Tech: Carbureted LS Engines – Ignition and Induction
Why? Why would you want to install a carburetor on an LS engine rather than use EFI? That is a question that is frequently asked on many of the message boards and forums that support the GM LS based engines. Contrary to what some might lead you to believe, let us assure you, there’s no increased risk in killing your motor if you run a carb over a fuel injected system. The reasons why a carb on an LS makes sense are pretty simple. In LS swaps or street/strip/race cars a carbureted LS is simple, cheaper, and often can make more top-end power than EFI.
In this tech article, we are going to show you how to install an LSX ignition specifically for carbureted engines with help from our friends at MSD Ignition.
MSD ignition has earned it’s reputation as a leader in ignition technology while at the same time keeping their product packaging looking very similar throughout the years. The ‘if it’s not broke, don’t fix it’ attitude is a big plus to performance car people, and the MSD ignition boxes are easily identifiable by sight and let people know that you are serious about speed.
MSD 6LS Ignition Controller
The MSD 6LS allows the user to map a timing advance curve, program the two step rev limiter or vacuum advance curve for your needs. There’s even a step retard in case you want to run a little nitrous in the mix. -Todd Ryden
MSD Ignition has come up with the perfect solution for guys like us that want to push the LS engine’s power curve to the max with the added benefit of no wiring headaches. We talked to MSD’s Todd Ryden about their cool ignition controller for LS engines, the 6LS, “For guys that want the advantages of GM’s aluminum small blocks without worrying about miles of wiring with typical EFI systems, our 6LS ignition controller allows them to mount a carburetor on the LS1/LS6 engines or the 6LS-2 on the LS2/LS7 engines. These controllers allow the user to map a timing advance curve, program the two step rev limiter or vacuum advance curve for your needs. There’s even a step retard in case you want to run a little nitrous in the mix.”
The MSD 6LS is a dream for guys that don’t care for wiring or want a clean retro looking engine bay with modern LS muscle. Requiring only connections for the coils, crank sensor, MAP sensor and the camshaft sensor, this ignition system is a simple way to go old school with natural aspiration.
- Runs a carbureted LS engine without complicated EFI hardware
- Map a timing curve using Pro-Data+ software
- Programmable two-step rev limiter, vacuum advance curve and step retard
- Direct plug-in to factory components
- Programmable via a PC through MSD’s Pro-Data+ software
Setting Timing and RPM Limits with the 6LS
MSD’s 6LS controller is programmable by means of simple plug-in modules, an optional hand held programmer, a laptop computer; giving the user a variety of ways to adjust RPM and timing. Using a laptop computer for adjustments may be intimidating to some racers, where as simply plugging in an MSD module or using the handheld controller may be a bit easier. The versatility of this ignition controller makes it a another big plus for car builders wanting to convert their LS EFI to distributorless carb-based system.
MSD Pro-Data+ Software
For those looking for maximum control over the timing and rev limits of the 6LS, MSD has the Windows based Pro-Data+ software. With Pro-Data+ you can plot timing curves based off of both RPM and Manifold Absolute Pressure (MAP) for vacuum or boost. You simply right click, add a plot, and drag it to the point on the table you want it to be, and you’re well on your way to creating your own completely custom timing curve. You can also set your desired maximum and minimum timing limits through out the curve by using the Data Editor Menu as safety precautions.
Step Retard For Nitrous Applications
The 6LS also has a built in step retard (Sw Retard) that can help you dial back your timing at a specific RPM point, making it ideal for cars running nitrous. The step retard is activated by introducing the pink wire in the 6LS’s wiring harness to 12v, and the amount of retard can be adjusted from zero to 15 degrees of timing in 1 degree increments through the Pro-Data+ software.
Built-In 2-Step Rev Limiter
Another great feature of the 6LS is that it has a built in 2-step rev limiter. The “RevLo” setting is for limiting your launch RPM on the starting line at the drag strip, while the “RevHi” setting is your maximum RPM safety net. Setting up the 6LS’s rev limiters is a snap; all you have to do is hook up the blue wire from the wiring harness to a 12v power source and wire in a button or switch. When ever the blue wire is receiving 12v, the RevLo setting will be activated. Let your finger off the button when you launch, cut power to the wire, and the RevHi setting will take it from there. Of course, the exact values for both rev limits can be set in the Dat-Pro+ software or the hand held programer.
Delivering The Spark: MSD Coil Packs and Plug Wires
MSD also makes two versions of stock-replacement coil packs for performance LS builds that compliment the 6LS controller. MSD’s Multiple Spark Coils (MSC) are direct replacements for the stock LS1/LS6 coils (Part #: 8245) or the newer style LS2/LS7 coils (Part #:8247). Both versions of the MSC coils are capable of producing 44,000 volts of spark energy in addition to their muliti-spark capabilities. Ryden explained to us that the, “MSC coils have a higher spark energy and voltage plus they are designed to work with MSD ignition controller’s multi spark capabilities. All this translates into an improved combustion process in the engine’s combustion chamber that you will feel in throttle response and a smoother idle along with better high RPM performance.”
