Breaking BIG!

[Don Johnson]

This!!

They give you all this mumbo jumbo how it's checking shit 100 times a second.. yet somehow The motor outruns the computer.. LOL I agree with you, something went wonky with that program.


Yup, this email string really got me thinking, concerned and asking questions relative to controlling RPM limits because shit does happen. Bottom line I understand that on my motors the electronics would prevent overrev under all conditions. Enen's should have too so something is up... Should not have seen those kind of sustained high RPM's which sucks.

I know that the MSD can control unloaded RPM, the electronics in my drag car controlled RPM at launch no problem, I could mash the throttle and it would come right up to its pre set RPM. Lost a drive shaft once, no problem.

 

[JBS]

This!!



These motors are open loop. Closed loop like a car has an O2 sensor and can make adjustments on the fly. Open loop is pre programmed and makes no adjustments while the motor is running. O2 sensors don't like water. So standard set in a boat is open loop. The motors may have a knock sensor to retard timing. By the time you hear a knock at high rpm it's probably too late. Those pistons look like they've seen a ton of detonation. Timing, bad injector, bad fuel, low octane fuel, low fuel pressure, or a bad program from the get go.

They just need a good polish with Husky hair

 

[Cole Trickle]

This!!

They give you all this mumbo jumbo how it's checking shit 100 times a second.. yet somehow The motor outruns the computer.. LOL I agree with you, something went wonky with that program.


Yup, this email string really got me thinking, concerned and asking questions relative to controlling RPM limits because shit does happen. Bottom line I understand that on my motors the electronics would prevent overrev under all conditions. Enen's should have too so something is up... Should not have seen those kind of sustained high RPM's which sucks.

I know that the MSD can control unloaded RPM, the electronics in my drag car controlled RPM at launch no problem, I could mash the throttle and it would come right up to its pre set RPM. Lost a drive shaft once, no problem.

Honestly I don't think there is an electronics system avaliable that would solve this 100%.

Physics come into play and when you are spinning a drive at 6500 rpms and something lets loose rpm's are going to fly to the moon before most electronics can limit them. I lost a drive shaft in a car at the drag strip and the motor over revved and bent some push rods.

I would imagine a boat would be worse and harder to control.

 

[530RL]

This!!



Honestly I don't think there is an electronics system avaliable that would solve this 100%.

Physics come into play and when you are spinning a drive at 6500 rpms and something lets loose rpm's are going to fly to the moon before most electronics can limit them. I lost a drive shaft in a car at the drag strip and the motor over revved and bent some push rods.

I would imagine a boat would be worse and harder to control.

I agree.

The only thing a MEFI system can really do with respect to limiting RPM is to cut the timing, cut the fuel, or both. If you take a load off of an engine accelerating hard when it it right near the limit, no amount of retarding the timing and no amount of cutting the fuel will stop the acceleration until it expends that energy. Yes, taking away fuel and timing will stop the continued acceleration of RPM but with a sudden loss of load and close to the limit, sixth grade math takes over.

 

[Enen]

At least the fix on Plan B was much cheaper.

View attachment 359325

LOL. It's easy to fix a boat when the problem is between the steering wheel and the drivers seat.

 

[djunkie]

This pic makes me think of life with one testicle.
]

Easy there.

 

[RiverDave]

I agree.

The only thing a MEFI system can really do with respect to limiting RPM is to cut the timing, cut the fuel, or both. If you take a load off of an engine accelerating hard when it it right near the limit, no amount of retarding the timing and no amount of cutting the fuel will stop the acceleration until it expends that energy. Yes, taking away fuel and timing will stop the continued acceleration of RPM but with a sudden loss of load and close to the limit, sixth grade math takes over.

Things in motion want to stay in motion. Things that are accelerating do not want to keep accelerating though. If they kill the spark at an rpm then that's it no matter how fast it got there..

 

[blacksockdown]

Your attitude is awesome.Great description of funtime(while it lasted) moment also! WellDone.

 

[Cole Trickle]

Things in motion want to stay in motion. Things that are accelerating do not want to keep accelerating though. If they kill the spark at an rpm then that's it no matter how fast it got there..

It took a fraction of a milisecond for that thing to rev to 8000 rpms and break that valve. I don't think it stayed above the redline that long but once things went bad that valve bounced around about a thousand times before the motor was shut down.

