With all the discussion lately surrounding piston speed, and rod to stroke ratio i decided to make a little excel graph displaying the difference in piston speed relative to RPM between an 89mm (LS) stroke and a 77mm (b16) stroke. You can see just one of the reasons clearly why b16's dont mind 9000 rpm.

LS is blue
B16 is pink

 

No techies are interested in this? surprising....

 

So the piston speed of the LS isn't completely linear?

I can't speak for anyone else, but this isn't exactly suprising, it's what must happen by the definition of the geometry of the motors. Good info though, many people don't understand what really goes on in a motor.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by drdisco69 &raquo;</TD></TR><TR><TD CLASS="quote">So the piston speed of the LS isn't completely linear?
</TD></TR></TABLE>

if youre referring to that little "hump" in the ls graph, i dont know why its there.... i went back and double checked it and all my math was correct. So for now, im gonna blame it on excel.

 

So what are the units of measurement then? MPH?

also, at what point in the stroke are you measuring the speed? near TDC the piston speed is slow, so i'm guessing you are gauging it at 90 degrees...?

 

Very cool.

You should do this with a stock LS/VTEC.

 

Not to steal your thread, but have a peep at this:

Engineer's Edge - Engine Formula's

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Greenery18 &raquo;</TD></TR><TR><TD CLASS="quote">So what are the units of measurement then? MPH?

also, at what point in the stroke are you measuring the speed? near TDC the piston speed is slow, so i'm guessing you are gauging it at 90 degrees...?</TD></TR></TABLE>

Its in FPM (feet per minute). The formula i used is for mean, or average piston speed. The speed of the piston changes with practically every degree of crankshaft rotation, so a graph of that, to me at least, is impractical.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by LsVtec92Hatch &raquo;</TD></TR><TR><TD CLASS="quote">The speed of the piston changes with practically every degree of crankshaft rotation, so a graph of that, to me at least, is impractical.</TD></TR></TABLE>

But you can find the maximum velocity, and the acceleration, which are practial, to a certain extent. I have the math somewhere, I'll have to find it.

 

You may want to label the graph for everyone else out there.

Good info, though.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by drdisco69 &raquo;</TD></TR><TR><TD CLASS="quote">

But you can find the maximum velocity, and the acceleration, which are practial, to a certain extent. I have the math somewhere, I'll have to find it.</TD></TR></TABLE>

I dont have time to graph it right now but max velocity for an LS stroke (89mm)at 8000rpm is 202.25mph while the max acceleration is 4.780mph.

B16 (77mm stroke)'s max velocity is 167.44mph while the max acceleration is 3.633mph.

 

mph isnt a measure of accel. is it mph/h or mph/s??

 

Check your units on acceleration, should be time squared.

 

I will check nothing!!!!!



j/k, im @ work right now, ill check it later...

 

i used to drag race a pontiac firebird with a cadillac 500. my buddy and engine builder said he wanted to get 6k rps out of it. no dice that damn engine has an almost 110mm stroke. i got a calculation on it done and i was running the same piston speed at 5k rps as a 5.0 ford at 8125 rpms. we glazed a few cylinder walls in our time but sure had some fun.

 

6k rpm out of a 110mm (4.323") isnt too bad. At 6000rpm your mean piston speed (4323fpm, same number as your stroke ironically enough) is still better than an LS (89mm) at 8000rpm. (4666fpm).

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by LsVtec92Hatch &raquo;</TD></TR><TR><TD CLASS="quote">

I dont have time to graph it right now but max velocity for an LS stroke (89mm)at 8000rpm is 202.25mph while the max acceleration is 4.780mph.

B16 (77mm stroke)'s max velocity is 167.44mph while the max acceleration is 3.633mph.</TD></TR></TABLE>

How could this be true? A higher revving(shorter stroked) engine should have FAR higher acceleration speeds after TDC... as well as having an overall higher velocity.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Greenery18 &raquo;</TD></TR><TR><TD CLASS="quote">

How could this be true? A higher revving(shorter stroked) engine should have FAR higher acceleration speeds after TDC... as well as having an overall higher velocity.</TD></TR></TABLE>

That depends more on rod length than stroke. A shorter rod engine will have faster acceleration from TDC. (Or one with a lower r/s ratio if thats how you prefer to look at it.)

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by LsVtec92Hatch &raquo;</TD></TR><TR><TD CLASS="quote">6k rpm out of a 110mm (4.323") isnt too bad. At 6000rpm your mean piston speed (4323fpm, same number as your stroke ironically enough) is still better than an LS (89mm) at 8000rpm. (4666fpm).</TD></TR></TABLE>

5k rpm with a gm crank on 110 mm is awesome. i threw out a few of them. i know.

 

Maybe GM has low quality cranks, im not aware of that, sorry....

 

I like it!