I was reading an artcile from grapeaperacing.com Connecting Rods

He talks about piston acceleration and labels as a pro for longer connecting rods that it will slow peak piston acc. going towards and away from TDC.

What Id like to know is if acc. decreases at TDC, does that reflect it acc. faster at BDC? and if so, is that good, bad, or indifferent.

Shorter rods have a higher acc. at TDC...again what at BDC?

ps. Im in a Roma right now! So might be a day or 2 until i get back to this post, im paying for internet access...

keep it alive for me! dont mind wandering of topic a little if its good discussion.

 

TDC and BDC speeds will be the same.
It would be impossible for them to be different unless the crank shaft is flexable or the rods stretch and compress like rubber.

Here is another post talking about this. There is also a couple diagrams that show the speed.
https://honda-tech.com/zero...age=1

 

Ah good read, ill have to wait til i get home to read all of it though, thanks.

 

TDC speed = BDC speed = zero.

Exactly at TDC & BDC the piston reverses & speed is momentarily zero.

Acceleration at TDC is larger than acceleration at BDC. As the rod gets longer they get more equal to each other.

With an infinitely long rod, the maximum piston speed is exactly at mid-stroke. As the rod gets shorter, the max speed is larger & the position it occurs is higher up in the cylinder.

 

Yet another recent link.

https://honda-tech.com/zerothread?id=1245052

 

Hey thanks, yeah being in rome i have to pay for internet access...soo....not much time to search archives! i just had to know right now

 

Actually, if you do the math and look things over, you will see that a longer rod leads to increased piston deceleration at BDC! Piston movement can be considered to be quasi-sinusoidal. In other words, it moves in a kind of sine wave, but not exactly. However, as the rod length increases, the piston motion becomes more and more sinusoidal. And sinusoidal motion means that acceleration at TDC is numerically equal to acceleration at BDC. With a finite length rod, acceleration is faster at TDC and slower at BDC compared to sinusoidal. But as rod length decreases, acceleration decreases at TDC and increases at BDC as the accelerations become more equal. This might seem to make a bad case for a longer rod. But not really. Although BDC acceleration icreases with a longer rod, the MAXIMUM acceleration experienced by the piston (which occurs at TDC with a finite length rod) actually decreases.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by StorminMatt &raquo;</TD></TR><TR><TD CLASS="quote">But as rod length increases, acceleration decreases at TDC and increases at BDC as the accelerations become more equal.</TD></TR></TABLE>

Fixed it for you.

Please see my post here:
https://honda-tech.com/zerothread?id=1245052

 

That link was already given

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by kevinoneill &raquo;</TD></TR><TR><TD CLASS="quote">That link was already given </TD></TR></TABLE>

I know.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by _BEN_ &raquo;</TD></TR><TR><TD CLASS="quote">TDC and BDC speeds will be the same.
It would be impossible for them to be different unless the crank shaft is flexable or the rods stretch and compress like rubber.

Here is another post talking about this. There is also a couple diagrams that show the speed.
https://honda-tech.com/zero...age=1
</TD></TR></TABLE> lol