Honestly that is about as much damage as I have ever seen to a piston and head from a broken valve. That thing was in there for a bit before it jumped ship and took out some other parts of the motor.

I vented an ls1 block to the point that you could see light on both sides. The piston decided it no longer wanted to be attached to the rod and ended up on the track and took out the heads, cam,crank on the way out....sucked

 

[530RL]

Things in motion want to stay in motion. Things that are accelerating do not want to keep accelerating though. If they kill the spark at an rpm then that's it no matter how fast it got there..

Yep, Newton generally agrees with that but the situation was a loss of a load with an accelerating engine. The rotating mass and flywheel has some momentum, or stored energy (kinetic) in it as it was accelerating the load. When that load goes away in a big way, even if you cut the timing or cut the fuel, the momentum of that rotating mass and flywheel will continue to accelerate until it expends that energy. Put more simply, it will not stop accelerating instantly. As long as that load goes away very far down the RPM curve no problem. But taking away the load right near peak RPM makes that stored energy more valuable, at least to the engine parts salesman. F equals MV(squared).

 

[Don Johnson]

I agree.

The only thing a MEFI system can really do with respect to limiting RPM is to cut the timing, cut the fuel, or both. If you take a load off of an engine accelerating hard when it it right near the limit, no amount of retarding the timing and no amount of cutting the fuel will stop the acceleration until it expends that energy. Yes, taking away fuel and timing will stop the continued acceleration of RPM but with a sudden loss of load and close to the limit, sixth grade math takes over.

Which is why you let the MSD handle the RPM limitation, MEFI is not the right way. I believe Enen's motor is MEFI over MSD. MEFI handles fuel and timing over the MSD. As I understand it is best to let the MSD handle the RPM limiter, it is much more effective and faster.

 

[pronstar]

RD is right.

If electronics cut fuel, then the flywheel won't accelerate to any speed greater than where it's at.

The flywheel's energy is kinetic, due to its rotational motion alone. It's not possible to have more stored energy lurking within it.

It's like a bullet leaving a barrel. The moment the gas pushing on it is gone, it decelerates - it doesn't keep accelerating.

 

[Tommy Gun Images]

What if the MSD is used on a treadmill?

 

[Outdrive1]

What if the MSD is used on a treadmill?

You know Tom....

 

[djunkie]

Yep, Newton generally agrees with that but the situation was a loss of a load with an accelerating engine. The rotating mass and flywheel has some momentum, or stored energy (kinetic) in it as it was accelerating the load. When that load goes away in a big way, even if you cut the timing or cut the fuel, the momentum of that rotating mass and flywheel will continue to accelerate until it expends that energy. Put more simply, it will not stop accelerating instantly. As long as that load goes away very far down the RPM curve no problem. But taking away the load right near peak RPM makes that stored energy more valuable, at least to the engine parts salesman. F equals MV(squared).

Same thing can handle with diesels. We called it a runaway. I was next to an old Detroit 8v92 that ran away. Thing went screaming and luckily a guy I was working with grabbed a hammer and smacked the fuel lines off it.

 

[Outdrive1]

Same thing can handle with diesels. We called it a runaway. I was next to an old Detroit 8v92 that ran away. Thing went screaming and luckily a guy I was working with grabbed a hammer and smacked the fuel lines off it.

The old Detroit two strokes would run on their own oil during a run away. You couldn't shut them off.

 

[djunkie]

The old Detroit two strokes would run on their own oil during a run away. You couldn't shut them off.

Well apparently slamming the fuel lines off of it worked that time. That thing was screaming.

 

[530RL]

RD is right.

If electronics cut fuel, then the flywheel won't accelerate to any speed greater than where it's at.

The flywheel's energy is kinetic, due to its rotational motion alone. It's not possible to have more stored energy lurking within it.

It's like a bullet leaving a barrel. The moment the gas pushing on it is gone, it decelerates - it doesn't keep accelerating.

Fair enough, we agree to disagree. Were talking about a rotating mass at a rate of acceleration. Not a mass at a constant rate.

