What does it take to burn pistons on a 500EFI
07-13-2007, 11:34 AM
#21
21 and 42 footers
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go to injector.com
Can't remember the guys name but it's Marren Fuel Injection up in the north eastern part of the country. Not only did he diagnose which cylinders were bad by testing the injectors, he sold me new ones cheaper than I could find anywhere.
07-13-2007, 02:49 PM
#22
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Just to respectfully disagree again, in a boat with open exhaust it's very hard, if not impossible, to hear if an engine is detonating. All the electronic safeties on the EFI motors are great but what about a carb motor? No knock sensor, no electronic fuel injectors just an antiquated fuel metering device called a carburetor. Change fuel filters as much as you want, some trash will still get into the bowls. One small piece of trash in a jet can lean it out and wipe out a couple pistons - and in a boat, under constant load, it won't take long. Or, here's another for you. How about your timing advance module takes a sheet while you're on the water. You could have put a timing light on it right before you left the dock but it still may take a dump while underway. Had it happen to a friend of mine. In one particular range of RPM the timing would begin jumping back and forth erratically and would sometimes stick in a far advanced position. Found the problem after it wiped out some internal parts. So, yes, most things can be prevented by keeping track of your rig and performing the required maintenance. But, parts do fail and sometimes you can't foresee the problem.
Just My .02
Just My .02
well.... that may be your experience but it isn't mine. my experience is that is that the only time this sort of thing happens is when people make mistakes one way or another...
and i am not talking about blower motors that can melt anything in a heartbeat with even the smallest of failures... but thats the risk associated with those motors... they are built to be edgy and they often are. what i am talking about are all the other cases that people write off to "random failure" or voodoo or bad luck. run reasonable compression ratios and make sure of the quality of your fuel. make sure that your fuel filters are good enough to keep your injectors and carbs clean.
make sure the rest of your hardware is in good shape ... and for the record i have NEVER seen an ignition fail to MORE advance... not once... ever. and what the hell are people doing running their systems on the "knock sensor" like its a rev limiter ? configure the motor and run good enough gas to keep it OFF the knock sensor...
what i find is that these type of failures happen to the same people all the time... other people somehow manage to run the same equipment for years and years and years with no failures what so ever...
do you think thats just luck ? i don't. i think some people just pay better attention to what they are doing than others.
and i can tell you that when my 502's were running at WOT and one of the injectors failed i both saw it on the tach and felt it and immediattly throttled back .... i knew instantly something was different. i didn't have to melt a piston to find that out.
07-13-2007, 03:49 PM
#23
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well.... that may be your experience but it isn't mine. my experience is that is that the only time this sort of thing happens is when people make mistakes one way or another...
and i am not talking about blower motors that can melt anything in a heartbeat with even the smallest of failures... but thats the risk associated with those motors... they are built to be edgy and they often are. what i am talking about are all the other cases that people write off to "random failure" or voodoo or bad luck. run reasonable compression ratios and make sure of the quality of your fuel. make sure that your fuel filters are good enough to keep your injectors and carbs clean.
make sure the rest of your hardware is in good shape ... and for the record i have NEVER seen an ignition fail to MORE advance... not once... ever. and what the hell are people doing running their systems on the "knock sensor" like its a rev limiter ? configure the motor and run good enough gas to keep it OFF the knock sensor...
what i find is that these type of failures happen to the same people all the time... other people somehow manage to run the same equipment for years and years and years with no failures what so ever...
do you think thats just luck ? i don't. i think some people just pay better attention to what they are doing than others.
and i can tell you that when my 502's were running at WOT and one of the injectors failed i both saw it on the tach and felt it and immediattly throttled back .... i knew instantly something was different. i didn't have to melt a piston to find that out.
and i am not talking about blower motors that can melt anything in a heartbeat with even the smallest of failures... but thats the risk associated with those motors... they are built to be edgy and they often are. what i am talking about are all the other cases that people write off to "random failure" or voodoo or bad luck. run reasonable compression ratios and make sure of the quality of your fuel. make sure that your fuel filters are good enough to keep your injectors and carbs clean.
make sure the rest of your hardware is in good shape ... and for the record i have NEVER seen an ignition fail to MORE advance... not once... ever. and what the hell are people doing running their systems on the "knock sensor" like its a rev limiter ? configure the motor and run good enough gas to keep it OFF the knock sensor...
what i find is that these type of failures happen to the same people all the time... other people somehow manage to run the same equipment for years and years and years with no failures what so ever...
do you think thats just luck ? i don't. i think some people just pay better attention to what they are doing than others.
and i can tell you that when my 502's were running at WOT and one of the injectors failed i both saw it on the tach and felt it and immediattly throttled back .... i knew instantly something was different. i didn't have to melt a piston to find that out.
