How often have you seen a carb versus fuel-injection test? We'll bet this one is far from the first you've read. The usual deal is a fuel-injection setup costing a couple of grand or more, pitted against an off-the-shelf carb and intake that you could own for about five hundred bills. That seems hardly a fair shootout. When the opportunity arose to do a dyno test of Holley's relatively inexpensive Commander 950 fuel-injection system for a small-block Chevy, I jumped at the chance. Before committing, I called Lloyd McCleary at T&L Engines Development to see if a) he had an engine to test it on, and b) I could use his dyno-cell NASCAR Holley carb, which has been refined to within a hair's breadth of perfection. The answer was "yes" in both cases, so all systems were go.
The Test EngineOur test engine is a T&L custom crate unit. Essentially, Lloyd has a range of basic crate motors that can be custom-spec'd in terms of cam, intake, etc., to suit the customer's requirement. The deal was that Lloyd's customer for this engine was looking for a 9.5:1 motor that did not need premium fuel. It also had to be totally streetable and fuel efficient. Lloyd quotes $4,332 for an aluminum-headed (Dart) 383 complete with an Edelbrock Air Gap Performer RPM intake and a handbuilt, blue printed, four-corner-idle Holly carb. Essentially, this motor, with the addition of the water pump and pulleys, is ready-to-run. Using the Holley Commander system (PN HLY-91004111), the cost goes up to $6,668. In either case, the engine would come with a dyno sheet showing it makes the power it is supposed to. In this instance, the minimum output for the carbureted version was 450 hp and 480 lb-ft. These are healthy numbers considering the moderate 9.5:1 compression ratio and the short (270 degrees advertised) flat-tappet hydraulic cam used for this motor's low-speed requirement.
Induction SpecsThe base blue-printed carb normally used on this T&L crate motor is a $450 item. This carb has custom calibrations developed for T&L from the NASCAR carb that was used for this test. As such, Lloyd pointed out to me that the difference in output from the regular carb to the dyno cell NASCAR carb is, at this power level, only about 5 hp and 5 lb-ft. However, I was bent on testing each system with similar, if not near identical, air flow. The NASCAR carb was a 1,000-cfm piece as was the Holley Commander system's throttle body. The only difference between the systems was the style of intake being used. For the carbureted test, an Edelbrock Air Gap Performer was used; this intake has proven extremely effective in terms of both low-speed and top-end output. In other words, the 1,000-cfm carb and intake, when used with an appropriate cam as in this instance, produces top-notch results. You can see we are not giving the fuel injection system any kind of break here. It has to go up against a winning combo, so if it is to shine, it has to do so on its own merits.
The Commander 950 Multi-Point fuel-injection system is a speed-density system (i.e. it does not rely on a mass air flow sensor). It's intended to convert carbureted, non-computerized, small-block Chevy engines to fully programmable multi-point fuel injection. It is available with a regular O2 sensor or, for about $600 more, with a wide-band O2 sensor. The system we tested was the second of these.
As such, the systems come pretty much complete with all the components and hardware needed for a custom installation. The aluminum intake manifold, billet aluminum throttle body, billet fuel rails, fuel injectors and related miscellaneous parts are partially assembled and tested prior to packaging. With the Commander 950 ECU, Holley's system offers all the features the typical hot rodder needs. By not offering some of the more esoteric features of more expensive systems, they appear have been able to simplify use and cut costs. We are hoping that our tests will show that this move equates to a more cost-effective system than would otherwise be the case.
Obviously, a fuel-injection system is always going to cost more than a carbureted system. Assuming you are in the market for a fuel-injection system, if improvements in drivability, mileage and output are seen, the cost of bringing an older style motor up to current fuel-delivery technology would seem to be cost effective.
The Commander's four-barrel throttle body rides on a single-plane intake manifold. Traditionally, we view such manifolds as having a top-end advantage over a two-plane intake, such as the Air Gap Performer. On the negative side, a single-plane typically gives away low-speed torque to a two-plane. Here, Holley is counting on the superior fuel atomization and the capability of precise calibration to redeem most, if not all, of the low-speed deficiency that might otherwise be seen. In this instance, a factor that is likely to close the low-speed torque gap between the two manifold styles is the fact that we are using a relatively short-duration cam.
As for top-end output, a single-plane intake such as used by the fuel-injection setup uses the flow capacity of the throttle more effectively. This means that if the engine needs more airflow than the 1,000-cfm carb on the Air Gap Performer two-plane, then our test engine should show more top end. Now it's time to find out.
Dyno TestingOur test 383 was first run in carbureted form. The calibration was to the point where any change of jets or air bleeds resulted in a poorer power curve. Only after we were well satisfied with the results from the carb/two-plane intake combination was the change-over made. Installing the intake and its principle hardware on the engine was straight forward enough. The only slow-down came when it was time to start hooking up all the wiring. Holley recommends reading the instructions in their entirety before starting an install. Based on this experience, that's advice that should be taken seriously. Using the instructions, everything went together relatively hitch free.
