i have a couple of things that i need help understanding engines

1. what;s the difference between a revy engine to a torque engine, in relation to bore and stroke

2. what camshaft profiles are used for a race/street tuned car to an all day family sedan

3. and just need confirmation on a rotarty, the way i understand is that, a rotarty works but have a triangle like thing, and that spark plugs are set up in way, that they fire when the triangle moves a certain degree, then this keeps rotating, do rotataries have a number of things, eg like 4 cylinders, or is it just one big fat triangle

i'm studying engines at the moment, and i'm confused about the three things above so if anyone can give me light, or point me in the direction that would contain the information i need, would be good, i have a couple of books, but i'm confused

Somewhere around here Ive car a car mag that has a good story about how rotaries work, if no one comes up with a good link I'll try to find it and scan it for you.

I'll get flamed for this but as a broad rule of thumb, the short stroke enginestend to produce power at higher revs and the long strokers tend to be torquey at lower revs.

A short stroke is where the stroke is less than the bore,
a long stoke is when its more than the bore and when they are the same its usually called square.

Flame away troops..........I did say broad rule.:D

i have a couple of things that i need help understanding engines

3. and just need confirmation on a rotarty, the way i understand is that, a rotarty works but have a triangle like thing, and that spark plugs are set up in way, that they fire when the triangle moves a certain degree, then this keeps rotating, do rotataries have a number of things, eg like 4 cylinders, or is it just one big fat triangle



You can read about how rotarys work here

http://auto.howstuffworks.com/rotary-engine.htm

hahaha i forgot about that site

thanks

i have a couple of things that i need help understanding engines

1. what;s the difference between a revy engine to a torque engine, in relation to bore and stroke

2. what camshaft profiles are used for a race/street tuned car to an all day family sedan

3. and just need confirmation on a rotarty, the way i understand is that, a rotarty works but have a triangle like thing, and that spark plugs are set up in way, that they fire when the triangle moves a certain degree, then this keeps rotating, do rotataries have a number of things, eg like 4 cylinders, or is it just one big fat triangle



1. As said before a general rule is the shorter the stroke the revier the engine. An engine engine with a long stroke will usually have good torque but not rev high. There are other factors that effect the ability to rev.

2. Race cams have higher valve lift and also the valve timing is suited to higher revs.

3. Rotaries usually come with 2 "triangles" but can come with 3 aswell

i have a couple of things that i need help understanding engines

1. what;s the difference between a revy engine to a torque engine, in relation to bore and stroke

2. what camshaft profiles are used for a race/street tuned car to an all day family sedan

3. and just need confirmation on a rotarty, the way i understand is that, a rotarty works but have a triangle like thing, and that spark plugs are set up in way, that they fire when the triangle moves a certain degree, then this keeps rotating, do rotataries have a number of things, eg like 4 cylinders, or is it just one big fat triangle

i'm studying engines at the moment, and i'm confused about the three things above so if anyone can give me light, or point me in the direction that would contain the information i need, would be good, i have a couple of books, but i'm confused

1. A revvier engine is one where the bore is larger than the stroke, these are called oversquare engines. A torquey engine is one where the stroke is closer to the bore. These are also oversquare. In most modern engines the bore is larger than the stroke, this is mainly due to the problem where if the stroke was larger than the bore the valves have problems letting enough air in. Diesels though can have a stroke larger than the bore and these engines are called undersquare. A square engine is one where the stroke and the bore are equal in case you hadn't already guessed.

The reason why engines with longer strokes produce more torque is due to the larger distance that the big end bearing is from the axis of rotation of the crankshaft. As torque is Force x distance, a larger distance with a similar force will produce more torque. This gif (http://en.wikipedia.org/wiki/Image:Cshaft.gif) may help people understand it.

The reason why torquey engines can't rev so well is due to the piston reaching it's maximum safe velocity/acceleration at lower revs. When both engines are at the same rpm the torquey piston must travel a further distance in the same time as the revvy engine due to the longer stroke. This means that the t piston must have a higher acceleration than the v piston. There becomes a point during the exhaust stroke where the forces to decelerate the piston become so large that they elongate the conrod to dangerous levels. Once this point is passed two things can happen, the conrod can break, sending the piston into the top of the head. Or it can elongate to a level where the piston will hit the valves/head. Neither of these outcomes are acceptable lol.



2. A racing cam will be of a higher lift, longer duration and have more valve overlap. The reason why, is that these cams are designed to create maximum torque at high rpm. At high rpm's the gasses travelling into and out of the piston are travelling at very very high speeds. Due to the high velocity these gasses have a high momentum. Also due to the short time interval between the BDC and TDC there is less time to get air into the engine and a longer duration is needed.

For instance, here are the standard and race cam profiles for a Suzuki Swift GTi
Standard 4000-8200rpm
8 intake opens (deg BTDC) 39
36 intake closes (deg ABDC) 79
224 intake duration (deg) 298
42 exhaust opens (BBDC) 79
10 exhaust closes (ATDC) 39
232 exhaust duration (deg) 298
18 overlap (deg) 78
7.5 valve lift (mm) 10.4

I got these figures from 21st Century Performance by Julian Edgar. In fact most of my understanding of this came from that book. I really really suggest you go out and have a look at a copy as it explains the cam stuff in more detail. It pretty much explains how modern performance cars work and how to properly modify them. (ie equations for tuning exhausts, intake runners, plenum chambers etc.)



3. Sorry. All I know about rotaries is that they break easily, are high maintenance and really go through the fuel.lol

Hope this helps you. Any questions just ask.

3. Rotaries usually come with 2 "triangles" but can come with 3 aswell





mmmmm triple rotor 20B :D

but there is singles as well i thinks, wait just found a 40A

and dont forget the 787B with a quad rotor 26B with 700hp

http://www.answers.com/topic/mazda-wankel-engine


i guess think of reving this way, when the stroke is short the movment for the piston is only small when doing 1 reveloution, but on a long stroke the piston has to move a lot further to revolve. so there for on a long stoke motor a X rpm the pistons will be moving faster if the short stroke motor is also at x rpm. and speed and weight then goes to momentum dont want the piston to want to just through the head