Let's ignore the fact that the load was dropped which would cause ever faster acceleration of the rotating mass. It takes a period of time for the rate of acceleration to slow. When you cut the fuel, the rate of acceleration of the rotating mass decays to zero acceleration. It does not go to zero acceleration instantly and simultaneously.

Dropping the fuel is not a brake, it will not take a rate of acceleration to zero simultaneously with cutting the fuel.

 

[Outdrive1]

Fair enough, we agree to disagree. Were talking about a rotating mass at a rate of acceleration. Not a mass at a constant rate.

Let's ignore the fact that the load was dropped which would cause ever faster acceleration of the rotating mass. It takes a period of time for the rate of acceleration to slow. When you cut the fuel, the rate of acceleration of the rotating mass decays to zero acceleration. It does not go to zero acceleration instantly and simultaneously.

Dropping the fuel is not a brake, it will not take a rate of acceleration to zero simultaneously with cutting the fuel.

Logically speaking.

 

[530RL]

Which is why you let the MSD handle the RPM limitation, MEFI is not the right way. I believe Enen's motor is MEFI over MSD. MEFI handles fuel and timing over the MSD. As I understand it is best to let the MSD handle the RPM limiter, it is much more effective and faster.

I'm confused. The MEFI handles everything, what is the purpose of the "MSD"?

 

[Cole Trickle]

I'm confused. The MEFI handles everything, what is the purpose of the "MSD"?

Simple it keeps the motor from over revving and eating itself when a drive brakes at wide open throttle

 

[pronstar]

Fair enough, we agree to disagree. Were talking about a rotating mass at a rate of acceleration. Not a mass at a constant rate.

Let's ignore the fact that the load was dropped which would cause ever faster acceleration of the rotating mass. It takes a period of time for the rate of acceleration to slow. When you cut the fuel, the rate of acceleration of the rotating mass decays to zero acceleration. It does not go to zero acceleration instantly and simultaneously.

Dropping the fuel is not a brake, it will not take a rate of acceleration to zero simultaneously with cutting the fuel.

I like a good debate, and maybe I can learn something :thumbsup

Let me ask a question or two:
If it continues to accelerate, then where is the energy coming from?
It's not kinetic, because that's energy due to motion.

Wiki (not a great source, I know) says this:
For Flywheel Energy Storage - when energy is extracted from the system, the flywheel's rotational speed is reduced.

What about the law of conservation of energy?
Simply stated - "energy in a system remains constant".
So if fuel isn't being burned to produce energy to produce the additional acceleration, then where is it coming from?

 

[530RL]

Simple it keeps the motor from over revving and eating itself when a drive brakes at wide open throttle

Got the intent.

The question was why do you need an MSD box or any other type of product with the MEFI. MEFI is a complete control system. They don't need anything else and you can program them to do what you want.

 

[Don Johnson]

I'm confused. The MEFI handles everything, what is the purpose of the "MSD"?

The MEFI computer, most likely Delphi, manages the fuel and ignition curve as well elements like knock sensors etc if being used. The MEFI computer sends a signal to the MSD box and the MSD box then in turn fires the coil. As explained to me the MSD can respond to rev limitation duties much faster then the MEFI computer, takes longer for the MEFI computer to shut down fuel at the injectors etc where the MSD can kill spark in milliseconds. My Teague motors are set up this exact way with MEFI over MSD, pretty typical setup.

On other perspective to consider, once ignition and/or fuel is killed to an engine the compression of the unfired cylinders is going to slow down the acceleration energy really fast.

 

[djunkie]

This could be the new plane on a treadmill thread.

 

[530RL]

I like a good debate, and maybe I can learn something :thumbsup

Let me ask a question or two:
If it continues to accelerate, then where is the energy coming from?
It's not kinetic, because that's energy due to motion.

Wiki (not a great source, I know) says this:
For Flywheel Energy Storage - when energy is extracted from the system, the flywheel's rotational speed is reduced.

What about the law of conservation of energy?
Simply stated - "energy in a system remains constant".
So if fuel isn't being burned to produce energy to produce the additional acceleration, then where is it coming from?

There are a ton of variables that you clearly understand but let's look at this in the engine example.

Rate of acceleration is energy.

Let's put it in two parts. Fuel was burnt to maintain the speed of the load and then more fuel was burnt to accelerate the speed of the load.

