Holley vs. Holley
It's EFI Versus Carb in a Big-Block Dyno Showdown
From the February, 2009 issue of Popular Hot Rodding
By Alan Rebescher
Like Chevy versus Ford, good versus evil, and The Rock versus Triple H, the classic confrontation between carburetors and electronic fuel injection is one that will probably never end. Carburetor fans rightly point out that their favorite air and fuel mixer is reliable, easy to install and tune, affordable, and capable of making serious horsepower. Champions of EFI counter by describing its excellent throttle response and driveability, precise tuning capability, and potential to build big power across the entire powerband.
When Holley Performance offered PHR the chance to match up their new Commander 950 EFI system for big-block Chevys against a Holley 750-cfm vacuum secondary/Street Dominator manifold setup, we gave into temptation. We screwed a 9:1 compression, iron-headed 454 together, threw it in to a '80 Camaro, and headed to the chassis dyno at Paul's High Performance in Jackson, Michigan.
Proprietor Paul Svinicki has plenty of experience with both carburetion and fuel injection systems, and his help proved invaluable. For added insurance, we brought along Cary Redman from Holley to do the tuning chores on the Commander 950.
So which system won--carburetor or EFI? As our test results will show you, the answer isn't quite clear cut. Let's take a look at what we found.
What Did We Learn?
When the tire smoke cleared and the computer spit out its results, several things were obvious: The Commander 950 likes more fuel--a lot. With the original 30-pound injectors, we made a best of 306 rear-wheel horsepower at about 4,300 rpm. Factor in a 20 percent drivetrain power loss, and that figure translates into 367 weak ponies at the flywheel. With the 36-pound injectors, rear-wheel horsepower jumped up to 323 at 4,700 rpm, or about 387-plus at the flywheel. That's 17 more rear-wheel and 20-more flywheel horsepower, with just an injector change. Throttle response was awesome, too; the Holley system gave our big-block a throttle more commonly associated with high-revving small-blocks.
The carbureted setup was pretty darn good, too. It made slightly more rear wheel horsepower (309) than the EFI with the 30- pound injectors, but 15 less than the EFI with 36-pound squirters. To squeeze 15- extra horsepower from the carburetor would have required rejetting at the very least, and perhaps upgrading to a 750- or even 850-cfm double-pumper. This doesn't include the considerable amount of time to swap and recalibrate a carburetor. What would take a good half-day with a carb took us less than two hours to do with the Holley system.
We chose the wrong torque converter. Not that there is anything wrong with the 3,500-stall B&M Holeshot converter, it just stalled far too high. The Holeshot worked well with the carburetor, which was track-tuned for making midrange- and upper-rpm horsepower. But, it was all wrong for EFI and its natural low and midrange-torque capabilities. As you can see from the dyno results, we did not get any data below 3,000 rpm--right where the Holley system makes most of its torque. We tried "rolling" the throttle to get some data below the three grand, but the high converter stall-speed, combined with the EFI system's throttle response, made that impossible. As a result, the carburetor looks to be the torque king, but that is misleading. We're convinced that with a 2,000-rpm stall converter to put us in the meat of the Commander 950's powerband, the EFI will produce monstrous amounts of torque.
Out of the box, the Holley systems were very closely matched in terms of peak horsepower. Even with some jetting changes, we don't think there's much more to squeeze out of the carbureted system without stepping up to a bigger unit. But with bigger injectors and a little reprogramming, the EFI made more ponies, even with a mismatched torque converter. Install a lower stall converter, and the Commander 950's torque-producing capacity, throttle response, and ease of tuning becomes very, very hard to beat.
Will this test put the carb versus EFI controversy to rest? Probably not. In our case, the systems were very closely matched in terms of peak horsepower and torque. But with bigger injectors, a lower stall converter, and another session at Paul's High Performance, there's no doubt we can get a bunch more power out of Holley's Commander 950 system, especially down low. You never know--we may be back for another round of Holley versus Holley!
The test bed for our Holley...
