Ton with style - 250 => shiny parts pics page 6

[advantage]

Re: Ton with style - 250

Apparently the Guzzi V8 was good for 187 mph with 75 hp.

As drag increase with the square of speed, I very roughly calculated that my 22hp would be enough to propel the GN to 101.3 mph, so that is quite the right ballpark.

187mph * 187mph / 75hp = 466 = 101.3mph * 101.3mph / 22hp

 

[scm]

Re: Ton with style - 250

Nope. Drag increases with v², hence performance with v³.

Your calculation should start like:

P1/v1³ = P2/v2³


Best regards
Sven

 

[advantage]

Re: Ton with style - 250

Nope. Drag increases with v², hence performance with v³.

Your calculation should start like:

P1/v1³ = P2/v2³


Best regards
Sven

Even better, that tells me 125 mph !
Well it is assuming only the V is 3

What it also tells me is my fabrication does not need to be up to the standard of a factory racing bike from moto guzzi (era being 1955 if I recall correctly)

 

[scm]

Re: Ton with style - 250

Yes, but the Guzzi's 187mph seem quite optimistic to me...

Best regards
Sven

 

[Hoofhearted]

Re: Ton with style - 250

Yes, but the Guzzi's 187mph seem quite optimistic to me...

Best regards
Sven

It is. The correct speed is 178 mph. Think about that Sven (and anybody else who reads this). 178 mph, 500cc, carburated (no fancy computer controls), 60 years ago. This was a country devastated by WW2 and could still produce a bike that would run 178.

 

[advantage]

Re: Ton with style - 250

It is. The correct speed is 178 mph. Think about that Sven (and anybody else who reads this). 178 mph, 500cc, carburated (no fancy computer controls), 60 years ago. This was a country devastated by WW2 and could still produce a bike that would run 178.

This would give me 113 mph (I took 83HP as I red the engine went from 75 to 83 on its devellopement programm)

But maybe this information is not 100% reliable being 60 years old.

Let's start from scratch :
The Suzuki hayabusa does those 187 mph with 185 HP which leads to 92 mph with my 22 HP

That is not quite what I expected but a fairing for the GN can be made much narrower, not to mention the tires and the ride height.
Plus the idea is to cover the front wheel wich might help too.

 

[Hoofhearted]

Re: Ton with style - 250

But maybe this information is not 100% reliable being 60 years old.

100% reliable. Electronically timed.

 

[advantage]

Re: Ton with style - 250

100% reliable. Electronically timed.

There's only one thing to say then :

Moto Guzzi rules !

 

[Swagger]

Re: Ton with style - 250

It's hard not to love the 'Guzi V8...what a machine!

Advantage: You could do worse that take advice from Bill (Hoofhearted), he's a land speed record holder after all. PJs advice on skinny tires at high pressure is a good one as well, I learned that in 2nd grade with my bicycle.....just before I popped my tire overfilling it I found that the harder it was the easier the bike was to go fast on.

To break 100mph, I think you will have to do some engine modifications. Since you don't mention what year your GN is or how many miles are on the motor, let's assume 'normal' use for a small run-about...meaning that if it was purchased used it probably didn't get much love. Luckily most of these little bikes are pretty under stressed. A quick 1st overbore will freshed up the rings and cylinder and while you're at it fitting a thinner base gasket and/or headgasket will help a bit with compression. You may be able to swap in the piston from a TU or DR for a bit more compression as well. Porting will be a big help, you note that the 4v must have more potential that the old 2v Ducati lump....perhaps, except that the Ducati got lots and lots of developement as they took their small bikes pretty seriously. Suzuki...not so much. Fitting a 30-32mm carb and a freer flowing exhaust will help too. Hopefully your GN has an electronic ignition, if not that might be an area to look into as well.

Do I think you can do it; brake the 100mph mark with your bike? ...sure I do.
Do I think it'll be simple? ....not so much.

