Keep her above 4000rpm and she'll thank you for it every day.

[Brucelee]

Why is the average piston speed of the 849 Sleeper important??

One of the biggest factors that engine builders use to predict engine reliability is “average piston speed”. In short, the peak rpm and stoke length are plugged into a formula to obtain the average piston speed in “feet per minute” (it’s a finer measurement than mph). Here are The numbers:

Stroke Length
68mm SuperJet
74mm Kaw750/800
SXR Setups

Stock OEM peak rpm
6150 rpm
6550 rpm


Piston speed @ stock RPMs
2742
3180
SXR stock

Piston peed @ 6800 rpm
3032
3301


Piston peed @ 7000 rpm
3122
3398
849 Sleeper

Piston peed @ 7200 rpm
3211
3495


Piston peed @ 7300 rpm
3255
3609


Piston peed @ 7400 rpm
3300
3592
Wet-Pipe

Piston peed @ 7500 rpm
3345
3641


Piston peed @ 7600 rpm
3390
3689


Piston peed @ 7700 rpm
3434
3738
Dry-Pipe




4000+ fpm – Completely unpredictable life span of crankshaft components

3700 fpm – Crank life can predictably be 20-35 hours

3500 fpm – Crank life can predictably be a full season of use

3300 fpm – Crank life is predictably 2-3 seasons of use

3100 fpm – Production unit range, predictably 4-5 seasons of use



It is common knowledge, among stand up racers, that modified SuperJets have considerably better crankshaft life than modified SXRs …. Average piston speed is the reason why. One of the best features of the 849 Sleeper is that it delivers the water-speeds of a high revving setup, but yields the significantly lower piston speeds that improve crank life. It’s true that the slightly increased weight of the 849 Sleeper pistons does slightly increase loads on the connecting rods. However that load increase is nowhere near the load increases subjected by the extra 400-700 rpms of the higher revving race pipe setups.

[Brucelee]

Remember the title of this post. The contention is that driving at higher RPMs (and by def. higher piston speeds) is GOOD for your car, ie your car will thank you.

The burden of proof is to show how high RPM driving is GOOD for your car.

I have shown evidence that it is not. Find me some expert evidence that high piston speeds are GOOD for your car.

Again, the engine is NOT a muscle. It does not improve under stress.

I don't have to prove the negative.

[blue2000s]

Originally Posted by Brucelee

Why is the average piston speed of the 849 Sleeper important??

One of the biggest factors that engine builders use to predict engine reliability is “average piston speed”. In short, the peak rpm and stoke length are plugged into a formula to obtain the average piston speed in “feet per minute” (it’s a finer measurement than mph). Here are The numbers:

Stroke Length
68mm SuperJet
74mm Kaw750/800
SXR Setups

Stock OEM peak rpm
6150 rpm
6550 rpm


Piston speed @ stock RPMs
2742
3180
SXR stock

Piston peed @ 6800 rpm
3032
3301


Piston peed @ 7000 rpm
3122
3398
849 Sleeper

Piston peed @ 7200 rpm
3211
3495


Piston peed @ 7300 rpm
3255
3609


Piston peed @ 7400 rpm
3300
3592
Wet-Pipe

Piston peed @ 7500 rpm
3345
3641


Piston peed @ 7600 rpm
3390
3689


Piston peed @ 7700 rpm
3434
3738
Dry-Pipe




4000+ fpm – Completely unpredictable life span of crankshaft components

3700 fpm – Crank life can predictably be 20-35 hours

3500 fpm – Crank life can predictably be a full season of use

3300 fpm – Crank life is predictably 2-3 seasons of use

3100 fpm – Production unit range, predictably 4-5 seasons of use



It is common knowledge, among stand up racers, that modified SuperJets have considerably better crankshaft life than modified SXRs …. Average piston speed is the reason why. One of the best features of the 849 Sleeper is that it delivers the water-speeds of a high revving setup, but yields the significantly lower piston speeds that improve crank life. It’s true that the slightly increased weight of the 849 Sleeper pistons does slightly increase loads on the connecting rods. However that load increase is nowhere near the load increases subjected by the extra 400-700 rpms of the higher revving race pipe setups.

Brucelee, what's the source of failure in this case? Is something breaking from stress or is it breaking from wearing out? I would bet that it's the former. You have to look at the cause for this to be useful information.

[Paul]

Anybody know the stroke of a 2.7?


Mean piston speed =0.167 x Stroke in inches x 7200 rpms.

[Paul]

Found it, it's 3.07 inches.

4000 rpms = 2051
5000 rpms= 2563
6000 rpms = 3076
7200 rpms = 3691

[Brucelee]

Originally Posted by Paul

Found it, it's 3.07 inches.

