LT1 Engine Build - Late-Model 383 Buildup The Finale

Here George Vrbancic adjusts the throttle cable from the dyno to the Arizona Speed & Marine billet throttle body. Since most of the dyno tests that the Vrbancics do are with carburetors rather than fuel injection, a few adjustments were necessary in order to make sure that the throttle blades opened all the way.

Here George Vrbancic adjusts the throttle cable from the dyno to the Arizona Speed & Marin

In the previous three parts to this story, we've focused on making sure the sum of all of the trick parts added up to one cool late-model stroker engine. While we're sure that all of the trick parts went together flawlessly, there's only one thing that really matters, and that's how she does on the dyno.

Making The Numbers!
Making an electronic, fuel-injected small-block spin the dyno needles into the upper horsepower and torque stratosphere is no small feat, to say the least. To do so required the special talents of both man and machine. To manage the 383's fuel and spark delivery, we employed the aforementioned C-Com engine computer. To manage the C-Com, we got help from one of the country's premier electronic tuners, Craig Railsback of BDS Blowers. Craig joined us with his laptop PC for two sessions and had our modern LT1 running virtually right on target with little effort.

Our goal on the dyno was to learn three things: How much power and torque will the engine make normally aspirated on pump gas; how much with the D-1 Procharger on 92 octane; and, for bragging rights, how much power we can make with the D-1 on racing fuel.

After meeting all three parameters, the first conclusion we made was that this combination of parts was perfect for a street engine. Despite the high-flow cylinder heads, our 383 stroker did not make any additional power after 6,000 rpm (probably due to the limited flow capacity of the stock-style LT1 intake). Essentially, on all three trials, the mighty mouse was screaming that its power was done at six-grand! But, as a tribute to how well matched this combination was, the power and torque curves were excellent, with peak numbers in all tests within a couple of hundred rpm of one another. And, with boost, the torque came on immediately and never fell off, all the way to redline.

So, you're probably wondering at this point what those magic numbers are. What was our goal originally? First, it was to make 700 ponies on good gas. Second, we wanted enough torque to get our not-so-lightweight '96 Camaro convertible up and running-in a hurry. With 110-octane racing fuel, our 383 hit unbelievable numbers of 735 horsepower and 693 foot-pounds of torque! And as far as those numbers being in a usable rpm range, power peaked at 5,600 rpm, while the top torque mark wasn't too far behind at 5,500 rpm. The torque curve was more like a table top on the graph, though, as the engine made more than 500 foot-pounds at 3,000 rpm and never dropped below 680 through shutoff.

The D-1 Procharger requires a special-built bracket arrangement to fit in the snug confines of a late-model F-body's engine bay. Despite its custom look, this setup was first-class. Note also the MSD large-diameter plug wires coming from the LT1's factory Optispark ignition.

The D-1 Procharger requires a special-built bracket arrangement to fit in the snug confine

We know what you're thinking at this point. With high-octane fuel, we got aggressive with the ignition timing. Not so! In fact, the timing was ultra conservative, according to Craig, at around 36 degrees, while maximum boost was just a hair over 10 psi. Everything worked perfectly during this session, which led us to come back and run the engine on pump gas both off boost and with the blower belt on.

With Unocal 92-octane premium unleaded being pushed through the Aeromotive Systems electric pump at a maximum of 65 psi, we ran a baseline test of the engine without running the blower, just to see how stout this 383 was. Now, considering that the compression of this engine was down to around 9.4:1 to allow for the additional boost, and add in the fact that the 72-pound injectors were designed more for a supercharged application, we weren't sure just what kind of numbers to expect. What we got was a pretty stout non-blown engine, with a maximum of 422 horses (5,600 rpm) and 420 ft-lbs of torque (5,000 rpm). This was with 42 degrees of total timing and a running temperature of 212 degrees F.

Doing the math at this stage tells us that we gained a whopping 313 horsepower and 273 foot-pounds of torque with good gas and 10 pounds of boost! Simply incredible.