07-13-2007, 09:29 PM
#24
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When you go from an injector that worked fine at 3/4 throttle and then it shuts down at WOT you go from full fuel to no fuel. Guess what? There is a lean condition in between and there is your burnt piston. Sometimes you get lucky, but many times its curtains. Now if its a blown enigine you F*cked. been there...
07-13-2007, 09:52 PM
#25
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This thread may be getting a little off topic.
in this thread is a picture of a piston with a hole melted thru it.
http://www.offshoreonly.com/forums/s...ghlight=piston
Here is thread about detonation
http://www.offshoreonly.com/forums/s...ghlight=piston
Here is thread with picture of one of my pistons.
http://www.offshoreonly.com/forums/s...ghlight=piston
I have destroyed many motors in my years but I ran the motors on the edge of detonation. Some time I would pass that edge.
in this thread is a picture of a piston with a hole melted thru it.
http://www.offshoreonly.com/forums/s...ghlight=piston
Here is thread about detonation
http://www.offshoreonly.com/forums/s...ghlight=piston
Here is thread with picture of one of my pistons.
http://www.offshoreonly.com/forums/s...ghlight=piston
I have destroyed many motors in my years but I ran the motors on the edge of detonation. Some time I would pass that edge.
07-15-2007, 10:49 AM
#26
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Let’s get back to the question originally asked. Do these 500EFI's provide a reliable power package? They can!! If you are running, not very often, as you say you are then do three things, Have the engines brought back to stock if not all ready. Have the engine builder set a conservative initial advance also make sure the ecu's are stock programs and finally hit the tank with a good fuel stabilizer each time you go out. You won't have to worry about a thing as long as nobody is trying to take the engines beyond stock. Make sure the props keep the RPM'S well below the redline as bumping up against same can burn pistons very fast. The knock sensors do go off but too late in my experience, so keep the timing conservative, keep the gas stabilized and keep the RPM'S well in the green.
07-15-2007, 12:18 PM
#27
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Here's a few excerpts from my notes (not written by me, just copied info from other sources) on burning pistons and etc.
This is also why pistons and such don't 'melt' when comb temp is much higher than a metals melting point.
Boundary layer.
This is also why pistons and such don't 'melt' when comb temp is much higher than a metals melting point.
Boundary layer.
The boundary layer is a thin layer of fuel-air mix just above the metal surfaces of the combustion chamber (see figure 2, above). Physical principles (aptly called boundary conditions) require that under normal circumstances (i.e. equilibrium combustion, which means "nice, slow and thermally well transmitted") this boundary layer stays close to the metal surfaces. It usually is quite thin, maybe a fraction of a millimeter to a millimeter thick. This boundary layer will not burn even when reached by the flame front because it is in thermal contact with the cool metal, whose temperature is always well below the ignition temperature of the fuel-air mix.
Only under the extreme conditions of detonation can this boundary layer be "swept away" by the high-pressure shock front that occurs during detonation. In that case, during these "far from equilibrium" process of the pressure-induced shock wave entering the boundary layer, the physical principles allured to above (the boundary conditions) will be effectively violated. The degree of violation will depend on (a) the pressure fluctuation caused by the shock front and (b) the adhesive and cohesive strength of the boundary layer. These boundary layers of air-fuel mix remain unburned during the normal combustion process due to their close proximity to the cool metal surfaces and act as an insulating layer and prevent a direct exposure of metal to the flame. Since pressure waves created during detonation can sweep away these unburned boundary layers of air-fuel mix, they leave parts of the piston top and combustion chamber exposed to the flame front. This, in turn, causes an immediate rise in the temperature of these parts, often leading to direct failure or at least to engine overheating.
