The flow of oil and air through the motor has an effect on efficiency and power. Here are some tips on routing your air and oil so that you can increase the life of the motor and possibly gain some power in the process.
Oil Pump Horsepower Drain
The oil pump in your dry-sump motor requires a certain amount of horsepower to pump the oil through the motor, filters and to and from the sump tank. The amount of HP it takes is directly dependent on how high a pressure the oil is under at any one point along the route and how efficient the plumbing is that the oil has to flow through.
One restriction lies in how the oil is routed through the oil pump. A more efficient plumbing of the oil flow can result in an increase of from 5 to 10 horsepower, depending on the type of engine. A study of fluid dynamics teaches us that a liquid will flow with less pressure (and effort) through a larger opening and through bends in the plumbing that are designed with a larger and smoother radii.
If we are scavenging from three locations in the engine into the oil pump, but exiting from only one outlet, the oil from at least two of the pump sections must pass through the chambers of other pump sections in order to flow out to the reservoir can. The proper way to exit the oil is out of each individual pump section into a collector manifold where all of the scavenged oil will flow to the reservoir.
Most top engine builders will tell you to run a manifold, but most aren’t willing to tell you how much hp gain comes from using one. It’s substantial. Since this added pressure (which is actually felt as resistance that requires more horsepower from the engine) is inside the pump itself, it will never register on the oil pressure gauge so as to be detectible. It will, though, register on an engine dyno.
Carburetor Jetting and Power Valve Adjusting
Most engine tuning related to air density and humidity is done with the fuel jets, but a more efficient way to adjust the air/fuel mixture to small changes in atmospheric conditions is by changing the air bleed jets instead of the fuel jets. These units are both easier to get to as well as more appropriate for matching the changes in air density to air/fuel ratio.
The air bleeds assist the fuel jets in supplying fuel to the air. Most classes of circle track racing allow carburetors with changeable air bleeds. In the past, changes to the fuel jetting did not adequately modify the air/fuel ratio to affect a gain in horsepower. It was learned that in many cases, it is more appropriate to make adjustments to the air bleed to see a noticeable change in horsepower.
Changing the fuel jets located on the metering block is time consuming, messy and a potential for fire. The fuel bowl must be removed to change fuel jets. This comes with a high probability of spilling some gas onto a hot motor and the risk of a flash fire.
The power valve is a fuel valve that provides additional fuel flow at higher rpm in a Holley–type of carburetor. It operates on vacuum and various PV’s open at different levels of vacuum. Low speed open throttle yields less pressure (meaning a more powerful suction inside the intake manifold) compared to atmospheric pressure than high rpm at open throttle. The vacuum in the intake manifold is reduced as the rpm increases and the power valve opens at a preset pressure level to provide added fuel for a more efficient air/fuel ratio.
If the PV opens too early the air/fuel mixture will be too rich and if it opens too late, the engine will starve for fuel, both resulting in a loss of horsepower. Before trying to work with the PV, it is best to know the amount of manifold vacuum you have.
If the PV closes at, say 5 inches of Mercury, it will open when the engine accelerates and the pressure in the intake manifold reaches that level. The engine might start out drawing 10 inches of vacuum on corner exit, be down to around 5 inches at the flag stand when the PV opens and be at 2 inches or less at the end of the straightaway at the engine’s highest rpm.
It’s best to try different PV’s, especially while the engine is on the dyno, to find the maximum efficiency and horsepower. Monitoring the Exhaust Gas Temperature would be a great way to judge the fuel burn efficiency at various rpm. Is this done on a regular basis? In reality, no, it is not.
Air Filter Tech
Most of us don’t think much about the air filter as it relates to horsepower, but there are some tuning tips that can help produce added horsepower. We need to think about how the air is routed to the carburetor and how we can improve the flow.
Four-barrel carburetors were designed originally to draw air from the sides. If we direct air from the base of the windshield through a tunnel to the carb, or from any one direction, we could be disturbing the function of the carburetor and not getting an even distribution of air/fuel mixture to each cylinder.
The entire surface of the air filter should be pressurized by the incoming air, not just the side facing toward the air inlet. Many engine tuners will tape off a portion of the air filter or build a wall in front of it to force the carb to draw its supply of air from all around the air filter in equal amounts.
Improved airflow is critical to how the carburetor works. That is why racers are particular about the design of air filter housing. Care should be taken to make sure that the air coming into the carb is flowing in from all sides.
Adequate airflow is equally important for the fuel bowl vent atop the carburetor. A minimum of 3/4 to 1 inch of space must remain above this vent so that the fuel bowl will be properly ventilated. These vent tubes can be cut shorter to provide more space between the top and the air filter box.
Proper Oil Filtering
An item unrelated to horsepower and more appropriately related to the survival of the engine is the filtering of the oil. The placement of the oil filter and accessory filters such as an Oberg filter is important for longevity. Having a ton of horsepower is of no use if the engine does not live long.
The Oberg filter is a screen and/or paper filter that is designed to catch larger diameter particles after they leave the engine and before they are pumped back into the system. It should be placed just downstream of the scavenging pumps between the pump and the reservoir can. It should be checked often for the existence of small particles that can mean a bearing is going bad or any other part failures is occurring. In the event of a catastrophic failure of the motor, the Oberg type of filter will catch large metal pieces.
The oil filter should be the last thing the oil passes through before entering the engine. The filter will prevent contamination from getting into the engine. The contamination could come from welding slag in aluminum oil coolers. Using old oil lines is another source of potential contamination. Never reuse old oil lines from blown engines because they may have pieces lodged in the lines. The lines are much cheaper to replace than a complete motor.
Exhaust Header Design for More Horsepower
The diameter of the header tubing must be correct for the size and design of the motor in order to produce maximum torque and horsepower. Installing the largest header tubing will not necessarily yield the best power numbers. Consult your engine builder for information on the best header design to use, and better yet, send your headers along to be used when the engine is on the dyno.
Always tie together the two sides of the motor with a crossover tube. This connection should be located within 30 inches of the collectors that are located at the ends of the headers for improved scavenging affect.
Coating the headers actually gets rid of the heat of combustion faster and moves it out of the pipe to help cool the engine as well as the engine compartment. On cool down, the mechanic will notice that working around the coated headers is much easier because they cool so much faster.
Talk to engine builders, or other racers who build their own engines and learn from their mistakes. The process of building an engine is, in and of itself, not necessarily a performance secret. So, many builders will share tips that may help you prevent costly errors and might even gain a few horsepower.