motorcycle displacement

[mjoekingz28]

I haven't followed racing much in the past few years, but recently started getting a few magazine subscriptions. What is it with racing recently, the rules are extremely stupid or I am mistaken somehow.

It appeared a good idea to someone to let certain engine configurations have a displacement advantage. Is this not the dumbest thing you've ever heard. If you can't make a Vtwin with 599cc to run with the I4s with 599cc then let it just be a race amongst the 4 cylinders. I think I also saw where Buell was allowed to have almost double the displacement (1100cc).

This just not seem right to me to do this.

 

[pottymouth]

I think the variety can make things more interesting. Look at how boring Nascar is with every little thing controlled by the sanctioning body.

 

[chad8]

Don't you mean the Francis family...
Horrible monopoly..

 

[d00df00d]

Originally Posted By: mjoekingz28
I haven't followed racing much in the past few years, but recently started getting a few magazine subscriptions. What is it with racing recently, the rules are extremely stupid or I am mistaken somehow.

It appeared a good idea to someone to let certain engine configurations have a displacement advantage. Is this not the dumbest thing you've ever heard. If you can't make a Vtwin with 599cc to run with the I4s with 599cc then let it just be a race amongst the 4 cylinders. I think I also saw where Buell was allowed to have almost double the displacement (1100cc).

This just not seem right to me to do this.



I don't know enough to talk about specifics, but I don't find it too outlandish to imagine that certain engine types will be better or worse at making power at certain displacements.

I remember hearing that when Formula 1 went from V10s to V8s, there was an issue with vibration: the V10s were through the worst of it by 14,000 RPM, but for the V8s the trouble started at 16,000 (both had redlines in excess of 19,000). This was a huge challenge for the reliability of the V8s. Maybe something roughly similar is involved in MotoGP.

 

[pottymouth]

Originally Posted By: chad8
Don't you mean the Francis family...
Horrible monopoly..


I don't even know enough about Nascar these days to know who is in charge. When I was a youngster, there were still some vestiges of the actual production car. Now, it is pretty silly.

I might actually watch again if they reduced the speeds and ran production cars with appropriate safety modifications only. Oh, and maybe a few right turns thrown in.

 

[Spazdog]

I don't know now.

I only dabbled in roadracing and found it to be quite a bit more money consuming than I cared for.

But if they limited the Buells to 1100cc, at least they kept the 1125Rs out of the mix. The Rotax powered Buell might have been an unfair advantage.

But as far as making a twin run with a 4 cylinder. If you jump into the wayback machine, that's exactly what Kawasaki did.
The Kawasaki EX500 was virtually identical in performance to the Honda VF500F Interceptor. The Kawi was a much simpler package but it went, turned, and stopped similar to the Honda. (except one was a parallel twin and the other a V-4 not a V-twin and an Inline 4)Depending on which magazine you read back then, both ran a 12.65 1/4 mi but from my experience, the EX500 was usually ahead at the end of the 1/8th mile track. That indicated to me that it had a powerband that was more useable by different riders.

But that was almost a quarter of a century ago....and my 2-valve per cylinder air-cooled GPz550 could beat them both with only a 54 cc advantage....

(just had to throw that out there. Gonna' stop now before I break my arm patting myself on the back)

 

[Klutch9]

Originally Posted By: mjoekingz28
I haven't followed racing much in the past few years, but recently started getting a few magazine subscriptions. What is it with racing recently, the rules are extremely stupid or I am mistaken somehow.


Nope, you're sane and not mistaken. I follow Formula 1 like nobody's business, and the quality of competition this year, and especially last, has been great. But the rules, regulations, and restrictions imposed are just silly. Any time that a nifty technology is implemented (i.e. the "F-duct", blown diffuser, etc.), the FIA bans it for the sake of an "even" playing field. Sorry, but isn't Formula 1 supposed to be the Holy Grail of proving grounds for new and upcoming automotive technology? Plus, the top 3 teams - Ferrari, McLaren, and Red Bull - will still win, so why even bother?

But at least Formula 1 allows different chassis and engines. IndyCar for the past 5 or so years has required every single car to be identical. It makes for weak competition and gets very monotonous watching them go round a track when they all look and sound the same.

 

[Eddie]

Porsche was forced to run their little 91 cu Inch cars against the 283 Cu Inch Corvettes in SCCA sport car races. Porsche's usually won but, totally unfair. All about dollars from those paying to watch. I quit going as it turned into a financial business instead of a sport where the best-in-class-wins.

 

[Mitch Alsup]

The problem is that the RPM limit for these kinds of motors is set by piston speed (5000 ft/sec).

The more pistons you have the shorter the stroke
For a fixed bore/stroke ratio; RedLine goes up with the cube root of the number of pistons.
So, if a 4 cylinder reaches 18,000 RPMs, a 2 cylinder could only reach 14286 RPMs.
Power is the product of displacment times RPMs.
So the 2 cylinder engine would be down 21% or conversely the 4 cylinders would have a 25% advantage over the 2 cylinder.
So, giving the 2 cylinders a 20% displacement advantage pretty much equalizes the field. The 4 cylinders have more top end power, the 2s have more bottom end torque. What is not to like.

And makes for good racing.

 

[beanoil]

Mitch has it. What's really cool is to watch the different sections of the track and see the advantages come out. Fast sweepers the nod would go to the inline 4's. Tight switchbacks, probably favor the V motors as they accelerate out of the corners. Neither has an advantage if the whole bike isn't in tune and set up correctly to get the power to the ground.

 

[A_Harman]

Getting power to the ground seems to be the Holy Grail for road racing motorcycle designers. I've read some articles in Race Engine Technology over the past few years where they say more cylinders are favored due to the lower peak instantaneous torque values that occur due to smaller cylinders firing. The Honda V5 was a good example of this. Giving more displacement to V-twins may give them the same power as the I4's, but getting that power to the ground would be a problem.

 

[Mitch Alsup]

If you Google up Big Bang Engine, you will see that it is the Twins that have the best kind of TQ going to the rear wheels. BB was developed inthe last several years of the 4 clyinder 500cc MotoGP bikes (2 strokes), and the teams found that by firing both cyclnders at teh same time, that the TQ/power was easier to ride and had better tire life while doing it.

With 2 big cyclinders (ala Ducati), the tire spins forward as one cyclinder fires. Then there is a lag allowing the tire to grip the road again before the second cylinder fires.

When you look at 4-bangers, the flow of TQ is more smooth, and this leads to the situation where when the tire does loose traction, it will spin up and not regain traction like the BB twins.

This BB theory is now being applied to 4-bangers with the dual-palne crankshaft in the new Yamahas, giving much like a Big Bang TQ delivery but with the overall power of the 4-cylinder.

 

[rpn453]

Interesting stuff, Mitch.

 

[bugman53]

Not only is the piston speed issue. But the more cylinders the more valves, carbs and total airflow In the cylinder head. A 4 cly had 16valves a twin has 8. Also 4 carbs v 2 ( or a single carb ie Harley) More airflow = more power. And that is also why they tend to make power at higher revs giving them more HP.

 

[tom slick]

If the racing is good (fun to watch) does it really mater how the rules are written to obtain that?