Only under the extreme conditions of detonation can this boundary layer be "swept away" by the high-pressure shock front that occurs during detonation. In that case, during these "far from equilibrium" process of the pressure-induced shock wave entering the boundary layer, the physical principles allured to above (the boundary conditions) will be effectively violated. The degree of violation will depend on (a) the pressure fluctuation caused by the shock front and (b) the adhesive and cohesive strength of the boundary layer. These boundary layers of air-fuel mix remain unburned during the normal combustion process due to their close proximity to the cool metal surfaces and act as an insulating layer and prevent a direct exposure of metal to the flame. Since pressure waves created during detonation can sweep away these unburned boundary layers of air-fuel mix, they leave parts of the piston top and combustion chamber exposed to the flame front. This, in turn, causes an immediate rise in the temperature of these parts, often leading to direct failure or at least to engine overheating.
07-15-2007, 12:38 PM
#28
VIP Member
respectfully disagree. if motor was built properly to start with , then pinging a hole in a piston or two is strictly a function of someone screwing up.
if it had bad gas due to age ( low octane as mentioned above) then its the guys fault that was dumb enough to try to run the boat w/ old gas...
same w/ the timing and injectors or jets or anything else...
nothing is plug and play when you are talking about high hp big v-8s ... its your job to make sure all that stuff is correct before you launch. if you are going to only run the boat a few hours a year then you solve the gas problem by not filling it full of gas and then letting it sit around... you keep absolute min fuel in it and fuel it fresh each time you go out and if its going to sit for 6 months then you drain it and make sure you run some marvel mystery oil thru the injectors and pumps...etc etc etc...
nothing " just happens"
if it had bad gas due to age ( low octane as mentioned above) then its the guys fault that was dumb enough to try to run the boat w/ old gas...
same w/ the timing and injectors or jets or anything else...
nothing is plug and play when you are talking about high hp big v-8s ... its your job to make sure all that stuff is correct before you launch. if you are going to only run the boat a few hours a year then you solve the gas problem by not filling it full of gas and then letting it sit around... you keep absolute min fuel in it and fuel it fresh each time you go out and if its going to sit for 6 months then you drain it and make sure you run some marvel mystery oil thru the injectors and pumps...etc etc etc...
nothing " just happens"
or they could of sold him bad gas?
Or like if it had a supercharger and was dynoed on 93 .What if one of the Irainain red dots was putting 87 in the 93 gas station tanks or even putting water in them
ya never know
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07-15-2007, 04:43 PM
#29
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yes....... you are correct. no question about it... my only point is that ( and i use my own experience here) if you are in an environment where you don't have a good handle on the variables... everything from your own time you can devote to staying on top of things to who you can trust in your area to stay on top of things to where you are buying your fuel routinely etc etc that those elements are as much a consideration in how you specify your motor configuration as which cam or any other hard part.... as mentioned above... the original question... "can a 500 efi be reliable " well ... sure. IF the compression ratio isn't screwed with... IF you run even borderline good gas... IF you don't send the ecu out to be screwed with ... IF IF IF....
whats a 500 efi... 8.75 to one ? good hi end well thought out injection ? a bottom end thats been in use for eons at well over the 425 this motor makes ? on paper , in stock trim, ide expect to run that motor for a long long time trouble free on almost any fuel that would burn... the problems always start when someone says " gee i read somewhere that if i just put another 20 lbs of fuel pressure in it or take the thermostat out or throw a way the factory ignition and put in some MSD piece of junk because it looks all zoomy or all id did was change this and that..........
then its " gee i can't understand why my oil if full of fuel" its this lousy injection.... why is my transom all covered in soot ? or " why did my motor run all its bearings at 50 hrs ?"
will that 500 efi be reliable ? absolutely.... its just like a good hard on... the less you f**k with it, the longer it will last and the less trouble it will be for you.
whats a 500 efi... 8.75 to one ? good hi end well thought out injection ? a bottom end thats been in use for eons at well over the 425 this motor makes ? on paper , in stock trim, ide expect to run that motor for a long long time trouble free on almost any fuel that would burn... the problems always start when someone says " gee i read somewhere that if i just put another 20 lbs of fuel pressure in it or take the thermostat out or throw a way the factory ignition and put in some MSD piece of junk because it looks all zoomy or all id did was change this and that..........
then its " gee i can't understand why my oil if full of fuel" its this lousy injection.... why is my transom all covered in soot ? or " why did my motor run all its bearings at 50 hrs ?"
will that 500 efi be reliable ? absolutely.... its just like a good hard on... the less you f**k with it, the longer it will last and the less trouble it will be for you.
Last edited by stevesxm; 07-15-2007 at 05:02 PM.
