Characteristics of different Engine configurations

[Muulka]

Hi all, I'm quite new to all of this technical side of things, and I was wondering why car manufacturers chose the displacements and Configurations of their engines, for example why Porsche has an obsession flat-6s, and why engines are so often strange 9in displacement size, sich as F1's 2.4L V8s.

Many thanks for any information.

[Jersey Tom]

What's strange about 2.4L?

[Muulka]

What's strange about 2.4L?

I like even numbers

Like 3.0 or 2.5. What is strange is how toyota has an engine that's like 2/3L or something....

[Jersey Tom]

Well, sorry to disappoint, but 2.5 is not an even number.

What happens if 2.5L is too much power, but 2.0 is not enough? Guess ya gotta go in between, no?

A number is just a number. Big deal. 5.7354724 liters seems like a pretty oddball number, but it equates nicely to 350 ci.

[Muulka]

Well, sorry to disappoint, but 2.5 is not an even number.

What happens if 2.5L is too much power, but 2.0 is not enough? Guess ya gotta go in between, no?

A number is just a number. Big deal. 5.7354724 liters seems like a pretty oddball number, but it equates nicely to 350 ci.

So the engine sizes are for the required power. That's what I wanted to know. But what are the advantages of using a V12 instead of, say, a V6? I don't really know that much about engines, and I want to learn more about them.

[WhiteBlue]

Considering the use of state of the art technology in a simplified view the torque and the power of an engine is proportional to the displacement. This is caused by the limitation of oxygen that the engine can suck in and use for the combustion process. The more air you have the more fuel you can burn.

This view only applies to similar engines with equal levels of rpm and no compression charging by turbo or superchargers. Obviously if you charge an engine with two bar pressure you achieve roughly twice the power from the same displacement. I will drop the issue of charging with this point and come to cylinder configs for naturally aspired engines.

Depending of the performance level of an engine and the type of fuel injection there is an optimum size of the combustion chamber or the displacement by cylinder. This is dictated by the physics of the combustion process. So bigger and more powerfull engines generally have more cylinders than smaller capacity engines.

Another point of consideration is the vibration caused by the oscillating movement of the pistons and con-rods. Configurations like V12 and V10 can be designed to compensate naturally almost all vibrations while V8, V6, L4 and L3 have to rely on multiple or single compensation shafts to dampen engine vibrations for passenger cars.

Naturally more cylinders means more parts, increased cost, more weight, more space, increased friction (except for very high rpm) and increased fuel consumption. The designer has to balance the benefits and constraints for the type of vehicle he wants to target with his engine.

Lately most new engines for road cars and racing cars are turbo charged with reduced displacement and designed with a reduced number of cylinders in order to make significant fuel efficiency advances.

This trend is triggered by technologies like high pressure direct injection, high compression ratios, variable valve timing and lift, high temperature turbo design, twin scroll and variable geometry turbo chargers. The modern turbo engines use waste energy from the exhaust, reduction of pumping losses, reduction of thermal losses and reduced friction to improve the power output from a given fuel supply.

[Muulka]

...

Thank you very much. Very helpful to such a novice as me.

[Sayshina]

Well, sorry to disappoint, but 2.5 is not an even number.

What happens if 2.5L is too much power, but 2.0 is not enough? Guess ya gotta go in between, no?

A number is just a number. Big deal. 5.7354724 liters seems like a pretty oddball number, but it equates nicely to 350 ci.

You might also point out that many engines wind up with "odd" displacements because that happens to be how much they could squeeze into their existing block without having to shut down the production line and retool. So the Toyota inline 4 went from 2.0L to 2.2L to 2.3L at last check.

Many of the engines currently used in production have been around for decades, changing the minimum the manufacturers can get away with from year to year.

Following on from what WB mentioned, Ferrari's most famous engine guy said back in the '60's that the ideal single cylinder volume was between 250cc and 350cc. You want your compression to be as high as practical for efficiency reasons, and there's a maximum limit to how fast you can ask your pistons to travel. This means a big cylinder volume either forces you to run at lower rpm, or forces you to use a pancake thin combustion chamber, both bad.

More cylinders for a given displacement will be able to run at higher rpm while avoiding the pancake dilema, and higher rpm allows you to pump more air/fuel over a given amount of time, meaning more power. Sort of.

WB, there are lots of V-8's and inline 4's running around the world without any counterbalance shafts.

