The Spares Company
Club Shop/Regalia
Parent Website
Contact Officials
Machine Registrar
Club Secretary
Membership Secretaries
MPH Editor and Forum Administrator.
Section Newsletters
Technical Databases
Photos
Home
What's new
Latest activity
Forums
New posts
What's new
New posts
Latest activity
Information
Bike Modifications
Machine Data Services
Manufacturers Manuals
Spare Parts Listings
Technical Diagrams
Whitakerpedia (Vincent Wiki)
The Club
MPH Material Archive
Flogger's Corner
Obituaries
VOC Sections
Local Sections
Local Section Newsletters
Miscellaneous
Club Assets
Club History
Club Rules
Machine Data Services
Meeting Documents
Miscellaneous
Essential Reading
Magazine/Newspaper Articles/Letters
Adverts and Sales Brochures
The Mighty Garage Videos
Bikes For Sale (Spares Company)
Log in
Register
What's new
New posts
Menu
Log in
Register
Install the app
Install
Home
Forums
Forums: Public Access
Tech. Advice: Series 'B' / 'C' 500cc/1000cc Bikes
Comet badly tuned or just underpowered?
JavaScript is disabled. For a better experience, please enable JavaScript in your browser before proceeding.
You are using an out of date browser. It may not display this or other websites correctly.
You should upgrade or use an
alternative browser
.
Reply to thread
Message
<blockquote data-quote="clevtrev" data-source="post: 22648" data-attributes="member: 187"><p>Detonation is not pinking, it`s pre-ignition. Detonation occurs after TDC. </p><p>Copied from Jtan.</p><p>There are many articles on the difference between the two at your Google </p><p>fingertips. Here is one:</p><p></p><p>Reprinted from Issue 54 of CONTACT! Magazine, published in January, 2000</p><p>All high output engines are prone to destructive tendencies as a result of </p><p>over boost, misfueling, mis-tuning and inadequate cooling. The engine </p><p>community pushes ever nearer to the limits of power output. As they often </p><p>learn cylinder chamber combustion processes can quickly gravitate to engine </p><p>failure. This article defines two types of engine failures, detonation and </p><p>pre-ignition, that are as insidious in nature to users as they are hard to </p><p>recognize and detect. This discussion is intended only as a primer about </p><p>these combustion processes since whole books have been devoted to the </p><p>subject.</p><p>First, let us review normal combustion. It is the burning of a fuel and air </p><p>mixture charge in the combustion chamber. It should burn in a steady, even </p><p>fashion across the chamber, originating at the spark plug and progressing </p><p>across the chamber in a three dimensional fashion. Similar to a pebble in a </p><p>glass smooth pond with the ripples spreading out, the flame front should </p><p>progress in an orderly fashion. The burn moves all the way across the </p><p>chamber and , quenches (cools) against the walls and the piston crown. The </p><p>burn should be complete with no remaining fuel-air mixture. Note that the </p><p>mixture does not "explode" but burns in an orderly fashion.</p><p>There is another factor that engineers look for to quantify combustion. It </p><p>is called "location of peak pressure (LPP)." It is measured by an </p><p>in-cylinder pressure transducer. Ideally, the LPP should occur at 14 degrees </p><p>after top dead center. Depending on the chamber design and the burn rate, if </p><p>one would initiate the spark at its optimum timing (20 degrees BTDC, for </p><p>example) the burn would progress through the chamber and reach LPP, or peak </p><p>pressure at 14 degrees after top dead center. LPP is a mechanical factor </p><p>just as an engine is a mechanical device. The piston can only go up and down </p><p>so fast. If you peak the pressure too soon or too late in the cycle, you </p><p>won't have optimum work. Therefore, LPP is always 14 degrees ATDC for any </p><p>engine.</p><p>I introduce LPP now to illustrate the idea that there is a characteristic </p><p>pressure buildup (compression and combustion) and decay (piston downward </p><p>movement and exhaust valve opening) during the combustion process that can </p><p>be considered "normal" if it is smooth, controlled and its peak occurs at 14 </p><p>degrees ATDC.</p><p>Our enlarged definition of normal combustion now says that the charge/bum is </p><p>initiated with the spark plug, a nice even burn moves across the chamber, </p><p>combustion is completed and peak pressure occurs at at 14 ATDC.</p><p>Confusion and a lot of questions exist as to detonation and pre-ignition. </p><p>Sometimes you hear mistaken terms like "pre-detonation". Detonation is one </p><p>phenomenon that is abnormal combustion. Pre-ignition is another phenomenon </p><p>that is abnormal combustion. The two, as we will talk about, are somewhat </p><p>related but are two distinctly different phenomenon and can induce </p><p>distinctly different failure modes.</p><p>KEY DEFINITIONS</p><p>Detonation: Detonation is the spontaneous combustion of the end-gas </p><p>(remaining fuel/air mixture) in the chamber. It always occurs after normal </p><p>combustion is initiated by the spark plug. The initial combustion at the </p><p>spark plug is followed by a normal combustion burn. For some reason, likely </p><p>heat and pressure, the end gas in the chamber spontaneously combusts. The </p><p>key point here is that detonation occurs after you have initiated the normal </p><p>combustion with the spark plug.</p><p>Pre-ignition: Pre-ignition is defined as the ignition of the mixture prior </p><p>to the spark plug firing. Anytime something causes the mixture in the </p><p>chamber to ignite prior to the spark plug event it is classified as </p><p>pre-ignition. The two are completely different and abnormal phenomenon.</p></blockquote><p></p>
