LT1 Block and Cams - LT1 Cam-O-Rama

Granted, it was a lot easier back in the day to just yank off the smog stuff and the Quadrabog and pick up some good power. But for those wanting to push that small-block a little faster than the next guy, a cam swap was the next step. The same philosophy holds true today; do all the bolt-ons, watch as your friends blow by you, then jump into the engine.

Though the architecture of the LT1 is based on the Gen I small-block and shares the same basic layout with a goodly portion of the parts interchanging between the Gen I and LT1, or Gen II small-blocks, there were several big changes. The design changes between these are beyond the scope of this article, but the big stuff includes a totally revised reverse-flow cooling design, the distributor moved to the front of the engine, and the camshaft and timing gears changed to allow them to drive the distributor and the water pump. That last little bit put a big hiccup in the hot rodding community as it totally ruled out using any of the myriad cams out there designed for the typical early small-block Chevy.

The Test Subject
Most '93-97 LT-powered cars now have well over 100,000 miles on the clock and as they are being freshened up, a good number of them have bumped the stroke to be reborn as 383s or 396s. A 383 was also the configuration we chose here, as it seemed to represent a growing portion of the crowd.

When GM discontinued the LT4 intake manifold a couple years ago, Edelbrock stepped up to the plate and started making their version. Dubbed the Air-Gap LT4 intake, it features typical LT4-style raised runners and a redesigned plenum. We swiped one of those pretty red pieces and featured it on our engine along with the Edelbrock dual 58mm throttle body. Between that intake and our short-block sat those Edelbrock's LT4 cylinder heads. Sporting beehive springs, 8mm valve stems, and 195cc runners that flow like the dickens, the heads complete a great bolt-on top end.

Our goal with this stroker is to test four different cams ranging from pretty mild, to lopey and wild. We'll start with the Edelbrock LT1 cam as our model since it completes the whole Edelbrock LT package. Moving forward we'll swap in three different COMP Cams sticks, all of them operating COMP Cams Magnum hydraulic roller lifters, pushrods, and roller rocker arms.

Engine management would be controlled through an EMS-Pro ECU available from EFI-Source. An integrated narrow-band as well as an Innovate wide-band O2 sensor would verify tuning decisions. The ECU would also tell the MSD 6AL2 ignition box when to fire the matching MSD billet Optispark distributor.

Dyno Testing
We wanted a good baseline to begin with. We know through past testing that typical 150,000 LT cars make about 225 rear-wheel horsepower through a six-speed, and that corresponds pretty well with their 285 advertised horses at the crank. Assuming the extra cubes we were running would add about 30 horses to the stable, that would set a baseline goal of 315 hp in otherwise stock trim. With a bushel full of cams and a team ready to burn our hands in the name of horsepower, we set out to Shackett Automotive in Nashville to strap our engine to their Superflow 901 dyno.

We started up our little stroker with the complete Edelbrock LT4 system, including the 218/218-at-.050-inch camshaft. The cam is relatively mild mannered and the engine fired up right off the bat with just a lovely hint of lope. A glance at the computer screen revealed the manifold vacuum at idle was a near-stock 28 kPa. After bringing the oil and water temps up, we dropped the hammer on the dyno and were stunned with the results: 430 hp and 461 lb-ft of torque. We were not expecting those kind of numbers. Granted, the Edelbrock heads flowed pretty well, but with the docile cam just bumping along, we didn't expect the combo to pick up over 100 hp from stock! We couldn't wait to bring on the bigger cams.

We popped off the valve covers and the COMP Cams rocker arms and got busy installing cam number two. COMP's 503 cam is one step bigger in duration than the Edelbrock cam. With 224/230 degrees at .050 inch, it would have a slightly more noticeable idle but still work with the stock 24-pound injectors (though pressure was raised to 52 psi from 43) and satisfy those wanting the sleeper effect.

We set the preload on the COMP Cams hydraulic roller lifters to zero, and brought the engine back to life. Again, wow! It pegged over 450 hp without breaking a sweat. This was moving steadily into big-block territory with just a basic bolt-together small-block.

Back into the steaming engine we went and installed cam number three. This was COMP's 467 cam with 230/236 degrees at .050 inch and a solid, lumpy idle. Based off some simple math, we knew we were at the end of what our tired stock 24-pound injectors could handle, so we went on a last-minute scavenger hunt looking for 36-pound injectors. We called a local shop and they said, "Sure, we got those," but when we arrived it turns out they never checked the shelf, so we were SOL. Or so we thought. The counter guy rooted around out back and came back with a set of DEKI 60-pound injectors that were way overkill for the engine, but we had to get it going, as dyno time wasn't free. We fouled a set of plugs before backing off the tune enough to run smoothly, but we were soon back in business.

