# cylinders vs displacement

[Forrest Gump 9]

Like the title said, number of cylinders vs the displacement of the engine, which one you rather have?

 

For example, do you rather have a 4.3l v6 engine or 4.3l v8 engine?

 

5.5l v8 or 5.5l v12?

 

Less moving part is better right? Am I on the right track?

[JuicedH22]

Same displacement with more cylinders will have smaller bore/stroke, which typically means it will have the capability to rev higher, make more hp

[Cordell]

So many other factors go into an engine like capacity to move air efficiently that I feel comparing # of cylinders to displacement is not really fair. Other factors aside I'd want a good balance, thats why small block V8s are so popular, good useable power, decent rev range, and they just sound good.

 

Maybe you should consider the strength of the engine with as little mass as possible, then get it to operate over 100% volumetric efficency, then you can see how much displacement you can get into that formula. Thats whats the best. Hows that for a lame attempt at sounding smart?

[BStowers023]

More cylinders

[unfunnyryan]

less cylinders with same displacement = less friction

[Littleguy]

From my general experience more displacement w/less cylinders = more torque/low end, less displacement w/more cylinders = top end power baby. And damn you Ryan for those ugly mugs in your sig.

[JuicedH22]

less cylinders with same displacement = less friction

 

ummmm, while true, that has minimal effect, and then theres the whole size of the bearing face, etc.... either way, you will win no technical argument with that.

[Green Bastard]

What about a big bore with a short stroke? In theory wouldn't you be able to make low end power and be able to rev it? Example: a 4g64 with a 4g63 crank (proper rods pistons and valvetrain) is able to rev to 11k rpms (so I've heard) where the stock redline is somewhere around 8k.

 

With that said, I know you could put in a better valvetrain and balance the motor to be able to squeeze out a few more revs, but could you make that much of a difference that way?

[JuicedH22]

Yes, an oversquare (more bore than stroke) will be able to rev higher and still have tq, but you are limited to the block design on what you can do.

[El Karacho1647545492]

Depends what you want it for. 500ci v8 will get you 1000 feet in one direction faster than anything else, but if you want to go around a track faster than anything you're looking at something like a 5L v12 Porsche 917, or a 2.4L v8 RB7 F1 car as examples.

[Green Bastard]

Yes, an oversquare (more bore than stroke) will be able to rev higher and still have tq, but you are limited to the block design on what you can do.

 

Just curious, how would it limit block design?

[JuicedH22]

No, its limited BY block design. rod angle, clearances, etc...

[Green Bastard]

Gotcha, I misread.

[gbracing81]

Larger cylinder bores promote better breathing abilities and more cylinders promote smoother revving. By adding more cylinders you shorten the time between firing pulses thusly giving a smoother running engine.

[Cordell]

Less moving part is better right? Am I on the right track?

 

If less moving parts was very important rotaries would be all the rage, but it's nothing more then a torqueless 6 cylinder (9 cylinder with triple rotor). This why I brought up the fact that there are too many factors in engine design to say something like number of cylinders or displacement has a simple direct effect on power production. If it was that simple you could be an engineer with basic high school math.

[FourString]

Less moving part is better right? Am I on the right track?

 

Yes, you are correct.

 

:gabe:

[Mensan]

No one has mentioned head flow yet. Total intake and exhaust port flow may be better on an engine with more cylinders, since you're adding more valves. I know this was the case with a Viper that I saw in comparison to a V8 engine of similar displacement. The V8 engines heads flowed better, but with 25% MORE valves, total flow was better on the V10, and it made better power.

[gbracing81]

No one has mentioned head flow yet. Total intake and exhaust port flow may be better on an engine with more cylinders, since you're adding more valves. I know this was the case with a Viper that I saw in comparison to a V8 engine of similar displacement. The V8 engines heads flowed better, but with 25% MORE valves, total flow was better on the V10, and it made better power.

 

I took it as all parts given being equal with the excepition to number of cylinders. Intake design, head design and so on. A larger cylinder bore will breathe better due to when the valve open the air/fuel won't "crash" into the cylinder wall and also the combustion chamber won't shroud the valve. Of course the chamber can still shround the intake chare on a larger bore; however with the larger bore you have more room to work with.

[Mensan]

I took it as all parts given being equal with the excepition to number of cylinders. Intake design, head design and so on. A larger cylinder bore will breathe better due to when the valve open the air/fuel won't "crash" into the cylinder wall and also the combustion chamber won't shroud the valve. Of course the chamber can still shround the intake chare on a larger bore; however with the larger bore you have more room to work with.

 

The only way to get the flow number as high on a similar displacement engine with less cylinders is to significantly increase bore/valve size, which can severely hinder port velocity. Do you understand the importance intake air velocity has on making power?

[Cordell]

The only way to get the flow number as high on a similar displacement engine with less cylinders is to significantly increase bore/valve size, which can severely hinder port velocity. Do you understand the importance intake air velocity has on making power?

 

Damn Eli you sound like an ad for Air Flow Research. This argument has been made over and over again in the LSx engine world, basically the cathedral style heads (especially the ones made by AFR) are claimed to have higher port velocity while the newer style rectangular ports are slower with more volume. Honestly I could care less to have this argument, but I just don't by into port velocity as being as big of a factor as companies like AFR (who have a big stake in the arguement) claim.

[Mensan]

Damn Eli you sound like an ad for Air Flow Research. This argument has been made over and over again in the LSx engine world, basically the cathedral style heads (especially the ones made by AFR) are claimed to have higher port velocity while the newer style rectangular ports are slower with more volume. Honestly I could care less to have this argument, but I just don't by into port velocity as being as big of a factor as companies like AFR (who have a big stake in the arguement) claim.

 

The argument was also made by Smokey Yunick, which to me, means it's gold.

[JuicedH22]

lol. Port velocity is extremely important. But must be coupled with pressure wave theory (and associated phenomena like reversion), port shape and length (friction), surface finish, port angle and any bends, as some of the major design considerations.

[6 Speed S4]

ill take less cylinders same dsplacement for 200 alex

[gbracing81]

The only way to get the flow number as high on a similar displacement engine with less cylinders is to significantly increase bore/valve size, which can severely hinder port velocity. Do you understand the importance intake air velocity has on making power?

 

Yes sir.

[Mensan]

Then I would assume that you understand that an increase in port size relative to bore size could, and most likely would, create a situation similar to the 351C heads, where the bore size was so large significant amounts of power were lost.