LSs1Power

iTrader: (5)

What would be the piston speed for 346cid (3.9 Bore x 3.622 Stroke) ,360cid (4 Bore x 3.622 Crank), 383cid (3.9 Bore x 4.0 Crank), 392cid (4.0 Bore x 3.9 Crank), 402cid (4.0 Bore x 4.0 Crank), 408cid (4.030 Bore x 4.0 Crank), 427cid (4.125 Bore x 4.00 Storke) and 454cid 4.200 Bore x 4.10 Stroke) at 7K RPM?

Whats the relationship between piston speed, HP and Displacment? Also when is piston speed too much?

I think Increase in Crank size would change the pistons speed while a bore increase shouldnt change anything right? Is there a formula we can use for calculating piston speed?

Old SStroker

Average piston speed (often called Mean piston speed) is calculated with a simple formula: Bore has nothing to do with PS calc. Obviously bore and stroke are both used to get the displacement you want.

PS (ft/min) = [stroke (inches) x rpm]/6

So the 7000 rpm max, 4 inch stroke LS7 has a PS of 4 x 7000/6 or 4666.7 ft/min. This is on the upper end of OEM piston speeds. A 3.26 stroke Nextel Cup engine has a PS of 5270 @ 9700 rpm. A F1 engine with a 1.565 stroke has a PS of 4956 ft/min. @ 19,000.

Maximum piston speed depends on stroke, rpm and to a fairly minor amount, on rod length, especially when you consider the fairly small range of rod lenghts available for a given stroke in a given block. Most comparisons use Mean (average) PS as calculated above.

In racing engnes where premature detonation is not a problem, most engines use the largest bores allowed which results in the shortest strokes and therefore lowest piston speeds for any given rpm. This keeps the friction losses down as well as keeping the loads on the rod down.

The 2005 F1 Mercedes 928 hp @ 18300-18500 rpm engine was rpm limited by rod strength according to Mario Illien, the designer. Interestingly, they were using slightly longer stroke and slightly smaller bores than the max bore allowed. Remember F1 engines run two races, practices, qualifying or about 850 miles in anger. A Cup engine probably runs around 600-700 miles in anger, but with half the rpm of a F1 (and a little more than twice the stroke) it only experiences about 1/2 of the piston gs.

Do a search for some lively discussion of the effects of PS. Not all contestants see eye-to-eye on things.

Remember that how I or anyone else explains things doesn't change how Mother Nature works. The fun part is figuring Her out.

My $.02

LSs1Power

iTrader: (5)

Doing the math on all the other combos

346 cid and 360 cid with a 3.622 Stroke has a 4225 PS at 7K RPM 25354

392-396 cid with a 3.900 Stroke has a 4550 PS at 7K RPM

383, 402, 408 and 427 cid with a 4.00 Stroke has a 4666 PS at 7K RPM.

438, 454 cid with a 4.100 Stroke has a 4783 PS at 7K RPM.


So assuming we got all of the setups down to 4225 PS which is the stock piston speed... Are they going to make the same power giving everything else the same?

For example a 3.900 Stroke at 6500 RPM would give 4225 PS
a 4.00 Stroke at 6335 RPM would give around 4225 PS
a 4.10 Stroke at 6185 RPM would give around 4225 PS.

gun5l1ng3r

One thing I never understood is how slow the pistons are acutally moving. 5,000 ft/min is a little bit less than 60MPH, i thought pistons moved at like 200 Mph or something like that. It just sounds like they are moving really fast. I know the acceleration is incredible (0-60-0MPH in like .5 second).

LSs1Power

iTrader: (5)

Looking at the Honda S2000 engine

The US model is running a 2.2L with a 3.57 Stroke at 8000 RPM which would yield a 4760 PS while the JDM model is running a 2.0 L with a 3.30 Stroke and push 9000 RPM which would put it around 4950 PS. Both engines makes the same HP even though the 2.0L engine is running the pistons around 2000 PS faster.

So can we conclude that running .1 L extra of displacment (Stroke Increase, not Bore) would equal 1000ft/min of extra PS to equal the same HP?

Old SStroker

More like .005 seconds for the trip. Two complete 0-60-0 in a rev. so 12000/min @ 6000 or 200 times per second.

Can you now see why a Cup piston feels over 5000gs and an F1 piston over 10,000gs?

Old SStroker

I don't think that is a logical conclusion. BTW, that's only about 200, not 2000 ft/min difference.

Look at how much torque each engine makes at power peak rpm.

Let's say they are 250 hp engines:

250 hp @ 8000 is 164 lb-ft.
250 hp @ 9000 is 146 lb-ft.

Now look at how much torque per liter @ power peak each engine has:

2.2L (164 lb-ft) has 74.5 lb-ft/L (~183 psi BMEP)
2.0L (146 lb-ft) has 73.0 lb-ft/L (~179 psi BMEP)

My conclusion is that the 2.2 engine does a better job of turning air & fuel into usable power than the 2.0L. IOW, each cc makes more torque at power peak rpm.

LSs1Power

iTrader: (5)

Opps yes its 200ft/min...

