Technical Corner : Engines

[Evs7]

Thought we could have a quick look into engines, mainly because it's all you seem to hear in MotoGP at the moment and also because I'd like to know and I don't know the full details.

It appears that most of the teams in the paddock are running on V4's although Yamaha are using a inline 4 someone correct me at any point if I am wrong.

There are several different configurations available for these engines, namely, Big Bang, Screamer, etc...

Big Bang is the firing order of the pistons is set to fire in pairs, where as a screamer does????

anyone want to fill in the blanks.

[Voodoo]

With a screamer the cylinders all fire one after another just like your bike. The theory is lets say it took four seconds for all the cylinders to fire, in a screamer that would be one second intervals but a big bang engine with them firing in pairs would take 2 seconds (for each bang). This gives the rear tyre more time to regain grip before the next power pulse. i.e. once a screamer starts to wheelspin it just wants to keep spining but a big bang or even a twin cylinder bike ends up having more grip. Obviously it all works a heck of a lot faster than four seconds.

In other words twins and big bangs are a lot better out of corners but screamers are far better down the straights.

Hope that made sense

[Stu]

you can get the power down earlier in the corner on a twin too not sure on the big bangs though

[Guest akey]

all right, this is primarily why moto-x bikes are genrally singles, the long time (relatively) between power pulses means tyres can regain grip.

Honda use a V4 (used to be V5) because it is easier to make cranks etc that enable the big bang type pulses, and also to reduce the frontal area of the bike, it also balences itself out a bit better than an inline engine because of the opposing forces in the crank, however it is more complex in terms of valve gear etc.

Twins produce alot of torque, but cant rev as high as 4 cylinder bikes of the same size, so they produce less HP (generally), hence the ducatis have alot of drive out of corners in WSB. This is all to do with momentum of the larger pistons.

A V4 is the logical best compromise with some of the caracteristics of both the V engine (pulsed power, good torque and balance) and 4 cylinders to allow a higher rev limit.

At one time the quest for higher revs led honda to develop a 6 cylinder 250 race bike, with tiny pistons it could rev to ridiculas limits (for the time).

erm what have i missed.

[Evs7]

so in conclusion.

BIG BANG - two of the cylinders fire at the same time in a pair.

SCREAMER - the cylinders fire 1,2,3,4 in a singluar motion.

V4 - Shaped like a V 4 cylinders, provides better balance

V Twin - Not quite as powerful at top end, but because of the slower pulse of the cylinders it provides better tractions and drive out of the corners.

Sound right so far?

[Stu]

so in conclusion.

BIG BANG - two of the cylinders fire at the same time in a pair.

SCREAMER - the cylinders fire 1,2,3,4 in a singluar motion.

V4 - Shaped like a V 4 cylinders, provides better balance

V Twin - Not quite as powerful at top end, but because of the slower pulse of the cylinders it provides better tractions and drive out of the corners.

Sound right so far?

 

and more torque

[Voodoo]

But can anybody explain why you'd have a big bang four cylinder engine as oppossed to a twin?

[Stu]

But can anybody explain why you'd have a big bang four cylinder engine as oppossed to a twin?

 

more bhp for the straights

[Voodoo]

But can anybody explain why you'd have a big bang four cylinder engine as oppossed to a twin?

 

more bhp for the straights

 

Do they just have more BHP or does the engine mapping change it into a screamer for the straights?

[Stu]

errr dunno

but with the 4 cylinders you will get the higher rev range

[Voodoo]

errr dunno

but with the 4 cylinders you will get the higher rev range

 

Actually I think your right

[Evs7]

well from my understanding of it once you have set the pistons in a certain firing order, thats all you can do until you take it apart and change it so you can either have big bang or screamer.

I did read somewhere that someone was trying to work on a solution so the firing order could be changed by the rider or through electronics on the bike. Not quite sure if I read that right.

Anyways just going back to the screamer for a minute, I've heard two different explanations and I haven't a clue. Someone told me that a screamer means that all the cylinders fire at once? or do they fire individually 1,2,3,4

Blooming heck Maths is easier to understand than engines.

[pumilio]

Someone told me that a screamer means that all the cylinders fire at once? or do they fire individually 1,2,3,4

Blooming heck Maths is easier to understand than engines.

 

Individually in a sequence - you'd bounce instead of roll down the road if it was the other way!

[Guest]

But can anybody explain why you'd have a big bang four cylinder engine as oppossed to a twin?

 

more bhp for the straights

 

Do they just have more BHP or does the engine mapping change it into a screamer for the straights?

 

I think turning a big bang into a screamer requires a different shaped crank and internal mods rather than just a digital remap.

Also, if evry piston fired at the same time the engine would be under incredible stress. It would essentially be an 800cc single. A screamer fires sequentially as far as im aware.

[Voodoo]

well from my understanding of it once you have set the pistons in a certain firing order, thats all you can do until you take it apart and change it so you can either have big bang or screamer.

I think your right

 

Anyways just going back to the screamer for a minute, I've heard two different explanations and I haven't a clue. Someone told me that a screamer means that all the cylinders fire at once? or do they fire individually 1,2,3,4

 

Individually, and for some reason fire something like 1,3,2,4

[Guest]

well from my understanding of it once you have set the pistons in a certain firing order, thats all you can do until you take it apart and change it so you can either have big bang or screamer.

I think your right

 

Anyways just going back to the screamer for a minute, I've heard two different explanations and I haven't a clue. Someone told me that a screamer means that all the cylinders fire at once? or do they fire individually 1,2,3,4

 

Individually, and for some reason fire something like 1,3,2,4

 

I think if the engine fired 1,2,3,4 it would create alot of lateral stress in the crank, it would be microscopically benidng over its longitudinal axis. It would also lead to heavier vibration i think.

Just guess work here BTW.

[Guest akey]

OK I will clear the firing order up.

The usual fireing order for an inline four is 1 3 4 2 in this order the outside pistons rise and fall together and the inside pistons rise and fall together helping to keep the engine in balance.

The big bang engine does indeed need a specialist crank to work well, but the main advantage is you get the large seperation between power pulses of the twin but without the rev limitations causes by the 2 heavy pistons, as you have 4 pistons!

this is the simplistic version so i hope it helps.