Another technical essay, this time a very basic one :D
23-11-2005, 11:00 PM
#1
Another technical essay, this time a very basic one :D
Right, seeing as everyone seems to be liking the technical articles and discussions that Stu has been doing a lot of and ive been doing a bit of, i thought i would dig something out that i wrote for another forum many years ago, its FAR more aimed at beginners as i realise that not everyone on here actually knows very much about engines, so this one is to hopefully spark some interest from people who are new to all this!
Basics of tuning an internal combustion engine
(4 stroke only, which almost all cars are).
Well before I can start to discuss tuning, first I will familiarise you with a little bit about how engines work and whats bits are called.
Okay, the basic components of prety much every engine are
block, pistons, rods, crank, cam(s), head, valves, manifolds, fuelling system, spark plugs
Ill deal with these one at a time frist, it should be pretty obivous to most readers but just in case.
Block, the actual main bit of metal that the negine is made from, the bit you can see from the outside.
Pistons, these move up and down inside the block when the engine is running
Rods, connect the pistson to the crank shaft.
Crankshaft, this is where the power comes out of the engine, the pistson moving up and down cause the crankshaft to rotate
Head, the top of the engine as you look at it in the car, at first glance seems to be the same as the block, but closer inspection will reveal a line between them (the head gasket)
Valves, located in the head and open and shut to allow the engine to take in fuel/air and to get rid of exhaust gasses
Cam, opens and shuts the vavles according to the position of the crank.
Manifolds, bolt on to the head and are used to get air/feul into and exhaust gasses from the engine as the valves open and shut
Fuelling system, located before the inlet manifold this is some way of mixing fuel and air (the engine needs both to run), can be either carbs or injection generally
Spark plugs, cause an eltrical spark inside the engine to burn the petrol
Right so what happens with this lot then?
Well essentially the engine works on a cycle:
SUCK
SQUEEZE
BANG
BLOW
Now at first glance that looks like a good night out by anyones standards! LOL! But the engine does this repeatedly, thousands of times a minute in fact!
If the engine is 4 cylinder the engine will have 4 holes in the block with 4 pistsons, each of them does exactly the same thing, so we only need to consider one of them, this applies the same wether its a 4 cylinder or a v8 or whatever.
Right, so here is the 4 strokes of the piston explained a litte:
SUCK: First the piston drop in the block, this draws air/fuel into the engine through the head.
SQUEEZE: Next the piston comes back up, squashing all the fuel/air to make it ready to explode
BANG: Then the spark plugs fire, this forces the piston back down rapidly, turning the crank as it goes, which is what gives the engine power.
BLOW: The piston comes back up to force the used fuel/air gasses out of the exhaust
Thats the fundamentals.
Take some time, go back over that, read it again and make sure you can picture this happening, cause now I am going to go over the same thing again, but with a little more detail about each stroke in the cycle, so you need to be confident with what I have just discussed first.
SUCK: Right, the piston as mentioned before will drop to suck air/fuel in, at the same time the camshaft will rotate to open the inlet vales, this opens the way to allow fuel/air to be sucked in from the carb/injection system, which at the same time will be mixing the fuel/air together
SQUEEZE: The piston comes up to squash the fuel/air mixture inside the engine, now in order to do this the valves have to shut first or it would leak back past them and out of the manifolds, the camshaft therefore rotates again to close the valves off
BANG: Valves are still all shut at this point. The spark plugs fire, this causes a spark to jump across the fuel/air mixture, makig it catch fire rapidly (ie an explosion), this explosion force the piston downwards
BLOW: The camshaft again rotates, this time to open the exhaust valve, this allows the engine to push the spend fuel andair (ie exhaust gasses) out of the head and through the exhaust manifold and into the exhuast.
Right, hopefully now you understand roughly whats going on inside the engine, and I can talk a bit more about how we can get it to produce more power.
As you can imagine, all the power of the engine comes ultiately from one place, and that is the explosions of the fueltaht push the pistons down, therefore every aspect of tuning(*1) will deal with maximising this explosion.
Right the first method of tuning, and arguabley the most important in most engiens, is to deal with the things on the outside of the engine first.
FILTERS AND EXHAUSTS
Right, perforamce filters and exhausts work by realising that standard items are oftendesigned more to be quiet than to allow the engien its best chance to breath effectively.
All air coming into the engine has to be filtered first, now a filter is effectively like a seive, it takes the big lumps of grit and stuff out of the air, the standard filters are designed by the manufactueres to operate quitely, and in order to do this they have to sacrifice power a litte by boxing them away, now there are two ways to improve this system, the first is to replace the cheap and nasty stadnard filter with a better one in the same box, and the second is to replace the whole box with an open filter.
