what causes the most stress on an engine?

[HiPSI]

pistons move in a straight line motion, rods move in an up/down and circular motion. the forces affecting these parts are not torque as torque is purely a twisting motion.

if you want to break it down to the basics the main thing here is cylinder pressures, the amount of force placed on a piston causing it to move through it's travel. good tuning keeps the pressures fairly even between cylinders, but as you increase HP, you're increasing the amount of pressure in the cylinders (more air/fuel=stronger burn=more pressure). the piston is pushing down on the rod when the cylinder fires and then the rod translates that motion into the crank to create torque. at a certain level, the force placed upon the rod will cause it to bend/break or you can shatter/blow a hole in a piston. in a perfect world these consistant pressures would make the engine more reliable as long as they are kept below the breaking point of the parts in the engine, but this is never the case.

this is where detonation comes in, because it causes huge spikes in the force upon the internals. preignition/detonation causes the air/fuel to burn while the piston is still traveling upward being pushed by the rest of the engine, so it's kind of like the difference between running your car into a stopped semi truck at 30mph or hitting the same semi truck head on when they're coming at you at 60mph. the forces placed on the parts are multiplied, and then suddenly your nicely tuned engine becomes shrapnel. the counterpart to this is heat, because as pressure increases so does the temperature (why tune by the EGT gauge ). extreme pressure causes extreme heat, which compounds the problem of bad tuning causing burned pistons/valves if you're lucky enough not to throw a rod through the block.

[Jaimecbr900]

Very good informative thread.

I have a friend that had a 5th Gen Max. He was going to build a stroker motor and had the parts laying there to do it. He was already running boost on his VQ motor. I was told that he wanted to find out how much the engine would take before messing up, since he already had another engine waiting in the wings. I was told that he turned up the boost (obviously he was upping everything else he could to keep up) and from what I heard it held. He was somewhere up there in the power levels you're talking about, 450-500hp. Again, this was heresay although I could make a phone call to find out for sure.

Point is that the VQ motor may have some issues with the rods, but I have a sneaky hunch that may be more related to tuning than inherently weak parts. Again, this is only my opinion, but I did do a ton of nitrous squeezing into my 95 Max with a VQ30 motor in it and the motor is still perfectly fine. I think that tuning properly with a good eye on the a/f is the key.

[tony]

Very good informative thread.

I have a friend that had a 5th Gen Max. He was going to build a stroker motor and had the parts laying there to do it. He was already running boost on his VQ motor. I was told that he wanted to find out how much the engine would take before messing up, since he already had another engine waiting in the wings. I was told that he turned up the boost (obviously he was upping everything else he could to keep up) and from what I heard it held. He was somewhere up there in the power levels you're talking about, 450-500hp. Again, this was heresay although I could make a phone call to find out for sure.

Point is that the VQ motor may have some issues with the rods, but I have a sneaky hunch that may be more related to tuning than inherently weak parts. Again, this is only my opinion, but I did do a ton of nitrous squeezing into my 95 Max with a VQ30 motor in it and the motor is still perfectly fine. I think that tuning properly with a good eye on the a/f is the key.

You are absolutely correct, there are some guys blowing their engine on the dyno at 5psi then there are others with 10k+ miles pushing 11-12psi and its all due to tuning.

[tony]

pistons move in a straight line motion, rods move in an up/down and circular motion. the forces affecting these parts are not torque as torque is purely a twisting motion.

if you want to break it down to the basics the main thing here is cylinder pressures, the amount of force placed on a piston causing it to move through it's travel. good tuning keeps the pressures fairly even between cylinders, but as you increase HP, you're increasing the amount of pressure in the cylinders (more air/fuel=stronger burn=more pressure). the piston is pushing down on the rod when the cylinder fires and then the rod translates that motion into the crank to create torque. at a certain level, the force placed upon the rod will cause it to bend/break or you can shatter/blow a hole in a piston. in a perfect world these consistant pressures would make the engine more reliable as long as they are kept below the breaking point of the parts in the engine, but this is never the case.

this is where detonation comes in, because it causes huge spikes in the force upon the internals. preignition/detonation causes the air/fuel to burn while the piston is still traveling upward being pushed by the rest of the engine, so it's kind of like the difference between running your car into a stopped semi truck at 30mph or hitting the same semi truck head on when they're coming at you at 60mph. the forces placed on the parts are multiplied, and then suddenly your nicely tuned engine becomes shrapnel. the counterpart to this is heat, because as pressure increases so does the temperature (why tune by the EGT gauge ). extreme pressure causes extreme heat, which compounds the problem of bad tuning causing burned pistons/valves if you're lucky enough not to throw a rod through the block.

This had to be the most helpful post I've seen yet, I appreciate the knowledge.

[Vteckidd]

this is where detonation comes in, because it causes huge spikes in the force upon the internals. preignition/detonation causes the air/fuel to burn while the piston is still traveling upward being pushed by the rest of the engine, so it's kind of like the difference between running your car into a stopped semi truck at 30mph or hitting the same semi truck head on when they're coming at you at 60mph. the forces placed on the parts are multiplied, and then suddenly your nicely tuned engine becomes shrapnel. the counterpart to this is heat, because as pressure increases so does the temperature (why tune by the EGT gauge ). extreme pressure causes extreme heat, which compounds the problem of bad tuning causing burned pistons/valves if you're lucky enough not to throw a rod through the block.

hence why most high horsepower turbo cars melt down on 4th gear pulls or pull on the highway cause the EGTs go through the roof. at least from whati have seen. lots of long pulls can blow shit up and melt pistons QUICK.

also, its a known fact the 350z motors have weak rods. yes you can get away with 10-12psi, for how long though? i mean, its possible, hell i have seen 450whp stock sleeves and rods in a honda motor, but if you are boosting ALL THE TIME EVERY DAY, it aint gonna last. not IMO

[HiPSI]

hence why most high horsepower turbo cars melt down on 4th gear pulls or pull on the highway cause the EGTs go through the roof. at least from whati have seen. lots of long pulls can blow shit up and melt pistons QUICK.

that is pretty true overall. long highway pulls, for example, will send me into the red (1600+ degrees) but bursts of WOT for a half mile or so at a time won't get it much over 1400 degrees (measured about 1" from the head flange in the exhaust manifold). it just goes back to square one, it's creating more pressure and more heat. if you stay in it for a long distance the pistons/cylinder walls will eventually soak up that heat and reach their melting point or at least a temp where they will be able to stretch/bend under the loads in the cylinders, then mr. engine goes bye bye .

and then again, a bunch of kids with stock SR's will slap on a T28 and turn up the boost well beyond what the stock computer/maf/injectors can handle and do the same thing in about 1/8 mile of jumping on the gas .

[Vteckidd]

that is pretty true overall. long highway pulls, for example, will send me into the red (1600+ degrees) but bursts of WOT for a half mile or so at a time won't get it much over 1400 degrees (measured about 1" from the head flange in the exhaust manifold). it just goes back to square one, it's creating more pressure and more heat. if you stay in it for a long distance the pistons/cylinder walls will eventually soak up that heat and reach their melting point or at least a temp where they will be able to stretch/bend under the loads in the cylinders, then mr. engine goes bye bye .

and then again, a bunch of kids with stock SR's will slap on a T28 and turn up the boost well beyond what the stock computer/maf/injectors can handle and do the same thing in about 1/8 mile of jumping on the gas .

i agree 100%. in turbo cars its critical to watch EGTs as it really coincides much more with detonation than a NA car.

Its funny to see guys shootign for 400whp but dont even have a EGT gauge