em you're serious.

Dyno Results
Superflow 901
Tested at Westech
Mopar Performance 360 cid 380 hp rated