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 [GP 125 & 250] Why hydroforming is not as good as welded cones?

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Institute of TwoStrokes



Nombre de messages : 148
Localisation : Australie
Date d'inscription : 15/10/2010

MessageSujet: [GP 125 & 250] Why hydroforming is not as good as welded cones?   Mar 10 Juil 2012 - 15:22

Howard Gifford a écrit:
Because I hydroform my pipes it will be easy for me to make a new template from an existing design and blow a pipe with a tapered center as the only change.

Hydro formed pipes DO NOT work as well as proper cone pipes. Only header sections should ever be hydroformed.
Frits will explain why............................................................ lol!
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Howard Gifford



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MessageSujet: Re: [GP 125 & 250] Why hydroforming is not as good as welded cones?   Mar 10 Juil 2012 - 16:53

I beg to differ! I have developed a technique (sort of a reverse engineering) that allows me to hold a tolerence of less than .5mm anywhere on the pipe. My hydroforming technique produces a ripple free pipe that does not have any sharp edges that can disrupt the wave. Even if a pipe is lazer cut and uses computer generated layout there is still an abrupt change in direction everytime the wave transitions from a straight section to a curved section.


Dernière édition par Howard Gifford le Mar 10 Juil 2012 - 16:58, édité 1 fois
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koenich



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Date d'inscription : 07/02/2012

MessageSujet: Re: [GP 125 & 250] Why hydroforming is not as good as welded cones?   Mar 10 Juil 2012 - 16:57

Howard Gifford a écrit:
I beg to differ! I have developed a technique (sort of a reverse engineering) that allows me to hold a tolerence of less than .5mm anywhere on the pipe. My hydroforming technique produces a ripple free pipe that does not have any sharp edges that can disrupt the wave. Even if a pipe is lazer cut and uses computer generated layout there is still an abrupt change in direction everytime the wave transitions from a straight section to a curved section.

so how do you do the hydroform stuff? i know the big machines are crazy expensive and you need huge knowledge to get good results...
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Howard Gifford



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MessageSujet: Re: [GP 125 & 250] Why hydroforming is not as good as welded cones?   Mar 10 Juil 2012 - 17:01

I use simple tools a torch a pressure washer and a hammer. The metal I use is 19 gage .041 forming metal. The secret is in the design of template and how it is blown up. On the bottom of page 40 of this thread there is a picture of a pipe I built using this process.
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koenich



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Date d'inscription : 07/02/2012

MessageSujet: Re: [GP 125 & 250] Why hydroforming is not as good as welded cones?   Mar 10 Juil 2012 - 17:14

Howard Gifford a écrit:
I use simple tools a torch a pressure washer and a hammer. The metal I use is 19 gage .041 forming metal. The secret is in the design of template and how it is blown up. On the bottom of page 40 of this thread there is a picture of a pipe I built using this process.

i saw the pic and all i can say is i am impressed!!! 0,5mm tolerance is really small for a homegrown process even with the huge hydroforming machines sth like 0,x mm is allready pretty good...

i knew some guys were doing it, but the output was rather useless IMO

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Howard Gifford



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MessageSujet: Re: [GP 125 & 250] Why hydroforming is not as good as welded cones?   Mar 10 Juil 2012 - 17:26

Hydroforming is not easy but with good forethought and good craftsmanship along with good process results can be repeated with good consistancy. I use an accurate weigh scale to know exactly how much water is in the pipe so I can duplicate the volume of each pipe exactly. I use a lot of construction lines in the prototype stage and measure each line circumference to see how far off the drawing the pipe has stretched to. I then adjust the template accordingly until I get the results that match the drawing within .5mm circumference. I can also vary the volume with the same design to test different volumes. I record the weight so I know the exact volume of each pipe and test each design to find the sweetspot. It is both a science and an art.
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koenich



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MessageSujet: Re: [GP 125 & 250] Why hydroforming is not as good as welded cones?   Mar 10 Juil 2012 - 17:41

Howard Gifford a écrit:
Hydroforming is not easy but with good forethought and good craftsmanship along with good process results can be repeated with good consistancy. I use an accurate weigh scale to know exactly how much water is in the pipe so I can duplicate the volume of each pipe exactly. I use a lot of construction lines in the prototype stage and measure each line circumference to see how far off the drawing the pipe has stretched to. I then adjust the template accordingly until I get the results that match the drawing within .5mm circumference. I can also vary the volume with the same design to test different volumes. I record the weight so I know the exact volume of each pipe and test each design to find the sweetspot. It is both a science and an art.

