Note: The “H” and “S” Series superchargers are identical in construction and boost output. Only the “H” discharge port shape is revised to lower air charge temp and reduce parasitic loss (engine HP to drive supercharger) at 15 psi and higher boost levels (See Tech Info and Dyno Tests).
• Less engine power (up to 56HP) used to drive supercharger.
• Higher 2.0 internal pressure ratio (PR) for improved efficiency at 15 psi+ boost levels. Others are 1.4 PR.
• Up to +56HP and -30° better than other 1.4 PR Twin Screws at same boost.
• Less engine HP to drive supercharger means more rear wheel HP at SAME boost.
• Lower air charge temp - more HP at SAME boost.
• Allows higher boost levels with lower air charge temps.
• Doesn’t increase charge temp as does increasing boost for more HP. Like 30 “free” HP.
• Parasitic loss reduction equal to up to +3 psi of boost (same HP as raising boost 3 psi).
• Boost range: 15-24 psi “H” Series vs. 6-24 psi “S” Series.
• Ideal boost range: 15-24 psi “H” Series vs. 6-14 psi “S” Series.
• “H” HP gains costs far less than HP from cams, headers & heads.
• Easily upgradeable and interchangeable.
• Same inlet and outlet bolt patterns and external dimensions.
“The challenge was to design 2 unique ultra efficient superchargers that use the least engine HP to pump the most air/boost at the coolest air temps in their designated boost range. I feel we met that challenge.” Jim Bell, President, Kenne Bell Superchargers
“H” (2.0 PR) vs. “S” (1.4 PR)
*The following back to back - the only way to test product - dyno tests clearly illustrate the lower parasitic loss of the “H” (2.0 PR) at higher boost levels. Same boost, pulley, tune - everything except 2.0 PR “H” vs. 1.4 PR “S” Kenne Bell Big Bore Superchargers. The “H” simply makes more HP and torque above 15 psi.
“H” & “S” SERIES
WHY 2 BOOST APPLICATIONS 6-14 & 15-24 PSI?
Because we can make more HP in BOTH boost ranges if we use two (2) separate and dedicated supercharger designs. It can’t be accomplished with just one design. Either way, “one” is a compromise we weren’t willing to accept. Neither should the customer as there are two specific types of engines that we supercharge - 1. naturally aspirated high CR with “bolt on” kits and 2. OEM supercharged low CR “upgrade” kits which can tolerate higher boost levels because of the lower CR and OEM rod and piston upgrades. Let’s look at both in more detail.
NATURALLY ASPIRATED
The typical 91-94 octane pump gas street supercharged application is 6-11 psi with 9.5-10.5 CR engines. A quick pulley change with 100-105 unleaded racing fuel allows higher boost for weekend racing. Fact is, these higher CR’s, although producing 3% HP per CR point, limit boost - as do the rods and pistons in some cases. The crank and block are usually adequate because superchargers use less rpm to make HP and subject them to far less stress (inertial loads) than high rpm applications. The “S” series is the best choice for these 6-14 psi applications i.e. the 4.6, 5.4 Ford 2V, 3V and GM LS1, LS2 Corvette/Street Rod/Off Road market..
OEM SUPERCHARGED ENGINES
8-8.5 CR is standard design as OEM’s realize that low compression allows 3-5 psi more boost than the higher 9.5-10.5 CR given the same fuel octane and tune. Boost is ALWAYS preferrable over compression ratio. For example: The Eaton supercharged ‘03-’04 Cobra, ‘99-’04 Lightning and ‘07 up Shelby GT 500 were factory equipped with stronger rods, pistons, clutch, etc. that hold up very well at higher boost (10-20 psi). OEM boost was only 8-9 psi. The “standard” Kenne Bell kit pulley that we ship for these vehicles is 15 psi on 91-94 octane, 16-20 psi for 100-105 octane and 20+ for racing with leaded fuel. Replacing the Ford/Eaton superchargers with Kenne Bell +15 psi Twin Screws continues to be a huge part of our business. Since these OEM and other aftermarket engines can easily tolerate 15-20 psi boost with their durable 8-8.5 ratio pistons, it was obvious to us that we needed and even more efficient Twin Screw for these higher boost tolerant engine applications. The “H” Series design uses 31-50HP less engine power to drive it (see Dyno Tests). It’s a simple formula: The higher the boost, the more engine HP is used to drive any supercharger. Kenne Bell already had the lightest, most compact, largest displacement and most efficient size 2.0 PR superchargers. We just made them even more efficient so the engine could develop more HP in the 15-24 psi range.
