Posted by David K on July 27, 2003 at 19:39:33:
In Reply to: Re: FISH: posted by Andrew on July 27, 2003 at 10:31:00:
Andrew:
("Poor class act for a high performance engine ?? The Savage hasn't got a high performance engine.")
Very true, but maybe some improvement is in order.
To the best of my knowledge the Savage Ignitor unit is an electronic switch that is not digital and therefore does not have an ignition timing curve (a unit like on a lawn mower).
I did not say: SPARK PLUG FIRING TIMING, in my posting!! I am not referring to when the spark plug actually sparks. I am talking about the actually moment and condition of the fuel burning. Don't you realize that the fuel can actually ignite without a spark plug? The ignition by excessive heat, compression, lean mixture and or low octane gas---is called DIESELING.
Did I say that I am having problems with my engine? No, I am not having problems with my engine!!
I am posting back to GP about his inquiry about changing the factory timing for more power. He asked the question a few posts before. It is a sensible point of discussion and I figured that you and others might be interested too. Apparently you took the statement to be stupid!? You are not understanding that the timing of an engine should vary as the driving conditions vary.
The spark plug fires ahead of top dead center of the compression stroke. The amount of, before top dead center is determined on when the actual fuel ignition occures. Too much lead and pre-ignition occurs. Too little lead and the ignition is late; after the piston has left top dead center (maybe half way down the stroke). It is ideal to have the ignition of the fuel, at the right time, so as to get the most energy out of a smooth burning push on the piston.
The variable changing of timing is part of most engine design (EXCEPT LAWN MOWERS that run at one-speed and one condition).
I am familiar with centrifugal weight mechanical advances, vacuum advances and the new computorizes/sensor feed back advance methods. There are different advance curves that can be installed/changed--- for hot-rodding or better power; if one wants to override the factory designs of the best EMISSION control. I do not believe that the Savage has an advance curve/variable timing mechanism.
Different octane fuel has a lot to with the timing of the fuel ignition.
I am talking about the partial or complete ignition of the gas-air mixture!
Low octane fuel burns very fast, thus a quick flame front. In contrast to high octane fuel which burns very slow, thus producing a retarded condition (flame front).
The shape of the chamber-wedge and the chamber swirl of the fuel has a lot to do with the ignition of the fuel. Full throttle results in a different fuel ignition (timing) then does partial throttle.
The compression ratio has a lot to do with the ignition timing. High compression results in advanced fuel ignition ("pre-ignition"). Low octane fuel is better suited to low compression, while high octane fuel is designed for high compression. The actual compression pressure, is not only, a product of the compression ratio, but of the amount of air fuel mixture entering the engine.
Even the temperature of the engine affects ignition timing of the fuel.
Andrew, you need to read up on the operating principles and design of 4-stroke engines. After you learn the basic theories of the internal combustion engine you will agree that the octane of the fuel has a most definite effect on fuel ignition timing.
"CHITTY-CHITTY-BANG-BANG" is the title of an old Hollywood movie, staring Julie Andrews. In this movie there is an automobile that flies (Chitty-Chitty-Bang-Bang).
This auto; has CHARACTER, is novel antiquated and nostalgic. I like to think of my Savage as being liken to this old BANG-BANG running car engine.
The Brochure for my Savage has a picture of my cycle next to a "Stirman" crop-duster biplane with the caption of something from the past--- Quote: "Call it a time machine." "The Savage 650 is a 1999 incarnation of the big singles of the '50s and the '60s." "So get in on the timeless tradition of a classic big-single." "Get on the Savage 650." Chitty-Chitty- Bang-Bang.
Lighten up Andrew.