Written by Mike Carpenter
Photography by the Author
When Bill Kuhlmann broke the 200-mph barrier in 1987 with a 615-cubic-inch engine combination, that history making run changed the industry forever. Nitrous began to earn wide acceptance and monster-displacement engines became the norm.
While breaking that mark remained a part of history, the 615 engine combo soon morphed into what we know today as the 632. It is the bread-and-butter engine choice for index-class racing, Quick 16, street-car classes, and even Top Sportsman and beyond.
Yet, while the displacement hasn’t changed, many don’t realize that other things have. Just as nature’s evolution improves the species, advancements in engine technology have done the same with the 632 engines of today.
“I’ve always worked with big motors,” Pat Musi said about his memories from years ago. “I remember we built a 512-cubic-inch engine back in the ’70s. Back then, people built motors like that with whatever stroke they could find and with junkyard blocks, but things have changed. A lot of people don’t realize those old 500-inch motors are very different from the same size engines NHRA Pro Stock uses now.”
Better metallurgy, CNC machining, improved technology and, of course, decades of practical race experience has resulted in the Edelbrock/Musi Signature Series 632 of today. The benefits are clearly seen with increased longevity, reliability and, of course, more power for everyday racers.
“The sky’s the limit for what you can spend on a 632 engine today,” Musi said with a laugh. “One of our customers just ran a 4.20 at 174 in PDRA’s Outlaw 632 class, but that engine has a ton of upgrades that not everybody needs. We wanted to build an updated 632 engine where we’ve worked a lot of things out. It’s an engine that’s priced right that any average guy can run and maintain—and it’s not a discount warehouse motor deal.”
Here’s an overview of what makes the Edelbrock/Musi Signature Series 632 such a great value on so many levels.
Any reliable engine combo, of course, starts with the block. Capable of supporting big-time horsepower, a good racing block is more than just a simple cylinder casing. The casting needs to be strong, resistant to cracking, and able to maintain its dimensions under extraordinary thermal variations and pressures. There also needs to be plenty of meat between the cylinder walls for overboring and accommodations made to improve oil flow for optimal lubrication and cooling.
While 632s have the same 4.840-inch bore center as standard big-block Chevys, the Edelbrock/Musi Signature Series 632 uses the proven Dart Big M block because of its overall quality and strength. It’s important to note, however, that they are using the latest available version as castings made after 2011 are slightly different and improved. Buyers should always want the latest updated components from a reputable engine builder rather than something less expensive that uses copycat assemblies or older engine components.
Some people may ask why a cast-iron block is the foundation of this combination rather than an aluminum piece. While the latter provides a weight advantage with easier repairs, there are trade-offs. Even with cylinder liners, the softer material in an aluminum block can change shape from rapid thermal expansion, which can result in abnormal wear, alignment issues, and diminished ring seal. The ferrous material in the Dart Big M block is extremely rigid and proven in countless sportsman applications.
With gun-drilled mains and fully profiled counterweights, the Callies 4.750 stroke 4340 forged-steel crankshaft is a perfect match with the true priority oiling system featuring stepped oil galleys in the Dart block, resulting in long bearing life. Pumping the Lucas Oil semi-synthetic 10W40 oil through the wet-sump system is a reliable Moroso high-volume, billet oil pump that feeds from a baffled Moroso 8.5-quart pan.
For the reciprocating assembly, Pat Musi builds all of his 632s with high-quality GRP aluminum rods and made-to-order Diamond pistons wrapped in Total Seal rings.
“For nitrous applications, we build these engines with a 14:1 compression while the naturally aspirated engines run 15:1,” Musi said about the short-block assembly. “Unless you lower the compression, the chances are that you’ll break a steel rod or spin a bearing, which is why we use aluminum.
“We also have people tell us that our motors sound different,” he added. That’s because we’ve done things to be sure they seal better.”
With everything needed for a rock-solid bottom end, the people from Edelbrock Performance and Musi Racing Engines used their collective resources to make this 632 stand apart from the rest. That’s no idle statement, as few in the industry have the research capabilities and practical experience to transform this assembly from a collection of parts to a race-winning powerhouse.
It’s not an engine combination that someone has just assembled. It’s an engine combination that’s been developed and optimized over decades to provide the best overall value for the dollar.
In simplest terms, the goal of any race engine is to get as much air in and out before and after ignition to create the highest possible cylinder pressure. Matching a fuel-delivery system along with an efficient intake; big cylinder heads with optimized ports; large valves; and properly configured combustion chambers are some of the main components that can make that happen.
With that in mind, Musi topped off the short-block assembly with a set of the acclaimed Edelbrock CNC-ported Big Victor 12-degree aluminum cylinder heads that he helped develop. Designed for blocks with the standard 4.840-inch bore center, these heads raise the performance bar when compared to other well-known, but dated designs.
“In working with industry experts, the goal was to address things that have been problems for a lot of years,” Musi said. “For instance, the head uses a rocker bar rather than individual stands. We straightened out some of the valve geometry and fixed some of the sealing problems. On a block that has a standard diameter big-block Chevy cam with the stock height, customers have found these heads will match up with anyone’s flow numbers.”
“People should remember, however, that just like dyno figures, flow numbers can be misleading,” Musi cautioned. “You can always get bigger flow numbers when you use a larger diameter 60mm cam that’s not in the stock location.”
With a thicker deck providing enough material for customization and the CNC-ported combustion chambers, the heads feature optimized intake ports with a raised-runner design that’s computer flow-matched to the Edelbrock Dominator intake. Valvetrain goodies include matched Manley valves, springs, keepers, retainers, and Bullet lifters. A Jesel belt drive is used to keep the custom-ground Bullet cam running in sync with the crankshaft.
The basic engine combos come with a single, 1,600-cfm APD 4500 series billet Enforcer and a Moroso vacuum pump for a strong metering signal. There’s also a Musi Single-Stage Fogger System available with Musi’s nitrous tuneup. Other build options, such as dry-sump oiling systems, sheetmetal intakes, and EFI are also available for each customer’s wants and needs.
“There’s a lot that people can’t see that’s been addressed when we built this engine combination,” Musi said. “One of the things that people like is that we’ve taken what we’ve learned over the years to offer some safe maintenance recommendations. For instance, depending on whether the engine is running nitrous or not, we can tell you that the rods will last 125-175 runs, the lifters last 150, and the valve springs last 300.”
As we said up top, the Edelbrock/Musi Signature Series 632 provides longevity, reliability, and of course, power for everyday racers—without being an everyday, run-of-the-mill assembly-line engine. Better yet, each engine comes with the knowledge and experience that few other engine builders can match.
That’s raising the bar!
Bullet Racing Cams
662 | 893 | 8022
Callies Performance Products
419 | 435 | 2711
248 | 362 | 1188
310 | 781 | 2222
Moroso Performance Products
203 | 453 | 6571
Musi Racing Engines
704 | 664 | 7051
800 | 874 | 2753