Stroker question

[aronmatic2]

Doesn't anybody care about pistonspeed & acceleration? @8k rpm you are in F1 territory with pistonspeeds around 45m/s & 5,5k G.
Piston quality is no issue? Forged pistons will live beyond the end of the world?

everybody is talking about this. 6500rpm. see?

[Billman]

how do you come at this number? With the 95,5 stroke you are at 8000 RPM at 25 MPS according to this calculator

http://www.csgnetwork.com/pistonspeedcalc.html

[Jamo]

how do you come at this number? With the 95,5 stroke you are at 8000 RPM at 25 MPS according to this calculator

http://www.csgnetwork.com/pistonspeedcalc.html

Calculator doesn't take into account block height and piston length.

[Billman]

and what has piston length to do with piston speed? same for the block height!

[Jamo]

http://www.slowgt.com/Calc2.htm#PistSpeed

Speed is measured over a distance

[EBR]

With shorter rods the max piston acceleration is much higher than with longer rods, and that is what matters. Average piston speed stays the same with the same stroke...

Eiríkur...

[Billman]

I want to use in the big deck 95.5 stroke with 158mm rods! I think it is not going to be a problem!

[quattro84]

You calculate average pistonspeed, not max pistonspeed! Your calculator doesn't take rod/stroke ratio into
Basic formula: a*cos(o)+sqrt(r^2 - a^2*sin(o)^2)

Piston axial acceleration (kinematic, closed-form solution for constant crankshaft angular velocity):
-a*cos(o)*w^2 + (a^2*w^2) * (1-2*cos(o)^2)/(sqrt(r^2-a^2*sin(o)^2) - (a^2*sin(o)*cos(o))^2*w^2)/(r^2-a^2*sin(o)^2)^1.5

where
a = crank throw
r = rod centers length
o = crank angle in radians
w = crank angular velocity in rad/sec

The above is based on taking two derivatives with respect to time of the formula for piston position:
position = a*cos(o)+sqrt(r^2 - a^2*sin(o)^2)

I can provide a (more complicated) version if you want to include pin and crank offsets from the cylinder axis (desaxation), or crankshaft angular acceleration.

http://en.wikipedia.org/wiki/Piston_motion_equations

I am an Engineer, not a Bachelor in Guesstimations

[caterpillar]

95,5 and 158 rods åad 236 deck, gives the same as 86,4 and 144rods and short 220 deck....the ratio

[Billman]

OOOOhhhhh, engineer!!! Then why dont you give us all data (we are not the experts here):

86.4mm stroke and 144mm rods for the 220 deck block
95.5mm stroke and 144 rods on 220 block
95,5mm stroke and 158 rods on 236 block

[quattro84]

@ caterpillar. Ratio will be the same, but acceleration will be different due to the difference in stroke. Thereby longer rods increase the possibility of buckling.
@ Billman. I am neither an expert. I just gave you the formulas work it out yourself. I ain't coming over to wipe your nose or tie your shoelaces do i?

What i'm after is durability. Sure, guys like Jonus rev over 9k with an stroker. But how many seasons till the next rebuild? how much hours on a set of pistons? He doesn't post up any of his findings.

[A80Avant]

i believe that since you can provide people with even a more complicated formula,why dont you just give us the result directly which will prove your point rather than ask people that have little to do with engineering figure it on their own??? Isnt it easier for you?

I as a doctor, wouldnt take your blood sample and then tell you to go figure it out on your own if you are sick or not,would i?

[EBR]

I searched a little bit more and found some more information on this subject.

First rule of thumb is mean piston speed! If it is kept under 25m/s things should be OK!
With 95.5mm stroke you have 24.99m/s mean piston speed @ 7850rpm and max piston speed 41.01m/s.

But in this case, with a rather low rod/stroke ratio, piston acceleration is more important! After reading this article I found out that the thickness of the top ring is also important:

http://www.unofficialbmw.com/all/engine/all_redline_rpm_vs_reliability.html

I sent 034motorsport an email asking what the thickness of the top ring is, since I have JE pistons from them, and Javad sent me an answer saying that it is 1mm! Which is good if you want to rev high.

Here is the "rule of thumb" table from the article, but I have changed it to mm and m/s^2

mm_________m/s^2
3.1750---------12,192
2.3876---------16,154.4
1.6002---------24,384
1.1938---------32,308.8
0.9906---------42,062.4 <---

If you download this excel file:

http://www.fileden.com/files/2006/11...kinematics.xls

You can put in stroke, rod length and rpm in DATA-1 and then you get a chart in CHART-1 and you can find max acceleration!
And if I try to be on the limit I get 41.700m/s^2 (4.26k G) @ 7800rpm!

When looking at these rules of thumb and the numbers I get, the outcome is:
Absolute max rpm on a stroker with 144mm and 95.5mm stroke is--> 7800rpm!!

I know there are more things that count when you want to find out how much you can rev your engine, but this hopefully answers some questions...

BUT! My plan will still be the same, stay under 6500rpm in my daily driving and IF the car produces more in higher rpm, go to maybe 7300rpm when racing

I hope this can be useful for someone and if you see something wrong in my calculations then post it here

Eiríkur B. Rúnarsson...

[Billman]

Objection! Are these formulas and the Excel file controlled by THE engineer???

Ok, jokes aside i will have a look and also see how would the 158 rod, 95,5 stroke i am planning compare to the original 3B ect setup.

[EBR]

Objection! Are these formulas and the Excel file controlled by THE engineer???

Ok, jokes aside i will have a look and also see how would the 158 rod, 95,5 stroke i am planning compare to the original 3B ect setup.

He he. I'm on first year learning to be an engineer if that's enough for you