V2 vs. V4 torque things that make you go hummm

G

Gwendy

New member
Why do V-twins have so much more relative torque vs. a V-4?

I thought the V was the torque but clearly not (RSV4 vs. a 1098 for example, ounce for ounce). For that matter, then, why aren't inline twins much more torquey and HPey?

Why do you need to rev the crap out of a V4 (hit the powerband, not ultimate revs) and yet fart along on a Duc and have constant power?
 
I suspect because the twin has larger pistons (related to the size of the amount of fuel burnt = larger power pulse) but then the in-line twin (side by side) is down to firing order and primary balance
Also consider the torque of a single cylinder to spread the comparison a little further.

'Farting' along on the Ducati is a result of the torque and not power.

Good question - looking forward to more educated responses
 
Yah thanks Brett, you brought the point home with the thumper inclusion. Yamaha made a wonderfully torquey bike that was a single. I think it was called SV650 but I don't remember.

So, if I'm correct on what you're saying, BORE is critical, i.e. more bore (piston diam.) per CC. But then why can't you make a HUGE inline twin with power? They never have power and have basically been abandoned.

Also why are Harleys so lame (sorry!), then? DOHC notwithstanding?

I said fart along only to convey that you don't need to do much to make a Duc work. Give it gas and put it in gear...
 
The SV650 is a Suzuki V-twin. Harley's biggest problem is that they weigh a ton, use push rods, use a primary drive to run the separate gear box and weigh a ton......oh did I already say that??

Harley's biggest step forward was the V-Rod. Sadly alot of purist Hardley's don't like it.
 
Outright power is also more or less directly related to rpm - the higher the rpm the more potential power you can generate. So with a large capacity twin that can't happen because there is a thing called the velocity of a piston to consider (MPV?). I forget the exact figures but there is a theoretical limit to how fast a piston can move inside the cylinder. This is also related to the actual weight of the piston as well and the frictional forces of the rings rubbing against the cylinder wall.
The more cylinders, the smaller the pistons and the shorter the possible stroke (not changing the overall capacity of the motor) and therefore they are able to rev a lot higher.

I think the harley boys who drag race them would not agree with you The harley being a 45 degree motor is once again down to the primary balance again I think which is why they rock and roll so much. The layout of the twin (90 or 45) also has compromises on the motor 'compactness' and position in the frame (weight distribution) and hence the overall design. It's always a compromise depending on what the engineers are after.
 
nono, in drag racing I agree. Even VH have done the Harley thing, though ultimately HD has never been the ultimate anything. A Kawi with supercharged Fred Flinstone gas will win, usually...

This just brings my original point home though, there is something magic about a v twin. Hell's Angels notwithstanding.

OK I'm getting the rpm/piston size thing, but then why didn't the CBX overtake the world? Why did Honda put so much effort into v4s then abandon it for IL4?

There were inline 6's winning races in the 60s. Something gave.

It seems IL4 is the ultimate way to make power, but it's RPM-crazy. Why not just set idle at 6K on an R1? It would make more sense.
 
I believe it's the stroke that gives the torque. A twin typically has a longer stoke than a 4 cyclinder.

EDIT: I may have misinterpreted your question. Yes, the "V" configuration typically gives a larger stroke and more torque. But both motors you asked about are "V's".

2010 Aprilia RSV4 stoke = 52.3 mm ---> 84.8 ft
 
Dimbaratto has a good point. To extrapolate that further if you had a 4 cyl with the same stroke as the Ducati then the bore is obviously smaller, which means less fuel burnt per cylinder negating the amount of torque you'll get.

Also is you think that the smaller the stroke the greater the rev = more hp then consider this. To make a 1098 for example, a high reving short stroke motor of the same capacity then the bore size would get so large to the point where you end up compromising the characteristics of the combustion chamber (among other things) and you end up with inconsistent and poor combustion which puts you backwards. This is part of the reason why they put dual spark into the big twins to remedy some of these problems.

Engineering can be a series of compromises unfortunately. In reference to the CBX 6 cylinder - and if we were to cap the capacity at 1000cc for arguments sake. You need 6 conrods for starters with potentially less power transferred to each etc etc. More weight etc etc. They may have one races in the day but possibly to keep something like that at the top of the pack they would have had to use exotic materials (in those days) to reduce weight etc. To much money for a production bike. Remember the 5 valve per cyl Yamahas ? I think they decided they were in the end too expensive to build and maintain for real world people over a sustained production lifetime.

An inline 6 also has width issues as well as the inherent centrifugal forces that come with a longer crank sitting cross wise in the frame. This is part of the reason why the V4 config is better.
I'm not sure why Honda went back to the IL4 config. Could simply be cost and ease of construction ?
 
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