Tuning a Carbureted LS

Necessary Tweaks

Jake Amatisto Feb 6, 2014 0 Comment(s)
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There will forever be something cool about a simple carburetor under the hood of your hot rod. Even though in these days of smart phones, iPads, and specifically in our world, self-learning EFI and programmable ignitions, some gearheads, even those with the modern third generation small-block, like to have the carb as an option. We have to admit that even though we love the easy power and affordability of the Gen III SBC, it's an ugly engine. The coil packs and wiring clutters the engine bay and without relocating them or going with aftermarket coil covers, these late model motors lack the smoothness of a conventional small-block, especially if you're sporting one in an old muscle car.

Such was the case for the mildly-cammed LQ9 we dropped in our 1966 Chevelle project car. Our goal was to put together an LS that looked like a factory GM powerplant from the 1960's. By using a carbureted LS intake manifold from Edelbrock (PN 71187) painted Chevy Orange and a 650 cfm Holley four barrel, we planned to make a new engine look nostalgic, while maintaining the factory coil-on-plug ignition. To do so, we set the car up with MSD's 6LS ignition system (PN 6010), which is the simplest way we've found to swap a carb onto the LS powerplant. By working off of the LS' 24-tooth reluctor wheel (MSD's 6LS-2 works off of the 58-tooth wheel), the 6LS box handles your LS engine's timing (not fuel) and can either be programmed with different timing curves with a laptop computer, vacuum style advance, or pre-programmed chips you plug into the box. By being able to map different ignition curves, adding nitrous or boost to your combination is easy and MSD's comprehensive Pro-Data+ software makes navigation a breeze. By the way, to install this piece you only need four connections; the coils, the MAP sensor, the crank sensor, and the cam sensor.

Msd Ignition 2/14

We had our nostalgic LQ9 engine in our Chevelle and running in no time, but like all brand new engine combos, it needed some tweaks for it to run as well as possible. It ran very rich (10.5:1 A/F ratio) and when you matted the throttle we could hear some detonation (pinging). Also, when we'd shut it off it wanted to keep running. Plus, we didn't know if the pre-programmed timing ramp chip we were running was even correct for a street car. Of course, wondering how much horsepower it put to the wheels was another reason why we contacted Westech Performance Group in Mira Loma, California. Master tuner Eric Rhee was able to work his magic and get the most from our reliable combo by adjusting the timing ramps and tweaking the carburetor and we even managed to pick up some horsepower while he was at it too. Here's what he did to make our Chevelle's tune ideal.

Quick Specs

  • 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
  • Does NOT control fuel

1966 Chevy 3/14

1. If you’re not familiar with the ’66 A-body we’ve been playing with lately; it’s LQ9-powered with an overdrive auto trans that made 495 hp on Westech’s engine dyno. We aimed to find out what it could make to the wheels once the tune-up was right.

Adjust Mixture Screws Of Holley Four 4/14

2. To smooth out the idle, Eric adjusted the mixture screws of our Holley four barrel. This simple step can help off-idle drivability. “We started with the basics,” Eric said. “If the mixture screws are all adjusted differently it can create stumbling issues or erratic idle.”

Rollers To 6000 5/14

3. With the engine running smooth, Eric blasted the first pull on the rollers to 6,000 rpm and 348 hp flashed on the screen. Not bad, but you could tell by the fumes that our Chevelle was a bit too rich.

Remove Holley Float 6/14

4. With the Aeromotive fuel log and Holley float bowls removed, Troy Goldie dropped the jets down by two sizes, from a pair of 78s to leaner 76s in the primaries. This typically will change the fuel ratio across the board, but there are other ways to improve the fuel curve at lower rpm, specifically, like the power valve and air bleeds, for example. We didn’t get into the air bleeds on this combo, but they can be adjusted to finely tune your engine’s air/fuel parameters at low rpm.

Map 7/14

5. We also added a MAP sensor while we were at it. The ignition curve in the MSD box works off of a signal from this sensor, so while the car ran well with a pre-programmed timing chip, we had to add this in order for the box to see what the engine’s manifold pressure was doing. This is all in an effort to improve gas mileage and responsiveness.

Rollers Air Fuel 8/14

6. Another pull on the rollers revealed a much happier air/fuel ratio (12.4:1) and at 6,200, the LQ9 laid down 360 flat.

Msd Ignition Box 9/14

7. At this point Eric delved into the MSD 6LS box and tried a different timing curve chip. There are six different pre-programmed curves from MSD for the LS engine, covering all levels of performance. However, the one we selected was obviously too aggressive and would cause the engine to detonate at WOT. We opted to tailor the optimum curve using the MSD Pro-Data+ software, which Eric accessed with a laptop. We ended up with about 35 degrees of timing in before 4,000 rpm.

New Timing Curve 10/14

8. At this point Eric delved into the MSD 6LS box and tried a different timing curve chip. There are six different pre-programmed curves from MSD for the LS engine, covering all levels of performance. However, the one we selected was obviously too aggressive and would cause the engine to detonate at WOT. We opted to tailor the optimum curve using the MSD Pro-Data+ software, which Eric accessed with a laptop. We ended up with about 35 degrees of timing in before 4,000 rpm.

Power Valve In Holley 11/14

9. To possibly improve drivability, the power valve in the Holley was also changed. The power valve increases the amount of fuel going to motor in a low manifold vacuum condition. In our case, we dropped it down from 10.5 to 9.5, which helped our rich condition at low rpm.

Stp Corrected Wheel 12/14

10. After a brief cooldown, Eric made another pull and netted a cool 366 to the wheels. Compared to the 495 we made of the engine dyno, we’re losing around 130 hp through the accessories, the 4L60E transmission and 12-bolt rearend. Something else to consider is how loose the converter is; a loose converter will put less hp to the wheels than a tight one, but will essentially be quicker at the dragstrip.

Dyno Testing 13/14

11. Also, the 495 number was made on the engine dyno with no accessories, so if you consider how many horsepower parasites there are when an engine’s in a car, a 129hp loss from engine to chassis dyno isn’t really that bad.

1966 Chevy Chevellet 14/14

12. With the detonation cleared up and the LQ running strong, the car’s owner, John Barkley, set out on a cross country road trip with his carbureted LS, successfully cruising from Louisville, Kentucky, to the salt flats of Bonneville and back home to sunny SoCal. While he admits the gas mileage wasn’t great, it was worlds better than what it would’ve been if he hadn’t got it tuned, we just have to give props to a man that navigated such a cool car on a couple thousand miles of America’s highways for the heck of it—and all with a classic carburetor and a classy car, no less. CHP

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