Pros and Cons of different engine types

[r1ckst4]

I dont know much about the technical stuff bout cars... well i know enough.

just wondering why cars use so many different types of engines? what r the pros and cons bout these engines? like the normal 4 strokes cylinders, 2 strokes, rotary, inline, W engine, DOHC, boxer... or other engines that i havent mention.

oh, and another thing... supercharger and turbo... pros and cons???


thanks!

[fa22_raptor]

Veryy veryyyyyy briefly:
4 stroke - More reliable than 2 stroke by far, but only one combustion stroke for every 2 revolutions of the cylinder which means less power.

2 stroke - Not really used in cars because it's very unreliable, but creates more power than a 4 stroke because there's a combustion stroke every revolution of the cylinder.

Rotary - Delivery of power is very smooth because there are less moving parts than a typical engine and this means it's also meant to be more reliable (in theory), but on some RX7s there were some apex seal leak problems. Fuel consumption is quite high because of the shape of the area where the fuel is ignited (it's quite elongated and hence a little less efficient somehow).

Different shapes of engines are a little more trivial because it depends on the application. In theory, if two engines have the same displacement and number of cylinders, they should have the same power and performance. In practice, manufacturers use different configurations due to a number of reasons some of which include: the space each type takes up, the different center of gravities, heritage/tradition etc. Also, I think inlines are a little smoother than Vs but I don't exactly know why. Ws are used simply because if there are lots of cylinders (eg. in the Veyron), it's impractical to use a V16 because of the space it would take up. I'm sure there are other reasons and all, but I'll leave that to someone who knows more.

DOHC stands for double overhead cam meaning that there are two camshafts for every cylinder head. These are used because for engines with greater number of valves per cylinder, all the valves simply do not fit on one camshaft, so two are used instead. These are seen on most cars with four and five valves per cylinder.

Boxer engines as used by Porsche and Subaru are used supposedly for their low center of gravity as the cylinders lie flat in the engine bay. Nowadays, it has become tradition for these two manufacturers to use them as well.

Superchargers... Hrmm... there are 3 main types of superchargers that are used and they all have their individual pros and cons. Do a search on them because I can't be bothered talking about them . It'll also be more informative.

Turbochargers- Unlike superchargers, these are not powered by the driveshaft, but rather the hot exhaust gases which result from combustion. As they don't use the engine's power, the have no parasitic effect on the power of the engine. The disadvantage of them though is that they need the exhaust gases to be flowing rather fast to produce decent power, and hence at low RPMs, they need time to spool up (known as turbo lag).

That sums it up I think, some of it may be wrong as this is only off the top of my head, but it should give you some idea hopefully. Someone else please elaborate and correct.

[charged]

Regarding 2 strokes,I raced 2stroke IT 250 and YZ250 Yamahas many years ago,with just general maintanence they would last a season easy on the same piston,changed rings every couple of events.Its only if you dont do maintanence u run into problems.Its like any race engine thats under high stress 2 or 4 stroke if you dont do your between event maintainence you run into problems.P.S I love 2 strokes only in dirt bikes though

[derekthetree]

all the different engine formations (v's, inlines, boxers etc.) all sound very distinctive. this is due to the harmincs of the shapes and what order the cylinders fire in.

[fpv_gtho]

I think inline engines are smoother than V's because in an inline engine, all the pistons are firing down to the same point, in a V, the left bank is essentially throwing the right bank off balance and vice versa with each ignition

[Matra et Alpine]

2-strokes are MORE reliable as they don't have complex valve train.
It was mainly emissions that killed the 2-stroke ( though now they're able to meet them but nobody wants one ) The need to add oil to the petrol probably l;ed forgetful owners to burn out engines fairly quickly

Vs are better balanced than inlines for the same number of cylinders and big engines.
Some Vs - dependant on cylinders and angle - are NOT well balanced
Usually V8,12 and 16 are well balanced and all the others aren't !!!
Also cross-plane (90 degree crank) 90 degree V are the smoothest 8s but need a heavy crankshaft counter-balance. Others often run counter-balance-shafts to keep everything smoot. I believe that this is easier to do with a V config than an inline.

[Sweeney921]

alright since I've been wondering, and this is the perfect thread for it, what are the pros/cons of boxer engines? Porsche must have a BIG reason for only using them.

[Matra et Alpine]

opposing firing order is naturally balanced and lowest CoG of all engines ( cos it's all flat ) USED to be it was optimal for air cooling too.

[KnifeEdge_2K1]

boxers also eliminate the need for ballancer shafts but due to packaging and cost reasons it is not a good choice for others

[GTR Dreamer]

and as far as i know is it does subaru just use boxers for their cars?
sound lovely by the way!

[r1ckst4]

cool, thanks for the replies guys... especially fa22_raptor, cheers man.

[VtecMini]

I'm going to borrow this thread for a few of my ponders too.

Diesel engines are only really let down by their relative lack of power without forced induction and their weight, but have great economy and lower emissions. Two stroke petrol engines produce a relatively high amount of power for their size and weight, but suffer from relatively poor economy and emissions (As far as I know anyway, I'm basing that ony the little I know about two strokes and what I've learned from my friends Aprilia RS250).

Bearing in mind the merits of a two stroke petrol engine, would it not be possible to produce a two stroke diesel for a car? I can think of quite a few reason why this would be a good thing in my head, but don't really have the technical knowhow to know whether or not it's as good a proposition as it sounds, or indeed feasible.

And the other thing... How does the VAG V5 engine work? Why isn't it all unbalanced and rubbishy? What are the merits of going to the effort of producing something like that when a straight 6 would suffice? And another thing... Why only 2 valves per cylinder? Was there perhaps a shortage of valves in the VAG after they used them all up in the 1.8?

[Matra et Alpine]

2-stroke diesel coudl have some major problems.

2-strokers are revving engines they are NOT torque and have relatively low compression.

Making high compression 2-strokers gets hard.
The benefits of no valves gets hard to stick with as the chamber pressures increase.

If you add mechanical valves and weight then there's really no benefit in being 2-stroker.

[Matra et Alpine]

I knew I had this somewhere.....

Diesel 2-stroke engine from Napier called the "deltic" - see why ? These were used mainly in ships and trains.

Warps the mind trying to work out how it all sucks squeezes bangs and blows

[KnifeEdge_2K1]

I think inline engines are smoother than V's because in an inline engine, all the pistons are firing down to the same point, in a V, the left bank is essentially throwing the right bank off balance and vice versa with each ignition

err i disagree ...

since the piston is connected to the conrod which is connected to the outside of the crank shaft that "point" you're talking about keeps moving

I dont remember the exact reasoning for using a V engine but its something to do with eliminating end to end vibration using distructive interference

also for compacting the engine, a v6 would be alot shorter then an I-6