270 V 360

You can only make a 4 stroke vertical twin fire one of the two ways. Triumph tried both. But they wanted their cruiser twins to sound more like a v-twin, so they started making a 270degree engine. I think they have now dropped the 360deg crank entirely. [Not sure on the new water cooled ones]. Why make 2 different cranks and cams for what is essentially the same engine ? It really makes little difference. ...J.D.

 

270° crank make's more torque for the same displacement and cam profile , 360° make's more horse power for the same displacement and cam profile.
The 360° needs to be revved a little bit harder than the 270° to achieve the same torque , HP is RPM related , torque more displacement or number of firing cylinders closer together ...
V6 or V8 motors are more torque than straight or horizontally opposed ..

So a 270° crankshaft motor is slightly more relaxed in its operations than a 360° As it requires a less aggressive throttle action to motivate !!

 

Well, three. Trivia: 270° maintains non-zero piston inertia. Whereas a 360° (and 180°), both pistons are dead stopped at the same time twice per revolution.

 

What you are saying is of course true. But basically the pistons have to rise and fall, either together or apart. It still takes two rotations of the crank to achieve one power cycle. ...J.D.

 

GTV99.
Welcome to the family. Wish you luck with the test and bike. With the right cans and a few tweaks you can make the triumphs sound really good. So good you can't tell the difference between the new and the classic.
Joe.

 

Welcome GTV99
I've got a 360° Bonneville, and it sounds just like my dad's bikes, with one exception.
I could hear my dad coming home from several streets away, whereas this modern bike is a lot quieter, so I only know it sounds "correct" because I know what the original bikes sounded like.

 

In reality, you could make any crank configuration that you want - it would make not one iota of difference to torque or power as each piston is operating on a cycle independent of any other.
The old XS250/400 Yamaha used to have a 180 crank and therefore a skewed firing cycle, likewise the TDM850 twin had a 270 crank and apart from the inherent difference in sound, the only real difference is in the resulting primary vibrations caused by the configuration..
As a kid, I always thought a 360 twin must be like riding a pneumatic road drill but in reality, two small pistons travelling together is no more vibratory than one big single of the same mass.
Superficial logic tells you that a 180 crank would be the smoothest from the point of view of primary vibrations but it isn’t!!! If you imagine a situation with both pistons at the same height and the crank pins at 90/270, the piston travelling upwards to TDC and back has much further to travel than the one going down to BDC and back. Each piston is subject to different forces imposed by the conrods and it is these out of balance primary forces which lead to significant tingly vibes when riding high performance two stroke twins vibrate at high revs and of course, same applies to a conventional 4-cylinder.
There will be an optimal configuration to damp out primary vibes without recourse to a balancer shaft but I don’t know what it is. Maybe 270 is nearer the mark than 180 or 360.
Not really important for us mere mortals - we either like a bike or we don’t. . . .

 

You are wrong ! 270° crank V 180° cranks do produce power differently !
Because 270° crank has a cylinder firing 90° after the previous , more torque in those 90° , 180° has more horsepower because the torque is spread over two 360°cycles 180° apart , horse power is slightly different and higher because there is less lost due to several causes being reduced friction on the combustion stroke , .. less .. torque in action.
Look up the power and torque given for 865cc Bonnie and America . You'll see they are slightly different !?

 

This is an interesting read... Honda’s Big Bang Moto gp bike !

https://motomatters.com/news/2008/02/24/guest_column_why_big_bang_engines_work.html

 

So from my old 865 /360 crank, the sound was the closest to the original sixties bonneville once you put crisper pipes on it (optional). The 270 crank is totally wrong sound for this type of bike as it’s closer to a Ducati sound therefore fake.

 

You can’t compare two different engines and attribute any differences purely to crank layout!!!
I’m sorry but your “explanation” is simply incorrect and you don’t appear to understand the relationship between power and torque.
Keep it simple . . . Take a parallel twin with a 360 crank and a conventional firing order. Now take the same engine, mechanically identical but where both pistons fire at the same time - call it a 0 degree crank if you like. Both engines are identical in every way except in the first, the firing sequence is evenly spaced and in the second, both pistons fire together and the engine thus functions and sounds like a single.
In each case, the combustion forces will be produced at different phases of crank rotation but overall torque will remain the same, power will remain the same and frictional losses can’t possibly change but the engines will sound completely different.
No doubt there will be some technical advantages of altering crank layouts but a simple change in layout will make not one iota of difference to torque or power without altering other parameters.
It is reasonable to assume that a different layout may facilitate other parameters to be changed and thus alter engine performance but crank layout alone won’t do a whole lot other than change the sound.

 

I see you still don't understand the V twin effect of a 270° throw crank.
Imagine , two men , working together. Both are strong fit young men 80/90 kg in weight. Both can run the 100m in ?12/13 seconds, both can lift 80 kg. So identical in strength. Now one man pushes a weight then very shortly afterwards the other assists, the first stops briefly and then gets a bit idle (exhaust stroke) then the second one does the same V twin ! Now both push alternatively , and rest (exhaust) alternatively. Parallel twin ! When both pushers over lap there is more thrust in action !! This is termed TORQUE and this is why in V twin configuration engine's produce more torque than any other timing order of ignition engine's .....
I'll say no more nuff said

 

Go back to the parallel twin with a zero degree crank - your argument would suggest that two cylinders working entirely independently of each other (except being mechanically linked to the same crank) would produce essentially twice the torque of the same two cylinders on a 360 cycle.
Of course, this is true if you take an instantaneous snapshot but measured torque is a function of sustained turning force, not an instantaneous one.
For the zero degree crank, you have a force of 2X, over a power cycle of perhaps 90 degrees, followed by a period of 630 degrees where (ignoring inertia) the engine is producing a negative force - ie exhaust, induction and compression for both cylinders
For the 360 crank, you have a force of 1X (minus induction and compression for the fellow cylinder) for twice as long . . . . 180 degrees.

In each case, the sustained force at the crank would be the same . . . introducing 270/90 cranks merely muddies the waters but the principle is the same.
I guess we'll have to agree to differ . . . . . . . .

 

To the OP.
It’s never quite as simple as a crank angle. Bore and stroke, compression, balancing, cam set up and exhaust design all go to add character to the sound and feel of a bike. Don’t throw your money at the first nice one you see… start looking about well before you need to and get a feel for what you like in a bike !

 

Two cylinders running in parallel , on the same stroke , is essentially one cylinder of double the capacity ! So hence the torque would be equivalent to said same ? V twin or 270° first cylinder starts the push , second cuts in before the push has finished , so it starts to multiply the force , it's adding from a higher level or starting point than the first cylinder to Fire ! It's not a mathematical equation , it's the result of beginning from a higher starting point . Mass that is stationary requires more force intially to get it mobile , once it's moving it requires little force to keep it going. It's this principle that makes Railway's a more economical way to move mass than road , as road's have more choke points where mass comes to a halt and needs restart ! Rail you can Time manage these ! The flywheel on any engine just stores and reduces the torque pulses in an engine , it doesn't fully negate them. Really large V twin engine's require massive flywheels in comparison to larger multi cylinder engines. Harley Davidson 42° V twin is a really great example , Massive torque No Horse Power , well nothing like what their displacement should !!

 

This guy has a lot of good videos on the subject.
https://youtube.com/c/mr2mk1hero

 

Want the authentic Triumph experience? 360 degree crank, like my old T140 and my current SE Bonneville. I tried a T120 a few years ago and it's a fab bike, but that engine felt all wrong. Sounded weird too, almost like a single at times.