[10th Warrior]

ok, there are plenty of V6s around 2.5L. my question is, which is more effiecent (both for fuel economy and power/torque generation) and why. please note, this is not a specific question about the EJ25, but about engine mechanics in general. what does lots of small cylinders provide that less larger cylinders doesn't, and vis a versa?

 

[Guest]

I think smaller pistons allow you to rev really fast. Wasn't Ferrari making like 2.5-3 liter v-12s a while ago? How big are the F1 engines? Granted the valvetrain has to be up to the task as well, but it seems to me that a bunch of tiny pistons would be better suited to turning 10k RPM than a couple of really big ones.

 

[awd]

If I am not mistaken the F1 engines are 3 liter v-10's.

 

[JGard18]

yeah, I believe that in generall, smaller cylinders means higher RPM's and higher horsepower. Larger cylinders, however, will give more torque down low.

Kinda like with motorcycle engines. Take a 650 V-twin (as I have), vs. a 750 4 cyl. the 650 twin makes more torque...but it's not as rev happy, and doesn't have the same high end power...

 

[spshultz]

I think smaller pistons allow you to rev really fast. Wasn't Ferrari making like 2.5-3 liter v-12s a while ago? How big are the F1 engines? Granted the valvetrain has to be up to the task as well, but it seems to me that a bunch of tiny pistons would be better suited to turning 10k RPM than a couple of really big ones.

Example:

I have an 85 Ford F-150 with 4.9L I-6. 9.0:1 compression, big engine. Rev's pretty damned slow. Sounds like it is going to blow up @ 4500rpm but the thing has amazing torque. A lot of those who use some sort of FI on these will lower the compression and lighten everything up so that they will spin faster. Even when doing this they still have awesome torque.

My truck may not win any races but hauling 2000lbs of brick in the bed with no noticeable difference in acceleration is very cool.

 

[RMCracing]

Actually, they made engines that were as small as 2.0 with 12 cy.
and they wined to 15 or 16 thousand RPM and some went even higher.
But NO torque in those babies!!!:nuetron:

 

[RS25.com]

ACTUALLY they made the engines as small as 1.0 and 1.5 liters, and yeah, the redline on a smaller pistoned engine is MUCH higher. Some of those F1 engines have over 1,000 horsepower! The Suzuki Bandit 400 motorcycle, for example, has a 14,000 (or is it 16,000) RPM redline. Not a ton of torque, but enough horsepower to go crazy. And that thing sounds scary when reved! (I was next to my friend on his Bandit and the noise from his engine made me think my engine was falling apart! )

Larger engines have more torque, generally, and less horsepower because they rev slower. Big rigs with giant engines, therefore, have much lower redlines. Probably about 3,000 to 4,000 RPM max, but tons of load-pulling torque.

 

[spshultz]

So (and I'm talking out of my ass here) would Torque be a product of rotational mass?

 

[JGard18]

not really...but it could be a factor, I suppose...

here, see this:
http://www.howstuffworks.com/fpte3.htm

so a larger compression area will generally mean a larger stroke, and a larger stroke means a longer "arm" providing the torque. (this will makes sense once you read the link)

 

[yamarocket630]

you wanna talk rpm? honda made a 5 cylinder 125cc (.125l) 2 stroke back in the 60's for GP racing that made max power at 20,000 rpm, and redlined at 22k! it had to run on low octane gas, cause the race fuel wouldn't burn fast enough.

 

[RMCracing]

oppps

 

[RaceCarRiot]

you wanna talk rpm? honda made a 5 cylinder 125cc (.125l) 2 stroke back in the 60's for GP racing that made max power at 20,000 rpm, and redlined at 22k! it had to run on low octane gas, cause the race fuel wouldn't burn fast enough.

i had the pleasure of seeing one run solo at daytona a couple years ago.

even when it was faaaaaar away on the back stretch people were STILL holding their ears. :lol: loud doesn't even begin to describe the sound...

 

[yamarocket630]

yeah, it sounds kinda like someone cutting sheet metal with a wood blade on a circular saw.

 

[DoorKnob]

Hello, I just wanted to mention that it's bad to have the cylinders too big because it takes longer for the flame front to reach the sides of the cylinders and the larger surface area sucks up more of that all important heat.

~Alan

 

[RaceCarRiot]

Hello, I just wanted to mention that it's bad to have the cylinders too big because it takes longer for the flame front to reach the sides of the cylinders and the larger surface area sucks up more of that all important heat.

sorta O/T, but this is why turbo'ed 2.5's are so prone to detonating...

 

[10th Warrior]

sorta O/T, but this is why turbo'ed 2.5's are so prone to detonating...

that and the high compression ratio.

thanks for all the info, everybody!