We intentionally damaged the CP4 in our 2016 Ford Super Duty to verify the effectiveness of the S&S Diesel Motorsport Gen2.1 6.7 Power Stroke CP4 Bypass Kit (Disaster Prevention Kit)… and we used it to haul our race trailer up to the Ultimate Callout Challenge. The skeptics call our kit snake oil, so we’re going all out to prove that it isn’t.
S&S Diesel Motorsport’s common rail diesel technology was recently featured in a very informative article on Dragzine!
“Your father’s diesel engines were known for being dirty and loud, and while unrivaled in longevity and efficiency — at least relative to their spark plug-equipped counterparts at the extreme end of the spectrum — they weren’t exactly all-out performers in the racing world. But diesel performance has come a long way, thanks in part to the efforts of companies like S&S Diesel Motorsport, who have driven technological leaps in fuel systems and engine management systems. The result are efficient, clean-burning, and quiet race engines capable of producing the kind of horsepower to run with their gas and methanol-fueled competitors.” – Andrew Wolf
We would like to take the time to lay down the facts of highly-modified S&S 6.7 Cummins injectors. Some may think that 250% over-stock fuel flow is the limitation of the 6.7 Cummins injector body. While we can’t speak for our competition, this is not true for S&S Diesel Motorsport 6.7 Cummins fuel injectors.
There are a few things to consider when using the % over stock categorization that the aftermarket has adopted. The % over number is calculated by flowing the nozzles by themselves, not the complete injector. For this reason, we would prefer to categorize our injectors by what their exact flow numbers are, but this is difficult without using a standard rail pressure and energizing time. For the time being, we also categorize our injectors on nozzle flow, yet we include a detailed flow sheet that shows the output of each complete injector.
We test our nozzles with the needle out, using the industry-standard Viscor SAE-J967 calibration fluid at 100 bar with a constant temperature of 40 degrees Celsius. On our test equipment, a stock 6.7 nozzle flows 1,200 cc/min and our largest 6.7 nozzle flows 6,600 cc/min, which we classify as a 450% over nozzle per the following equation: (6,600 – 1,200)/1,200 = 4.5 or 450%.
Since we are a company founded by OE engineers, we prefer to use data to prove our point, rather than expecting the diesel industry to blindly take our word for it. So, let’s compare the actual fuel delivery per stroke of stock 6.7 Cummins injectors and a set of our 6.7 Cummins injectors with 6,600 cc/min nozzles, more commonly known as 450% over injectors. Late-model (‘13-‘18) stock 6.7 Cummins injectors flow slightly more than the early-model (‘07-‘12) 6.7 injectors, so we’ll use both for our test.
OE Bosch 6.7 Cummins Injectors
S&S 6.7 Cummins 450% Injectors
We can compare output in mm3/stroke at 1,700 µSec for all injectors. Output of the early 6.7 Cummins injector is 150 mm3/stroke, output of the late 6.7 Cummins injector is 165 mm3/stroke, and the average output of our 450% set is 632.5 mm3/stroke. Below are calculations for the increase in fuel delivery per stroke of both variants of stock 6.7 Cummins injectors:
Increase from Early 6.7 Injector – (632.5-150)/150 = 3.22 or 322%
Increase from Late 6.7 Injector – (632.5-165)/165 = 2.83 or 283%
When comparing the stock 6.7 injectors to our 6.7 injectors with 450% over-stock nozzles, the nozzle flow increase and actual fuel delivery increase are not the same, yet a 250% increase in actual fuel delivery is NOT our limit. Moreover, a 322% increase in fuel delivery through the complete injector is what our 6.7 Cummins injectors with 6,600 cc/min nozzles and accompanying body modifications can do.
Consistency
Some people may be under the impression that consistency is impossible for highly-modified aftermarket injectors. This is also not true for S&S Diesel Motorsport injectors. Below are datasheets for 42 different 2,000+ horsepower capable injectors with no more than 2.12% variance per set, and 5.9% total variance across all 42 injectors.
7 Tightly Balanced Sets of S&S 6.7 Cummins 350% Injectors
42 S&S 6.7 Cummins 350% Injectors with 5.9% Total Variance
The Bosch factory spec at the same rated point on stock injectors is 8% total variance. Not only are S&S Diesel Motorsport 6.7 Cummins injectors capable of delivering roughly 322% more fuel than stock injectors, they are balanced to tighter tolerances than stock injectors.
There’s more to high-performance common-rail diesel injection than nozzle size, at least for S&S Diesel Motorsport. In a perfect world, fuel injectors would open exactly when they are electrically energized, in the real world there are fluid dynamics to contend with, and injection rate shape tells us exactly what the injectors are doing during, and after, the energizing time. Proper common-rail injector nozzle flow is measured using calibration fluid at standardized and tightly controlled temperature and pressure. This is typically published in units of cubic centimeters per min (cc/min) and is presented to the public as a percentage increase from stock flow. Percentage over stock has become the industry standard designation for injector size, yet that number is based off of the nozzle only. In theory, a 100% over-stock injector will deliver twice the fuel as a stock injector during energizing time, but that only accounts for nozzle flow. What if the injector can open and close quicker, or have higher peak flow during the same energizing time? That is where injection rate shape comes in. Rate shape is a curve that shows injection quantity over time for each individual injection event. The area under the curve being the total quantity injected. Rate shape is a tool that we use to first see, and then balance each set of injectors to not only total quantity, but complete injection profile.
This technology is not available to the majority of fuel system manufacturers, and without the ability to see the rate shape, they fall short on balancing when and how the fuel is injected. Since the area under the curve is total quantity, it’s possible for many different rate shapes to net the same amount of fuel. Having control over injection rate shape allows us to build more advanced and precise common-rail diesel fuel injectors that are calibrated as a set for a specific application.
