Piston Weights

Ernest Montague afm199 at earthlink.net
Thu Mar 13 19:26:05 PDT 2008

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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