All-Billet 903 cid Pro Mod Engine - Engine Builder Magazine

All-Billet 903 cid Pro Mod Engine

Pat Musi of Musi Racing Engines has been meticulously developing and tweaking his 903 cid Pro Mod engine combo since 2010. We got to see the latest and greatest version of this nitrous-powered billet beauty. Check out our first Engine of the Week of 2024!

Engine of the Week is presented by

In 2023, we got the chance to showcase a bunch of cool engine content from our visit to Musi Racing Engines, and 2024 kicks off much the same, with one more engine from the mind of Pat Musi. Pat’s 959 cid Pro Mod big block Chevy engine platform has become a staple for the Mooresville, NC shop and many of its drag racing customers. However, this all-billet 903 cid version of that engine showcases a few little nuances as it’s for a customer in Sweden. The engine was getting ready for assembly while we were in Mooresville, and Pat walked us through the full build.

Pat Musi Pro Mod billet block from CN
Pat Musi Pro Mod billet block from CN. This one is 903 cid.

“These engines used to be 865 cubic inches, and I was the first to do a 903 cubic inch version,” Musi says. “We’ve been developing this motor since 2010. We have a lot of customers who run this engine, and the engine has come a long way. It’s always got my little tweaks and changes because I’m never happy. I’m always tweaking something. This is the latest and greatest, and this one is actually going to Sweden.

“Our bread and butter is our 959 because all the rules are for 959, but in Sweden, they have to run 903, so we’re building him a 903. It’s still the basic foundation of a 959 – billet block and billet heads, etc.”

Pat Musi CN billet block
The block features specific specs from Pat Musi.

On this 903 cid Pro Mod build, Musi is utilizing a billet block from CN Blocks in Texas, and the heads are from Dart, which are spec’d only for Musi Racing Engines. The only way to get these heads is on a Musi-built Pro Mod engine.

“These engines are all done to my specs,” Musi says. “The cam tunnel is my spec. We have our spec bearing and our spec cam. People try to copy my stuff all the time, but we’re always ahead of them. By the time they copied it, we’re onto something new, so we kind of laugh about it. We’re always thinking out of the box. That’s what I’ve done my whole career. We’re always in a development stage. It’s the way to stay ahead.”

billet Musi/Dart cylinder head
This billet head from Dart can only be had on a Musi-built engine.

Aside from the billet block and billet heads on this 903 cid engine, Musi ensures the rest of the components are of the highest quality as well. Despite the supply chain forcing shops like Pat’s to get engine parts from various sources, Pat has maintained a number of long-time component suppliers. In this engine, Pat utilized a tool steel camshaft, GRP rods, a Sonny Bryant crankshaft, Jesel valvetrain and a Jesel belt drive, PSI springs, Victory valves, a Musi-built intake manifold, and a Kinsler throttle body, which is finished in-house.

“The good thing about buying an engine from us is everything is on the shelf,” he says. “If you need a valve or you need a block – we have it. We have rods, we have pistons, we have all the components here – injectors, nitrous parts, throttle bodies, even complete engines. There’s nothing for this engine we can’t have to the racer pretty fast.

903 cid Pro Mod big block Chevy engine

“Our inventory has probably gone up 300% since Covid. Unfortunately, it takes a lot of capital, but thank God we’re in a good place now and we are able to keep up with it. It’s a challenge having the parts.

“Another thing about us is we have 150 of these engines in circulation around the world. I never thought it would come to that. When we did the [Dart] billet head, me and [Richard] Maskin did that head at PRI about six years ago. He asked how many sets I was thinking. I was scared to death. We’re talking $25,000 for a set of heads. I told Richard let’s do six and see how it goes. Well, I think we sold 12 sets at the show. From there, I think we’re up to serial number 154 or something. It’s crazy – who would’ve thought?”

Musi intake manifold

Lastly, this wouldn’t be a Pat Musi-built drag race engine without copious amounts of nitrous. This particular 903 engine has six stages on it.

“We run nitrous depending on the customer’s brand of choice, but we use all of them,” he says. “We used to do our own nitrous, but now we rely on Switzer Dynamics or Speedtech and it’s really up to the customer. If they leave it to me, then we’ll pick something out.”

This all-billet 903 cid Pro Mod engine is capable of 1,800 horsepower NA. With the nitrous cranked up, Pat says the engine is in the neighborhood of 3,200 horsepower!

Engine of the Week is sponsored by PennGrade1Elring – Das Original and NPW Companies. If you have an engine you’d like to highlight in this series, please email Engine Builder Editor Greg Jones at [email protected].

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