4000 rpms = 2051
5000 rpms= 2563
6000 rpms = 3076
7200 rpms = 3691

Good info. Mass times velocity SQUARED equals momentum.

Every time the piston goes down, it has to be pulled back up.

[blue2000s]

Originally Posted by Brucelee

Good info. Mass times velocity SQUARED equals momentum.

Every time the piston goes down, it has to be pulled back up.

momentum is actually 1/2 x mass x velocity squared.

[Brucelee]

Originally Posted by blue2000s

momentum is actually 1/2 x mass x velocity squared.

================================================== ==================

My head hurts!


I have found conflicting anwers to the formula for momentum. It seems physics is not that precise after all.



Deborah,
First, energy and momentum are very different properties.

An object takes time to stop moving. The momentum of an object can be
describes as the amount of force required to stop the object in one second.
When a constant force is applied to an object, it is the force multiplied by
the time over which it is applied that yields the change of momentum of the
particle. Also, momentum is a vector: it has a direction to it. Momentum
points in the direction of an object's velocity.

An object continues to travel while its velocity drops to zero. The kinetic
energy of an object can be described as the amount of force required to stop
the object over a distance of one meter. When a constant force is applied
to an object, it is the force multiplied by distance traveled along the SAME
AXIS as the force that determines the change of kinetic energy. Kinetic
energy is a scalar: it has no direction.

An object changing direction but neither speeding up nor slowing down is an
example of changing momentum but not changing kinetic energy. If the object
does speed up or slow down, both momentum and kinetic energy will change.
For example, consider throwing a rock upward at a certain speed. If you
double the rock's initial speed, the rock will require twice the time and
four times the distance to reach zero speed. Thus, the rock with the
doubled speed has twice the momentum and four times the kinetic energy.

Dr. Ken Mellendorf
Physics Instructor
Illinois Central College

Momentum is m*v, and kinetic energy is m*v*v/2, so if momenta and energies
are the same, we have:
1) m1*v1 = m2*v2
2) m1*v1*v1 = m2*v2*v2
using (1) in (2) yields
m1*v1*v1 = (m1*v1)*v2 -> v1 = v2
using this in (1) shows that m1 = m2
So, yes, if a particle has the same momentum and the same kinetic energy
as another particle, their masses and velocities must be equal

But having the same momentum does not by itself imply having the same
energy. A heavy particle moving slowly can have the same momentum as
a light particle moving swiftly.

--
Tim Mooney
Advanced Photon Source, Argonne National Lab.

[Brucelee]

Stress leads to fatigue, wear comes from friction, these are two totally different mechanisms.

Are you suggesting that stress does not lead to wear? If I incease the stress on a bearing are you suggesting that it does not wear faster than if I lower the stress? Are you suggesting that engines that are supposed to run at very high piston speeds don't need to be engineered to handle the stress?

Are you suggesting that if I run my Boxster at 6K rpm, that concussion, heat, friction, and mechanical stress are not all higher than if I run it at 3K RPM? What about the impact of higher temps on metal fatigue?

I can't see any way out of this for you. Explain how all the factors that contribute to metal stress and wear are not higher at higher piston speeds and higher RPMs.

[Brucelee]

Brucelee, what's the source of failure in this case? Is something breaking from stress or is it breaking from wearing out? I would bet that it's the former. You have to look at the cause for this to be useful information.

I believe that the amount of STRESS that you place on a motor contributes to it wearing our or breaking.

I don't think that there is any question that a bearing is stressed more at high rpms vs low rpms, all things being equal. Ditto, connecting rods, pistons, valves, etc.

That is why racing oil is developed, to deal with unique stresses that normal motors don't experience.

[blue2000s]

Are you trying to change the focus of the back-and-forth?

There was a comment made on wear, I made my statement about the study on wear, showed a review and synopsis of the study that was conducted by a technologist at GM, described why it's true, and the next comment was off topic. What happened there?

[blue2000s]

Originally Posted by Brucelee

Brucelee, what's the source of failure in this case? Is something breaking from stress or is it breaking from wearing out? I would bet that it's the former. You have to look at the cause for this to be useful information.

I believe that the amount of STRESS that you place on a motor contributes to it wearing our or breaking.

I don't think that there is any question that a bearing is stressed more at high rpms vs low rpms, all things being equal. Ditto, connecting rods, pistons, valves, etc.

That is why racing oil is developed, to deal with unique stresses that normal motors don't experience.

Stress leads to fatigue, wear comes from friction, these are two totally different mechanisms.

Racing oil is developed to increase the amounts of additives needed for the best lubrication. Highway use vehicles have laws on the additives that can be added, racing cars don't.