455 Stroker Motor Build

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Old April 17th, 2008, 10:56 AM
  #41  
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That "among other things" thing, is why I don't make cam suggestions in forums.
it's probably wise advise...
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Old April 17th, 2008, 11:17 AM
  #42  
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but I have not seen how to calculate piston speeds at different degrees of crank rotation.
found something. It's not a formula, it's more of a series of charts.
It talks about where and when maximum piston speed is achieved and why.
It also points out what the difference is between this and 'Mean Piston Speed',
which is the formula you referred to earlier.
Neat stuff.

On the previous page it explains how long/short rods alter speed.



http://www.epi-eng.com/piston_engine...celeration.htm
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Old April 17th, 2008, 01:26 PM
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Originally Posted by 88 coupe
At 3000 RPM, the piston speed will be 2125 feet per second and at the end of each stroke, the piston comes to a complete stop, then reverses direction, regardless of rod length.

However, at 90° and 270°, the piston will be traveling faster with the 7" rod.

Norm

How did you figure out it would be traveling faster at 90 and 270 degrees.
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Old April 17th, 2008, 01:51 PM
  #44  
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How did you figure out it would be traveling faster at 90 and 270 degrees.
read.


http://www.epi-eng.com/piston_engine...celeration.htm
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Old April 17th, 2008, 02:44 PM
  #45  
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Originally Posted by Rallye469

sorry I didn't know we were on the second page when I posted my other question.
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Old April 17th, 2008, 04:01 PM
  #46  
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Good stuff.

Originally Posted by 88 coupe
........ However, at 90° and 270°, the piston will be traveling faster with the 7" rod ........
But,

Originally Posted by www.epi-eng.com
In fact, the effective length of the rod at any point is the actual rod length multiplied by the cosine of the angle between the rod and the cylinder centerline.
maximum velocities would occur slightly before 90° and after 270°.

Norm
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Old April 17th, 2008, 05:30 PM
  #47  
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maximum velocities would occur slightly before 90° and after 270°.
It's a good read, right !?!?!?!?
I actually feel smarter having read it.

Tried to explain to my girlfriend why I was so immersed in the topic
and how a long rod engine converts to different piston velocities
over a shorter rod engine and...long story short- she's not nearly impressed.

Last edited by Rallye469; April 17th, 2008 at 05:33 PM.
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Old May 2nd, 2008, 02:21 PM
  #48  
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Originally Posted by rccktmn2
If your using the stock 425 rods and a stock 455 crank your not really making a stroker motor. The only way to make a stroker motor is to increase the stroke at the crank, if you use this setup all your doing is moving the piston closer to the head and increasing compression ratio.
Ah, I see. After thinking about it alittle more I see what you mean.
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Old May 23rd, 2008, 11:16 PM
  #49  
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angle determines speed

Originally Posted by rccktmn2

I will agree with you to a certain point. As the crank pushes the piston toward the head on a long rod the piston will stop for a very brief moment, then the crank has to bring the rod back around to take the piston back down the cylinder. On the long long rod the piston will be at tdc longer and bdc longer than the short rod simply because it takes the crank longer to swing the long rod vs. the short rod. I believe the physical speed of either one is still the same though. It's not the speed of the piston it's the speed of the cycle. The long rod does push the piston higher therefore speeding up the cylcle.
The reason the short rod has higher speed movement is due to the angle of attack for the rod relative to the piston. At 90 degrees crank angle for every mm of crank movement the piston moves 2. 90 degrees is the switchover from acceleration to decelleration or viceaversa. From tdc to 90 degrees the piston is accelerating. from 90 to 180 it is decellerating and from 180 to 270 degrees it is accelerating up and so forth. Since the longer rod has less angle of attack relative to the piston it doesnt accelerate quite so fast thus its speed is relatively lower.

I hope I got that right... logically it seems so to me. Its one of the major primary differences to a bourke engine.
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