SUPERCHARGED VERTICAL THROTTLE ASSEMBLY A vertical throttle assembly on a blower is a common combination that started in the 1950s and is carried over today in many nostalgia and professional motorsports events. It is popular due to fast throttle response from the throttles (and FI nozzles) down close to the blower inlet.These FI throttle assemblies are extremely popular from an appearance standpoint. The tall height usually sticks out of the hood on full-bodied performance cars. It often blocks the drivers view but makes a striking appearance.
Tuning
Tuning is a matter of matching jetting to the blower size and overdrive. There is a huge amount of power available from a relatively simple blower setup and a large amount of torque from idle on up. This type of fuel injection is easy to set up with a Roots or screw blower.Frosting at idle from methanol fuels can change the idle speed if nozzles are located anywhere near the throttle plates, especially at humid, cool evening operation. Fuel volume is linear with engine speed. Because of this, it is easy to match with linear fuel pumps:
Hilborn,
Enderle,
Waterman, and others common to this setup.
Drivability
Mechanical fuel injection on a positive-displacement supercharger is not recommended for the street. However, again, with high-stall torque converters coupled with the broad torque curve from the blower, they are frequently driven on the street. Roots blowers are relatively inefficient, and highway fuel mileage in a high performance engine on the street may be only a couple miles-per-gallon.
Racing regulations
These throttle assemblies are allowed in many drag racing modern and nostalgia classes, and in many top-speed event classes around the world. Additionally, they are common in many boat racing classes around the world. They are not common in most circle track racing, due to the inherent naturally aspirated nature of that form of racing.
Cost
These supercharged vertical fuel injection setups are one of the highest horsepower-per-dollar combinations of the mechanical fuel injection world. Throttle assemblies with the fuel system for the blower are reasonable in price, only hitting the wallet for a couple thousand dollars.Roots blowers are reasonably priced and there are many used ones available as well. In addition to new systems, many blower component suppliers inventory a lot of low-cost used parts for sale for this combination.
Enderle’s smallest hat model, the Bug Catcher, is seen on a low-cost, cast tunnel ram manifold on a popular small-block Chevy V8. This hat model is rated at 3,300 cfm for a very high horsepower potential.
Hat-type fuel injection with a tunnel ram, atop naturally aspirated engines is popular, and for good reason: the lower profile of the hat assembly provides more driver vision in many center-steering, front-engine configurations. Show-quality installations can feature well-finished tunnel-ram manifolds to further increase the visual appeal of this setup.Gene Adams, a well-known fuel injection expert in drag racing, ran a back-to-back test. On a record-setting nostalgia nitro dragster, he compared a stack-type fuel injection setup to a tunnel-ram with a fuel injection hat. “The tunnel-ram and fuel injection hat on nitro made more power at all engine speeds,” according to Adams.
Tuning
Tuning is similar to other naturally aspirated setups. However, large throttles and rapid vacuum loss in the manifold, when the throttle is slammed open, necessitates solid fuel transition circuit adjustment. A properly set up fuel injection system, idling on the rich side will not bog when the throttle is slammed open.Lugging an engine with a clutch may be more troublesome with mechanical fuel injection because this setup does not have any fuel modulation with engine loading.
Drivability
This type of fuel injection is probably less drivable at low-speed and part-throttle than other fuel injection configurations. For drag racing, it is usually coupled with a high-stall-speed torque converter. With full-throttle launches against a transbrake, response is recovered for quick 60-foot times.
Racing regulations
The hat type is allowed in most motorsports classes that allow mechanical fuel injection, however in some circle track racing, the stack types may be specified.
Cost
When a cast tunnel-ram manifold is used, this is a lower-cost way to achieve a high-performance fuel system, even over premium carburetors. This is especially cost effective and very common for motorsports classes where methanol will be run.
This engine features a traditional hat injection on a high output blower in a late-model Hemi V8 racing engine. Power levels ranging from 1,200 to 3,500 horsepower on methanol fuel are easy to attain with different blower setups. Similar configurations on nitro can go far beyond that.
Hat-type injection on a supercharged engine is a very common setup. The low profile of the hat helps with vision-limited vehicle configurations. The forward-facing throttle assembly lends itself to ram-air performance increases. It is also considered very visually appealing. This combination is one of the ultimate to satisfy the ego.
Tuning
For tuning, jetting is again sized to the blower setup. For drag and top-speed event racing, the most common modes of operation are part-throttle, low-RPM to full-throttle, and high-RPM.Racing automatics with torque converters work well with fuel injected, blown engines such as this. The torque multiplication from a typical racing torque converter provides a lot of tire spinning power.Low-end torque is so great that a clutch would work well, although best with alcohol fuels that can be run rich without plug fouling. Imagine pulling a gear with a blown alcohol engine in front of a manual transmission! Our blown alcohol racecar idled at 2,300 rpm for the best drivability. You could not stall our engine at idle, even in gear with the brakes on. It would push through the brakes. Some race teams set up dual brake calipers to hold the car against a torque converter. Others use really sloppy converters with a lot of slip at idle in gear to hold the vehicle.For boat racing, prop-slip makes this an easy combination to get working really well. Abundance of low-end power makes getting on-plane a breeze, even with a large diameter prop that lugs a marine engine.
Drivability
Hat injection on a supercharged engine has very high horsepower capability. While it is most often run on methanol, blown fuel injection is sometimes run on gasoline or E85. Nostalgia nitro classes with 6-71 blowers reach 2,600 horsepower. Professional nitro classes with 14-71 blowers and very high volumes of fuel can exceed the 10,000 horsepower mark.Blown fuel injection is not recommended for street use due to very poor mileage. However, due to high torque, a blown fuel-injected engine is quite streetable behind even a medium-stall-speed converter. We encountered a blown alcohol street machine a while back that averaged 2 miles per gallon. It had a 60 gallon fuel capacity on board – giving the car a bit over a 100-mile effective range.