great! i really like the way you record all data and handle it

maybe it is just because i recently had a training on that stuff - but you should get in touch with six sigma for engineers and minitab, with this stuff you log the data, display it and get some nice conclusions
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Howard Gifford



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MessageSujet: Re: [GP 125 & 250] Why hydroforming is not as good as welded cones?   Mar 10 Juil 2012 - 17:50

Im still waiting for Frits to explain why hydroforming is not a good as welded cones
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Frits Overmars

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MessageSujet: Re: [GP 125 & 250] Why hydroforming is not as good as welded cones?   Mar 10 Juil 2012 - 19:40

Institute of TwoStrokes a écrit:
Hydro formed pipes DO NOT work as well as proper cone pipes. Only header sections should ever be hydroformed. Frits will explain why ...
Howard Gifford a écrit:
Im still waiting for Frits to explain why hydroforming is not a good as welded cones
If you believe everything Institute of TwoStrokes writes, you are beyond salvation anyway
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Institute of TwoStrokes



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MessageSujet: Re: [GP 125 & 250] Why hydroforming is not as good as welded cones?   Mar 10 Juil 2012 - 21:04

Frits Overmars a écrit:
Institute of TwoStrokes a écrit:
Hydro formed pipes DO NOT work as well as proper cone pipes. Only header sections should ever be hydroformed. Frits will explain why ...
Howard Gifford a écrit:
Im still waiting for Frits to explain why hydroforming is not a good as welded cones
If you believe everything Institute of TwoStrokes writes, you are beyond salvation anyway

true and in lots of trouble

Dimensional accuracy, sharper changes in cross section to begin with. Even Yamaha changed from stamped Ti pipes to welded cone, just like Aprilia,KTM, HRC and Suzuki.
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GrahamB

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MessageSujet: Re: [GP 125 & 250] Why hydroforming is not as good as welded cones?   Mar 10 Juil 2012 - 21:36

Institute of TwoStrokes a écrit:
sharper changes in cross section

Yes, but why is that a good thing?
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rgdavid



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MessageSujet: Re: [GP 125 & 250] Why hydroforming is not as good as welded cones?   Mar 10 Juil 2012 - 22:02

i would of thought to "tell" the gases/signals what to do with more definition or over definition (because of momentum),


you naughty signal do what you're told lol!

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Howard Gifford



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MessageSujet: [GP 125 & 250] Why hydroforming is not a good as welded cones?   Mar 10 Juil 2012 - 23:59

A welded cone straight pipe probably is superior to a straight hydroformed pipe but the problem is the fitment. Making a pipe out of rolled cones fit into a chassis means that there are a big number of intersections where a cone is welded to another cone. Even with a whole bunch of cones there is still the fact that straight sections intersect at an abrupt angle. With some dollying the angles become blended but with a hydroformed pipe it is a continous curve. Ideally the perfect pipe would be smooth as a babies bottom with no seams or bumps to rob the intensity of the wave. In the real world it is a matter of fabrication and the craftsmanship of the fitter that makes one pipe perform better even with the same design. My method eliminates all but one or two of the lateral seams and creates a perfectly smooth transition. One problem with stamped pipes is the flexure at the welded seam. Stampings produce a radius bend where the two halves join. This allows for some expansion springiness that also robs energy from the wave. Hydroformed pipes have virtually no flex since they are stretched into shape. The bigghest reason people are wary of hydroforming is because very few people can get the tolerence right. With rolled cones the metal is not stretched so the end product is very close to the drawing first time. I sometimes make 3 or 4 prototypes before the design matches the drawing. I have a standing bet with any of my competetors that if they can show me a pipe that works better than mine I will pay them $200.00 as long as I can copy their pipe and my hydroformed copy doesnt work better than theirs.
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Seb4LO

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MessageSujet: Re: [GP 125 & 250] Why hydroforming is not as good as welded cones?   Mer 11 Juil 2012 - 4:48

Acoustic device , à pipe is an acoustic device don't Forget that ....