When all fuel is taken away, the "rate" of acceleration slows to zero and then as you say, the rotational speed is reduced.

The "rate" of acceleration does decay, but RPM's will continue to rise at slower rates now that fuel has been cut.

In this case, an amount of fuel was being burnt to maintain the speed of the load and accelerate the speed of the load. Then the load goes away. What happens, the rate of acceleration increases dramatically as the energy being burnt remains constant, but the load went away.

Then, the fuel was cut, but the rate of acceleration already became very fast when the load went away. So RPM's rise at slower rates, but continue to rise until all of the energy from the acceleration is expended.

You are correct in the sense that the rate of acceleration stops growing and decays but as Aaron's engine can attest, RPM's continued to rise.

 

[530RL]

The MEFI computer, most likely Delphi, manages the fuel and ignition curve as well elements like knock sensors etc if being used. The MEFI computer sends a signal to the MSD box and the MSD box then in turn fires the coil. As explained to me the MSD can respond to rev limitation duties much faster then the MEFI computer, takes longer for the MEFI computer to shut down fuel at the injectors etc where the MSD can kill spark in milliseconds. My Teague motors are set up this exact way with MEFI over MSD, pretty typical setup.

On other perspective to consider, once ignition and/or fuel is killed to an engine the compression of the unfired cylinders is going to slow down the acceleration energy really fast.

Fair enough, way above my skill set. I use MEFI to control the coil and the spark as it was designed to do so. Learn something new every day.

 

[welldigger00]

I agree 530. A good example of the load, then sudden no load with engine accelerating is when you hit an ice patch driving a car up a hill.

 

[530RL]

This could be the new plane on a treadmill thread.

Can a Cessna 172 fly with a groundspeed of zero?

 

[djunkie]

Can a Cessna 172 fly with a groundspeed of zero?

Don't get them going.

 

[Outdrive1]

Can a Cessna 172 fly with a groundspeed of zero?

What does ground speed have to do with anything? Lol.

 

[530RL]

What does ground speed have to do with anything? Lol.

If you have no groundspeed, you can't crash

 

[Outdrive1]

If you have no groundspeed, you can't crash

You'll never reach terminal velocity sitting on the ground.

 

[djunkie]

You'll never reach terminal velocity sitting on the ground.

Just go to ludicrous speed.

 

[Tommy Gun Images]

Can a Cessna 172 fly with a groundspeed of zero?

Yes...

 

[Outdrive1]

Just go to ludicrous speed.

You ever see a grown man naked?

 

[Tommy Gun Images]

What if the MSD is used on a treadmill?

This could be the new plane on a treadmill thread.

Which thread?

 

[Tommy Gun Images]

You ever see a grown man naked?

You ever been in a Turkish prison?

 

[Outdrive1]

You ever been in a Turkish prison?

Do you speak jive?

 

[djunkie]

Do you speak jive?

I picked a bad day to stop sniffing glue.

 

[Enen]

A few top end pics.

 

[Havasu Hangin']

They give you all this mumbo jumbo how it's checking shit 100 times a second.. yet somehow The motor outruns the computer.. LOL I agree with you, something went wonky with that program.

I agree. When I grenaded one of my drives, the parasitic loss pulls the engine down faster than the mechanical freewheeling...the rev limiters did their job.

And when running in the ocean, those limiters saved my neck more than once....lol.

 

[Tommy Gun Images]

Do you speak jive?

Roger, Roger...

 

[spectra3279]

You should have had a rolled up towel handy

 

[Outdrive1]

You should have had a rolled up towel handy

Did you know the Cheatah deck boat runs 90plus on a water pickup speedo with a 525?

I'm just saying.

 

[spectra3279]

I can make my 40 horse John boat do over a hundred on a pitot tube speedo.

 

[Outdrive1]

I can make my 40 horse John boat do over a hundred on a pitot tube speedo.

That's almost fast

 

[BDMar]

2 things:
(1) ECM's, whether MEFI, Motec, DFI, Holley, or whatever, tell the Ignition box or ICM (if coil per cylinder) when to spark. They don't create spark.
(2) When ignition and fuel (fuel is also cut in EFI) are cut in a rev limiting situation, the engine is not free wheeling. You aren't considering the compression in every cylinder that's acting as a brake. When all cylinders are firing, the combustion causes a power stroke that overcomes the piston moving up in another cylinder creating the compression. The amount it overcomes the compression stroke (and friction) is the HP (simply put). With no power stroke you have an 8 cylinder brake.

