Piston Weights

Randy Grein randygrein at comcast.net
Thu Mar 13 23:27:13 PDT 2008

Heh. Less success and more time. This will be about season 25 for me -  
a couple seasons off for bad behavior; I started in '80.
Randy Grein, WMRRA #41

On Mar 13, 2008, at 7:29 PM, zoran wrote:

> actually I have been building and fixing motors/bikes for at least  
> 30 years.I just did not do it for other people as much as now.
> and 08 is going to be my 20th year racing.
> still about 40 years behind Earnie :)
> Zoran Vujasinovic
> Twin Works Factory
> 775-786-4881
> www.twfracing.com
> ----- Original Message ----- From: "Ernest Montague" <afm199 at earthlink.net 
> >
> To: "Suzuki SV650 Mailing List" <sv650 at micapeak.com>
> Sent: Thursday, March 13, 2008 7:26 PM
> Subject: Re: Piston Weights
>> Actually when I came to the list Zoran  had the most knowledge, and  
>> Randy had a lot of good ideas. I've picked up a bit over the years,  
>> mostly because I do most of my own work and crash too much (LOL).   
>> I think KC showed up a year or two later.
>> KC has been building motors forever.  I remember him from twenty  
>> years ago, when I was a kid for forty. Back before SVs. I was  
>> picking his brains then, I doubt he remembers.
>> On Mar 13, 2008, at 6:24 PM, Randy Grein wrote:
>>> There are a few others, while not builders or engineers have  
>>> significant experience/knowledge regarding racing. Ernie generally  
>>> knows what he's talking about. Z and KC are major builders and  
>>> racers (former); you guys have what - about 40 years experience  
>>> between you? I (usually) know what I'm talking about although  
>>> there are days... (grin). I'm pretty good with the physics of  
>>> racing and condensing explanations into layman terms but leave the  
>>> actual engine building to guys with the specialized knowledge to  
>>> do so. The racers here generally have years of experience and do  
>>> (most) of their own work.
>>> The knowledge/BS ratio is pretty high here, esp. compared to some  
>>> other lists I've read. A pure BS answer lasts about 30 seconds and  
>>> I can't recall an actual fight about anything. Feel free to chime  
>>> in - a lot of tech discussions are like this one, very  
>>> collaborative.
>>> Randy Grein, WMRRA #41
>>> Micapeak SV list admin
>>> On Mar 13, 2008, at 3:54 PM, Ernest Montague wrote:
>>>> You are getting decades of experience from a couple of the top  
>>>> engine builders around, neither of whom has a degree in  
>>>> engineering. However their bikes win races. Take that for what it  
>>>> is worth. I know there are a couple engineers on the list. My GF  
>>>> is an engineer.  (PE) Her job is to run a company that monitors  
>>>> the growth of invasive species in the SF bay.
>>>> On Mar 13, 2008, at 3:31 PM, Jake Meyer wrote:
>>>>> I know I'm a n00b here, but I have to ask - how many people on  
>>>>> this e-mail
>>>>> list are engineers?  mechanics?  I'm just wondering how many  
>>>>> years of
>>>>> design/build/repair/modify experience is sitting in my inbox on  
>>>>> any given
>>>>> day...  I'm a mechanical engineer with only about 7 years  
>>>>> experience working
>>>>> on cars.  Zero experience on bikes :) - so thanks to everyone  
>>>>> for sharing
>>>>> your knowledge and experience.
>>>>> Jake
>>>>> On 3/13/08, KC Gager <kc at brgracing.com> wrote:
>>>>>> Spot on Randy
>>>>>> The problem with piston weight is the surface area that the rod  
>>>>>> has on the
>>>>>> crank. It is design for X weight and the oil film will hold X  
>>>>>> weight. If
>>>>>> you
>>>>>> make x heavy old film goes away and boom.
>>>>>> KC Gager
>>>>>> BRG Racing Products
>>>>>> "We Have Sickness For Quickness"