Welded cones separates better the acoustic proprieties or each section whereas an hydroformed one as only one mecanical section ...
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GrahamB

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MessageSujet: Re: [GP 125 & 250] Why hydroforming is not as good as welded cones?   Mer 11 Juil 2012 - 7:45

SEB4LO a écrit:

Welded cones separates better the acoustic proprieties or each section

Yes but this pre-supposes that a cone is the ideal shape for a "section". A cone has the property that the area grows with the square of the distance down the pipe, which means the proportional change of area decreases, hence the amount of energy in the returned wave decreases.

Now on any modern pipe you see a multi-stage diffuser, with each stage having a steeper cone angle. The question is, does each stage of such a diffuser have a different function, or are they just approximations to an ideal continuously varying shape?

In the first case, a made-from-cones pipe would possibly be better (at a very precise rpm) than hydroformed; in the second, the hydroformed pipe has the possibility to be better.

There is a reason trumpets and other wind instruments are not made out of separate cones!
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Frits Overmars

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MessageSujet: Re: [GP 125 & 250] Why hydroforming is not as good as welded cones?   Mer 11 Juil 2012 - 7:57

SEB4LO a écrit:
a pipe is an acoustic device don't forget that ....
Acoustics is a subdivision of gas dynamics. As long as wave amplitudes stay within certain limits, you can get away with simplifying some gas dynamic laws. The wave amplitudes in an engine can exceed these limits a thousandfold. So an exhaust pipe is definitely not an acoustic device; it does not obey the 'laws` (approximations would be a better word) of acoustics. It does make noise; in that respect you are right, Seb Wink

@Howard Gifford: it seems like you know what you are talking about, Howard.

@GrahamB: I tend to agree.
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Howard Gifford



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MessageSujet: Re: [GP 125 & 250] Why hydroforming is not as good as welded cones?   Mer 11 Juil 2012 - 15:08

I agree with you Graham. A difuser of multi angles ideally would be a blend of an infinite number of angles without any sharp transition. I do agree that there are definite "events" happening in the ehaust flow that respond to defined sections of the pipe. I like to close my eyes and think about what is exactly happening inside the pipe and imagine what these events looklike from inside the header pipe. When the exhaust first opens (event1) I imagine this super hot high pressure wave coming at me down the header section at near supersonic speed. As the wave passes by me I see it reducing the pressure in the cylinder. The pressure decreases very quickly to almost atmospheric as the wave reaches the first part of the difuser.
(event2) Now I imagine the wave travelling down the difuser. (event3) This creates a strong negative wave reducing the pressure in the header just as the transfers open (event4) . The negative wave results in a lower than atmospheric pressure area in the header and is maintained by the continuation of the wave. To keep up the intensity of the reflection more and more cone angle is needed as the wave uses up energy. (event5) This negative reflection extends into the cylinder and into the transfers and all the way to the carburetor resulting in airflow created solely by this event . Now I imagine the wave reaching the end of the difuser (event 6) and the negative reflection stops creating for an instant a stopage in flow out the open exhaust port. By now I see the transfer ports close (event 7) and this gas air charge just sitting there in the exhaust port held there by the now closed transfers. Then I look down the pipe and see this massive echo reflection (event 8) coming back the otherway that creates a high pressure wave. it is much shorter than the first wave and has a bit less intensity since a lot of the energy has been used up. Now as the wave passes by the center section it hits the difuser (event 9) that now acts as a baffle reflecting a secondary wave but miraculously some of the wave makes it back to the exhaust port (event 10)and just before the port snaps shut this charge that was sitting there is shoved inside the cylinder and trapped (event 11). The remaining wave reflects back and forth in the pipe losing energy and escaping out the stinger (event 12). until all is calm again and starts over at (event 1) Timing all these events is like choreography. One mis timed step and the whole dance party goes to hell!
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Frits Overmars

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MessageSujet: Re: [GP 125 & 250] Why hydroforming is not as good as welded cones?   Jeu 12 Juil 2012 - 8:59

Howard Gifford a écrit:
.... The remaining wave reflects back and forth in the pipe losing energy and escaping out the stinger (event 12). until all is calm again and starts over at (event 1)
I am with you all the way up to your 'event 11' Howard. But events don't calm down after that.
In another forum ( [Vous devez être inscrit et connecté pour voir ce lien] ) I dropped a remark about the optimum effective exhaust timing being 180°. Naturally someone asked why, so I had to come up with an explanation. This is what I wrote.