[QUOTE="clevtrev, post: 22648, member: 187"] Detonation is not pinking, it`s pre-ignition. Detonation occurs after TDC. Copied from Jtan. There are many articles on the difference between the two at your Google fingertips. Here is one: Reprinted from Issue 54 of CONTACT! Magazine, published in January, 2000 All high output engines are prone to destructive tendencies as a result of over boost, misfueling, mis-tuning and inadequate cooling. The engine community pushes ever nearer to the limits of power output. As they often learn cylinder chamber combustion processes can quickly gravitate to engine failure. This article defines two types of engine failures, detonation and pre-ignition, that are as insidious in nature to users as they are hard to recognize and detect. This discussion is intended only as a primer about these combustion processes since whole books have been devoted to the subject. First, let us review normal combustion. It is the burning of a fuel and air mixture charge in the combustion chamber. It should burn in a steady, even fashion across the chamber, originating at the spark plug and progressing across the chamber in a three dimensional fashion. Similar to a pebble in a glass smooth pond with the ripples spreading out, the flame front should progress in an orderly fashion. The burn moves all the way across the chamber and , quenches (cools) against the walls and the piston crown. The burn should be complete with no remaining fuel-air mixture. Note that the mixture does not "explode" but burns in an orderly fashion. There is another factor that engineers look for to quantify combustion. It is called "location of peak pressure (LPP)." It is measured by an in-cylinder pressure transducer. Ideally, the LPP should occur at 14 degrees after top dead center. Depending on the chamber design and the burn rate, if one would initiate the spark at its optimum timing (20 degrees BTDC, for example) the burn would progress through the chamber and reach LPP, or peak pressure at 14 degrees after top dead center. LPP is a mechanical factor just as an engine is a mechanical device. The piston can only go up and down so fast. If you peak the pressure too soon or too late in the cycle, you won't have optimum work. Therefore, LPP is always 14 degrees ATDC for any engine. I introduce LPP now to illustrate the idea that there is a characteristic pressure buildup (compression and combustion) and decay (piston downward movement and exhaust valve opening) during the combustion process that can be considered "normal" if it is smooth, controlled and its peak occurs at 14 degrees ATDC. Our enlarged definition of normal combustion now says that the charge/bum is initiated with the spark plug, a nice even burn moves across the chamber, combustion is completed and peak pressure occurs at at 14 ATDC. Confusion and a lot of questions exist as to detonation and pre-ignition. Sometimes you hear mistaken terms like "pre-detonation". Detonation is one phenomenon that is abnormal combustion. Pre-ignition is another phenomenon that is abnormal combustion. The two, as we will talk about, are somewhat related but are two distinctly different phenomenon and can induce distinctly different failure modes. KEY DEFINITIONS Detonation: Detonation is the spontaneous combustion of the end-gas (remaining fuel/air mixture) in the chamber. It always occurs after normal combustion is initiated by the spark plug. The initial combustion at the spark plug is followed by a normal combustion burn. For some reason, likely heat and pressure, the end gas in the chamber spontaneously combusts. The key point here is that detonation occurs after you have initiated the normal combustion with the spark plug. Pre-ignition: Pre-ignition is defined as the ignition of the mixture prior to the spark plug firing. Anytime something causes the mixture in the chamber to ignite prior to the spark plug event it is classified as pre-ignition. The two are completely different and abnormal phenomenon. [/QUOTE]
Insert quotes…
Verification
The Series 'A' Rapide was known as the '********' Nightmare?
Post reply
Home
Forums
Forums: Public Access
Tech. Advice: Series 'B' / 'C' 500cc/1000cc Bikes
Comet badly tuned or just underpowered?
This site uses cookies to help personalise content, tailor your experience and to keep you logged in if you register.
By continuing to use this site, you are consenting to our use of cookies.
Accept
Learn more…
Top