piston weight
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Re: piston weight
messed this up
Last edited by Mark O'Neal on Wed Nov 29, 2017 10:40 pm, edited 1 time in total.
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Re: piston weight
I think the OP was asking how much centrifical force will add to the theoretical weight of the piston at TDC . . . . . . But I could be wrong, we will wait for Mark's cat scan for final answer.
Bill
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Re: piston weight
FWIW, the most power our shifterkart engines ever made was with the heaviest pistons. The extra meat in the head of the piston allowed us to run a more radical ignition curve and combustion chamber shape without detonation. The lesson we learned was that piston mass isn’t the only consideration when choosing a piston to make the most power. Not sure how applicable this is to large 4 stroke engines, but physics is physics.
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Re: piston weight
So, not excessively mouse-powered?
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Re: piston weight
This reminds me of the old 347 vs 351w SBF debate.GRTfast wrote: ↑Wed Nov 29, 2017 11:05 pm FWIW, the most power our shifterkart engines ever made was with the heaviest pistons. The extra meat in the head of the piston allowed us to run a more radical ignition curve and combustion chamber shape without detonation. The lesson we learned was that piston mass isn’t the only consideration when choosing a piston to make the most power. Not sure how applicable this is to large 4 stroke engines, but physics is physics.
It also makes me wonder how this applies from a fuel economy perspective. Say if you're building an engine for a strictly street car or tow rig and want to get the best mpg out of it. Would a 100 gram, or even 200 gram, difference in piston weight make any difference on an engine built to cruise down the highway at 2500 rpm?
Re: piston weight
$15 at today's rates.redgoldstein wrote: ↑Wed Nov 29, 2017 7:17 am how much is 14 grams worth in a 7000 rpm motor new piston weight a little more thanks
There is no S on the end of RPM.
Re: piston weight
Piston weight in a street build is not as important as in a race only build. A 4" stroke engine hits over 10,000 fpm by 73 degree ATC @ 8900 rpm. Doesn't everyone try run the lightest piston without sacrificing the integrity of it; I know I do.
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Re: piston weight
As mentioned by several , "weight" alone has NO affect on HP unless it is missing from an area that could allow distortion enough to hurt ring seal or cracking. Removing 14 grams directly under the wrist pin or out of ONE valve pocket are a couple of obvious examples that would lead to failure in most cases. When I did Nascar stuff ( before the engine parts weight rules) the engine builders were obsessed with weight reduction. When the new minimum weight rules came down , The heavier pistons actually made MORE power with strategically added weight to reduce flex. Same for light weight pins. Pin flex absorbs power and causes pistons to crack.
I'm not Mark but I do have a similar model cat scanner at home.
INERTIA is a totally different matter . Heavier piston and pin weights will make engine bearings "unhappy" MUCH more quickly at elevated RPM. Inertia weight changes radically every 1,000 that the RPM is increased. The longer the stroke , the bigger the problem. Rod length is also a contributor.
I'm not Mark but I do have a similar model cat scanner at home.
INERTIA is a totally different matter . Heavier piston and pin weights will make engine bearings "unhappy" MUCH more quickly at elevated RPM. Inertia weight changes radically every 1,000 that the RPM is increased. The longer the stroke , the bigger the problem. Rod length is also a contributor.
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Re: piston weight
Bore_=_4.6___Stroke_=_4.75___Rod_Length_=_6.7___RPM_=_8500
Piston_Weight_=_555.0___Rod_Weight_=_650.0
Small_End_Rod_Weight_=_216.6666___Big_End_Rod_Weight_=_433.3333
Rod_CG_/_Distance_from_Small_End_=_4.466667______GAS_PRESSURE_=_0
Crankpin_/_Rod_Big_End_Acceleration_=_156811.3
Crankpin_/_Rod_Big_End_Rotational_Force_=_4656.161
____________Reciprocating____Total_____Piston_Side___Piston
Crank_Angle____Force_________Force________Force__Inertia_Force
__Degree_______Pounds________Pounds_______Pounds______Pounds
___.000_____11230.718_____15886.880_________.000____8077.385
======================
Bore_=_4.6___Stroke_=_4.75___Rod_Length_=_6.7___RPM_=_8500
Piston_Weight_=_541.0___Rod_Weight_=_650.0
Small_End_Rod_Weight_=_216.6666___Big_End_Rod_Weight_=_433.3333
Rod_CG_/_Distance_from_Small_End_=_4.466667______GAS_PRESSURE_=_0
Crankpin_/_Rod_Big_End_Acceleration_=_156811.3
Crankpin_/_Rod_Big_End_Rotational_Force_=_4656.161
____________Reciprocating____Total_____Piston_Side___Piston
Crank_Angle____Force_________Force________Force__Inertia_Force
__Degree_______Pounds________Pounds_______Pounds______Pounds
___.000_____11026.964_____15683.126_________.000____7873.631
Stan
Piston_Weight_=_555.0___Rod_Weight_=_650.0
Small_End_Rod_Weight_=_216.6666___Big_End_Rod_Weight_=_433.3333
Rod_CG_/_Distance_from_Small_End_=_4.466667______GAS_PRESSURE_=_0
Crankpin_/_Rod_Big_End_Acceleration_=_156811.3
Crankpin_/_Rod_Big_End_Rotational_Force_=_4656.161
____________Reciprocating____Total_____Piston_Side___Piston
Crank_Angle____Force_________Force________Force__Inertia_Force
__Degree_______Pounds________Pounds_______Pounds______Pounds
___.000_____11230.718_____15886.880_________.000____8077.385
======================
Bore_=_4.6___Stroke_=_4.75___Rod_Length_=_6.7___RPM_=_8500
Piston_Weight_=_541.0___Rod_Weight_=_650.0
Small_End_Rod_Weight_=_216.6666___Big_End_Rod_Weight_=_433.3333
Rod_CG_/_Distance_from_Small_End_=_4.466667______GAS_PRESSURE_=_0
Crankpin_/_Rod_Big_End_Acceleration_=_156811.3
Crankpin_/_Rod_Big_End_Rotational_Force_=_4656.161
____________Reciprocating____Total_____Piston_Side___Piston
Crank_Angle____Force_________Force________Force__Inertia_Force
__Degree_______Pounds________Pounds_______Pounds______Pounds
___.000_____11026.964_____15683.126_________.000____7873.631
Stan
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Offering Performance Software Since 1987
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David Vizard & Stan Weiss' IOP / Flow / Induction Optimization Software
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