At this point we shouldn't have been surprised to see the Edelbrock heads and intake support a solid 470 hp and 489 lb-ft of clutch-punishing torque with the third cam. I don't care who worked on dad's old double-hump heads, very few modified old-school small-blocks made this kind of power on a real dyno. And most were not fun to drive.

With cam number four, we jumped straight to the bottom of the page. No use trying to sneak this car past the neighbors late at night. This dude lopes. And let's face it, at this stage you want it good and loud. The COMP 468 cam runs 242/248 at .050 inch and idles at a tooth-rattling 48 kPa.

At this point we had already run through 10 gallons of gas, and we had to make a last-minute run down to the local Kwik-Stop to get another five gallons of junky 10 percent ethanol-infested 93-octane juice. If this 11.5:1 bolt-together engine could survive 50 dyno pulls on this swill, it could live on anything.

Back at the dyno, we fiddled with the fuel curve. She liked to be lean at around 13.5-14:1 AFR. She also liked a little timing. We set the curve to peak at 35 degrees total, and pulled the handle. Six guys huddled in a control room big enough for two, and we jockeyed for the best view of the dyno screen. When the pull peaked and the screen flashed up the numbers we actually cheered: 500.4 hp.

Conclusion
We learned quite a bit from this exercise. First, cam swaps with an LT1 are no more difficult than with an old-school small-block. In fact, they are a little easier as there is no break-in process. Second, with a little extra stroke, Edelbrock's LT4 top-end kit blows away their modest power claims. Third, even with a mondo camshaft, it is entirely possible to use the EMS-Pro to create a totally driveable power-monger. This little stroker took a beating and came back again and again for more. Say what you will about the short-lived Gen II engines, but don't ever say they won't make power.

As soon as we were done wringing the most we could out of the Edelbrock intake, we left the big cam in there and installed what we lovingly call the "bread box" intake. We honestly had no idea how it would fare compared to the beautiful red intake that had performed so well. Not surprisingly, the gurus from the big E knew their stuff as their LT4 intake bested the bread box through almost the entire rpm range ... until 5,900 rpm that is. From there on up, the bread box did as it was designed to do and was able to feed just a little more air to the mill and pick up just a couple of horses. Was it worth it? Maybe, if you plan on using only a high stall converter and revving the wee out of the engine. Otherwise, save a bunch of time and effort and stick with what papa Vic puts out.

The heads use lightweight 8mm valve stems with 2.02/1.57-inch stainless steel valves and beehive springs that according to our spring tester were easily good for more than .600 lift. They have fully CNC-ported combustion chambers as well as CNC-blended intake and exhaust runners. The only issue we had was that the large 195cc runners had a port entry that was larger than either the LT1 or LT4 intake gaskets. This was easily remedied by using a set of Felpro 1206 gaskets, and punching out a new set of boltholes in them. With flow numbers better than the factory LT4 heads and much less scarce, it makes the Edelbrock heads an easy choice.

The Edelbrock LT4 intake manifold is every bit as nice as the heads. It uses an Air-Gap design to cool the runners and plenum and accepts all the factory sensors and bolt-ons as well as a 58mm throttle body without any extra grinding. A super nice red powdercoat mimics the finish of the GM LT4 intake. No port matching was required to mate the Edelbrock intake to their heads. Though they suggest some matching may be required if using this intake on factory heads. Together, the pieces of the Edelbrock top-end kit form a perfectly matched combo clearly capable of massive power.

There are a number of options for triggering the ECU. After lengthy searching, we found a way to run it based off the Optispark pickup, but we wanted something a little simpler. Following the do-it-yourselfer attitude of the Megasquirt world, we rounded up an old Holley hall-effect crank trigger wheel, scavenged a crank sensor from an LS1 engine, and cobbled up a sensor mount. Correctly assuming there would be a learning curve, we got everything together on our run-in stand instead of wasting precious dyno time. The initial setup was fairly straightforward, and the engine fired up without much effort. The problem came whenever we tried to rev it above 3,000 rpm and it would stutter and stumble. After lengthy calls to EFI-Source tech dude Scott Clark-aka "Dieselgeek" on the boards-we went through a couple of different crank triggers and sensors, but it turns out we were just getting noise in the crank trigger wires from having them routed too close to the injectors. A quick rerouting and the engine ran like a dream. Tuning changes were quick and easy, and most didn't require turning off the engine, though I wouldn't suggest that technique in a moving car. For just over a grand, we had a fully optioned ECU with 12x12 resolution tuning tables that worked as good as anything on the market.

The distributor isn't the only place where MSD is moving forward. Recently, they unveiled their 6AL-2 ignition box. Destined to take the place of the venerable 6AL that has been a staple in racing and hot rods for years, the 6AL-2 uses digital technology instead of an analog design. This allowed MSD to put additional features like a built-in two-step and optional hall-effect trigger pickup into a smaller case. More features, less space, what's not to like? As always, they even went through the effort of printing their wiring diagram on the back of the box for those of us who immediately destroy all instructions upon receipt.