The frist method yields less power, but doesnt increase the noise level, the second method will allow much more air, but youll hear the engine breathing more (and a lovely noise it is too). A hybrid of the two methods is to keep the box but to drill holes in it to allow more air through, dont do this if you dont know what you are doing as you may stop the filter working if you drill the wrong side!
Once the 3rd stroke (bang) has happened in the engine, we move onto the 4th stroke, now at this point the engien tries to quickly get rid of as much as the old fuel and air as it can, but its only got a split second to do it, so it will never succeed compeletely, when the gasses leave the engine they go into the exhuast, now winding there way down the exhaust quitens them down, but at the same time it stops the engine from being albe to get rid of the gasses as quick as it would like to. A performance exhaust, quite simply is one that allows the gasses to leave the engine more quickly, ususally by being made of a bigger diameter pipe than the standard item(*2).
MANIFOLDS
Right, as you can imagine, every time the engine breaths in (induction) it sucks fuel and air in through the inlet manifold, and every time it breathes out (exhaust) it breathes out through the exhaust manifold.
Standard manifolds are sometimes quite restrictive, so modificications can be made to them to allow them to flow better, or they can be repaced by a different (usually larger) item.
HEAD MODS
The cylinder head sits between the actual engien and the manifolds, so anything going through the manifolds has to go through the head to, so again a better rate of flow equals more power, there are several ways of achieving this:
Bigger valves - the vavles open and shut to allow the had to breath, if they are made larger they flow better
Port mods - the ports are the tunnels in the head that gasses flow though, they can be made bigger and also reshaped in order to allow this to happen more easily
Compression Increase - on the second stroke (SQUEEZE) the mixture is squeezed to allow it to ignite better, by increasing the compression we can increase how will this happens, this is a very complicated subject though, too much and youll damage the pistson, so BE CAREFUL with compression.
CAMSHAFT
The camshaft opens and shuts the valves, so by changing it to a different camshaft that opens them for longer, we can gain more power, for some fairly complicated reasons I wont discuss here if you open them for too long, you will lose out on power at slow engine speeds (low revs), but gain on powerat higher engine speeds (high revs).
When choosing a camsahft it is essential to consider what the engine is going to be used for, race car engines are needed only at high revs, so large sacrifices at lowrevs can be made, on a road engine though this will cause 'Cammy' behaviour, where the engine loses power lower down and therefore becomes unpleasant to drive.
(*1)well for now, its not totally true as Ill cover other tuning later such as balancing)
(*2)There is actaully a lot more to it than this, but at this stage, thats the only factor we are going to discuss
Basics of tuning an internal combustion engine
(4 stroke only, which almost all cars are).
Well before I can start to discuss tuning, first I will familiarise you with a little bit about how engines work and whats bits are called.
Okay, the basic components of prety much every engine are
block, pistons, rods, crank, cam(s), head, valves, manifolds, fuelling system, spark plugs
Ill deal with these one at a time frist, it should be pretty obivous to most readers but just in case.
Block, the actual main bit of metal that the negine is made from, the bit you can see from the outside.
Pistons, these move up and down inside the block when the engine is running
Rods, connect the pistson to the crank shaft.
Crankshaft, this is where the power comes out of the engine, the pistson moving up and down cause the crankshaft to rotate
Head, the top of the engine as you look at it in the car, at first glance seems to be the same as the block, but closer inspection will reveal a line between them (the head gasket)
Valves, located in the head and open and shut to allow the engine to take in fuel/air and to get rid of exhaust gasses
Cam, opens and shuts the vavles according to the position of the crank.
Manifolds, bolt on to the head and are used to get air/feul into and exhaust gasses from the engine as the valves open and shut
Fuelling system, located before the inlet manifold this is some way of mixing fuel and air (the engine needs both to run), can be either carbs or injection generally
Spark plugs, cause an eltrical spark inside the engine to burn the petrol
Right so what happens with this lot then?
Well essentially the engine works on a cycle:
SUCK
SQUEEZE
BANG
BLOW
Now at first glance that looks like a good night out by anyones standards! LOL! But the engine does this repeatedly, thousands of times a minute in fact!
If the engine is 4 cylinder the engine will have 4 holes in the block with 4 pistsons, each of them does exactly the same thing, so we only need to consider one of them, this applies the same wether its a 4 cylinder or a v8 or whatever.
Right, so here is the 4 strokes of the piston explained a litte:
SUCK: First the piston drop in the block, this draws air/fuel into the engine through the head.
SQUEEZE: Next the piston comes back up, squashing all the fuel/air to make it ready to explode
BANG: Then the spark plugs fire, this forces the piston back down rapidly, turning the crank as it goes, which is what gives the engine power.
BLOW: The piston comes back up to force the used fuel/air gasses out of the exhaust
Thats the fundamentals.
Take some time, go back over that, read it again and make sure you can picture this happening, cause now I am going to go over the same thing again, but with a little more detail about each stroke in the cycle, so you need to be confident with what I have just discussed first.
