Ford Mustang DSS Competition Engine Swap - Project ProCharged Pony - 331 Ways To Waste An LS1

In the last six months, our Midnight Blue Metallic Mustang project car has logged a mere 145 miles. Winter and travel have prevented further accruement, so there is some anticipation of getting the pony up and running. It's been too long since we last rumbled down the road, offering 3,500 rpm worth of Team Bassani to the nearest contender.

That's all about to change as we've successfully swapped in our DSS Competition Engines 331ci stroker short-block with help from Crazy Horse Racing in South Amboy, New Jersey.

Why did we pick a 331-inch motor over many of the other popular stroker kits you may ask? We posed the same question to Tom Naegele of DSS and here's what he had to say:

"Our 331 offers the best combination of rod ratio, piston design and ring package for the given 8.2-inch deck height engine. Some people don't consider the frictional losses, poor ring seal and compromised piston design that the larger strokers create. You can fix the problems associated with bigger strokers by using a taller 8.7-inch deck FRRP block, but that incurs more cost. A 331 is almost 40 hp better at 6,000 rpm than a 347. With the 331, we use a 5.315-inch rod, which allows for better ring placement on the piston and proper space between the top and second ring.

"The 347 is good for heavier cars where extra low-end torque is needed. Early on, many builders were using (and some still use) the wrong piston ring packages. This gave this combination a bad reputation for consuming oil. In some extreme cases, the poor rod ratio can even collapse cylinder walls as it side loads the piston in the cylinder really hard. But a 347 is good for 15-20 ft-lb more torque at 3,000 rpm.

"The 327ci stroker is a 331 with a standard bore. It's not a good choice for big-valve cylinder heads due to valve shrouding. The .030-inch overbore of the 331 unshrouds the valves and the machined block offers torque plate honing that a stock block wouldn't normally have. Both of these attributes are worth up to 40 hp. It's really a non-engine builder's combo as anyone with a toolbox can put one together. But you leave a lot of power on the table.

"The 318/320 was an economical combination we used to build before when modern strokers were still very expensive, but they're kind of obsolete now. When you get into the 355, bigger is not always better. Rod ratio, piston design and ring seal are traded for extra cubic inches. Some builders don't think about what they are giving up to obtain those cubic inches-usually around 40 to 50 hp and some reliability. This kit is not very popular anymore."

With that said, the 331-cubic-inch stroker package made sense to us since we would be using a stock-block. DSS has made great strides in getting the factory iron to survive under three times the stock power output, but it has its limit like anything else.

Tom Naegele and Jimmy LaRocca of LaRocca's Performance (Old Bridge Township, New Jersey) both agreed that 520 rwhp (600 flywheel) is about the limit if you want the engine to last. Our 331 is certainly capable of making much more power simply by turning up the boost or changing the cam and intake manifold to a more supercharged-specific application. However, we intend to keep our pony completely streetable and have no intention (at this time) of installing a rollbar, so we don't see the need to push the envelope. And 500 lb-ft of torque is a lot of power to put down to the asphalt and a task not easily accomplished. With a clear vision of what we wanted to do, we set about swapping in the new engine.

We were still using the stock camshaft in the old engine because of piston-to-valve clearance, but with the DSS pistons we were able to sling in a performance bumpstick. We chose the Comp Cams XE274HR hydraulic roller, which features an advertised duration of 274 degrees intake, 282 degrees exhaust, and duration at .050 is 224 degrees intake, 232 degrees exhaust. Gross valve lift is .555-inch intake/.565-inch exhaust and the lobe separation is 112 degrees.

It's designed for an rpm range of 2,200-6,200 rpm and it is the same cam that Richard Holdener used in his "Ultimate Guide to Cylinder Heads" article (November 2003). His combination was a 10.25:1 compression 331 and our Brodix ST 5.0R heads came directly from the engine dyno test. With a carburetor, the combination made 434 hp and 437 lb-ft of torque.

It's not necessarily the best blower camshaft, but we went with Holdener's theory that the best supercharged engines are maximized in naturally aspirated form. This allows you to use less boost to attain the same or better performance. Plus Richard has run the same camshaft in his street car for quite a bit of time and was happy with its drivability and performance. That meant a lot to us since ours is primarily a street car.

When you get to this power level, you'll find that there are a lot of ancillary items that need to be replaced with better pieces. Even at stock power levels, the factory engine mounts are easily taxed and if your ride is a high-miler like ours, chances are they're completely shot. We called up Holcomb Motorsports in Lumberton, North Carolina, to get a set of Energy Suspension polyurethane mounts. We wanted them to be strong, but we didn't want to resort to a solid mount.

Holcomb also provided us with a new harmonic balancer/dampener. The Engine Works piece is made by Romac and is SFI approved. Our stock balancer was still holding together, but with the considerable investment in the short-block, we didn't want to skimp here.

Another item that we decided to upgrade was the bellhousing. Holcomb shipped us a Lakewood blowproof steel housing that is also SFI approved. It's a little overkill for our "street car," but you can't powershift without your ankles.

Of course, gaskets, a new oil pump, paint for detailing the engine, oil and filter and coolant are all necessary to complete the build. Crazy Horse Racing in South Amboy, New Jersey, handled the engine assembly and installation and had the Mustang up and running in no time.

While Crazy Horse is fully capable of tuning our pony, LaRocca's Performance has been tuning our ProCharged pony since day one, and therefore we already had baseline horsepower and torque numbers from the Dynojet there. That being the case, we headed back to have LaRocca check the tuneup prior to making some dyno pulls.

LaRocca recommended that we step up in injector size from 42 lb-hr to 50 lb-hr. MSD provided us with a set of its competition 50 lb-hr injectors that we complemented with a 3.5-inch Pro-M Univer mass-air meter. The Univer was designed with the ProCharger's blow-through nature in mind and can be calibrated to your particular injector size when ordered. The computer, mass-air meter and injectors all work in concert to provide the engine with the appropriate amounts of air and fuel, so it is essential that they all know each other.

With the new injectors and meter, we found that the computer had a hard time opening the injectors properly to provide the desired idle. Whereas the '94-up tuning software allows us to adjust the injector's minimum pulse width, the '93-earlier software does not offer that option. To remedy this, we reinstalled the 42 lb-hr injectors and compensated with added fuel pressure (50 psi instead of 43 psi).

LaRocca was indeed right about us needing bigger injectors as the 42s begin to max out around 6,000 rpm. The steady 11:1 air/fuel ratio begins to head north towards 12:1 by that time, but it is still in the safe zone.

With the air/fuel ratio to his liking, LaRocca began tuning for power. At 10 psi of boost, our previous peak dyno figures came in at 473 hp at 5,500 rpm and 474 lb-ft of torque at 4,700rpm. This was with 4 degrees of timing retard and the same 11:1 air/fuel ratio. With zero retard and the same boost, the Mustang laid down 512 hp at 5,800 rpm and 500 lb-ft of torque at 4,700 rpm. In a 3,100-pound car with a good suspension, that's 9-second power folks.

As we mentioned before, this combination is easily capable making another 80-100 hp with a little more boost and maybe a different camshaft. But, we're fairly certain we've got enough to take care of those LS1 Corvettes, Camaros and Firebirds, not to mention most everything else on the road. We even came across a Maserati on the way home. He thought he was a contender, but half throttle in second gear was enough to put a few car lengths between us in a matter of seconds. LS1s? Forget about it. Let's find some turbo 911s.