Why less cylinders?

[ksa8907]

Originally Posted by RobertISaar

you also have less displacement. make up the difference in displacement via a larger bore and torque will be quite similar to what it was before changes. possibly better, since the valves won't be as shrouded.

then there's the whole "a shorter stroke will allow longer rods" argument that comes up in certain circles.

Not trying to argue here, in fact I agree. By increasing the bore you are increasing the force on the crank. Chrysler gained 30tq/hp by increasing the bore of a 3.2 by 4mm making the 3.5 stroke remained the same but compression increased because of the larger bore.

[RobertISaar]

well, in any case, there's no magic involved, and like every engine decision ever, compromises must be made.

i actually like the thought of a 2 liter V8... or maybe L8... 250cc cylinders have been done FOREVER, i would probably gladly take the small efficiency hit to have a smoother, better sounding engine.... but i'm also an enthusiast of that sort. most of the general population is not.

[NHB]

Originally Posted by RobertISaar

i actually like the thought of a 2 liter V8... or maybe L8... 250cc cylinders have been done FOREVER, i would probably gladly take the small efficiency hit to have a smoother, better sounding engine.... but i'm also an enthusiast of that sort. most of the general population is not.

If sound is a factor, we will prever 3 cylinder engines over 4 bangers. Many motorcyclists seem to enjoy the noise of two cylinder engines...

[baldlobo]

2.5l I4 ohv tbi
wet manifold tuned for a set rpm range
shrouded valves in cylinder head
counter balancing shafts

2.5l 60v6 ohv mpi
mpi intake(can be tuned better then a wet intake manifold)
cylinder head valves are less shrouded due to mounting
No balancing shafts
possibly better camshaft specs

2.5l I6 dohc mpi
due too the change in camshaft layout, valves have to be canted at an angle in order to be efficiently activated; resulting in less valve shroud
longer intake manifold.
no balancing shafts


ps. there are alot of things that can change an engines efficiency
AutoZine Technical School

[ksa8907]

Getting back to the original question. For high volume production models, its all about cost. Chrysler had to add a second sets of plugs in the hemi just to meet emissions, but they're cheap as hell to build.

[320touring]

as stated before, less cyls=

lower manufacturing cost

Less energy Loss (friction and surface area for head dissipation)

Better torque for the same capacity (e.g my dad's 2.0 4pot Avensis has more torque than my 6pot 320i)

better/easier packaging (less engine bay space required)



however, gimme a small capacity v6/straight 6 or v8 over a 4pot any day- the noise is just sublime!

building a car as a saleable tool= fewest cyls possible to meet design critera

building it as an engaging, dynamic and emotive "desirable" object, then more cyls and better sounds please!

[Slow_s10]

Originally Posted by RobertISaar

well, in any case, there's no magic involved, and like every engine decision ever, compromises must be made.

i actually like the thought of a 2 liter V8... or maybe L8... 250cc cylinders have been done FOREVER, i would probably gladly take the small efficiency hit to have a smoother, better sounding engine.... but i'm also an enthusiast of that sort. most of the general population is not.

Have you ever heard of the Hartley V8s? They are 2.8L V8s that redline at 10,000 rpm, make around 400 hp and only weigh like 200 pounds. It's basically two Hyabusa V4 motorcycle engines stuck together. They're pretty nutty... and crazy expensive.

But if that's not quite crazy enough, they also have bored out versions 2.9L and 3.0L that make 450hp, and 500hp respectfully, and if you really want to go nuts they even make twin turbocharged versions that make up to 1000hp. Heaven forbid I ever win the lottery because I would buy a stack of them.

[razor02097]

Small V12 engines are for one thing. Smooth operation. There are several videos around with the coin test. The operator balances a coin on it's end on top of the engine then starts it up. The coin stays put. THe engine idles and revs very smooth. The power is there at almost any RPM. However they aren't economical. There are a lot of moving parts and friction points so power is lost just moving all of those parts.

Many people buy a V6 because they are smoother and offer more power yet still get decent fuel economy. In production cars in order to get V6 power from a 4 cylinder and still meet emissions you have to use premium fuel and a turbo. Generally a V6 in that case would be more economical due to the lower cost of maintenance and the fact you can use 87 octane.

People don't buy V8 engine vehicles because they are efficient. They buy them for fun or out of necessity. The new trend isn't I4 replacing V6 it is V6 replacing the V8. Case in point is the ecoboost engine. You can get crap loads of HP and torque from that turbo V6. Enough to tow with...yet the vehicle is economical enough to make it your daily driver.

[elhigh]

I know everyone will have already addressed the issues of thermal efficiency, friction etc. But there's a really simple one:

Cost. More cylinders means more tooling, more weight, more fasteners, more work to make the engine. If you're building an economy car, there's already next to no profit margin in it. If you can screw together the engine with fewer parts, less tooling, fewer workers, do that.

[razor02097]

Originally Posted by elhigh

I know everyone will have already addressed the issues of thermal efficiency, friction etc. But there's a really simple one:

Cost. More cylinders means more tooling, more weight, more fasteners, more work to make the engine. If you're building an economy car, there's already next to no profit margin in it. If you can screw together the engine with fewer parts, less tooling, fewer workers, do that.

Actually if they can shoehorn in an existing engine and transmission assembly available from another platform it will save them more money than trying to tool up for a basic engine build. Even if it costs a little bit more per unit to physically build it will cost a lot less if there is a larger run (quantity of engines built in a given period of time). Simply put in manufacturing more units = less cost per unit. Which is why you often find the same basic engine in several different vehicles. Sure marketing, decals and engine covers will vary but the heart is the same.