By: Ray T. Bohacz.
Engineering is nothing more than a series of compromises. You identify each and then try to minimize or accept the adverse effect. When I teach this principle, I reference tires. A drag slick is great on the starting line but a poor choice to drive home on in the rain.
Hot rodding any vehicle is an engineering exercise, and often little thought is given to engineering. Back in the early days, that was not the case. Today, with the myriad of parts offered, many hot rodders have become bolt-on experts. Buy it, take it out of the box, and bolt it on. Hey… the magazine said it would work!
TorqStorm is a company that recognizes that. Being part of the community themselves, they know that two vehicles of the same model and engine type, modified by individual owners, will often not be able to accept many of the “so-called” bolt-on parts. Close, but no cigar.
I will now switch direction for a few paragraphs.
The installation of a TorqStorm supercharger is an efficient and cost-effective way to gain considerable power with minimal compromises. But a few things need to be recognized.
Unlike a turbocharger, a supercharger is crankshaft driven. Thus, the volume of air moved by the impeller is directly linked to the engine speed. The air column at 3,000 crankshaft rpm will be the same at WOT or with the transmission in neutral.
This does not occur to such an extent with a turbo. It responds to the exhaust heat to operate the turbine wheel.
So, if you jump on your supercharged car and then quickly close the throttle, the blower is still running at a high speed. Then, the full force of the impeller output is slammed against a closed throttle plate (carburetor or EFI). The air then bounces back into the volute. When this occurs, the compressor wheel is shocked by the air colliding with it. This can damage the fins on the compressor and, over time, cause excessive wear on the bearings on which the shaft rotates. In addition, the air becomes heated since it is exposed to a cavitation-like dynamic.
To eliminate this destructive effect a blow off valve (B.O.V.) is integrated into the supercharger between the discharge of the volute and the air flow entry into engine. In years past, the slang for a B.O.V. was a sneeze valve due to the sound it often produced when acting as a pressure relief.
When the throttle is suddenly closed and the flow from the supercharger is high, the pressure in the inlet pipe will increase dramatically over what the engine would typically see. In simple terms, the B.O.V. is spring-loaded. When the pressure overcomes the spring pressure, a port to the atmosphere is opened and the pressure released. Problem solved.
The B.O.V. and the intercooler
Physics dictates that for every 10 degrees F the incoming air temperature is changed, power is affected by one percent. Cooler air produces more power, and hotter air produces less power. This fact is the basis for integrating an intercooler into a supercharger system.
Once an intercooler is fitted to the vehicle, all of the benefits of a B.O.V. remain, but there is one primary concern.
In this installation, the B.O.V. must be mounted between the supercharger discharge and before the intercooler’s inlet.
In a perfect world, the intercooler would be mounted in a straight line from the supercharger exit, and the heat exchanger’s core would be both thermally efficient (able to reject heat) and offer minimal internal flow loss.
It must be noted that the air does not like to make turns and will suffer a flow loss when asked to do so.
The flow loss will then act like a restrictive kitchen drain. The air will back up into the supercharger. But… the B.O.V. is located there. So, when the restriction pressure becomes high enough, the spring opens the port, and the boost you paid for goes out into the atmosphere and never enters the intercooler, let alone the engine.
The TorqStorm technical line has assisted customers who were experiencing up to 14 psi higher than the manifold boost number and levels of imbalance of 300%, drastically reducing the engine’s power output. This was all due to an inefficient intercooler installation.
Mitigating the flow bottleneck
For the majority of TorqStorm’s clients who want to upgrade to an intercooler, an off-the-shelf option is not offered. Even if it is, you must do your homework and be an educated buyer. These are some of the questions you must ask:
• How efficient is the core in heat transfer?
• What is the flow loss across the heat exchanger (a 10% flow loss is considered the maximum to accept)?
• You need to be concerned with how efficient the flow path in and out of the intercooler is (minimal number of bends). Tight radius bends and large size transitions are concerns too.
• Where will the intercooler be mounted?
The task needs a good deal of thought before you open your checkbook. Just because someone is selling an intercooler kit for the car you have does not mean it is efficient.
Except for a newer body style, such as a Mustang or Challenger, you are best served by creating your own system. First, determine the location the intercooler will mount (airflow across the core is paramount) and make a cardboard cutout of the rough dimensions. Then, start shopping for an efficient core that will fit that area and have the inlet and outlet where you need it to be.
To imagine the tubing’s path, I liked to invest $10.00 in corrugated metal, flexible, and expandable dryer vent hose to make the mock-up. You will not use this, but it is easy to work with to model the flow path to the intercooler and back out again. Once you have a basic idea, shop for tubing and get the welder out!
You may be able to find pre-made tubes that you can connect with a silicone turbo hose used on a diesel engine. The job will then look very professional and sturdy.
Since this is truly an engineering exercise it is essential to install in at least two places leak free pressure test ports. Even though you did your best when designing the system, actual pressure readings need to be measured. At the minimum, read the pressure into and out of the intercooler. Be prepared to change your original design once you obtain pressure readings.
The intercooler may not be as represented. Once satisfied with the pressure drop, you can use the same ports to measure the temperature drop across the intercooler.
To bring this full circle, it is essential the intercooler be thermally efficient and not cause flow restrictions that prematurely open the B.O.V. A TorqStorm supercharger is one of, if not the most efficient centrifugal blowers made. Don’t diminish it with a poor intercooler and installation. The science does not lie!