 

[advantage]

Re: Ton with style - 250

Advantage: You could do worse that take advice from Bill (Hoofhearted), he's a land speed record holder after all. PJs advice on skinny tires at high pressure is a good one as well,

Hell yeah !
I noticed with a big smile on my face that the knowledge on here is really good and you guys are friendly too.
As I said earlier, all I can get from you guys is your big experience and your sympathy for outsiders.

To break 100mph, I think you will have to do some engine modifications. Since you don't mention what year your GN is or how many miles are on the motor, let's assume 'normal' use for a small run-about...meaning that if it was purchased used it probably didn't get much love. Luckily most of these little bikes are pretty under stressed.

Engine mods are step 2, I want to focus on fairings / gearings and geometry first (my bike wispers "longer swing arm" on all the "hi"-speed bends ...

A quick 1st overbore will freshed up the rings and cylinder and while you're at it fitting a thinner base gasket and/or headgasket will help a bit with compression.

That is what I had in mind.
I calculated (but might be wrong as it's on my work computer), shortening the barrel 0,15 mm is good for +1 CR
But I don't want to go to high as it kills top end (done it on a XF 650, gained nothing at the top)

You may be able to swap in the piston from a TU or DR for a bit more compression as well. Porting will be a big help,

I thought TU was just a cosmetic evolution of the GN ?
Well apparently you got an injected version in the US with only one exhaust pipe so it might be quite different.

you note that the 4v must have more potential that the old 2v Ducati lump....perhaps, except that the Ducati got lots and lots of developement as they took their small bikes pretty seriously. Suzuki...not so much.

I don't want to go on an argument about it as I did not open neither a Ducati or Suzuki small single.
It is just that I have in mind the following statements :
More valve area for a given capacity = more power
Centraly located plug = more power
Flatter piston = more power.

On the other hand if the GN 250 had twice as more power as a GN 125, it would do 24 instead of 22, that's an extra 10% despite the 125 being a 2 valver ...

But there is a lot you can get with an hairy cam (as seen on race bikes) and the GN is 260° inlet and exhaust, plenty room for improvements I believe ...

Fitting a 30-32mm carb

Already have a CV 34 mm, might switch to a 33mm pumper if needs arise.

and a freer flowing exhaust will help too. Hopefully your GN has an electronic ignition, if not that might be an area to look into as well.

Yes it has.
I can convert to a microsquirt if the curve needs tailoring but that would be step 3 or 4 !

Do I think you can do it; brake the 100mph mark with your bike? ...sure I do.
Do I think it'll be simple? ....not so much.

If there is no challenge, there is no point

 

[advantage]

Re: Ton with style - 250

Hi folks,

Just red the other day the Guzzi had 73 hp yes, but at the rear wheel so new calculations says with 25% loss and all the stated HP from the factory (most unlikely), I could do 109 given aerodynamics as good as the Guzzi V8 and relevant gearing.

And by the way, engine cuts around 9,5K, peak power being at 8,5.

 

[advantage]

Re: Ton with style - 250 _ updates

Hi folks,

Not been around for a while but nothing much happened to the bike either except for the last few weeks.

First, results : I have been able to hit 87,5 mph almost on flat.
This is due to new sprockets (from 15*41 to 16*39) and chain but more importantly an aero mod wich is very not "Do the Ton" styled ...

Ugly as hell but efficient.
And there is more to come since the bike is still not able to hit it's peak power in 5th (yet it is still faster than before)

What I need to do before trying to get any faster is to make it more stable at speed since she can be very scary.
There I need advice.
I am thinking thicker fork oil and washers to make the spring more constrained.

Also, I found out I could go for a nice rear swing arm and wheel setup from a supermoto mopped :

I need to convert either the bike to cantilever or the swing arm to twin shocks, the second being my favorite, what do you think ?

Also, the wheel doesn't have an inbuilt shock absorber in the hub.
Fine for a 2 stroke mopped but I am a little worried about engine braking / loss of traction with the 4 stroke 250 single : opinion please !