As Havasu Hangin said, rev limiters do control the engine during a drive failure. I've not only witnessed it, I've seen it on a data log. The highest I've seen an engine go past the limiter 150 rpm's on a 6500 rev limit setting. A high end ECU reacts WAY faster than an MSD limiter. I would assume that Aron's rev limiter is with the MSD since he has a MEFI ECM. There is no way Aron's engine would have gone to 8000 unless his rev limiter was set to 8000 and it NEVER would have stayed there if the rev limiter was functioning properly.

 

[RiverDave]

Yep, Newton generally agrees with that but the situation was a loss of a load with an accelerating engine. The rotating mass and flywheel has some momentum, or stored energy (kinetic) in it as it was accelerating the load. When that load goes away in a big way, even if you cut the timing or cut the fuel, the momentum of that rotating mass and flywheel will continue to accelerate until it expends that energy. Put more simply, it will not stop accelerating instantly. As long as that load goes away very far down the RPM curve no problem. But taking away the load right near peak RPM makes that stored energy more valuable, at least to the engine parts salesman. F equals MV(squared).

Fair enough, we agree to disagree. Were talking about a rotating mass at a rate of acceleration. Not a mass at a constant rate.

Let's ignore the fact that the load was dropped which would cause ever faster acceleration of the rotating mass. It takes a period of time for the rate of acceleration to slow. When you cut the fuel, the rate of acceleration of the rotating mass decays to zero acceleration. It does not go to zero acceleration instantly and simultaneously.

Dropping the fuel is not a brake, it will not take a rate of acceleration to zero simultaneously with cutting the fuel.

The flywheel stores energy, it doesn't create it. The instant (not a half a second later etc.. The very instant) you stop supplying it with energy (via the crank, through the rods, through the wrist pins, through the piston, from the combustion chamber) it starts decelerating. The weight of the flywheel determines how much energy is stored. The parasitic drag or Hp of the engine, plus the function of the weight of the flywheel will determine how fast the engine can accelerate or decelerate without a load.

If you take away the HP (even under acceleration) the fly wheel will want to stay in motion. An engine with a heavier flywheel will continue to self destruct longer then one with a lightened flywheel, but it won't continue to accelerate once the supply line of HP has been cut.

This is why drag cars with lightened flywheels can run from idle to a 10k+ redline back to an idle in a second or so.. They also launch at RPM. Take your family truckster car with a heavier flywheel (easier to drive and not stall at lower rpm) and rev it and it will take a second to rev up (loading the flywheel with kinetic energy) and then another second or two to return to idle (dispersing the energy). If you want to try an experiment yourself go out to your car and rev the motor.. Don't pay attention to the gauges as their maybe a delay in most family trucksters tachs.. Listen at the exact point to the engine when you let off the throttle on a quick rev and things will hang for a half a second (not increase) and then decelerate. The lighter the flywheel the quicker the response you will get. At no time will things ever continue to accelerate once the throttle has been cut.. Or if you ripped the cool wire out etc..

I'm not an engine builder and I have no idea how an MSD or a mefi implements a rev limiter.. If it is slowly trying to retard timing I could see how it might overshoot the rpm.. But if they have it set to cut ignition at xy rpm, then rest assured if it actually did its job it would never make it to Z, because the laws of physics (not my opinion) say it is impossible for it to ever get to z.

For some odd reason the initial failure in Aaron's boat was in fact the rev limiter.. All the other failures are a result of that, and from what I would guess some previous problems..

Like I said, I'm no engine builder.. But I did sit under an apple tree once. (Physics joke)

RD

RD

 

[pronstar]

The Second Law of Physics:
F=MA

If the mass of the flywheel is positive, and you're saying the rate of acceleration is positive, then force must also be positive.

If we stop adding energy (force), then what is accelerating the flywheel?

I agree 530. A good example of the load, then sudden no load with engine accelerating is when you hit an ice patch driving a car up a hill.

That's because your foot is on the accelerator, supplying the engine with fuel/energy to increase the rpm.