Engine Compression Ratios: What They Are, How They Work

J&P Cycles® has partnered with Ironworks Magazine to provide great content from their publication for our readers. For additional, great content like this, make sure to check out Ironworks at www.iwblogger.com.

Engine Compression Ratios:  What They Are, How They Work

One of the most commonly asked questions we hear at Delkron is: “If I use these parts what will my engine’s compression be?” This seems to be one of the most misunderstood areas of building a performance engine. In this short series of articles we will discuss both types of compression ratios—Mechanical and Corrected—and how to calculate them.

First let’s understand just what compression ratio means and how it affects the internal combustion engine. Compression ratio is simply the volume of the cylinder and the volume of the combustion chamber of the cylinder head when the piston is at Bottom Dead Center (BDC) and the volume of the cylinder head combustion chamber when the piston is at Top Dead Center (TDC). Let’s use a hypothetical engine to make things a little simpler. If we have an engine, at BDC that has a swept volume of 900cc in the cylinder and a combustion chamber volume of 100cc, then this volume is reduced to the 100cc of the combustion chamber at TDC this would be a compression ratio of 1000:100, or reducing it fractionally, a compression ratio of 10:1.

Compression ratios can be a double-edged sword in many ways. First, the higher the compression the more power the engine will make. This is due to being able to extract greater mechanical energy from a given amount of air/fuel mixture that is created by its higher thermal efficiency. Higher compression ratios place the molecular structure of the fuel and air into a smaller area, along with the adiabatic heat of the compression, which causes a greater evaporation and mixing of the fuel droplets in the combustion chamber.

High compression engines make great power, but it needs to be understood that engines with higher compression require fuel of higher octane and grade. Low octane, low grade fuels can cause severe and irreparable damage to an engine due to detonation. Detonation is caused when the fuel self-ignites under compression—not during the firing phase of the ignition system. Detonation can be the cause of connecting rod failures, piston failures, and more.

Just as high compression wants better fuel, the other side of the coin is running higher octane fuels in low compression engines. Running high octane fuel in a low compression engine is, well, throwing good money down a black hole. You are not going to make any more power than you would using the correct, lower octane fuel due to the fact that the lower compression engine just simply does not have enough compression to support the higher octane fuel. Running high octane fuels in a low compression engine is many times the reason riders bitch and complain about tuning issues of carburetors, ignition systems, etc.  In many cases the only reason that the operator feels more power is due to the fact the he has spent more money so it must be working!

A simple rule to remember is that the lower the octane the faster the burn, and the higher the octane the slower the burn. This is why high compression engines like higher octane fuels because they burn slower and are not as prone to self-ignition, or detonation. The same rule applies to low compression engines liking lower octane fuels; lower compression engines do not have to work as hard to light the fuel mixture due to the lower octane fuel burning faster with out a lot of compression.

*RESOURCE
DELKRON Inc.
Bedford, Ohio
440-786-8820/866-335-5766
www.delkron-mfg.com

Story and Photos by Steve “Posie” Pfaff, Delkron

Leave a Reply

Your email address will not be published. Required fields are marked *

You may use these HTML tags and attributes: <a href="" title=""> <abbr title=""> <acronym title=""> <b> <blockquote cite=""> <cite> <code> <del datetime=""> <em> <i> <q cite=""> <s> <strike> <strong>

  1. Pingback: 2 Lotus F1 teams | Auto advice Blog

  2. Pingback: Q&A: is a puch moped a 2 stroke or a 4 stroke engine? if 2 stroke, what mixture ratio is it? | Buy a Moped

  3. Pingback: A Look at the Different Types of Pellet Rifles | Ultimate Fishing and Hunting Blog

  4. Pingback: Benefit Through Internet Marketing Or Online Marketing! | Welcome To Marketing

  5. Pingback: Tampa Web Marketing Firm Introduces Innovative SEO Strategy | Welcome To Marketing

  6. Pingback: Take Your Business To New Heights With Search Engine Marketing Company | Welcome To Marketing

  7. Pingback: Internet Marketing Best Internet Marketing Solutions without d? Think too | Welcome To Marketing

  8. Pingback: Internet Marketing: Create a Buzz in the Internet through Search Engine Marketing! | Welcome To Marketing

  9. Pingback: The miracle of art voltage? Rielle. | Uncategorized | Information about Penis Enlargement!

  10. Pingback: PPC Bid Management | Welcome To Marketing

  11. Pingback: Significant Facts Of Your Motorized Bicycle | Buy a Moped

  12. Pingback: A Fasten Tech with search engine optimisation | RoAce's 123 Power System Blog & Marketing Tips!

  13. Pingback: Diesel Exhaust System | Diesel Performance Parts

  14. Pingback: Our Automotive Blog » Why Folks Use Diesel

  15. Pingback: Mechanical Compression Ratio | Motorcycle Parts and Accessories Blog

  16. Pingback: Tweets that mention Engine Compression Ratios: What They Are, How They Work | Motorcycle Parts and Accessories Blog -- Topsy.com