1973 Honda CB350 - how much power?

I don't happen to think that 120 is a particularly outrageous speed, and
you'd need to put airplane wings on the thing in order to get enough lift
to worry about getting light. A bike isn't much more aerodynamic than a
brick. A 200+mph F1 car, yeah, you want a little down-pressure
to get your tires to stick a little better in the turns...

On a bike, in a straight line under 150mph, the friction coefficient of
the tires isn't particularly relevant. NASCAR drivers run around, what,
180-190(?) and I don't recollect seeing much in the way of wings on them.
Some ground-effects stuff maybe.

If you wanted to talk about how tight a turn one could make at 120mph,
using the street tire rubber compounds that were available 30 years ago,
well, friction coefficient would factor in. But not in a straight line.

Your calculations are incorrect because you are starting with a faulty
premise. Wind resistance is not a primary factor in terminal velocity in a
non-aerodynamic object. An ordinary red brick would have considerably more
wind resistance than a perfectly round lead sphere, would it not? But if
you drop them from the same height, at the same time they will both reach
terminal velocity at the same time and hit the ground at the same time.

Frankly, 120mph isn't all that fast and it really didn't take any
engineering or mechanical wizardry to reach it with that machine, just a
simple sprocket/chain change to get a little more out of the top end.

If I had had any inkling that a bunch of otherwise supposedly
knowledgeable people in a "tech" newsgroup would take the stand that this
relatively easy feat was a ludicrous impossibility and start a shitstorm
of pronouncements that "it couldn't be done", I'd have kept silent.

Would I start another shitstorm if I said the same modification to a
Suzuku TS100 would get it to 85mph?

It doesn't matter what numbers you plug in, your answer will be
meaningless because the starting assumption is incorrect.

I am *amazed* at how many people are jumping to tell me I'm full of shit,
while backing that up with nothing more than theoretical musings of how
"it can't be done", instead of coming up with some actual, FACTUAL
information on this machine such as the original factory specs from the
manual such as horsepower, speed, gearing and ratios and the number of
teeth on the stock rear sprocket.

Armed with that information, it would be a relatively simple task to
calculate just how little (or much) effort it takes to do what I said.
Since it's been 30+ years, I can't be *completely* sure, but I think that
I used a sprocket that had only 6 or 8 fewer teeth. Then you all could
really pound me into the sand with REAL info instead of bullshit...or is
everybody here unwilling to get the real facts because they might be shown
to be wrong?

To that end, I have located someone who owns one of these machines and
requested that he send me any available info. I will also check any other
sources I can find such as the local Honda shop, etc.

 

Nonsense. It still won't do 120mph without a very steep hill and a
hurricane tailwind. Do you *really* think that a sprocket change makes
it as fast a CB750?

We wish.

You are still, and it grieves me to say this, full of shit.

 

Er, that was me.... ;-)

Er, that was me. For a 360, anyway.

 

Which was my point. Perhaps you missed that part.

Given a machine designed to particular specifications for a particular
maximum load capacity, why don't you explain to my ignorant self just
exactly what happens if you change the gear ratio by reducing the size of
the rear sprocket say, from 48 teeth to 42 teeth, a reduction of roughly a
bit under 15 percent?

Will it hurt acceleration performance?

Will it increase top speed?

Suppose we reduce the max load by 50 percent,
how will this reduction affect acceleration performance?

Suppose we reduce the max load by another 50 percent,
for a total reduction of 75 percent, how will this affect
acceleration performance?

Is a 50 to 75 percent reduction in load sufficient
to offset, if not negate, the loss of acceleration
performance of the 15 percent reduction in the rear
sprocket?

 

Hey, I have to admit that I am not married to the idea of power increasing
by the cube of the velocity. It wouldn't be the first time someone put up
impressive-looking BS on Wikipedia.

After doing a few sample calcs of my own it blows up pretty quickly into
the ridiculous range for real world examples of 300 km/hr bikes that make
about 150+ hp. So you are probably right when you say it's something
between the 2nd and 3rd power for the velocities and bike-shaped objects
that we are interested in.

Thanks for an interesting discussion.

 

No, TOG didn't miss anything. Power/weight ratio is nearly meaningless
when you are concerned with top speed.

On almost all bikes, all this will do is make it an absolute slug,
acceleration-wise.

Without a doubt.

Almost certainly not. Most bikes have their gearing set up so their
top speed is limited by the engine's maximum available power, that
speed coincides more or less roughly with the engine's redline in
top gear. There are many exceptions to this rule (specifically
tourers with tall top gears optimized for low-rpm cruisng) but for
most bikes they're not too far off.

