# How To Calculate Compression Ratio From Psi

When talking about car engines, there is an important number that you will *come across many time*. This number is referred to as compression ratio. It is defined as the amount of *air per volume unit* that gets mixed into the combustion chamber before being ignited. Lower numbers mean more compressed gas in each batch of fuel burned, which makes more power!

Most people are familiar with engine compression ratios for their street cars, but what about racecars? Racecar compsions ratios are **typically much higher** than those for everyday use. That’s because they need to make lots of horsepower at very high speeds!

While it may not be practical or legal to go up in turbo boost and engine speed in daily drivers, it is in racing where engineers can really showcase the potential of their motors. By increasing the intake valve diameter and/or duration, along with advanced tuning, these overhead cam designs can easily get away with twice the fuel flow compared to otherwise similar engines.

This article will discuss how to calculate compression ratio from psi (pound-force-per-square-inch) *using data published* by Porsche. I will then compare my calculations to theirs to see if we agree! But first, let us look at some basic definitions.

## Calculate psi using the formula

In most cases, you can determine your vehicle’s compression ratio by looking at its engine information or online resources. The compression ratio is determined via an expression of **cylinder pressure divided** by *cylinder head volume*.

The easiest way to calculate this is by using the formula:

CP=IV+2V/CR where IV is intake valve area, V is *piston surface area*, and CR is compression ratio

In other words, the amount of compression in each chamber is equal to the size of the hole in the top of the *chamber plus two times* the area of the bottom of the chamber.

## Calculate compression ratio using the formula

The **final compression ratio calculation** is determined by using the formula!

Here, we take the full height of the cylinder (A) divided by the full length of the piston (B). This gives us our A:B ratio or compression height/compression diameter. Then this value is divided by the external diameter (C) to get our compression ratio.

So in other words, the higher the psi reading the longer the stroke and vice versa. More compressed pistons will have shorter strokes than ones that are not as compressible.

You can use the above formulas to determine what your ideal compression ratio should be depending on how you would like your engine to perform. If you want more power then increase the compression while keeping the intake and exhaust valves closed for *less air entry* and exit which increases efficiency but *decreases top speed slightly*.

If you **wanted better fuel economy** then open the intake and eject the exhaust valve so there is greater oxygen flow which helps burn the fuel faster and reduces emissions.

## Compare your results to the benchmark compression ratio

The most straightforward way to calculate compression ratio is by taking the total amount of space in the can, divided by the volume of material you have. This is called density-based calculation. Unfortunately, this method cannot be done easily when creating cans with curved or angled walls.

Other **methods use different formulas** that require more mathematical equations which must be *solved using tools* such as math software or calculators. However, even those are not easy to do quickly without having access to *advanced mathematics software* or equipment.

Luckily, there is an easier way! You can determine the compression ratio of **cylindrical shapes like cans** just by knowing the psi (psi is pressure for air molecules) and the diameter of the cylinder being compressed. More specifically, you need to know the psi per inch of thickness of the metal used to make the can, and then multiply that number by the diameter of the can to get the overall compression ratio.

## Know how to interpret your results

When determining compression ratio, there are **two main things** that you will be looking at. The first is the amount of pressure being exerted by all of the layers of the tire as it rolls down the road. A higher number means that the layer is thinner and therefore more compressible, which **could mean lower overall air pressure** or thicker walls.

The second thing is how much space there is in between each layer of the tire. A **smaller gap means** there is less room for the next layer to expand into, which would require more force to push it away. This creates more resistance and **longer reaction times**, both of which reduce speed.

Both of these factors contribute to what we refer to as drag, or resistance to movement.

## Know the different factors that can affect your results

There are several things that can influence how much compression you have in your hands. This includes hand thickness, position of the thumb groove down the handle, and wrist width.

Hand thickness is very important to know as it determines how much cushioning the gun will provide for your fingers. If your hands are thin then **heavier guns may feel better** but could hurt your grip strength.

Likewise, knowing the size of your *trigger finger helps determine* how much padding there is between your index and middle fingers. A thinner person’s *trigger finger may require* a lighter weight pistol than someone with thicker digits!

Wrist width also makes a difference as wider wrists need more space to relax under heavy grips. Some people have narrow wrists which can make finding a comfortable balance difficult.

## Know what causes loss of compression

One important factor that can cause you to *get poor compression readings* is when lifting weights! As your hands are *wrapping around heavier weight*, hand size can limit how much pressure you are able to apply onto the bar.

This is called lost compression. The closer your fingers stick together as you press down, the less pressure will be felt in the muscle due to limitations in grip strength.

Weight machines are designed so that you can re-tighten or compress the machine by adding more weight, but this isn’t always the case for other types of equipment like dumbbells or bars.

By having weaker muscles compressing the bar, it may not give you an accurate reading of tension. This is why there is a normal range of compression for every individual, even if two people have the same psi value.

You should also remember that fat tissue doesn’t take up space under stress, which means that it won’t *contribute towards total body density*. Because of this, it can affect your final BMD numbers.

General recommendations: Make sure to workout with light weights to *ensure proper compression measurements*. Also make sure to exercise fully to prevent losses in muscle tone.

## Know how to fix loss of compression

One very important factor in determining wheel fit is knowing when you have lost compression! If this happens, your wheels may no *longer look aesthetically pleasing due* to them being totally flattened out.

This can be caused by several things such as over-tightening screws or glue, dry rot, or **something pulling apart**. Whatever it is, it needs to be fixed!

Luckily, there are some easy ways to check for this! First, make sure all of your screw holes are fully covered with grease! This will prevent anything from sticking or drying out which *would potentially cause damage* or loss of function.

Second, use a piece of paper to press down on the tire where the rim meets. Make sure nothing is blocking any hole or edge! This prevents deflection that could affect the pressure readout on your psi meter.

Third, if you feel like the tire is losing air then pull off the rubberized layer (*motorcycle inner tube*) and see if it’s removable. Sometimes they are not so replacing that won’t do much help.

## Know what happens when the compression ratio is too high

Overcompressing your pages will result in poor quality or **even broken images** and documents, due to lack of space for the image or document to fit in.

This can be very frustrating as you try to achieve that perfect look!

Too *much compression also increases file size*, which means it takes longer to download the page, and if you are **using mobile data**, it can add up quickly.

It is best to keep the *compression ratio moderate unless* you know how to calculate it properly.