Big Bang Vs Screamer?

Question

Can someone explain in simple terms what the difference is between the big bang and the screamer. is it the length of stroke ? and what is meant by even fireing ?

I should point out this is a reference to motorcycle engines.

I did get the advantages and disadvantages bit. just wondered what the difference was mechanicaly.

Answer 1

Big bang engines were designed to try and stop high sides, which they have done, saying that you can still high side but it is rare with the 800,s, you can still see high sides in 125,s and 250,s which still use the 2 stroke formula.  Big Bang means that when the cylinders are ignited they fire in close succession, then there is a slight gap for the other cylinders to fire, which in effect gives the bike more traction, and is more manageable coming out of corners. The old 500/2strokes the power used to come on in one mass, they were harder to ride, but a good rider was spectacular, with the tyres smoking and sliding.

Answer 2

Well, the big bang is what makes the big screamer!!...oh, wait...oh - motorcycles.....never mind! (lol)

Answer 3

I'm guessing it is to do with the revs - a long stroke and therefore a smaller bore  tends have lower revs but also it's dependant on cylinders and if it's two or four stroke - due to firing of the plugs.

Just think of a two stroke 250 vs V-twin 4 stroke - one screams the other has a lovely solid sound...

2-strokes tend to scream based on firing every 2nd stroke and the back pressure needed.

Answer 4

Hi Proc

Its all to do with firing order and crankshaft design. ie when the pistons go up and down in the cylinder.

A screamer will have an even distribution of firing within one revolution of the crankshaft. So 4 evenly spaced bangs per rev.

Think of a Big Bang as a V twin. So a 4 cylinder engine has 2 pairs of cylinders. Each pair will go up and down the cylinder at (more or less) the same time. So now you have 2 bangs per revolution. The 2 bangs are bigger than the 4 individual of the screamer, and because there is also more time between bangs, there's also more time for the rear tyre to recover some grip. Thats the theory anyway.

Liken it to the difference between the 4 cylinder 1000's and twins in WSBK.

Answer 5

Morning Proc,

The above answers seem to have covered it for you, and as I often come across  as the Benny Hill of the racing section, I'm not going to say anything about the length of the stroke (or big bores v little ones) phnar phnar!

"Even firing" is just what it seems like (smooth burble ish sound)  an example of uneven firing is a Harley engine - which has a different firing order so is more like a prolonged ripper of a f**t in the bath (well, sort of)

Hope that helped - or that someone puts me straight if I am in fact talking out my butt!

Answer 6

The big bang was [ said to be a mistake ] by a HRC techie who put the HT leads on in the wrong firing order.

It turned up in pre season testing at the end of 1991 / 1992 season.

This is one of the main reasons how Mick Doohan just wasted everybody at the start of the season.

The revised firing order made the massive, nasty kick of the 500 a little bit smoother to handle.

This was called the Big Bang engine. It used a 90 degree crank.

The god like figure of Jerry Burgess worked on the idea more and in early 1994 toyed with idea of a 190 degree crank. This was the screamer. Even smoother delivery still, however it revved like a mad man in a padded cell.

It was this engine that took Alex Criville to his blue ribbon championship. In the same year, Mick was bored of winning EVERYTHING and went back to to the pre big bang engine.

This shows where the real talent was !!