The Commander system has a base program that allows the engine to be started. Once running, the O2 sensor swings into the grand scheme of things. Basically, it keeps the engine running while the base program is modified to achieve the map the engine requires. Setup for normal street driving can be done on the street, and to very good effect. For part-throttle use, mileage and drivability are the issues, not WOT power. This means setting up on the street, for the street, is actually a better deal than trying to set up part-throttle on the dyno. Doug Aitken, T&L's dyno guy, did a part-throttle setup that was good enough to beat the carb in terms of throttle response and fuel efficiency. However, he did point out that the real fine-tuning had to take place in the vehicle. Our main concern was outright power production, and although this can be done at the drag strip, a chassis dyno is the real answer.
Because the results had to be meaningful, we took whatever time was required with both the carb and the fuel injection. In all, this took up about three days of time on the dyno. In the end, it was pretty clear that there was little, if any, additional calibration power to be had from either the carb or the fuel-injection. The chart Fig 1 shows the dyno results.
ConclusionsFrom the test results, we can see that the fuel-injection on the single-plane intake beat the carbed two-plane at low speed up to 2,900 rpm. Between there and 4,400 rpm, the two-plane Air Gap Performer intake showed superior results. This was probably due to more appropriate runner lengths for this speed range. From 4,500 up, the single-plane fuel-injection system started to establish superiority, and at the top of the range (over 5,800) the fuel-injection setup was substantially better.
Looking at these numbers we can say some of the results were sort of expected, others were not. The better top-end of the fuel-injection setup with its single-plane intake was almost a given. What was not so easy to figure out was why it was better than the two-plane down at the bottom of the rpm range. A best guess could be that this result was a combination of more accurate mixture ratio, better atomization, and possibly more appropriate intake length at the rpm. The shorter average length of the fuel-injection manifold's runners compared to the two-plane intake's longer runners could have meant it coincided at a multiple of what was needed, where as the longer two-plane runners did not. But that is all conjecture. When the engine reached its mid-range rpm, Edelbrock's two-plane reached the range that has so often proved to be its strong point. The result is that it was up as much as 12 lb-ft over the injected setup.
Based solely on the output figures, it may look like the fuel-injection is a lot of money for very little advantage, as the average power is only marginally better. The WOT dyno figures, however, do not tell the complete story. First, the advantage seen by the user of a fuel-injection setup is much smoother running at cold start. In practice, the engine behaves just as if it is already warmed up and ready to go. Also, a 60-mph cruise fuel-consumption test reveals mileage advantages. The calibration capabilities of the fuel-injection versus the carb are such that it is much easier to maximize mileage with the fuel-injection. Uniform mixture distribution between cylinders also aids mileage. Last on the list is engine wear. Because the fuel is controlled so much better, especially at cold start, bore wash from excess fuel is virtually eliminated. The result is that cylinder bore and ring life is extended.
Power Post ScriptInspection of the Holley fuel-injection system's intake manifold showed that there was a substantial boss where the injection nozzle entered the roof of the intake manifold. This looked like it could interfere with flow. If it did to any real extent, this boss could cut the power potential of the manifold. Not good when it is being tested against one of the best flowing two-plane intakes on the market. Just to see what effect the boss had, a test was run on T&L's flow bench. A head was set up with the valve open to 90 percent of the lift we would expect to use on a moderately hot street cam. The flow at this intake valve lift was 250 cfm. When a performer rpm intake with the 1,000-cfm carb was installed, the average flow dropped to 230 cfm. The same test for the Holley single-plane with its 1,000-cfm throttle body resulted in a flow of 225 cfm. I then streamlined the boss and widened the port around it so the area stayed more constant. It was really only a quickie job, but the result was 236 cfm! This was really interesting. The fuel-injection setup appeared to be making a marginally superior top end with slightly less cylinder head air flow capability. Based on 40 years of air flow work and dyno testing, I would have to say that aero work on the bosses would have been a solid 12 hp, and maybe as much as 15, in favor of the fuel-injection setup.