It will help.

Any weight reduction helps improve acceleration-- that was never in
dispute.

Maybe. Impossible to say without having a specific case to
consider.

Weight reduction has nothing to do with top speed, assuming
you have an essentially unlimited distance, otherwise you
are talking about an acceleration contest, as in drag racing.
Get that concept firmly entrenched in your mind. You keep
confusing acceleration with top speed.

I really don't know why I bother responding. At the risk of
being accused of resorting to an ad hominem attack, you appear
to be incapable of grasping the most basic concepts relating
to power, acceleration and top speed.

 

Indeed. It's a long time since we had such an awesome demonstration of
total ignorance and stupidity here.

 

No. It will almost certainly reduce it in top gear, meaning top speed
will be attainable in a lower gear. Unless, of course, the bike was
massively undergeared to begin with.

If, by load, you mean weight, it will improve it.

See above

We're not talking acceleration - we're talking top speed, in this
thread. They are two different things. You said gearing up a CB360 will
make it hit 120mph. Everyone else says you're talking shit, and you are.

You are truly, truly ignorant. And stupid.

 

May I second that? All this maths goes way over my head, bud it's always
interesting to see a well-reasoned argument.

 

No.

I don't know diddly squat about your machine or what modifications could
be done to it.

Yeah, I know, you're inclined to say that I don't know diddly squat about
_anything_.

 

The evidence for that is overwhelming.

 

I apologize if it appeared to be an attack. I just feel that the use of
the term "terminal velocity" is not correct in this discussion. As I
understand the usage of "terminal velocity", it refers to the speed to
which an object will accelerate (at a rate of 32 feet/sec/sec) when
dropped from a sufficient height.

To me, assuming that "terminal velocity" has anything to do with the
discussion is a faulty premise and renders any equations meaningless.

If I misunderstood what you were trying to say, again, I apologize.

Yes, I realize that you are the one who has been giving the greatest
latitude in this discussion, and I appreciate it.

No, I do not have a degree. I do have, however, *some* education in
various disciplines as well as practical experience.

I might concede that two speedometers could be off by some percentage, but
not by a huge margin. I didn't check their calibration. But I will go to
my grave swearing that that both of those machines would reach an
"indicated" (a term someone else used elsewhere in this thread) 120mph.
When it comes to something *I* experienced*, something that I saw with my
own eyes, I will not be convinced that it didn't happen no matter how many
numbers are thrown out to say it "didn't" happen. Yeah, I put the motors
way past redline.

After reading some of the other responses I realize that the speedos
*could* have been off and lacking any calibration data I should not be
saying it was an "absolutely guaranteed 120mph". But how much error are we
talking about here?

I certainly didn't intend to start a shitstorm like this. I only wanted to
say that those were some pretty damn good motors as far as I was
concerned. But insinuating that I'm a liar and being flamed as a "stupid
sod"? I damned sure would have kept silent had I known this would happen.

That speedo hit 120, and broke there. The cops were pissed about all of
the time they spent looking for my body because, as bad as the bike looked
after the wreck, they didn't think the rider could have survived, let
alone leave the scene under his own power.

 

I will concede that the speedo *could* have been off, but not by all that
goddam much. Certainly not enough to justify the trash-talking that was
dished out right out of the gate. Seems to me that some people are just a
little too eager to flame.

The front wheel was the factory wheel. I didn't check the calibration of
the speedo, in those days I didn't care much about speed limits.

 

10-15%. At an indicated 120mph, that means a true top speed of as little
as 103mph, and that under "favourable" conditions.

 

Oh yes, it could.

No shit.

 

**** me sideways, this thread is bringing out every ignoramus on the
planet.

 

LOL, to think you might have missed out if I weren't so "ignorant" and
such a "stupid sod".

 

You are.

As has been noted, you display an ignorance that's truly impressive. The
refusal to acknowledge that means your stupidity is just as impressive.

 

We do have a specific case. Since I don't have the specific data as to the
gearing, etc. I left it general, allowing one to make reasonable
assumptions as regards the ratios and loads to arrive at a general idea.

I'll not accuse you of an ad hominem attack. If I read this right, you are
saying that you believe *I* am saying:

Less weight = higher top speed (period).



That is NOT my intention. What I am saying is that:

1) Taller gearing = higher top speed

2) Taller gearing imposes a performance hit on low-end acceleration

3) Less weight means I can AFFORD to sacrifice the low-end
performance in exchange for the top-end gain.

That's it.

 

<Shakes head in amazement>

****, you're stupid.