Possible General Ignorance But................

[offo]

Could someone explain why on inline bike engines we have two, three or four carbs but on most cars there is only one.
I was thinking about this the other night in bed while the wife was snoring, with one carb the production costs would be lower, there would be no need to balance the throttle bodies & with the performance of a lot of cars these days i became a tad puzzled so i am just curious as to what the advantages to bikes are.

[mjsracing]

I think the general answer is that the tradeoffs for a car and a sport-y bike engine are different. Single carb is less expensive and easier to maintain, but likely has less performance than multi carbs. May also have to do with space. Fitting a single carb large enough for all the cylinders may be a big space utilization design challenge.

[skipperT]

... What Mjs said.
Performance is the biggest advantage I believe (though I am no engineer).
There are some bikes that use single/dual carbs or throttle bodies for multiple cylinders, GL1500 goldwing comes to mind. Most common on twins, like all H-Ds, Roadstars, some Suzukis IIRC. Trade off on the Big Twins is emissions, usually one cylinder is more efficient than the other. Harley and Yamaha both have gone to a fuel injector for each cylinder as a way to control that more tightly.
The other biggie is Airbox size. I could be wrong, but more cylinders drawing air from the same place create a need for a much larger airbox size. Difficult to hide that on a small, narrow motorcycle frame.
-S

[offo]

Thanks guys, i will be able to lay & listen to the wife snoring tonight with a contented mind!

[rodan]

It's mostly a question of RPM and intake velocity. Most cars operate at RPMs that would be lugging around on a bike. Single throttle bodies, with a plenum (air chamber) and longer runners optimize intake velocity at lower RPMs for good torque and driveability. Bikes operate at a much higher RPM, and a direct shot into the cylinder head, and individual throttle bodies works better. H-Ds are an exception on the bike side, but they operate at relatively low RPM. A BMW M3 (E46 6 cyl) is an exception on the car side, using individual throttle bodies.
 
Horses for courses...

[andmoon]

All bike carbs I've seen are single barrel. Car carbs have multiple barrels. Some cars had multiple carbs. I think it has a lot to do with space. Many small ones vs one big one.