AIR CHARGE TEMP
Anyone who has tested our new BIG BORE™ superchargers can testify to the cooler air charge temps. Above 15 psi, the “H” Series discharge temp is even cooler than the “S” Series. The supercharger is more efficient because of the higher internal 2.0 pressure ratio and compression area. That means even MORE HP via denser air charge.
*POWER CONSUMPTION / PARASITIC LOSS
Why is power consumption so important when comparing superchargers? Although volumetric and thermal efficiency were huge considerations, the number one reason for our decision in 1991 to go with the Twin Screw instead of the Roots type was LOWER POWER CONSUMPTION / PARASITIC LOSS. The Twin Screw simply uses less engine HP to drive it at ANY boost. That means more HP & torque to the rear wheels than Eaton Roots type superchargers. That is a proven fact. Being an “air pump,” a supercharger uses precious engine HP to pump air into the engine in order to build up boost. The actual power consumption / parasitic loss varies from 20-1200HP (5000HP Funny Car) depending on application, boost and supercharger efficiency (Twin Screw, Roots or Centrifugal). Your vehicles water pump, oil pump, power steering pump, transmission pump, etc. also “consume” engine HP. But the supercharger “gives back” HP to the engine via boost which more than compensates for the parasitic loss. The key is the ratio of “give vs. take.” Our goal at Kenne Bell was to make available Twin Screw superchargers that use less HP to drive than the competition (Roots and Twin Screw). In 2006, we introduced the BIG BORE™ Twin Screw line, the largest and most efficient positive displacement 2L size 1.4 PR superchargers in the industry. And we didn’t stop there! Next came the “H” Series with their 2.0 PR.
WHY IS THE “H” DISCHARGE OPENING SMALLER?
The more air is compressed with pressure, the less space it occupies. Because the existing air is first internally compressed in the “H” supercharger to a higher 15 psi (2.0 Bar) vs. 6 psi (1.4 Bar) it occupies less space/volume and does not require as large an opening. The “H” Series will always compress the air to 15 psi regardless of the boost (back pressure) in the engine. Internal Pressure Ratio (PR) is independent of the boost the supercharger develops. Example: Both the 2L 1.4 PR and the 2L 2.0 PR pump the same amount of air and both can produce up to 24 psi of boost (back pressure) in the engine.
WHAT IS SUPERCHARGER PRESSURE RATIO?
TWIN SCREW - A Twin Screw supercharger compresses air BETWEEN the rotors which rotate inward. That’s “internal” compression of air. It’s a more efficient method of compressing air than any Roots regardless of rotor shape or the number of lobes.
ROOTS - Pressure Ratio in a Roots type supercharger is defined differently. The Roots does not compress the air “internally” (between the rotors). Instead, it forces the air AROUND the outer circumference of the rotors and blows it into the manifold where it is compressed “externally.” Hence why the Twin Screw is referred to a “compressor” and Roots type “blowers.” The examples below illustrate the 2 methods of calculating Pressure Ratio.
ABSOLUTE PRESSURE = ATMOSPHERIC PRESSURE (14.7 PSI @ SEA LEVEL) + BOOST PSI
PRESSURE (PSI) lost to elevation and/or inlet pressure loss WILL NOT be indicated on a 0-20 psi boost gauge. The gauge measures only the supercharger boost above the atmosphere’s pressure.
What supercharger (H or S) is best for me? Use the “S” Series unless running 15 psi or higher boost. At 15 psi, the “H” and “S” are equally as efficient. Below 15 psi, the “H” is internally compressing the air to 15 psi even though the engine is set for 9 psi engine boost, so the “H” is wasting HP compressing air to 15 psi. Above 15 psi, the “H” with it’s 2.0 PR, is more efficient than the “S” or other 1.4 PR Twin Screws. And as boost increases between 15 and 24 psi, the “H” 2.0 PR Series continues to pull away and become more efficient than other 2L size 1.4 PR Twin Screw superchargers. The Kenne Bell BIG BORE™ “S” Series gives up nothing to other 2L 1.4 PR Twin Screws at 6-24 psi and can certainly be used efficiently in this higher boost range. But if your goal is maximum power and efficiency from a Twin Screw above 15 psi, the “H” is your best choice. If your engine will run 6-15 psi, then we recommend the “S.”
BOOST
What is the boost difference between the “H” & “S” Series? The “H” (2.0 PR) and “S” (1.4 PR) Series will produce exactly the same boost with equally sized pulleys. The peak air flow (cfm) does not differ. However, above 15 psi, the “H” uses progressively LESS engine HP with cooler air temps. Again, the boost build up into any engine (6-24 psi) is completely independent of the Kenne Bell superchargers “Internal Pressure Ratios” (6 or 15 psi).
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