[Pandamasque]

May I just add that many smaller production engines have displacement aimed at particular legislation (taxes) and insurance realities. In many countries it makes no sense to have a 1900cc or 2050cc engine, because you end up paying more tax if you're over 1999cc etc.

[alelanza]

Another point of consideration is the vibration caused by the oscillating movement of the pistons and con-rods. Configurations like V12 and V10 can be designed to compensate naturally almost all vibrations while V8, V6, L4 and L3 have to rely on multiple or single compensation shafts to dampen engine vibrations for passenger cars.

WB, there are lots of V-8's and inline 4's running around the world without any counterbalance shafts.

True, i've never seen balancing shafts in a crossplane V8, and i doubt there are many flatplanes out there that have them. On the other hand V10s do need balancing shafts. It should be added that inline 6s have perfect natural balance (and a V12 is just two inline 6s) and boxer 6 cyl engines also achieve natural balance. Where did you wrongly translate this from WB?

But as for the OP's question, there's no easy answer, there's too many variables to consider and it's hard to deem one config wrong or right over another without taking all variables into account, so if you want to really know i suggest you start reading . As for the examples given, Porsche's flat 6's as i mentioned are perfectly balanced and have a nice low center of gravity. That and the fact that manufacturers try to stick to certain things to achieve differentiation and 'heritage/character', ie Mazda's rotaries, muscle car burbly crossplane V8s, italian screaming v12s and flatplane v8s, Honda's NA small inline 4s and now we even have 500s back with a 2cyl, and this latter engine appears to be quite a technical achievment for various reasons.
As for F1 2.4 V8s, that is the mandated config by the FIA, in fact a myriad characteristics of that engine are in the rulebook. It was a step taken mainly towards cutting down the top speeds that were going out of control with the previous V10s

[hecti]

Another point of consideration is the vibration caused by the oscillating movement of the pistons and con-rods. Configurations like V12 and V10 can be designed to compensate naturally almost all vibrations while V8, V6, L4 and L3 have to rely on multiple or single compensation shafts to dampen engine vibrations for passenger cars.

WB, there are lots of V-8's and inline 4's running around the world without any counterbalance shafts.

True, i've never seen balancing shafts in a crossplane V8, and i doubt there are many flatplanes out there that have them. On the other hand V10s do need balancing shafts. It should be added that inline 6s have perfect natural balance (and a V12 is just two inline 6s) and boxer 6 cyl engines also achieve natural balance. Where did you wrongly translate this from WB?

But as for the OP's question, there's no easy answer, there's too many variables to consider and it's hard to deem one config wrong or right over another without taking all variables into account, so if you want to really know i suggest you start reading . As for the examples given, Porsche's flat 6's as i mentioned are perfectly balanced and have a nice low center of gravity. That and the fact that manufacturers try to stick to certain things to achieve differentiation and 'heritage/character', ie Mazda's rotaries, muscle car burbly crossplane V8s, italian screaming v12s and flatplane v8s, Honda's NA small inline 4s and now we even have 500s back with a 2cyl, and this latter engine appears to be quite a technical achievment for various reasons.
As for F1 2.4 V8s, that is the mandated config by the FIA, in fact a myriad characteristics of that engine are in the rulebook. It was a step taken mainly towards cutting down the top speeds that were going out of control with the previous V10s

last time i checked, a v10 with a 72 degree bank angle needs no balance shafts. correct me if im wrong

[alelanza]

Most of the ones i'm aware of have them, though as always i would imagine that the more racing oriented ones will do without them, as the small imbalances are considered to be ok for less refined applications. But in the end a V10 at any degree is not naturally balanced, you either balance it or live with the not as smooth behavior.

[Ciro Pabón]

Naturally balanced engines include Porsche's flat ones (which explains the strange obsession they have with their SUPERIOR engines).

Anyway, I know this is hard to believe, but for years, 2 liters has been the non official limit for engines that comply with noise, vibration and harshness limits (NVH). The larger the engine, the more expensive it is to comply. Thus, smaller engines in F1 give you cheaper (or better yet, less expensive) cars. Yeah, sure.

[Carlos]

Basic engine balance:
http://en.wikipedia.org/wiki/Primary_ba ... ry_balance

Following the branching terms highlighted in blue exposes a wealth of contributing material.

[alelanza]

Naturally balanced engines include Porsche's flat ones (which explains the strange obsession they have with their SUPERIOR engines).

I find the term flat to be somewhat generic, that's why i specified boxer 6s. Flat is often used to describe 180 deg Vs, which share crankpins, whereas a boxer has separate crankpins for each piston