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Toilet Training

Whoops! Carburetor and Distributor Make Big LS1 Power

Jun 29, 2005

Despite the overwhelming influx of EFI, the carburetor (sometimes referred to as the "toilet") stands as the preferred choice. Hot rodders are known as a resourceful lot and the prevailing mothers of invention, but in this case, the high-performance arm of the very people who developed the EFI system for the LS1 engine are the curious, can't-leave-it-stock neurotics.

Lucky for us, the gearheads at GM Performance Parts seem to have beaten the aftermarket at its own game. Edelbrock, who made its name on the intake manifold, is the only supplier to date who has stepped forward with a carburetor conversion for the LS1 ("Sand Paper," page 66).

Now that the new millennium small-block is an accepted form of re-powering, and with the new 6.0L LS2 as well as the 505hp LS7 being offered as crate motors, the carbureted iteration will undoubtedly be lowered into more engine compartments than you can shake a camshaft at. No electronics or computer to worry about--just hook up the loud pedal linkage, tweak the distributor, and blast into the ozone. Racers (e.g., NHRA, IMCA, USAC) who are bound by rules that forbid computer controls now have a compact, vibrant, and robust alternative to the traditional small-block.

In anticipation of this prospect, Ed Taylor outfitted a stock displacement (346ci) LS1 crate engine with a livelier camshaft and CNC cylinder heads, and applied the GMPP intake manifold and a Holley HP 750-cfm carburetor. The mechanical fuel pump and aftermarket distributor were driven off an eccentric and a gear on the camshaft, respectively (see image). Further, the headers fitted to the test rocket were Kooks with 1 7/8-inch primary pipes dumping into Flowmaster 2 1/2-inch Super 40 muffs. The camshaft is Crane Cams piece (PN 144HR00061) featuring 222/234 degrees of duration at 0.050 inch, a 0.551-inch lift on both valves, and 112 degree centerline.

As we have witnessed with our own crate demon, the LS1-engine family offers excellent power production in a lightweight package (395 pounds with accessories and cast-iron exhaust manifolds). And moxie? Boy, does it flat ooze durability. Taylor's whipping dog has about 700 pulls on it (1,400- to 6,500-rpm range), 130 of 'em under a Magnuson blower making nearly 600 hp and still not a wisp of blow-by.

With the nylon OE intake manifold, a GM Hot Cam, and CNC cylinder heads this engine produced 492.9 hp at 6,200 rpm and 459.7 lb-ft of torque at 4,900 rpm. The numbers from the carburetor combo impressed even the GM engineer who designed the Gen-3 heads, as they were never meant for full wet flow. In EFI form, the fuel sprays down on the cathedral roof of the port and toward the intake valve. Let's take a peek over Taylor's shoulder as he turns the screws at Kenny Duttweiler's dynamometer and see how well the Fred Flintstone Conversion faired against the infinitely adjustable medium of electronic fuel injection.


Taylor began with a GMPP LS1 crate motor that had been used as a mule for parts evaluation for GM and several aftermarket manufacturers.

First, he removed the stock intake manifold, fuel system, coil packs, and wiring.

Next, Ed removed the stock accessory drive, harmonic damper, front cover, oil pan, and oil-pump pickup. The pickup is bolted to the oil pump, and there is no way to slide the oil pump off the end of the crank until the pan and pickup are (temporarily) removed.

He unbolted the oil pump and carefully set it aside.

After removing the timing chain and the top portion of the timing gear, Taylor used this bitchin' Craftsman captive puller to take the lower timing gear from the crank snout.

Since a keyway slot for the damper/bottom pulley is not designed into the Gen-3 small-block crankshaft, Taylor drilled and pinned the snout to locate the new ATI damper (with the now-necessary timing marks). He did this by installing the drill fixture supplied by ATI that locates off the keyway on the bottom timing gear.

He drilled the crank snout with the bit and locator bushing supplied with the tool; then he changed bushings and used a reamer to set the final fit of the locator pin. You must install the bottom timing gear and the oil pump before you can install the pin.

Since Ed upgraded the timing chain to a double-roller set, it was necessary to space the oil pump forward about 1/16 inch for clearance, as facilitated by these spacers supplied in the timing-chain kit.

Taylor aligned the oil pump by sliding two 0.002-inch feeler gauges between the crankshaft and the pump drive. Once the pump is aligned, tighten it down. Then be sure to check the clearance again.

Once the timing chain and gears were in place, he installed the first half of the distributor/fuel pump drive spud and torqued the three mounting bolts to 25 lb-ft.

The second half of the drive spud went on next, was torqued to 40 lb-ft...

...and followed by the locating dowel pin.

Ed hid the works with the new front timing cover. Note that one of the top bolts must be changed to a flat-head fastener to accommodate fuel pump clearance.

Using the locator pin, he installed the ATI damper. Taylor secured the damper with a new (reusable) ARP bolt (PN 234-2503), and torqued it to 250 lb-ft.

To fit this application, Stewart custom-made this standard-rotation water pump for the GMPP kit.

Since there is no longer electronic provision for the stock knock sensors, the OE lifter valley cover must be removed.

The replacement cover features a K&N breather stack and breather.

Fel-Pro gaskets (PN 1312-3) replace the stock GM O-rings that seal the intake manifold to the heads.

Ed then affixed the GMPP intake manifold (PN 88958675 ) with ARP 6x50mm bolts and torqued them in sequence. The carburetor is a Holley 750 Street HP (PN 82751). Taylor made the best numbers with #72 primary and #82 secondary jets.

A Performance Distributors (DUI) big cap HEI unit (PN 31820) was fitted with a small-block Ford drive. Ed had Performance Distributors tailor a short timing advance curve limited to 15 degrees of mechanical advance. With the carb/distributor combo, the LS1 does not like any more than 29 degrees of total timing (whereas EFI trim tolerates 25 degrees total).

The front pulleys and bottom drive adapter are also part of the kit.


Performance Distributors
Memphis, TN 38132
ATI Performance Products
Baltimore, MD 21207
Chevrolet Performance Parts
Detroit, MI 48232
Duttweiler Performance
Saticoy, CA 93004
Kook's Custom Headers
North Bayshore, NY 11706

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