As anyone with any knowledge of high performance engines in particular knows, getting air into the combustion chamber in spades is the leading ingredient to making horsepower. And in drag racing, forced induction systems, such as supercharging, are the quickest way to accomplish that. Superchargers operate off the crankshaft, which spin the supercharger’s impeller and force high-pressure air into the engine’s cylinders. While it’s true that power adders do plenty of work all on their own, they too — just like a naturally-aspirated engine— benefit greatly from the introduction of clean, fast-moving air into the supercharger inlet, which only serves to multiply the boost being delivered to the engine.
In years gone by, the centrifugal superchargers that are so popular in drag racing were mounted on the front of the engine block and driven by a belt off the supercharger. This location made getting fresh air to the blower a bit difficult, and racers would commonly vent scoops in the hood down to the inlet, or just allow the blower to “suck” ambient air under the hood without any forced air at all.
These days, however, belt drives have been largely replaced by gear drives, which situate the supercharger out in front of the engine near the front bumper, in a prime spot for forcing air in — much in the way racers have been positioning turbochargers for years. And so with that has come the need for more dedicated supercharger inlets to “clean up” the air being both pulled and forced into the blower at everything from a dead-stop on the starting line to 200-plus miles per hour.
Recognizing a need in the market for such a product, our friends at ProCharger, long one of the sport’s leading manufacturers of high performance and racing superchargers, developed a Bellmouth supercharger air inlet in the latter half of 2014, designed to be installed on the inlet of their racing supercharger units. The inlet is intended to help increase performance by just that much more by directing the clean, cool air directly into the supercharger’s impeller.
We got our first look at ProCharger’s prototype Bellmouth at the PRI Show in Indianapolis in December 2014, and we recently spoke with Senior Performance Technician Sergio Shifman to discuss in greater detail the advantages the relatively simple, yet valuable, new product brings to the table.
“We wanted to offer something direct from ProCharger that has the best practices possible applied to its design for racers looking for an inlet for their supercharger,” says Shifman. “This is what we think is going to make our unit perform up to its full potential.”
We’ve always known that you need some type of funnel, but in some of our recent testing, we’ve really begun to understand just how much a proper shape, angles, and diameters from the impeller on out help with airflow. – Sergio Shifman, ProCharger
“Now that the gear drive is so much more common, the placement of the blower is out away from the engine,” says Shifman. “And so you’re seeing more and more racers with holes in the front end of their cars. That transition has made the use of air inlets more realistic.”
Shifman goes on to say, “We’ve always known that you need some type of funnel, but in some of our recent testing, we’ve really begun to understand just how much a proper shape, angles, and diameters from the impeller on out help with airflow. Also at the very edge, having it curl back, we found to even deliver an edge in how the air flows.”
After the engineering design was completed, a prototype was machined and the team went to work testing it on their own in-house supercharger dyno to get a better understanding of the inlet’s performance in an environment that more closely simulates real-world use
, versus a computer model. Shifman relays that exact boost numbers through their testing are hard to calculate, as different engines and superchargers are going to return vastly different results.
On the surface, the Bellmouth (and other third-party products like it) seem like relatively straightforward products that simply give the supercharger opening more real estate to swallow up the incoming air. However, the Bellmouth is anything but, as ProCharger engineers put countless hours of research and development time into forming every angle of the bell, from the shape and angle of the “bowl” section itself, to the rounded lips on the edges.
These rolled edges, Shifman says, are of benefit even in heads-up categories like Ultra Street, where holes in the front bumper are not allowed. This is because ambient air being pulled in under the hood is still able to flow into the impeller much smoother than without any bell at all. Regardless of the layout, however, it comes down to cleaning up the air and cutting through the high and low pressure areas, and the turbulence commonly found around the inlet of the supercharger, to get the air inside to make horsepower.
“The impeller isn’t just pulling in a big tube of air, right into the round inlet — it can be pulling more from the outer edges,” says Shifman. “The superchargers usually pull air really well from the center and right in the middle, with turbulent air in between. This airflow pattern can then shift and change at different speeds and engine RPM.”
During the development phase, ProCharger created prototypes for the F-1X and F-1X-12R, along with the big F-3R-136 — its most popular hardcore drag racing superchargers — and will soon be putting all three into full production. The company plans to later add Bellmouths for every supercharger in the F-Series line, including the F-1, F-2, and F-3.
After extensive field-testing with the Bellmouth over the last year, ProCharger’s engineers went back to work and scaled down the original prototype design, in order to allow for better fitment in already-cramped engine compartments. Despite the overall reduction in size, however, they were able to maintain virtually all of the airflow properties of the prototype, thus arriving at a smaller, more affordable (and competitively priced) end product with all of the same performance advantages.
The Bellmouths will be manufactured from billet aluminum, and anodized in black, with the ProCharger logo laser-etched, just as the prototypes have been. While the F-1X-12R and F-3R-136 share the same housing and inlet diameter, the Bellmouths for each, as well as the F-1X, will be specifically designed for each supercharger, with slight nuances in the shape and angles catered to each supercharger. They’re also designed proportionate to the inlet size, making the F-1X version slightly smaller than its counterparts.
“Everything is designed for best practices and for the specific aerodynamic curvature for a given inlet size, so each one has a slightly different inner and outer diameter and depth and overall profile,” says Shifman.
