In our last segment, Danger Mouse (DM) practically blew the roof off when it made more than 600hp on pump gas with help from a "little" Weiand blower. That was super-cool and for a short while we couldn't figure out what to do next that could top that. But after our visit to the COMP Cams/Superflow Advanced Engine Technology Conference in Colorado Springs, Colorado (see: "Power of the Spoken Word," page 90), and hearing Lance Ward from Fuel Air Spark Technology (F.A.S.T.) talk about the power and benefits of EFI, we knew what we had to do next.
EFI PotentialAlthough it's still relatively expensive, the benefits of EFI far out-weigh its costs. EFI is easier to start and runs better on the street. Its self-tuning capabilities make it adaptable to any situation. Cold mornings, hot summer days, mountain driving, or all-out hauling, EFI can handle them all and will probably save you a few bucks at the pump in the long run too. Today's EFI systems are very easy to install and if you turn a computer on and plug it in, then you can tune EFI.
As the aftermarket sees the value in EFI and continues to hire and train more computer-savvy tech heads, the average guy on the street will benefit from the true plug-and-play systems being developed. Most of the aftermarket EFI systems from companies like Accel, F.A.S.T., Holley, and others come with ready-made fuel and spark timing tables, also known as "maps", to get any car going once the system is installed. And if you're laptop is plugged in, you can have a buddy tune the car as you drive without ever lifting the hood!
And trust us when we tell you that you do not have to be a computer wiz to tune these things. All it takes is a fair understanding of how an engine burns fuel to make power and you're already about 75% there. Then it's just a matter of learning the operating system's ins and outs, some computer knowledge is helpful here, and you'll be tuning for power. If we can do it, anyone can.
Dyno Testing Part 11 Carbureted PowerSince we're always trying to compare our tests to something relevant, we wanted to compare EFI power to a properly tuned carburetor. As it turned out, the carb made almost as much power as the EFI. And it took us a whole day's worth of tuning to get the EFI past the Demon carb at peak power. But look at the extra low-end torque the EFI made in Test 22 (w/ 30-lb/hr injectors at 50 psi) and you'll see one obvious benefit of EFI.
EFI MagicTuning an EFI motor is a lot more fun than tuning a carbureted one. The reason is simple; you don't have to lift the hood. Once the system is running, you just need to check the ignition advance with a timing light to make sure it matches the spark setting in the ECU and then close the hood and start driving. In our case, we shut the dyno cell door and started pulling.
Over 75 pulls later, we made the most power using the least amount of fuel (low BSFC number) ever. Sometimes a low BSFC just means you're running on the ragged edge of lean, but we checked the spark plugs very carefully and the dyno's knock sensor never even whispered. Some of this month's extra peak power could also be at least partially attributed to a new proprietary hydraulic roller cam from COMP Cams that we installed. Although it did give up some low-end torque compared to the other cams we've tried, 483 peak horsepower from an 8.5:1 compression, 355-cid small-block is very fierce.
8th Series Of Dyno TestsUnless listed, no other changes were made for any test.
Danger Mouse specs for Part 11:
355 cid, 8.5:1 cr, 4.030 bore, 3.48 stroke, 5.7-inch rods
Test 21: TFS aluminum heads (Summit Racing PN TFS-30400013-CNC, 72cc chambers, 195cc runners, 2.02/1.60 valves), Edelbrock Victor EFI manifold (PN 29785), Comp Cams Xtreme Energy EFI prototype hydraulic roller camshaft (281/288 adv dur, 230/236 dur at .050, .544/.555 lift w/1.6 rockers, 113 LS) straight up. Comp Cams 1.6:1 Pro Magnum roller rockers, Speed Demon 750 carb, 36 degrees total advance.
Test 22: Installed F.A.S.T. EFI system with Accufab throttle body and 30-lb/hr injectors at 50 psi
Test 23: Switched to 36-lb/hr injectors at 50 psi.
|Test 21||Test 22||Test 23|
|* = peak|
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BSFC And Proper Injector SizingThis can get tricky. Fuel injectors are rated by how many pounds of fuel they'd flow wide open in one hour at a given pressure, typically around 43.5 psi. Yet, horsepower output, fuel pressure, the engine's Brake Specific Fuel Consumption (BSFC = pounds of fuel consumed per horsepower per hour), and the injector's duty cycle, all determine proper injector size.
Since we know DM worked very efficiently with its Demon carb running in the low-to-mid .400 BSFC area, we wanted to test the EFI in the same range. We figured BSFC would be around .400 and we'd need a minimum injector duty cycle of .85, which means that at max power, the injector will be open 85% of the time. Keep in mind that fuel flow through the injector is affected by fuel pressure, as pressure goes up, volume goes up and as pressure goes down, volume goes down.
We ran most of our tests at 50 psi so the actual amount of fuel flowing through the injectors was higher than its rated figure. You can plug your own figures into this equation to estimate injector size needed for your application. It's safer to estimate a .500 BSFC, not the .400 we used, unless you know your engine can run that efficiently. We used the following formula to estimate injector size for Danger Mouse.
Injector size = (HP x BSFC) / (Number of Injectors x Duty Cycle)Ex: 480hp engine w/ 8 injectorsBSFC = .400480 x .400 = 1928 x 0.85 = 6.4192 / 6.4 = 30 lb/hr
The math says that with 8 injectors operating at 85% and .400 BSFC, Danger Mouse would need a 30 lb/hr injector. We also tried larger 36 lb/hr injectors at both 43 and 50 psi (Test 23), which made the a little more peak hp, but averages fell off and low-end torque dropped enough to be noticed on the street.
Keep in mind that horsepower estimates in all these calculations are at the flywheel, not the rear wheels. A less efficient engine, (i.e. higher BSFC figure), will need more fuel pressure and bigger injectors.