The test bed for our Holley EFI versus carburetor showdown is this 454ci big-block Chevy. With a two-bolt block, stock crank and rods, Sterling 9:1 hypereutectic pistons, a .549-inch/.558-inch lift Lunati Bracket Master II cam, and large oval port iron heads, it's a good street and mild race motor. Perched on top is our carbureted system, consisting of a Holley 750-cfm carburetor (PN 3310) and a Street Dominator dual-plane intake manifold. The 750 was treated to a secondary metering block conversion with number 80 jets and a 4.5 power valve.
It ain't no beauty, but our...
It ain't no beauty, but our '80 Camaro was just fine for the flogging we subjected it to. On the Dynojet at Paul's High Performance, it took just four runs to max the 454 out at 309 hp and 375 lb-ft of torque. We did cheat a little by running the car down the local quarter-mile before the dyno session. It turned consistent 12.60s at around 105 mph--the only tuning we did was to swap the stock number 72 primary jets for 78s.
This is the Holley Commander...
This is the Holley Commander 950 MPI Engine Management System. It features a 1,000-cfm billet throttle body, machined fuel rails, 30-pound fuel injectors, and an adjustable pressure regulator, all factory assembled. The little black box is the electronic control unit, or ECU. It is programmed via software loaded in a laptop computer.
While it may look intimidating,...
While it may look intimidating, hooking up the Commander 950 wiring harness isn't that difficult. Each connector only fits its intended sensor or controller--you can't mix up the connectors. There are connectors for throttle position, oxygen, MAP, MAT, coolant sensors, idle air control motor, injector harness, ignition and distributor, and the ECU, plus wires for switched ignition, battery, ground, fuel pump, oil pressure, tach, and transmission park/neutral safety switch. A separate injector harness and all necessary senders are supplied as well.
Holley's Cary Redman swaps...
Holley's Cary Redman swaps the carbureted intake for the new EFI system. It goes on just like a regular big-block carbureted intake--we used Fel-Pro intake gaskets (PN 1212) and some RTV silicone on the end rails, then torqued the manifold to 35 ft-lb.
Holley supplies a high-pressure...
Holley supplies a high-pressure inline fuel pump with the Commander 950. Since we already had a Holley Volumax fuel pump and filter installed near the tank for the carbureted setup, we plumbed the new pump close to the engine and ran a dual-pump system. Since the Camaro was a carbureted car from the factory, we had to run a 3/8-inch fuel return line (the silver tube in front of Cary's hand) for the EFI. Note the oxygen sensor plumbed into the 3-1/2-inch collector on the Hooker 1-7/8-inch primary header.
While the Commander 950 instruction...
While the Commander 950 instruction book is pretty good, it didn't warn us about throttle cable length--the Camaro's stock cable was about a 1/2-inch too short. Fortunately, Holley made the throttle linkage adjustable, allowing us to run the cable as is. Making a new, longer cable would be the better solution, though.
The Commander 950's ECU must...
The Commander 950's ECU must be mounted inside the car to protect it from the elements and to make it easier to hook it to the laptop computer. We mounted ours on the floor, right next to the B&M Pro Ratchet shifter and Auto Meter Ultra-Lite water temp and oil pressure gauges. Make sure to double check each and every wire connection. We spent an hour trying to figure out why our laptop wasn't getting a signal from the ECU, only to discover we didn't have a fuse in the wire leading from the Holley Pro Strip Annihilator ignition to the ECU.
Here, the induction system...
Here, the induction system is assembled and wired, ready to go. You can see how we mounted the throttle cable (and a temporary return spring), the coolant sensor (lower left), Idle Air Control motor (right side of throttle body), and Manifold Absolute Pressure (MAP) sensor just above the IAC motor. The distributor is a Holley Annihilator electronic unit.
With the Camaro finally idling...
With the Camaro finally idling and revving cleanly, we strapped it to the Dynojet to see how much power the Commander 950 would deliver. After a couple of easy runs, Paul Svinicki put the hammer down--and ran right into a torque converter that flashed as soon as he hit the throttle. The B&M Holeshot converter was stalling around 4,200 rpm--way too high for an engine with a powerband that starts almost 2,000 rpm lower. We had the same problem with the 750-cfm carburetor, but it wasn't as severe. "With the carburetor, I could at least roll into the throttle," Paul said. "But with the EFI, there was no way to ease into the gas."