When the exhaust port opens, a pressure pulse starts moving through the exhaust pipe. It is reflected at the end cone and it should be back at the cylinder just before the exhaust port closes.
Next a part of this reflected pulse bounces off the partly-closed exhaust port and a residual pulse starts moving down the exhaust pipe. This residual pulse too is reflected by the end cone and starts moving back to the cylinder. Ideally it will arrive at the exhaust port just when the port opens again. Then the cylinder pressure and the pressure of the residual pulse combine their energy and the resulting pulse will be stronger than the pulse from the previous cycle. And the combined pulse from the next cycle will be stronger still, and so on; we have achieved true resonance.

Some may argue that we want a low pressure in the exhaust pipe when the port opens because then the spent gases will experience less resistance while leaving the cylinder. But that is not true. Gas flow depends on a pressure difference ratio. But once that ratio reaches 2, the flow velocity will reach Mach 1, the speed of sound. Raising the pressure difference any further will not raise the flow velocity any further.
The cylinder pressure at exhaust opening can be as high as 7 bar and the pressure of the reflected pulse will be about 2 bar. Thus the pressure ratio is well above 2, so lowering the pressure in the exhaust duct outside the cylinder will not do any good to the flow.

What has the exhaust timing got to do with the 'true resonance' I mentioned above?
The initial pulse starts moving at Exhaust Opening and it has to be back at Exhaust Closing, or a little earlier. This pulse travels with the speed of sound and its journey up and down the exhaust pipe will take t seconds.
The residual pulse starts moving at Exhaust Closing and it has to be back at the next Exhaust Opening. This pulse also travels with the speed of sound and its journey up and down the exhaust pipe will also take t seconds.
So from EO to EC takes t seconds and from EC to EO also takes t seconds. In English: the exhaust port should be open just as long as it should be closed.
Assuming that the crankshaft rotates with a uniform speed, this means that the crank angle during which the exhaust is open must be equal to the crank angle during which the port is closed. So both angles must be 180°.

I developed this line of thought some 40 years ago, but when I first published it in 1978 (in the motorcycle magazine Moto73 of which I was the technical editor) everybody called me crazy. Some people still do, but I got used to it .

Above I made a couple of assumptions. The crankshaft does not rotate with a uniform speed, but at high revs the deviation is negligible. In case you really want to know, I did the math for the Aprilia RSA125. At a nominal rpm of 13,000 the minimum rotation speed is 12970 rpm @ 107° after TDC and the maximum value is 13031 rpm @ 356° aTDC. What's more significant: the deviation in crankshaft position from truly uniform rotation is always less than 1°. So that really is negligible.

Second assumption: both the initial pulse and the residual pulse move with the speed of sound. Not true: the pulse pressures in exhaust waves are so high that acoustics rules do not apply any more. We are dealing with gas dynamics here and the stronger a pulse, the faster it moves. Since the residual pulse is weaker than the initial pulse, they move at different speeds. But we will leave this aside for now.

Third assumption: the initial pulse starts moving as soon as the exhaust port starts opening. More or less true, but we are not interested in the first weak appearance of the pulse; we want to know when the pulse reaches its maximum amplitude. And that requires a certain amount of open exhaust port area. It turns out that for our desired theoretical exhaust timing of 180° we will need a geometrical exhaust timing of about 190°, depending on the shape of the port: does it open gradually or does it open over its full width all at once.

The obvious question will be: why has the Aprilia RSA125 a geometrical exhaust timing of about 200°? True, at 190° the maximum torque value would be higher, but the engine would not want to rev because the blowdown time.area would be too small.
The 200° are a compromise: a bit less torque and a bit more revs; as long as the torque decline is smaller than the rpm rise, we gain horsepower.
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remasy



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MessageSujet: Re: [GP 125 & 250] Why hydroforming is not as good as welded cones?   Jeu 12 Juil 2012 - 9:06

Thank you Master!
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Frits Overmars

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MessageSujet: Re: [GP 125 & 250] Why hydroforming is not as good as welded cones?   Jeu 12 Juil 2012 - 9:13

You're a quick reader, Remasy!
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remasy



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MessageSujet: Re: [GP 125 & 250] Why hydroforming is not as good as welded cones?   Jeu 12 Juil 2012 - 9:18

Héhé
I readed it right after you post it... (7min to read it fastly diagonal... But I will need more time to "study" it)
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GrahamB

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MessageSujet: Re: [GP 125 & 250] Why hydroforming is not as good as welded cones?   Jeu 12 Juil 2012 - 11:49

remasy a écrit:
Thank you Master!