 

[crazypj]

Re: Ton with style - 250

You need to junk the top box before you get hurt.
I'm surprised it does 60 with that set up
That moves the center of pressure way to fa back and is giving major instability issues.
Just keep it as a cheap to run commuter

 

[advantage]

Re: Ton with style - 250

You need to junk the top box before you get hurt.

Na, it's just cardboard, it's not gonna hurt anyone ...

I'm surprised it does 60 with that set up

Actually 87 mph, 74 being the MPG.
I coast down tested it with and without several times and from 83 to 40 mph, the improvement given by the tail is 4% in used energy

That moves the center of pressure way to fa back and is giving major instability issues.

I ride the thing and the stability issues happens at speed leaning on one side, I blame the geometry of the bike

Just keep it as a cheap to run commuter

You're missing the point, it is stated in the post title : Ton with STYLE !
If there is no challenge, there is no point !

Just to entertain you a little more, I have my share of overtaking various bikes (usually 600) on my commute to work where there is a big downhill (mandatory for keeping up with the bigger bikes) and then 3 vicious bends that I know like the bottom of my pocket.
Let's say that more than one must have been surprised / ashamed.
Last one was an R6 but fear not, he made his point in the straight ...

 

[advantage]

Re: Ton with style - 250

So, back to the point :

Bike stability at speed :
Would stiffer springs along with thicker oil help ?
Would longer wheelbase help ?

 

[alexmac]

Re: Ton with style - 250

What are you blind? PJ just told you why you have stability problems.

 

[Hoofhearted]

Re: Ton with style - 250

Looking at your photos I'm left wondering what is with the big chunk of corrugated board on the back? OK. I know its for streamlining but you really don't need it that size. It almost looks like you are trying to top the ton sitting up. Running a small capacity engine you need to reduce DRAG. In any way you can reduce drag. Bars, mirrors, turn signals all cause drag. Smoothing the airflow off your body and behind you will give you a big gain.

Your engine will only make so much HP. Your gearing will only pull so much. Eventually HP and gearing reach a point where drag beats them. The more you can reduce drag the higher that point becomes. That is what you should be aiming at.

 

[advantage]

Re: Ton with style - 250

What are you blind? PJ just told you why you have stability problems.

Actually, I forgot to mention the stability issue is not related to the presence or absence of the "aerodynamical device" as it happens before its installation.

I didn't quite manage to understand the centre of pressure concept but am working on it.
To be honest, GN being "light custom" with quite high a fork angle, the fact they are quite a SWB and that I lowered the front 1" making it less stable than they already not are so I really blamed the DNA of the bike, hence the longer swing arm idea.

But I understand this forum is not a cardboard friendly kind so sorry about that.

Lowering of the driver through clip ons and reworked seat is on hold until I find some parts at a good price.

I'll keep it posted anyway.

 

[crazypj]

Re: Ton with style - 250

Na, it's just cardboard, it's not gonna hurt anyone ...

I ride the thing and the stability issues happens at speed leaning on one side, I blame the geometry of the bike
You're missing the point, it is stated in the post title : Ton with STYLE !
If there is no challenge, there is no point !

There's nothing 'wrong' with taking a low power bike and making it faster/better handling.
Swapping rear wheel IS a real good move.
Did you even look at any aerodynamic accessories before you 'built' you streamlining?
The top box IS the reason for instability, it's trying to lift front by pushing down on rear.
It was a problem 40+ yrs ago on any lightweight bike, it's the same problem today :
There actually is a reason big tourers are so heavy, it aids stability simply because it's more difficult to get the lumps changing direction

 

[advantage]

Re: Ton with style - 250

Sorry about the cardboard incident, I decided to check the validity of the concept saying the back of the bike is as important as the front in a very crude way.
It might happen again but I swear I won't tell.

Thing is, as ugly and unprofessionnial this thing is, it does work.
I picked up 4 MPH between sitting upright with the Thing in the back vs tucking.


I am still after the Ton with a cheap 250.