caffeineracer

What makes a single different than a four cylinder during that critical time when both riders are rolling on the throttle, out of the turn. Still leaned over in the turn both riders are balancing power and traction 'getting the power to the ground' to get the best drive coming out of the turn.
Say both riders apexed the slowest part of the turn at 45 mph and 5000 rpm.
This rpm may be high for the single and low for the four but it will make it easier to compare the power pulses that need to be transferred to the ground.
The strategy here is getting on the gas as early and hard as possible without powersliding the bike into a crash.
Controlled wheel slip under power is the goal here without highsiding.

Both riders are powering out of the turn now, the single is putting power pulses to the ground every 19.2".
So 19" of coasting in between pulses to regain traction after breaking it loose.
Rpm rises when engine load is removed during the power pulse (breaking traction with the road) so the next pulse could come sooner and harder.
This is balanced out by road distance between pulses (19") and relatively heavy flywheel weight of a single.

Meanwhile the in-line four is laying down the power with smaller pulses at the rate of 1 every 4.8".
When a power pulse strong enough the break traction occurs, load is removed, rpms rise quicker with less flywheel weight, and the next pulse arrives four times sooner than the single.
If this repeats itself, with pulses getting stronger as the rpms rise, soon most all load is removed and the engine revs to peak hp for the throttle setting the rider is at.

And this might happen:
http://download.head-shake.com/movies/DPT2.mpg

Now a twin would be half-way between the single and four cylinder.

But a 90 degree V-twin would be closer to a single in power delivery.

Because a 90 degree V-twin has an uneven firing order, it fires at 270 and 450 degrees.
So at 45 mph at 5000 rpm the rear tire rolls 7.19" Bang, 4.79" Bang, 14.39" Bang.
One medium coast, like a twin.
One short coast, like a four.
One long coast, like a single.
With a relatively heavy flywheel to slow rpm rise.
This gives the rider a more 'user friendly' power delivery coming out of a turn.

Here's the math part:


Slip and Grip or how spread out over the tire's surface the power pulses are.

Say a motorcycle's going down the road at 45 mph at 5000 engine rpm.

Power pulses with a four stroke single engine is 1 power pulse every 2 revolutions.

5000 rpm x 60 = 300,000 revolutions per hour,

300,000 / 45 miles = 6666.66 engine revs per mile,

mile to inches = 63360 inches,

==============
63360 inches per mile
6666.66 engine revs per mile
63360 / 6666.66 = 9.5" per rev
4 cylinder = 4.7" per pulse
2 cylinder = 9.5" per pulse
1 cylinder = 19.0" per pulse
==============

63360" / 77" circumference tire = 822.857 tire revolutions per mile,

6666.66 engine revs per mile / 822.857 tire revolutions per mile = 8.1 engine revolutions per tire revolution,

with a four stroke single engine that's 4 power pulses per tire revolution, or 1 every 19.2"

A twin makes 8, one every 9.6"

An in-line 4 makes 16, one every 4.8"

A 90 degree V-twin has an uneven firing order, it fires at 270 and 450 degrees.

So 2 engine revolutions in 19.2"

720 degrees of engine rotation in 19.2"

.02666" per 1 degree of engine rotation,

So 270 degrees = 7.19"

450 - 270 = 180 degrees

180 = 4.79"

720 - 450 = 270 + 270 = 540 degrees

540 = 14.39"

So rear tire on the 90 degree V-twin rolls 7.19" Bang, 4.79" Bang, 14.39" Bang.

~Jeffers

jschmidt

This is, of course, the theory currently being applied to 4 cylinder "big-bang" racing engines. I think its merely a fad. But I really don't know.

RymerC

looks like someone has too much time on their hands...

NOrrTH

I didn't know that. Thats cool to know, thanks

superbling

Yeah, I really wouldn't use the word "fad" as that denotes it belongs with things like clothes or Ipods.

This has been known by engineers for a very long time. Especially honda since they built some real hum-dingers in the small bang dept: 6 cylinder 250 and a 5 cylinder 125 or was it a 50 (?) back in the sixties. These were bears to ride given the pathetic tire traction back then.

icebud

What a nice post Caffeineracer, very interesting!

but seem you have take to much... cafeine

thegreep

The thing that isn't discussed is torque (or HP) per pulse which has to have something to do with the whole equation. if you had bot a 4cyl and a twin and a single all making 50ft/lbs of torque the single would get it all in one shot where the 4 would have it broken down into smaller amounts. I'm not a math whiz, but this has to figure in how much speed is gained and traction lost per second or inch.