MSD recommends using their Super Conductor 8.5 spark plug wire set (Part # 32813, 32819, 32823 or 32829) to take full advantage of the spark energy from the coils to the spark plugs. The spark plugs can only use the energy transferred by the plug wires, so if the plug wires don’t transfer all the energy created by the coils, you’re losing potential energy and more complete fuel combustion.
Moroso Remote Coil Mount Brackets
So you’ve got the old-school look of the carb and intake manifold going in your hot-rod, but coil packs on the valve covers keep giving you away that your engine is something more modern. Relocating the coils isn’t just about looks either – moving them away from the heat radiating off the engine could greatly increase the coils working life span.Well, Moroso has a creative answer to relocating the coils off the valve covers with their Remote Mount Coil Brackets (Part # 72395). These stainless steel brackets are meant to prevent cross-firing from one coil to another, and can accommodate both OEM and aftermarket coils.
Intake and Carburetor
A look at Edelbrock’s LS Carb Manifolds…
- Dual Plane for Broad RPM Curve
- Cathedral Port LS1/LS2/LS6
- Great for Street Use
- Single Plane for Up to 600 HP
- Available for Carb or EFI
- Up to 7,500 RPM Capable
- Single Plane Competition
- Serious Racing Potential – 8,000 RPM
- LS1/LS2 Cathedral Port
- Perfect for LS3 and L92 conversions
- Works great up 7,500 RPM
- Single Plane Street/Strip – Excellent for large CI engines
RPM Air-Gap Dual-Quad LS1: (Part #75187)
- Dual Carb LS Intake for Twin Carbs!
- Cathedral Port LS1/LS2/LS6
- Show Car Look!
For our engine, we actually chose the Edelbrock Super Victor LS1 #28095 EFI intake. Even though we were using a carb, we liked the idea of being able to switch to EFI down the road. With the Edelbrock intake, we simply made plugs that blocked off the injector bungs. That’s really the only difference. The Super Victor LS1 is a serious high-RPM intake perfect for 600 HP and up engines that are either large displacement or rev up to 8,000 RPM. It’s a perfect fit for a 427 ci engine like that on our project engine. It’s about 1-inch taller than the GM intake or the standard Victor LS intake, so you’ll need to make sure you have adequate room under hood. We utilized a K&N drop-filter that lowered our filter 1.5-inches for hood clearance on our Chevelle.
The Other Option – A Distributor?
Another option for adding a carb to an LS engine involves converting to a distributor spark control system. Why consider a distributor? There are arguments that a distributor system can handle much higher horsepower and RPM levels than the stock or M50 coil-on-plug system can handle.
Chevrolet Performance offers an LS front distributor drive cover (Part #88958679) that allows for the use of a small block Ford-style distributor and mechanical fuel pump. Most aftermarket kits for this conversion include your choice of Carter fuel pumps (part # 6904 for street application, #60454 for street/strip, #60968 for race applications) with the recommendation to use ProForm distributor (Part # 66969R), or MSD’s small diameter Pro Billet Distributors (#8382 or 8579) with an MSD ignition controller.
Full Race Distributor Setup
Though definitely not street-oriented, a Jesel Valvetrain belt-drive distributor setup like the one we’re employing on Project BlownZ is another option for the truly hard-core. Driven off the cam via a toothed belt, the Jesel distributor incorporates a cam position sensor for timing data sent to the standalone ECU, and the large-diameter cap sends the spark to the appropriate lead from the high-output coil.
Mounting the Chevrolet Performance front cover and retro looking Chevrolet Performance Bowtie valve covers (Part #25534398 and 25534399) change the entire look of the LS engine to a more traditional looking GM powerplant. The Chevrolet Performance front drive kit comes with a machined front cover, fuel pump and distributor drive gear, color coded spacers, assembly bolts, and the front cover seal.
Converting to a distributor controlled ignition timing setup using Chevrolet Performance front cover requires a few additional components for the front drive system to work properly. A Stewart long style GM water pump is required for correct drive spacing. An accessory drive kit is also required so that the power steering pump, air conditioning and the alternator drives can be driven by the engine. Wegner Automotive makes a complete kit (part # WAK 010) for the conversion that includes all necessary brackets, pulleys, stainless hardware, belts, OE tensioner, Long Stewart water pump, ATI Dampner, 140 amp alternator, GM type 2 power steering pump, and Saden AC compressor. Wegner’s WAK011 contains the same components except the air conditioning unit.
Our research showed that Mr. Gasket’s distributor hold down clamp (Part #9860) was an often overlooked item would be a necessity to complete the distributor conversion. Along with the hold down clamp, a nice set of plug wires and spark plugs should be added to the list.
Taking a Step Back
While a lot of people will consider taking an LS engine and retrofitting a carburetor and stand-alone ignition system as a step in the wrong direction, for many hot rodders and racers it makes perfect sense. The truth is that carbureted LS engines can make just as much horsepower and torque as ones running EFI (if not more), and when you couple that with the simplicity that a carb offers it’s easy to see why many gearheads go this route. Hopefully we’ve shown you that even setting up an ignition system for a carb’ed LS can be an easy job, that can even give you more control and tuning ability.