Often times, when tests are done on different forms of induction, no matter how hard the tester tries to limit variables, there is more than one change happening at a time. Now, that’s fine, if all those changes are a required part of the system being compared, but what’s not really fine, is that those background changes in the system often account for a large part of the results, but it’s all attributed to the frontman.
For example, testing carb-style throttle-body injection systems versus multi-port EFI systems. At worst you can have a short-runner single-plane carb style manifold on one, and a long-runner, small-throttle-body EFI manifold on the other. Or, you might have a 90-degree adapter elbow and massive throttle body on that single-plane intake manifold to test the port injection.
At best, those tests are skewed towards the setup the engine was built around, and at worst, any gains or losses are attributed to the injection type alone, rather than looking at the system as a whole. That’s how blanket statements like “carbs will always make more power than injection” get started, and will then refuse to die.
Enter Steve Morris Engines. Being the inquisitive type, Morris recently had an engine on his dyno for a buddy, and thought, “You know what might be interesting? Running this thing with a [Holley] Sniper (the carb-lookalike throttle body injection EFI system) and then leave the Sniper throttle body on, disconnect all of the fuel and electronics from it, and run the multi-port injection.”
What Morris is proposing is about as fair of a test of only the fuel injection system as we’ve ever seen done. Using the same throttle body, the same intake manifold, the same air-fuel ratios, and the same timing, Morris intends to only alter the location of the fuel injectors.
The Test Mule
First, a quick rundown of the engine being used in the test. It’s nothing radical, just a turbo big-block Chevy engine, without its power-adder. Featuring 572 cubes of displacement from a square 4.500-inch bore and stroke, the short-block features Diamond pistons, Callies rods and crankshaft, and a compression ratio suited to a turbocharged engine.
Up top, a set of out-of-the-box Dart Pro1 345cc aluminum heads direct the air, and a solid roller cam (optimized for turbocharged as opposed to naturally aspirated performance) actuates the Trend pushrods and Jesel rockers. A stout combination, no doubt, but nothing that is going to require insane tuning, or surpass the Sniper system’s capabilities.
“Keep in mind, this does have a turbo camshaft in it, and the engine will tend to lay over. It just doesn’t have enough camshaft for an N/A application,” says Morris. “It’ll make a lot of power in the lower and middle ranges, but then it lays over because it’s such a small camshaft, N/A.” After making a solid 3,000-rpm sweep, we see a solid graph, which, as Morris predicted starts falling off at about 6,300 rpm. The peak numbers are 733 horsepower at 6,200 rpm and 723 lb-ft of torque at 4,300 rpm.
This is part 1 of a 3 part series on testing Throttle body EFI and MSD ignition to Multi port part 2 then to coil on plug part 3.
Posted by Steve Morris Engines on Wednesday, May 6, 2020
After a quick swapping of fuel lines and electronic connections, the multi-port injection was ready to go, still using the Sniper throttle body unit as just a mechanical throttle body. The only difference in the configuration is where/how the fuel is entering the engine. After two pulls to get the identical 13.0:1 air-fuel ratio dialed in, Morris is happy with the numbers.
With a little bit wider pull, this time staring at 3,800 rpm and carrying out to the same 7,000 rpm the readout shows 738 horsepower at 6,000 rpm and 719 horsepower at 4,900 rpm. So a peak horsepower gain of five horsepower, and a loss of 4 lb-ft of peak torque, for the multi-port injection.
However, when overlaying the graphs, those differences appear more substantial, as the MPFI’s mid-to-upper-range torque curve (4,600 rpm to 6,500rpm) has significantly more area under it. The horsepower curve naturally follows suit — much more than the difference in peak torque RPM differences might suggest.
As we’ve said before, and will continue to say, no one test will ever be the end-all-be-all, but this is pretty interesting, especially since it’s not that often you get to conduct tests with so few parameter changes. Does this mean that port injection is worth more power than throttle body injection? Maybe, maybe not. In this particular case, it was.
And then, to further muddy the waters, Morris then performed a third test, which we’re linking to, here, if you’re interested, with a coil-on-plug ignition swap. But, since that really distracts from the clean, direct comparison here, we’ll let you explore that part on your own.