|DYNO RESULTS: |
COMMANDER 950 VERSUS CARBURETOR
|RPM ||TQ1 ||TQ2 ||HP1 ||HP2 ||TQ Diff ||HP Diff |
|2,600 ||431.0 ||418.0 ||213.4 ||206.9 ||13 ||6.5 |
|2,700 ||444.1 ||424.6 ||228.3 ||218.3 ||19.5 ||10.0 |
|2,800 ||455.0 ||436.6 ||242.6 ||232.8 ||18.4 ||9.8 |
|2,900 ||463.7 ||451.1 ||256.0 ||249.1 ||12.6 ||6.9 |
|3,000 ||463.7 ||464.0 ||264.9 ||265.0 ||-0.3 ||-0.1 |
|3,100 ||465.8 ||470.5 ||274.8 ||277.7 ||-5.0 ||-2.9 |
|3,200 ||469.2 ||477.0 ||285.9 ||290.6 ||-7.8 ||-4.7 |
|3,300 ||471.1 ||477.3 ||296.0 ||299.9 ||-6.2 ||-3.9 |
|3,400 ||475.9 ||476.6 ||308.1 ||308.5 ||-0.7 ||-0.4 |
|3,500 ||478.0 ||482.6 ||316.5 ||321.6 ||-7.6 ||-5.0 |
|3,600 ||477.0 ||484.7 ||327.0 ||332.2 ||-7.7 ||-5.2 |
|3,700 ||473.2 ||486.0 ||333.4 ||342.4 ||-12.8 ||-9.0 |
|3,800 ||473.0 ||483.1 ||342.2 ||349.5 ||-10.1 ||-7.3 |
|3,900 ||472.0 ||478.0 ||350.5 ||355.0 ||-6.0 ||-4.5 |
|4,000 ||467.0 ||477.3 ||355.7 ||363.5 ||-10.3 ||-7.8 |
|4,100 ||468.5 ||474.0 ||365.7 ||370.0 ||-5.5 ||-4.3 |
|4,200 ||469.0 ||474.0 ||375.1 ||379.1 ||-5.0 ||-4.0 |
|4,300 ||470.2 ||477.0 ||385.0 ||390.5 ||-6.8 ||-5.5 |
|4,400 ||472.7 ||475.6 ||396.0 ||398.4 ||-2.9 ||-2.4 |
|4,500 ||474.5 ||473.6 ||406.6 ||405.8 ||0.9 ||0.8 |
|4,600 ||478.3 ||467.4 ||418.9 ||409.4 ||10.9 ||9.5 |
|4,700 ||476.3 ||470.3 ||426.2 ||420.9 ||6.0 ||5.3 |
|4,800 ||475.6 ||473.6 ||434.7 ||432.8 ||2.0 ||1.9 |
|4,900 ||470.2 ||470.5 ||438.7 ||439.0 ||-0.3 ||-0.3 |
|5,000 ||468.4 ||468.0 ||445.9 ||445.5 ||0.4 ||0.4 |
|5,100 ||465.1 ||464.0 ||451.6 ||450.6 ||1.1 ||1.0 |
|5,200 ||460.5 ||459.1 ||455.9 ||454.5 ||1.5 ||1.4 |
|5,300 ||451.0 ||449.1 ||455.1 ||453.1 ||2.0 ||2.0 |
|5,400 ||442.0 ||441.0 ||454.5 ||453.4 ||1.0 ||1.1 |
|5,500 ||435.8 ||432.8 ||456.4 ||453.2 ||3.0 ||3.2 |
|5,600 ||429.9 ||427.5 ||458.4 ||455.8 ||2.4 ||2.6 |
|5,700 ||418.6 ||417.0 ||454.3 ||452.6 ||1.6 ||1.7 |
|5,800 ||404.0 ||397.1 ||446.2 ||438.4 ||7.0 ||7.8 |
|5,900 ||392.0 ||379.9 ||440.4 ||426.9 ||12.1 ||13.5 |
|Ave. ||458.8 ||458.2 ||369.4 ||368.9 ||0.6 ||0.5 |
From these results, it can be seen that the Commander 950 injection and manifold kit (TQ1 and HP1) was better at the low-end and top-end than its big-cfm carb counterpart (TQ2 and HP2) on a two-plane Air Gap Performer. All through the middle range the carb/two-plane intake combo was top dog.
CounterpointThe EFI-versus-carburetor argument has raged since the first EFI cars hit the streets in the 1980s. For many people, carburetors are the easiest and quickest way to get their project on the road. EFI isn't always a walk in the park. You've got to convert your fuel system to EFI with a high-pressure pump and lines, you've got to wire that pump, then run your harness and sensors. Then you wire-up and hide the control box, and when you're finished, you've got to drive around with a laptop in your car all week. To many, it's worth it; once you get it running, the cold starting, economy, and drivability (especially in colder climates) is unequalled. So it's a balancing act. The cost, installation and tuning process are the swing factors. Some people like to get up and running quickly for as little money as possible. That means a four-barrel carb and a trusty air-gap style manifold like the excellent one pioneered by Edelbrock.
The carb setup has a lot going for it. It's less than half the price of an EFI system, anyone can install it, and 9 times out of 10, the tune is perfect right out of the box. And best of all, the carb only gives up the smallest edge on the dyno to the EFI. You'll already be driving your carbed Air Gap manifolded engine while the other guy is still putting pennies in his piggy bank. In many areas that matter, the carb wins out. What do you think? Drop me an e-mail at firstname.lastname@example.org, or post your opinion on our message board at www.popularhotrodding.com.