SUCK: Right, the piston as mentioned before will drop to suck air/fuel in, at the same time the camshaft will rotate to open the inlet vales, this opens the way to allow fuel/air to be sucked in from the carb/injection system, which at the same time will be mixing the fuel/air together
SQUEEZE: The piston comes up to squash the fuel/air mixture inside the engine, now in order to do this the valves have to shut first or it would leak back past them and out of the manifolds, the camshaft therefore rotates again to close the valves off
BANG: Valves are still all shut at this point. The spark plugs fire, this causes a spark to jump across the fuel/air mixture, makig it catch fire rapidly (ie an explosion), this explosion force the piston downwards
BLOW: The camshaft again rotates, this time to open the exhaust valve, this allows the engine to push the spend fuel andair (ie exhaust gasses) out of the head and through the exhaust manifold and into the exhuast.
Right, hopefully now you understand roughly whats going on inside the engine, and I can talk a bit more about how we can get it to produce more power.
As you can imagine, all the power of the engine comes ultiately from one place, and that is the explosions of the fueltaht push the pistons down, therefore every aspect of tuning(*1) will deal with maximising this explosion.
Right the first method of tuning, and arguabley the most important in most engiens, is to deal with the things on the outside of the engine first.
FILTERS AND EXHAUSTS
Right, perforamce filters and exhausts work by realising that standard items are oftendesigned more to be quiet than to allow the engien its best chance to breath effectively.
All air coming into the engine has to be filtered first, now a filter is effectively like a seive, it takes the big lumps of grit and stuff out of the air, the standard filters are designed by the manufactueres to operate quitely, and in order to do this they have to sacrifice power a litte by boxing them away, now there are two ways to improve this system, the first is to replace the cheap and nasty stadnard filter with a better one in the same box, and the second is to replace the whole box with an open filter.
The frist method yields less power, but doesnt increase the noise level, the second method will allow much more air, but youll hear the engine breathing more (and a lovely noise it is too). A hybrid of the two methods is to keep the box but to drill holes in it to allow more air through, dont do this if you dont know what you are doing as you may stop the filter working if you drill the wrong side!
Once the 3rd stroke (bang) has happened in the engine, we move onto the 4th stroke, now at this point the engien tries to quickly get rid of as much as the old fuel and air as it can, but its only got a split second to do it, so it will never succeed compeletely, when the gasses leave the engine they go into the exhuast, now winding there way down the exhaust quitens them down, but at the same time it stops the engine from being albe to get rid of the gasses as quick as it would like to. A performance exhaust, quite simply is one that allows the gasses to leave the engine more quickly, ususally by being made of a bigger diameter pipe than the standard item(*2).
MANIFOLDS
Right, as you can imagine, every time the engine breaths in (induction) it sucks fuel and air in through the inlet manifold, and every time it breathes out (exhaust) it breathes out through the exhaust manifold.
Standard manifolds are sometimes quite restrictive, so modificications can be made to them to allow them to flow better, or they can be repaced by a different (usually larger) item.
HEAD MODS
The cylinder head sits between the actual engien and the manifolds, so anything going through the manifolds has to go through the head to, so again a better rate of flow equals more power, there are several ways of achieving this:
Bigger valves - the vavles open and shut to allow the had to breath, if they are made larger they flow better
Port mods - the ports are the tunnels in the head that gasses flow though, they can be made bigger and also reshaped in order to allow this to happen more easily
Compression Increase - on the second stroke (SQUEEZE) the mixture is squeezed to allow it to ignite better, by increasing the compression we can increase how will this happens, this is a very complicated subject though, too much and youll damage the pistson, so BE CAREFUL with compression.
CAMSHAFT
The camshaft opens and shuts the valves, so by changing it to a different camshaft that opens them for longer, we can gain more power, for some fairly complicated reasons I wont discuss here if you open them for too long, you will lose out on power at slow engine speeds (low revs), but gain on powerat higher engine speeds (high revs).
When choosing a camsahft it is essential to consider what the engine is going to be used for, race car engines are needed only at high revs, so large sacrifices at lowrevs can be made, on a road engine though this will cause 'Cammy' behaviour, where the engine loses power lower down and therefore becomes unpleasant to drive.
(*1)well for now, its not totally true as Ill cover other tuning later such as balancing)
(*2)There is actaully a lot more to it than this, but at this stage, thats the only factor we are going to discuss
some simple plain talkin there 
26-11-2005, 12:18 PM
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http://www.keveney.com/otto.html
Just thought this might help some people visualise whats going on......
I started making one just like this, but why bother when someone else already has........
Hope its useful.
Just thought this might help some people visualise whats going on......
I started making one just like this, but why bother when someone else already has........
Hope its useful.
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