High Performance Engines

There are many things to consider when it comes to building a high performance engine. First of all will the engine be in a race car or a car that is driven quite frequently on the street. If your wallet has no limits and you want the best of both worlds of being able to drive your car on the street and take it out to the track on the weekends and run 1/4 mile times that astonishes the crowd, then we will make some suggestions on building a high performance engine like no other.

First of all if you want the engine to run on pump gas without any power adders such as nitrous oxide, superchargers, blowers, turbos, etc. then you want to build the largest cubic inch motor you can get away with and put it in the lightest car possible. When I say large cubic inches I am talking about a motor in the 672 range. Sure you can build something smaller but the easiest way to build power in a pump gas high performance engine is big cubic inches.

We also want an engine that makes peak horsepower in the 5500-6000 rpm range. This means we can build a high horsepower engine that will live for a long time considering all the components are carefully matched and the machine shop along with the engine builder knows what they're doing.

For more on how to build a high performance engine visit Hotrod Pitstop.

How to Choose a Carburetor for Your Engine

The size of the engine has a lot to do with how much air can be drawn into the cylinders. Rpm range and volumetric efficiency of the engine also play a big role on carburetor selection.
Carburetor manufacturers rate their carburetors flow capacity in cfm (cubic feet per minute). The cfm rating is the amount of air that can flow through the carburetor at wide open throttle when 1.5 inches of vacuum is applied. When a race engine is under WOT it must have at least 1 inch of vacuum differential between the air inside the intake manifold and the air outside the carburetor (atmospheric pressure). This differential causes air to continuously flow through the carburetor at a minimum velocity.

You would be surprised how many inexperienced racers bolt on the biggest carburetor they can find thinking it will help scoot their car down the track. They think if the carburetor was too big it would be smoking black out the exhaust pipes. In fact, bolting on a carburetor that is too large for an engine will do just the opposite. That's right! It actually leans out the engine because the velocity of air slows down significantly anytime you increase the barrel size of a carburetor. This results in lower vacuum in the venturi which results in less fuel being pulled into the air stream. The end result is an engine that bogs when launching the car off the starting line.

Visit Hotrod Pitstop to find out more about Choosing a Performance Carburetor for your engine.

Performance Carburetor Basics Functions Tuning

The carburetor utilizes air flow through the barrels to draw fuel out from the bowl(s). All carburetors work on two basic principles. One principle is the Bernoulli effect and the other is the venturi effect. Vacuum increases along with velocity in regard to The Bernoulli effect. If a carburetor is developed based on this principle it will have a fuel nozzle placed in the high velocity/low pressure (vacuum) region which allows the drawing of fuel into the air stream and atomizes it into a tiny mist of fuel droplets.

A carburetor that is developed and operates on the venturi effect will have a venturi (narrow passageway) in a tube that is responsible for increasing flow velocity. The carburetor will have a venturi area in the middle of the throat that increases velocity of the air stream. A booster venturi is placed in the main venturi area to further create air velocity plus create a region of very low pressure (vacuum). The fuel nozzle will be located in the booster venturi where there is the most vacuum. This allows fuel to be drawn into the air stream and atomized into tiny droplets. The position of the throttle plates/valves will determine how much air and fuel can enter the engine.

Visit the Performance Carburetor Basics page to read complete details.

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Adjusting Roller Lifter Valve Lash Big Block Chevy

There are a couple of ways to adjust valves on engines that have solid or roller lifters. The first way is to bump the engine over preferably with a remote starter switch so you can be under the hood watching the movement of the valvetrain. The idea is to SET THE INTAKE VALVE LASH when the exhaust valve just starts to open. SET THE EXHAUST VALVE LASH when the intake valve is MID-WAY to closing. That's it!

This is the simplest and fastest way for the beginner. There are even faster ways by doing multiple cylinders at a time but I won't go into that right now.You also need to understand that cams are not perfect, and although lobe base circles should not have any runout, they often do. Not only that but some cams can have relatively long tappet ramps which can cause problems when setting the lash as I stated above. If you really want a perfect setting you need to make sure the lifter is positioned perfectly on the base circle before any adjustments are made.

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Proper Engine Valvetrain Alignment

The correct lifter bore alignment is normally found with a B-H-J fixture, which works in much the same manner as the one that centers the cylinder bores. If a lifter bore is out of alignment, many engine builders can ream it out, insert a bushing, and then re-cut the lifter bore in the correct location. This can help in a couple of areas. First, an improved alignment between the lifter and the cam lobes helps ensure that both wear properly, which is a concern with the high spring rates being used today. Second, when a cam is designed, it is assumed that the lifters are in the correct locations. If they are off by a degree or two, they will contact the camshaft at a different point from where the designer intended and make the valve opening and closing events happen either earlier or later than intended. This, of course, is going to cost you power.

This actually involves two steps-properly locating the cam bores and the lifter bores-but they work hand-in-hand. Earlier, we mentioned boring and honing the cam tunnel, which is done to ensure the bores are the correct size and in alignment with each other. Valvetrain alignment takes it a step further by ensuring that the camshaft centerline is the correct distance from the crank centerline. This can be off slightly on mass-produced blocks and can affect cam timing.

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