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Testing Carb Combos on a Gen III LS Smallblock - Thoroughly Modern Mouse

Richard Holdener Feb 1, 2009
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The LS engines have a lot to offer, including all-aluminum construction (on many), impressive head flow, and even simple cam swaps.

Let's take a quick survey. By a show of hands, who out there is a fan of the small-block Chevy? I see every hand in the house up. OK, maybe that was an easy one. Survey question number two. Who is a big fan of the Gen-III LS1 motors? While most hands remain in the air, there are still a lot of holdouts who prefer the original small-block, and for good reason. It was, after all, the engine that all but revolutionized the industry. Any one out there know how many race winners have been powered by small-block, Chevys over the years? Given their proliferation in all forms of motorsports, it would likely take a lifetime just to gather all the data, but suffice to say it is a lot. Whether the modern motor will ever be able to eclipse the original in this category is irrelevant, but that doesn't mean it should be dismissed, as the LS1 and Gen-IV LS2 and LS3 families have a great deal to offer.

While the original 23-degree small-block has a great deal to offer, just imagine the power offered by a set of 18-degree race heads. Now take that one step further, and you have the 15-degree valve angle offered by the factory LS1/LS2 heads. While the aftermarket is full of performance headgear for the original 23-degree motors, you can literally port your factory LS1 or LS2 heads and have all the flow of some of the very best aftermarket heads for your original small-block.

The gains don't stop with high-flowing aluminum cylinder heads, as modern motors also sport a factory aluminum block. Imagine how cool you'd be running around with an all-aluminum block. These days, all you have to do is yank a modern Mouse from a late-model Camaro sitting in a wrecking yard, and you have that all-aluminum small-block you've always wanted. Now toss in a quick cam change, an ultra-lightweight composite intake, and the ability (in injected form) to knock down over 25 miles per gallon, and you have the makings of a serious powerplant.

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LS6 vs. Lunati Voodoo Cam-6.0L LS1
When we assembled the engine to prepare for dyno testing, all we had available in terms of production camshafts was a factory LS6 cam. While we were hoping to test the mild Lunati Voodoo cam profile against the factory LS1 cam, testing against the more aggressive LS6 cam netted some impressive power gains throughout the rev range. With 0.531 lift and a 212/218 duration split, the mild (but powerful) Lunati Voodoo grind offered as much as 15 hp and 22 lb-ft. of torque. Previous testing against a stock LS1 cam (on a mild 5.7L LS1) showed as much as 31 hp.

What's that you say, you don't want to trade your simple and reliable carburetor for the complexities of fuel injection? No problem, as the aftermarket has come to the rescue in the form of not only carbureted intakes for the modern fuelie motors, but also the necessary electronics that provide a simple solution to the ignition dilemma. In fact, the ignition conversion on the Gen-III motor is arguably easier to install and program than a conventional distributor. Leave it to MSD and Edelbrock to provide a direct plug-n-play system to allow the use of a carbureted intake on the LS1.

Using the Edelbrock/MSD Timing Control Module, we were able to run one of five different ignition curves, though they now offer a completely programmable system to allow the user to dial in the desired ignition timing at all map points. What we liked most about the system was its ease of installation, as the Timing Control Module came with a wiring harness that plugged directly into the factory LS1 coil packs, cam, and crank position sensors. This plug-and-play system is actually easier than the weights and springs associated with recurving a conventional distributor.

Having a carbureted Gen-III engine is reason enough for many enthusiasts to celebrate, but we here at Super Chevy would never stop at a simple carbureted conversion. Since we planned on having our thoroughly modern Mouse on the dyno, we decided to run a few tests on the carbureted beast. Before getting to the testing, one thoroughly modern test motor was in order.

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Single vs. Dual Plane-6.0L LS1
Since we ran the 6.0L LS1 in carbureted form, we decided to run the time-honored test of single vs. dual-plane intakes. In the single-plane corner was the GMPP intake, while Edelbrock supplied a Performer RPM dual-plane intake. As we have come to expect, the single-plane intake made the most peak power, but the dual-plane produced exceptional torque. Down at 3,200 rpm, the dual-plane intake offered an extra 44 lbs-ft of torque. The single-plane took over from 4,800 rpm on up, bettering the dual-plane by 10- to 12-hp. The decision comes down to where you want your power. For most street applications, the extra 44 lbs-ft will be much more beneficial than the extra 10-12 hp at the top of the rev range. For those looking to maximize power production, the single-plane puts up the big peak number.

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NA vs. NOS Plate (150-hp)-6.0L LS1
Of course there is no denying the power potential of a good nitrous system. Case in point, the simple NOS plate system installed on this 6.0L LS. With the push of a button, our humble street motor was transformed into a serious strip terror. Adding an extra 150 horsepower required only that we keep the bottle pressure constant (with a bottle warmer) and retard the timing by 4 degrees. We took the liberty of adding a bottle of Lucas Oil octane booster to the 91-octane pump gas (from Rockett Brand) as a hedge against detonation. We figured the 150 hp shot deserved no less. As if the extra 150 horsepower wasn't exciting enough, just wait till you feel the extra 170 lbs- ft. of torque!

While we had both LS1 and LS2 crate motors at our disposal, we decided to build one instead. Since we planned on running some juice to it, we decided forged internals were in order. A call to Lunati netted a steel crank (3.662 stroke) along with the necessary forged rods and pistons designed to fit into our 6.0L truck block. I know what you are thinking, where is all that wonderful weight savings we were raving about earlier? Truth be told, we have big plans for this particular mill, but the same components (or even factory equivalents) could be used at this power level, including the factory 5.7L LS1 or even 6.0L LS2 aluminum blocks. While the 6.0L block shared the 3.662-inch stroke with the smaller 5.7L, the additional displacement came from the larger bore offered in the 6.0L. With the Lunati internals stuffed inside our freshly machined 6.0L block, our short-block was ready for action.

Next up were the cam, heads, and intake. Originally, we wanted to start our testing with a factory LS1, but all we had at our disposal was an LS6 grind. Compared to the stock LS1 cam, the high-performance LS6 grind offered both more lift (0.525 versus 0.500) and duration (204/218 versus 198/209). The reason we wanted to start with the factory cam was that we had a mild Lunati Voodoo cam waiting in the wings. The Lunati Voodoo cam offered 0.531 lift (on both the intake and exhaust) along with a 212/218 duration split. Note that the Lunati specs were only slightly wilder than the factory LS6 cam, but the Voodoo grind offered accelerated ramp rates to further improve power production. Once on the dyno, we planned a direct cam comparison.

With the factory LS6 cam in place, we installed a set of AFR 205 Mongoose heads. The AFR heads featured full CNC porting to enhance flow. Designed for performance street use, these AFR 205s flowed nearly 300 cfm. The AFR heads were topped off with a single-plane intake from GM Performance Parts and a 750 HP carburetor from Holley. Finishing touches on the 6.0L motor included a set of Hooker long-tube (F-body) headers feeding a set of collector extensions and a Meziere electric water pump.


Chevrolet Performance Parts
Detroit, MI 48232



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