In The Field
ProCharger’s Bellmouth has already been put through its paces on the racetrack, notably on the NMRA and NMCA Street Outlaw Mustang of Phil Hines and on David Pearson’s world-beating Outlaw 275 Mustang that presently owns the elapsed time record for a 275 radial tire car.
Hines first ran the Bellmouth at the NMRA World Finals in Bowling Green, Kentucky in the fall of 2014, where he made what was then the quickest pass in Street Outlaw history with a blistering 6.87 at 202 mph on his Mustang with an F-1X blower out front. Earlier this year, he reset the NMRA national record with a 6.80 at 208 mph blast in Maryland.
Pearson, who has also been running a Bellmouth on his F-3R-136-equipped Mustang since late 2014, demolished the 275 radial record books in the second half of this year, running as quick as 4.10-seconds in the 1/8-mile. Pearson shared with us that he’s seen about a one-pound increase in boost through the use of the Bellmouth. Fellow 275 radial racer John Urist, a longtime ProCharger runner with his NMRA Street Outlaw Mustang, confirmed similar findings of around one additional pound of boost in his testing of the Bellmouth.
Bellmouth Real World Testing
Frontal air has been a debated topic among forced induction drag racers for the last five to six years, but there really are two separate topics being discussed. The first is the ‘ram-effect’ of frontal air when traveling at a high rate of speed. The second is the advantage of using a bellmouth on the compressor inlet. It becomes challenging to test this A to B in a real world dynamic environment, due to weather changes, vehicle setup, and tuning differences from run to run. Testing on the dyno might be promising, until you realize that it has none of the dynamic elements of airflow moving into the compressor or bumper at varying speeds (0 mph at the beginning of a run, 150-210 mph or more depending on your race cars speed and race track length).
With a 275 or 10.5-inch drag radial-equipped car such as BlownZ, it’s rare that we’re able to go down the racetrack in an A to B fashion with the same tune in the same weather conditions due to the large number of variables we have to contend with. We do have some real world test data with the bellmouth, but we would consider it only relative to generally indicate the ProCharger Bellmouth performance in combination with a forced ram-air front air setup.
In our initial testing, in 3,800-4,000 feet of air density and 83-86 degree of air temperature, with a hole in the bumper but no bellmouth or ‘ram-effect’ tubing connecting the supercharger to the front bumper, our 441 cubic-inch race engine produced an average of 6.4 pounds of boost at 4,000 rpm on the transbrake, and a total boost pressure of 27.2 pounds at the 1/8-mile mark over three runs.
We had two subsequent test sessions with the ProCharger bellmouth, and with the addition of ‘ram-effect tubing’ connecting the bellmouth directing to the front bumper hole. In the first, at 3,200-3,400 feet density altitude, and 86-88 degree air temperatures (and no other changes), over four runs, the ProCharger bellmouth/ram-air combination averaged 7.6 pounds of boost on the transbrake at 4,000 rpm, and a total boost pressure of 28.6 pounds. Using a loss reference chart calculating the native density of altitude to air pressure correction, we get roughly a .53-pound gain due the air density differences. This would indicate that the bellmouth produced an additional .67 pounds of boost on the transbrake, and 0.87 pounds of boost at the 1/8-mile mark. Candidly, this is a far from scientific result, and doesn’t factor in back-to-back testing protocol, engine rpm, exact blower speeds (corrected to engine rpm), barometer corrections, or water grains. But it’s still a relatively useful general indicator of the bellmouth’s effectiveness.
In the second session, the air was better — approximately 2,600 density altitude over two runs, with 85-87 degree air temperatures. Boost pressure increased to 8.2 pounds on the transbrake and 29.1 pounds at the 1/8-mile mark. Applying the same loss reference chart, it projected a total boost increase of .94 pounds over the baseline, meaning the bellmouth, even when corrected for these air conditions, produced an additional 0.86 pounds of boost on the transbrake, and 0.96 pounds at the 1/8-mile mark.
When evaluating this data, there are three key things to keep in mind. One, these results were compiled over three different test sessions and fail a traditional A to B testing protocol. Two, they only measure the effectiveness of the bellmouth, but also of sealing the bellmouth to the front open hole in the bumper with a tube (10.5-inch diameter), in our case. Three, we employed a general loss reference chart for air pressure to air density. It may be that the bellmouth is responsible for increased boost at low engine speed and vehicle speeds, and that the sealed frontal air is responsible for increases in top end boost. Or not. What’s clear is that likely the most common, and most effective, combination of air flow enhancements is to run a bellmouth, a front air opening, and to seal it to the front of the bumper.
Every combination is different, and at this level, with over 2,000 horsepower on tap, and changing weather and track conditions, every run is different at some level. It’s not an easy thing to test, but our data indicates a performance improvement with the bellmouth and sealed front inlet air.
At the end of the day, with the competition in heads-up drag racing so fierce and engine and power adder combinations dialed-in, the difference between winning and losing is often a game of tiny incremental steps forward in horsepower. And as such, racers are constantly in search of a tool that will give them another much-needed hundredth of a second here and hundredth of a second there. For supercharged racers, the new ProCharger Bellmouth inlet, a simple bolt-on device, helps to deliver that minute edge in horsepower that might be needed to outrun their nitrous and turbo counterparts.