>>>>>> KC at brgracing.com
>>>>>> http://www.brgracing.com
>>>>>> (925)672-5789
>>>>>> -----Original Message-----
>>>>>> From: Randy Grein [mailto:randygrein at comcast.net]
>>>>>> Sent: Thursday, March 13, 2008 6:19 AM
>>>>>> To: Suzuki SV650 Mailing List
>>>>>> Subject: Re: Piston Weights
>>>>>> No. Neither reciprocating nor rotating mass affect torque. An  
>>>>>> increase
>>>>>> in rotating mass evens out power output making it easier to  
>>>>>> feather
>>>>>> the throttle (like spinning coming out of  a corner), and does  
>>>>>> provide
>>>>>> a slight increase in acceleration (measured torque and power on a
>>>>>> Dynojet dyno), but the few grams we're talking about here between
>>>>>> pistons isn't enough to notice. Piston weight does affect the  
>>>>>> optimal
>>>>>> crank balance; go light or heavy enough and you'd increase  
>>>>>> vibration)
>>>>>> but the primary impact is on crank/rod stress. Big heavy  
>>>>>> pistons break
>>>>>> cranks at high rpms.
>>>>>> Your drive line deformation argument is interesting, but except  
>>>>>> for
>>>>>> the clutch basket springs and sprocket cushions there isn't any  
>>>>>> to
>>>>>> speak of at this level. Parts that deformed enough to materially
>>>>>> impact power delivery, even instantaneous power delivery would be
>>>>>> deforming significantly and break in short order. Yes, there is  
>>>>>> some
>>>>>> deformation, which is why we don't make cranks out of aluminum,  
>>>>>> but
>>>>>> for the effect you're thinking of to be noticeable deformation  
>>>>>> would
>>>>>> have to be plastic and on the order of 10-20 degrees of crank  
>>>>>> rotation
>>>>>> every half  engine rotation.
>>>>>> Randy Grein, WMRRA #41
>>>>>> On Mar 13, 2008, at 5:35 AM, Ilya A. Kriveshko wrote:
>>>>>>> Steve Robertson wrote:
>>>>>>>> So do those boat anchor Wiseco pistons make good torque :-)
>>>>>>> I understand it's a joke. But pretending for a second you were
>>>>>>> serious,
>>>>>>> let me ask the gear heads on the list: would a heavier  
>>>>>>> *reciprocating*
>>>>>>> mass affect torque figures? And how?
>>>>>>> My own gut feel is that unlike heavier rotating mass, heavier
>>>>>>> reciprocating mass would actually reduce output torque.
>>>>>>> Heavier *rotating* mass would increase the mean torque over  
>>>>>>> the cycle,
>>>>>>> by borrowing from the sharp and short power peak and spreading  
>>>>>>> it
>>>>>>> around
>>>>>>> the ~3x wider valley. Normally, the sharper the power peak  
>>>>>>> (i.e. the
>>>>>>> quicker it changes), the more of its energy gets dissipated via
>>>>>>> material
>>>>>>> deformation in the drive line. Lowering and widening the peak  
>>>>>>> allows
>>>>>>> the
>>>>>>> various stresses to rise and fall at a slower rate, thereby  
>>>>>>> wasting
>>>>>>> less
>>>>>>> energy on component deformation, and delivering more of it to  
>>>>>>> the
>>>>>>> output
>>>>>>> shaft.
>>>>>>> However, it seems that heavier *reciprocating* mass would not  
>>>>>>> have the
>>>>>>> same full-cycle peak spreading effect. It would rather amplify  
>>>>>>> the
>>>>>>> harmonic of positive and negative inertial torque effects that  
>>>>>>> is
>>>>>>> overlaying the combustion torque curve. If anything, that would
>>>>>>> produce
>>>>>>> more sharp combined torque rises and falls, creating peaks and
>>>>>>> valleys,
>>>>>>> producing more stress, sapping energy and wearing components.  
>>>>>>> The
>>>>>>> torque
>>>>>>> measured on the output shaft would probably fall.
>>>>>>> Anyhow, that's how I explain it to myself. Barring confusing
>>>>>>> terminology
>>>>>>> and lacking clarity, do I have the right picture in mind?
>>>>>>> --
>>>>>>> Ilya

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