Mistakes that weaken a supercharger’s performance

Mistakes that weaken a supercharger’s performance

Bertie S. Brown:

Rick Lewis

Rick Lewis

Though they don’t cater to the Corvette market or late-model Ford Mustangs—none from 1994 to present due to congested engine bays—TorqStorm Superchargers’s product manager, Rick Lewis, has dealt with hundreds of incoming queries in the first eight years of the firm’s history. Here are five of the most common:

1) Compression ratios and intercoolers

“The compression ratio for pump-gas engines is crucial,” says Rick Lewis. “TorqStorm recommends ratios of 9.1 to 9.5:1.” Higher ratios usually require an intercooler.

“But if you are running less than 12psi of boost and under 10:1 compression ratio with a blow-through carburetor or venturi-style throttle body fuel injection,” insists Lewis, “ you can still achieve significant power increases without an intercooler, even on pump gas. Blow-through carburetors do a very good job of controlling intake charge temps.”

2) What increases in power can I expect?

“Our single centrifugal supercharger, which supports 700+hp and generates boost of 6-8psi., increases engine power by about 40 percent over stock performance,” claims Lewis. “Add a second unit, which collectively generate 12-15psi., and the engine’s power output potentially doubles.” Note that the fuel pump must support 21psi of fuel pressure and it relies on a return line to the tank.

BoostRegulator

Via this small-bore hose, the fuel pressure regulator is connected to a port on the intake manifold below the carburetor throttle plates (see brass ports on carb baseplate above).  Engines run on an air-fuel mixture of around 12.0:1 (that is 12 portions of air to 1 portion of fuel). Because the supercharger introduces additional air, additional fuel must also be added to maintain the correct mixture. This requirement is governed by the fuel pressure regulator

3) Carburetors and regulators

The fuel delivered to a carburetor on a normally aspirated engine operates at 6 or 7psi. But the blow-through carburetor is designed to operate from 5psi to boosted pressures that can reach 18psi on a forced-induction engine. This task is achieved by the introduction of a boost-referenced fuel pressure regulator. Via a small-bore hose, the regulator is connected to a port on the intake manifold below the carburetor throttle plates. In this way it reads boost and increases the fuel pressure by 1psi for each additional 1psi of boost. Blow-through carburetors also possess more robust floats to deter crushing under pressure. In addition, their jetting is different and they operate with sealed throttle shafts to prevent leaking under pressure.

4) EFI, injectors, pumps and tuning

In all likelihood most supercharger kits, particularly EFI kits are installed by specialty shops that use a chassis dynamometer and a laptop computer to obtain the correct tune. Rob Walden of LWA, an Atlanta tuning firm that uses HP Tuners software, says, “Supercharger manufacturers do not provide any kind of tune, they just supply the software, the tuner kit, to enter the vehicle’s ECU to modify the tune. So most tuning would be conducted by someone with the expertise and a chassis dynamometer.”

5) What camshaft spec is best?

The lobe separation angle or LSA is the angle in camshaft degrees between the maximum lift points, or centerlines, of the intake and exhaust lobes.

The lobe separation angle or LSA is the angle in camshaft degrees between the maximum lift points, or centerlines, of the intake and exhaust lobes.

Installing a camshaft designed specifically for a supercharged engine is best. But often the existing camshaft works surprisingly well and those with lobe separation angles of between 112 to 116 degrees are ideal. Of course, when cruising down the road, and thus not building boost, nothing more than a normal camshaft is required.

However, to realize maximum power with narrow lobe separation angles there is a sound argument for installing a more suitable cam. Rob Walden says, “Your aim is to trap as much boost in the cylinder as possible. The success or failure in achieving this is affected by the camshaft’s lobe separation angles and valve overlap. Too much overlap and you’ll blow your boost out the exhaust.”

Generally, naturally aspirated engines run narrower lobe separation angles of around 106 to 108 whereas supercharged, turbo or nitrous engines operate with 112 to 114 and higher. On larger displacement units 116 to 118 degrees of separation are common.

On all late-model EFI vehicles, TorqStorm offers their superchargers as Tuner Kits only, which means they don’t include ECU or fuel management.

Lamar Walden

Rob Walden

“Often an EFI supercharger kit requires an upgraded fuel pump or a booster pump,” says Walden. Booster pumps increase their fuel delivery by increasing their voltage output—higher voltage spins the pump faster. Also they are boost-referenced, which means that as the boost increases so too does the fuel pump pressure—thus the pump’s volume keeps pace with the engine’s demand at a corresponding rate. Alternatively, should greater fuel delivery be required, a larger in-tank pump could suffice.

Fuel injector sizes are determined by the engine’s power output. They are calculated in pounds-per-hour of fuel dispersed. For example, 25lbs-per-hr is sufficient to support 350hp; 45lbs-per-hr is sufficient for 500hp and so on.

Lastly, hot air expands and cold air condenses—the colder the air the better the cylinder-filling to say nothing of its deterrent to detonation. Thus, adding an intercooler when costs permit is never wasteful.

And one more for good measure: Clearances

Clearance questions, particularly in the engine bay, around the alternator and above the carburetor seem to be the chief concerns.

Says Rick Lewis: “We provide chassis drawings. With regard to alternator relocation on the small-block Ford and big-block Mopar—both A body and B body, we have mocked-up all those components and though the clearances appear to be close to the engine, they are adequate.” However, the most prominent clearance question involves the carburetor hat. The conventional carburetor hat measures 3.5in deep—although low-rise carburetor hats are still available that measure 2.400in.

Source

Attn: Rick Lewis
TorqStorm Superchargers
Grand Rapids, Michigan
(616) 706-5580 (6am-4:30pm EST)
Sales@TorqStorm.com
www.TorqStorm.com

 

Attn: Rob Walden
Lamar Walden Automotive
Doraville, Georgia
(770) 449-0315 x301
lwarob@gmail.com
www.lwaengines.com

2 Comments

  1. I’m curious as to the preference of the crankshaft stroke length. Does the supercharger function better with a longer or shorter stroke? I’m building an LS engine and can alter my CID either way. So what would the supercharger prefer in your opinion?

    Reply
  2. Al, pursue the longer stroke. You will increase your cubic inch displacement, your low-end torque, and your new supercharged engine will require fewer revs than the naturally aspirated unit. Naturally aspirated engines don’t have a compressor and, hence, rely on engine revs to draw the air into the cylinders. The longer stroke combined with the supercharger’s compressor will build torque before the naturally aspirated engine could flow the equivalent amount of air. This was Porsche’s secret at Le Mans for years: low-end torque meant improved driveability in traffic, increased corner exit speeds, and fewer revs to accomplish it.

    Reply

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