Frits, what surprises me is the very small variation of rotational speed, compared to what you expect in a 4-stroke due to the so-called "inertia torque". Of course there the ratio of rotational / linear inertia is much smaller because of the more over-square design. First I was thinking "V-twin" then had to remind myself it was the 125 :)

Otoh, 125's need a balance shaft, I guess that also contributes to the rotational / linear ratio...

Or is it that there is a fotuitous cancellation of the inertial effects by the compression slowing the system at the point where a free spinning crank would be speeding up, ie approaching TDC?
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Howard Gifford



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MessageSujet: Re: [GP 125 & 250] Why hydroforming is not as good as welded cones?   Jeu 12 Juil 2012 - 12:58

Thats why we all wait for your response with our ears and eyes wide open. Every day we learn something!!! Thank you Frits. With your explanation would it make sense to come up with a method of asymetrical exhaust port timing to harness the residual wave energy and keep adequate blowdown ? I toyed in my mind and on the drafting table (yes i'm old school) with offsetting the cylinder. This effectively would increase the stroke and gives asymetrical timing depending on the amount of offset. With some thought you may be able to time the porting to get the initial wave and the secondary waves in sync. That would liven things up!
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Frits Overmars

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MessageSujet: Re: [GP 125 & 250] Why hydroforming is not as good as welded cones?   Jeu 12 Juil 2012 - 13:23

GrahamB a écrit:
Frits, what surprises me is the very small variation of rotational speed, compared to what you expect in a 4-stroke due to the so-called "inertia torque". Of course there the ratio of rotational / linear inertia is much smaller because of the more over-square design....Or is it that there is a fortuitous cancellation of the inertial effects by the compression slowing the system at the point where a free spinning crank would be speeding up, ie approaching TDC?
Yes. (I love questions that can be answered with yes or no). The pics below may be helpful.

As you say, four-strokes in general have bigger bores and less rotational intertia, and there was something else... O yes, they fire only once for every two revolutions.
A very strong influence in the irregularity of crankshaft rotation is rpm. The energy required for a 10% rpm variation within one crankshaft revolution rises with the square of the rpm. In other words: high-revving engines do not need heavy flywheels. Or, to put it another way, the irregularity diminishes with rising rpm.

You may also want to take a look here: [Vous devez être inscrit et connecté pour voir ce lien]

[Vous devez être inscrit et connecté pour voir ce lien]

[Vous devez être inscrit et connecté pour voir ce lien]

[Vous devez être inscrit et connecté pour voir ce lien]

[Vous devez être inscrit et connecté pour voir ce lien]


Dernière édition par Frits Overmars le Jeu 12 Juil 2012 - 13:45, édité 2 fois
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Frits Overmars

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MessageSujet: Re: [GP 125 & 250] Why hydroforming is not as good as welded cones?   Jeu 12 Juil 2012 - 13:30

Howard Gifford a écrit:
...would it make sense to come up with a method of asymetrical exhaust port timing to harness the residual wave energy and keep adequate blowdown ? I toyed in my mind and on the drafting table (yes i'm old school) with offsetting the cylinder. This effectively would increase the stroke and gives asymetrical timing depending on the amount of offset. With some thought you may be able to time the porting to get the initial wave and the secondary waves in sync. That would liven things up!
You need a certain amount of blow-down time.area, but you also need a certain amount of blow-back (for lack of a bettter word) time.area. Moreover, offsetting the cylinder or the piston pin may seem to have a noticeable effect, but don't forget that in doing so you also offset TDC and BDC. So in the end the effect is not as large at it would seem at first sight. I do not feel it is worth the hassle.
As I keep saying, I like to keep things simple (if only because otherwise I might not see the wood for the trees ).
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MessageSujet: Re: [GP 125 & 250] Why hydroforming is not as good as welded cones?   

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[GP 125 & 250] Why hydroforming is not as good as welded cones?
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