Big Bang engine

I was just wondering if anyone here has ever run a big bang engine before.For those who do not know it is typically a 2 or 4 cylinder engine where the companion cylinders both fire at the same time basically making a 2 cylinder fire like a single and a 4 cylinder fire like a twin. I love unique engine concepts and would like to try this myself for a future project.

I keep thinking about doing this for a rallycross engine, either with a half a V8 keeping the odd-fire crank and cam, or with a DOHC V8 with one bank's cam 180 out.

My favorite, though, is a Subaru with one bank 180 out, but that one would be so uneven in its firing that idling would be difficult. Kawasaki (I think) made an engine that uneven, and they needed an electric motor to drive the crank at low engine speeds. I think the Kawasaki was a four that fired two cylinders, then 90 degrees later fired the other two. The Subaru engine would be 180-540 firing degrees.

But in traction limited applications, the uneven firing order is supposed to be awesome for acceleration. I wonder what a big-bang engine in a FWD car would do for the car's ability to turn under power.

Why? what's the advantage beyond 'I can'?

Knurled wrote: But in traction limited applications, the uneven firing order is supposed to be awesome for acceleration. I wonder what a big-bang engine in a FWD car would do for the car's ability to turn under power.

I still don't get how this helps. Two engines, one a regular 4 cyl turning 5,000rpm, that's 42 firings per second, same engine as big bang and technicaly it's still 42 firings per sec, but in 20 events per sec. How does this help accel?

Confuzled me.

They tried this in MotoGP for awhile I believe. Supposedly it helped with traction in that the power pulse occurred and then there was a long interval to the next power pulse. This helped the motorcycle maintain grip through it's teeny tiny contact patches while dealing with immense power being put through those same patches.

Here's an article on the subject that explains some benefits and problems with the design.

Yep the drivetrain and tires absorb the shock of each pulse of power so it's harder to break traction. Think of it as using a torque stick correctly, with an impact wrench, vs. incorrectly with a hand tool.

aren't Harley V-Twins sort of like this?

I love it when counter-intuitive theories and/or practices turn out to be as good if not better than traditional theories!

Just makes me feel a little dumb but I'm ok with that!

Gearheadotaku wrote: aren't Harley V-Twins sort of like this?

Yeah, but why start with a sucky engine?

It was a popular modification for flat track motorcycle racing because of the added traction, but i guess they made it illegal. Harley v twin's were not big bang they fire 315-405, But can be modified with a cam change to fire 45-675, and they do not even need ignition modification as they already use wasted spark design from stock. I believe for it to be a true "big bang engine" it needs to be an even fire engine which the Harley is not. I have a Nissan v6 that would sound pretty cool as a "triple" six. It would be a lot of work,but very unique. I love this forum, very knowledgeable people.

Xceler8x wrote: They tried this in MotoGP for awhile I believe. Supposedly it helped with traction in that the power pulse occurred and then there was a long interval to the next power pulse. This helped the motorcycle maintain grip through it's teeny tiny contact patches while dealing with immense power being put through those same patches. Here's an article on the subject that explains some benefits and problems with the design.

I think they were also dealing with harmonics in the carcass of the tire. I think that the newer super hard carcasses pretty much eliminated the need for a big bang engine in MotoGP though I admit to not knowing exactly what the new 1000's are running. What's really cool are the fans that run high end microphones at the tracks and analyze the sounds to determine what firing order the bikes have. They can even tell you how long the shift time is on the new seamless gear boxes. I love MotoGP tech and the fans that love it.

Start at #1 and continue reading. Everything should make sense, and you'll learn a dick load. http://www.epi-eng.com/piston_engine_technology/engine_technology_contents.htm

Skip to #18 for the direct explanation of why big bang seems like a cool idea.

mazdeuce wrote: I think they were also dealing with harmonics in the carcass of the tire. I think that the newer super hard carcasses pretty much eliminated the need for a big bang engine in MotoGP though I admit to not knowing exactly what the new 1000's are running. What's really cool are the fans that run high end microphones at the tracks and analyze the sounds to determine what firing order the bikes have. They can even tell you how long the shift time is on the new seamless gear boxes. I love MotoGP tech and the fans that love it.

I dropped out of following MotoGP after the first "Faster" movie came out. Watching that blew my mind sufficiently though. Sounds really cool what you're talking about the high end mic's and the engine noises. I wonder how much the top teams are paying them for data on the competitors?

Gearheadotaku wrote: aren't Harley V-Twins sort of like this?

Not really at all. They're a shared journal engine, so they never fire at the same time. I believe they do fire on the same rotation, so one fires right after the other.

It was popular with Yankee motorcycles. Yankees were twins. American made bottom ends with Ossa gear box and cyl and cranks the cranks were splined in the middle so you could change the deg between firing you could have a twin or a "Twingle"

My sister dated a guy that messed with Model T stuff. He described cutting the crank, rotating it and making a huge 2 cylinder.

hmmmmmmmmmm, don't I remember an old Norton motorcycle having both cylinders fire simultaneously???

The idea w/ the Yamaha GP bikes was to give the tire longer between power pulses to hook back up. With the Harley XR750s in flat track it was to smooth power delivery as wall as getting better drives off the corners.

I don't see a huge advantage to doing this w/ cars relative to the effort required, but it's fun to talk about, and there's always someone who is going to try to win it in the shop rather than through perfect preparation and lots of perfect practice.

Gearheadotaku wrote: aren't Harley V-Twins sort of like this?

That's supposed to be where the idea got started... V-twins walking away from more powerful even-firing fours on dirt tracks.

It's like how doing a burnout is way easier once you get tires broken loose, but on a much smaller scale.

In reply to Xceler8x:

The teams all do it as well, but the dedication the fans have to the technical side of the sport is pretty impressive.

http://www.youtube.com/watch?v=3gFhiQx9OmY

Back in the 80's?? when Honda was trying to compete with Harley on the dirt tracks at least one team was running a "twingle".

The AMA runs a race on the 1/2 mile track at the fairgrounds here every year. I was working part-time at the local Honda dealer and the team came to the shop the evening before the race for publicity purposes.

I remember some long discussions about the "twingle" idea. And from what I recall it was used for better traction on the dirt tracks.

I think Yamaha had a problem with a big-bang inline-four beating the bottom end out of the engine over time. Something else to consider.

oldeskewltoy wrote: hmmmmmmmmmm, don't I remember an old Norton motorcycle having both cylinders fire simultaneously?

A lot of vertical twin motorcycle engines like Nortons, Triumphs and BSAs had both pistons going up and down together but they fired on alternate revolutions. Other vertical twins (the old Honda CB350 was one) had the pistons going up and down separately.

pres589 wrote: I think Yamaha had a problem with a big-bang inline-four beating the bottom end out of the engine over time. Something else to consider.

It's a race engine. If it finishes the race, it's lasted long enough. If it is competitive, then frequent rebuilds are an acceptable tradeoff.