For those of us old enough to remember '80s Reaganomics and learning about new math in school (what was the point of base 8 numbering anyhow?), our idea of tricking out a car used to be adding a set of Cherry Bombs and a Holley 750 double-pumper to the requisite '79 Camaro and promptly destroying a set of T/A Radials. A day or two has passed, and the LT1 F-bodies littering the Auto Trader have become the '79 Camaros of today. They're cheap, you can sort of work on them, and they still do great burnouts.
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 calm before the storm....
The calm before the storm. After setting up the 377ci LT1 test mule engine on the dyno, we gave it a good night's rest before spending two solid days burning our hands on hot oil and headers, cursing our mistakes, and finally cheering with glee.
When they came out, the LT1 engines (LT1, LT4, and L99) had few choices for aftermarket cams, and if a custom cam was built, then who could figure out how to tune the thing? Fortunately in the last several years, the aftermarket has expanded its cam offerings and the availability of tuning software has made it cheap and easy to bump the power of these engines just like we would've back in the day. So what's the problem? Well, everyone talks about this cam or that, but nobody has really buckled down to see what's what on a dyno. We wanted to change that.
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.
Teardown between rounds of...
Teardown between rounds of camshaft testing started with removing the front parts of the LT1 engine. We removed the MSD distributor cap to verify that the rotor was located correctly on the camshaft dowel pin upon reassembly, though most reasonably competent workers can line it up without removing the cap. We got it wrong twice so we took no chances.
We started with a core from a typical 150,000-mile car, and thanks to low-tension rings and the glory of fuel injection, it had basically zero wear on the cylinder walls, so we torque-plate honed it at Revolutionary Performance and Machine in Mt. Juliet, Tennessee, and kept it at standard bore (actually making our engine 377 ci). We internally balanced an Eagle cast-steel crankshaft and matching SIR 5.850-inch connecting rods, as they are great for street/strip use and come at a reasonable price. Wiseco forged pistons with thermal barrier coatings were used as insurance against any poor tuning decisions. Mahle/Clevite bearings and ARP main studs were a given for the engine as we didn't want any surprises in the bottom end. Naturally, we would use pump gas for the final tests. I will admit we were a little nervous, as the compression was on the high end of the spectrum at 11.5:1. Early cast-iron-headed small-blocks couldn't handle that but the reverse-flow cooling and advanced combustion chamber design of the Edelbrock Xtreme LT4 heads we chose led us to believe we could pull it off without any problems.
COMP Cams was our choice for...
COMP Cams was our choice for valvetrain parts for the LT1 stroker. We set preload on the Magnum hydraulic roller lifters to zero, and just moved the poly lock an extra eighth of a turn to snug it in place. Throughout the sessions, we saw no signs of valve float, even as rpm crested 6,600.
Out with the old, in with...
Out with the old, in with the new. Once the Edelbrock 2108 cam showed off its stuff, we couldn't wait to throw the bigger cams in there. We noticed that the Edelbrock cam was "back-halved," meaning it used steel billet as a core, but with a softer oil pump drive gear sandwiched onto the rear, whereas the COMP cams were all iron billets. Both designs were perfectly compatible with the factory oil pump drive gear mounted in the block. Two roads to the same destination.
Tuning with EMS-Pro was as...
Tuning with EMS-Pro was as simple as moving the red "X" to the spot you want to change-both timing and fuel parameters are adjusted this way. The green dot indicates where the engine is currently. In this case, we just swapped in the big boy cam and were trying to get it to idle down.
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.
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.
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.
The CNC-machined combustion...
The CNC-machined combustion chambers on the Edelbrock heads show an efficient design that when matched with the LT engine's reverse-flow cooling, showed no signs of knock, even with 11.5:1 compression.
We slapped the Edelbrock heads...
We slapped the Edelbrock heads on our Superflow SF-600 flow bench and were pleased to see them flowing 250 cfm on the intake, and 187 cfm on the exhaust at .600 lift; they outperformed the famous factory GM LT4 heads.
Beehive valvesprings come...
Beehive valvesprings come standard on the Edelbrock LT4 Extreme heads, and tested out at 125 pounds on the seat; the installed height on every valve was dead nuts on. Viton valve seals are also used instead of cheap rubber to keep from breaking down under extreme heat.