firing 2 clys at once

[hoffy]

I remember a few years ago when Honda were first making a name in CART, that there big break thru in performance was to fire 2 cylinders at the same time.

Can anyone tell me why this is an advantage?

[Airhead]

It's hard to say without knowing the specs of the engine. As this effects scavenging, power pulses and drivability.

In two stroke 500cc GP bikes, the 'big bang' engines had 180 degree cranks that fired cylinders together. They were powerful but harder to ride.

So I have efectively not answered the question I think.

[RWC]

No the big bang engines were EASIER to ride.The doubling of the torque pulses and doubling the time interval between them was just what was needed to get the most feel out of the rear tyre.Before big bang engines only the very best riders could rear wheele slide those overpowerfull things effectively.Suddenly the 500's were easier to ride & not so many riders were having the violent highside crashes.Since then electronics have improved & they've found ways to get slightly more overall grip by going back to more even firing order engines with a type of traction control.
It sounds like honda were making an engine that put out torque pulses that they'd found to give the best traction/feel.Sometime on this forum someone mentioned a cosworth f1 engine that had been modified to a big bang type.It's still being used in british hillclimbes i think.

[THR]

yup. Roy Lanes F1 4L Ford v8 uses big bang. it sounds lovely! it seems to work very well for hillclimbs.

[DavyboyLT1]

Originally posted by hoffy
I remember a few years ago when Honda were first making a name in CART, that there big break thru in performance was to fire 2 cylinders at the same time.

Can anyone tell me why this is an advantage?

For awhile, when Honda first entered CART, their V8 fired each cylinder individually. To become competitive, they switched to an even-firing engine (that's what they called it, even if it may not be the correct term, I'm not sure), i.e. one that fires 2 cylinders at once. That is what the other CART engines were already using at the time. It essentially makes the V8 act as if it were a large 4 cylinder.

I think that the big advantage is in terms of engine "pumping efficiency", with respect to it being a turbocharged powerplant. Essentially, engineers discovered that 4 larger pulses of exhaust gas per cycle (as apposed to 8 smaller ones) are better at keeping a turbo running at maximum pressure.

This, by the way, is all coming from memory - so if anyone finds errors in my explanation, please correct me.

[RWC]

Ah Ha!That's feasable.There's a pop off valve on cart engines so it's difficult to find ways to sneak more through.Sounds like they found the best size duration of intake pulse that wouldn't blow the valve and worked back from there.I guess they found the best way was to have two cyls charging at once which partially fooled the valve.Back in the mid eighties in F1 they were accused of running turbos big enough to completely overwhelm the (then new 4bar limited)pop off valves.No specific rule against though-others did it too.Then in '88 with the 2.5 bar limit they were the only ones running thier OWN pop off valve before the main one .They found that if the main one popped it would lose all pressure for several seconds,so anytime the pressure got to 2.45 bar the small bleed valve cut in,which usually saved the main one from popping.I wonder how much effect the duel firing cart engine effected traction(was that also part of the reason for doing it)?

[DavyboyLT1]

Originally posted by RWC
I wonder how much effect the duel firing cart engine effected traction(was that also part of the reason for doing it)?

I don't recall traction being an issue for them; I only remember horsepower being the reason for firing 2 cyls. at once.

Once again, "this is all coming from memory".