Another problem we had was...
Another problem we had was a lack of fuel. Fuel pressure was going down as Paul hit wide-open throttle (WOT). Ideally, pressure should rise 6 to 10 pounds when going from idle to WOT. When we checked the regulator, we found the adjustment screw was turned all the way out. We fixed that and got fuel pressure back to 42 psi at WOT, but the engine still wanted more fuel, and the 30-pound injectors were maxed out at 100 percent of their duty cycle.
Paul Svinicki graphed our...
Paul Svinicki graphed our runs on the Dynojet computer. We tested three combinations--carbureted, EFI with 30-pound injectors, and EFI with 36-pound injectors (see graphs). The 750-cfm carb made 308-peak horsepower , while the Commander 950 with the 30-pound injectors and 50 psi of fuel pressure made a touch less at 306. Then we swapped in the 36-pound squirters, recalibrated the Commander 950's fuel maps, and bumped fuel pressure back to 42 psi (we left timing at 42 degrees total for all three runs). It took just three pulls to generate 323 rear-wheel horsepower, beating the carb by a solid 15 hp. The only thing we couldn't do a fair comparison on was torque. Our 3,500-stall B&M Holeshot converter was biased to the carburetor's top-end tuning, and totally wrong for the EFI's natural low and midrange powerband--it flashed at 4,700 rpm on our last run with the big injectors. With a 2,000-stall converter, the Commander 950 would trounce the carburetor's peak torque figures.
INSIDE THE COMMANDER 950>/strong>
While the Commander 950 MPI Engine Management System is not a "plug-and-play" deal, Holley has made it very user-friendly for the enthusiast who has a basic understanding of how EFI works and can get around in a Windows-format laptop computer.
The Commander 950 measures airflow by either Speed Density or Alpha-N. Speed Density calculates airflow and fuel requirements by comparing engine vacuum (measured by a Manifold Absolute Pressure (MAP) sensor) and rpm to a value table in the Electronic Control Unit (ECU). This requires camshafts with less than 240-degrees duration (at .050 with a 110-degree or higher centerline) to keep vacuum high at idle for maximum driveability. Alpha-N is for race engines with aggressive cams and/or fully prepped cylinder heads. It doesn't rely on engine vacuum--it determines air and fuel requirements by measuring engine rpm and airflow via throttle position.
The Commander 950 comes with an oxygen sensor to run in "closed loop" mode for good part-throttle driveability and fuel economy on the street. For racing, you can run "open loop" without the O2 sensor. This lets you richen the air/fuel mixture for maximum power without fighting the ECU's programming. Since our 454ci V-8 is a relatively mild street/strip engine, we stuck with Speed Density in the closed loop mode.
Tuning is based on maps for fuel enrichment and spark, easily accessed by pull-down menus. The maps are organized into cells, which represent fuel injector pulse width (fuel map) and degrees of timing (spark map). You can change the values in the cells while the engine is running so you can see the changes in real time. There are also pull-down graphs depicting the shape of the fuel and timing curves. The graphs are useful for smoothing out any high and low spots in the curves. The maps and graphs from our dyno session show you how the Commander 950 plots fuel and spark.
The Commander 950 has additional tables for Idle Air Control (the motor on the throttle body that controls idle quality and part-throttle driveability), closed-loop operation, and operating a nitrous oxide system. There is also a Data Logger feature that allows you to gather data on the engine as it's running, then save it to the computer for later evaluation. It's a great feature for fine-tuning or pinpointing problem areas.
Tuning the Commander 950 is the electronic equivalent of swapping jets and changing distributor weights, but the system gives you far more control over engine performance than you could ever have with a carburetor and a conventional ignition system. Once you get the hang of it, EFI really is the better way to feed an engine.
HOLLEY EFI W/30lb. Injector
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HOLLEY EFI w/36lb. Injectors
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