Would the engine(rods, pistons, crank, etc...) have the same amont of strain from running a 3.30 and 3.57 Stroke even though they are running the same PS. So it will be 8300 RPM for the 3.57 VS 9000 RPM for the 3.3 Stroke.

joecar

If you want to look at piston speed at any angle of crank rotation using graphing software...

https://ls1tech.com/forums/showthrea...60#post4705260

l = rod length
r = half stroke

At 7000 RPM, w = 2.pi.RPM/60 = 733 rad/s

You can put in the formula for v without multiplying by w
(w just scales the velocity for different RPMs),
and plot for 0° to 360° or 0 to 2.pi radians.

joecar

Are these all the combinations there are...?
For each of these, what rod length and piston height combinations would be used...?

joecar

Here's some plots of piston motion for the above combinations,
assuming stock rod length 6.125" and constant RPM
(rod length does not make much difference to piston velocity)...

Chart shows piston motion wrt to crank angle

L=rod length
R=half stroke


L=6.125 R=1.811
max dx/dA = +/-1.888976 in/rad at A = +/-75°
7000 RPM: max v = 1.888976 in/rad * 733 rad/s = 1385 in/s = 6923 ft/s
6000 RPM: max v = 1.888976 in/rad * 628 rad/s = 1186 in/s = 5931 ft/s

L=6.125 R=1.950
max dx/dA = +/-2.047242 in/rad at A = +/-74°
7000 RPM: max v = 2.047242 in/rad * 733 rad/s = 1501 in/s = 7503 ft/s
6000 RPM: max v = 2.047242 in/rad * 628 rad/s = 1286 in/s = 6428 ft/s

L=6.125 R=2.000
max dx/dA = +/-2.104814 in/rad at A = +/-73°
7000 RPM: max v = 2.104814 in/rad * 733 rad/s = 1543 in/s = 7714 ft/s
6000 RPM: max v = 2.104814 in/rad * 628 rad/s = 1322 in/s = 6609 ft/s

L=6.125 R=2.050
max dx/dA = +/-2.162914 in/rad at A = +/-73°
7000 RPM: max v = 2.162914 in/rad * 733 rad/s = 1585 in/s = 7927 ft/s
6000 RPM: max v = 2.162914 in/rad * 628 rad/s = 1358 in/s = 6792 ft/s


I used the following equations with generic graphing software:

position
= x
= r.cos(A) + sqrt(l² - r².sin²(A))

velocity
= v
= dx/dA.dA/dt
= ( -r.sin(A) - r².sin(A).cos(A)/sqrt(l² - r².sin²(A)) ).w

acceleration
= a
= d²x/dA².(dA/dt)²
= ( -r.cos(A) - r².(cos²(A) - sin²(A))/sqrt(l² - r².sin²(A)) - (r²)².sin²(A).cos²(A)/sqrt(l² - r².sin²(A))³ ).w²

w = dA/dt = 2.pi.RPM/60 = constant

where:
l = rod length (distance between piston pin and crank pin)
r = crank throw radius (distance between crank pin and crank center, half stroke)
A = crank throw angle (from cylinder bore centerline at TDC)
x = piston pin position (from crank center along cylinder bore centerline)
v = piston pin velocity (upward from crank center along cylinder bore centerline)
a = piston pin acceleration (upward from crank center along cylinder bore centerline)
w = crank angular velocity in rad/s

LSs1Power

iTrader: (5)

Most of them.... Rod length starts from 6.125 on the sub 408cid to 6.06 or so on the 408+ cid, but since rod length wont affect PS that much then it doesnt really matter.

joecar

I just wanted to have some numbers so I could run a few more graphs to show how much it didn't matter.

LSs1Power

iTrader: (5)

I can get them for u if i dig more. I hope someone who know it post the rods length for each one of those rod length.

joecar

Thanks.

I know that half stroke + rod length + piston height has to match the block deck height + gasket thickness,
but I wasn't sure what the various available rod lengths were.

I tried searching but I got all the wrong hits (lol... articles regarding 'rod' and atricles regarding 'length'...).

LSs1Power

iTrader: (5)

That would be another cool thread to start maybe.

racer7088

The point people usually never see is that these different engines do not see the same rpms so the increased strokes of unlimited engines almost always result in more hp and lower rpm. If you can turn the same rpm with the increased stroke you have to be a bad *** or the other guy has to be a total patsy of an engine builder. Therefore most of the time more stroke equals more power and more reliability and less friction and more efficiency.

LSs1Power

iTrader: (5)

I thought when you run more Stroke you will have more friction due to higher PS which puts more strain on the engine?

Also what did you mean with more efficiency? Better VE?

racer7088

You WILL have more friction at the same rpm and load with a larger engine whether its from either bore or stroke or both but you will not actually be at the same rpm or load with the larger engine or you will be going much faster.

To drive at the same speeds and rates of acceleration as the smaller engine you will see lower rpm and friction with the larger engine. This is why you run huge engines that turn low rpm when you need a lot of power but you need the engine to last forever.

Efficiency means how much power you can make out of a given amount of fuel and air. The larger strokers are always more efficient as evidenced by their lower BSFC readings and their higher power with the exact same heads etc.

joecar

So are we all in agreement that more stroke = more torque at same RPM,
and HP = TQ x RPM / 5252 so more power follows by virtue of more torque.