Lidio
12-23-2004, 12:10 PM
There’s been talk on some of the other posts about connecting rod strength or lack there of on the 4.6L motor in the MM’s. I skimmed through a few posts on this recently and don’t remember or didn’t note who to address or reply this to specifically, but I thought I talk about it in my own forum real quick any way (actually a little long).
The only real problem I’ve found over the years with the modern connecting rod in the 4.6L is its ability to stay conformed on the big end where the rod bearing is. We’ve seen more 4.6’s spin rod bearings then any other Ford motors we’ve ever worked with. The old 302’s or 5.0’s almost never had rod bearing issues. We’ve had 4.6L’s come to us with spun rod bearing with almost no MOD’s done to the car other then maybe a gear change and some exhaust work. Certainly not some thing big like a blower or a NOS system.
There are some who believe that the current rods in our MM will not break or have a problem with to much load and can really only break apart in the event of an over rev or high rpm condition where the piston actually rips the rod in half. I do believe this can happen and probably has happen to quite a few people. But I assure you that what most people think is a stock rod failure on a 4.6L that’s had a substantial power-adder installed was most likely a piston failure first that lead to a major rod failure afterwards instantly.
What I’ve learned is that the single, weakest part on the inside of our MM’s and many other 4.6L engines is that with out a doubt it’s the piston hands down! If you detonate them a little bit for a little while, your OK for the most part and of course fix the tune. If you detonate them a little harder and don’t catch or hear it, you will eventually break the top of the piston around the ring land. When this happens all you loose is compression in the 4.6’s and other then a hurt piston, the block and crank end up typically being completely reusable of course with a proper bore/hone job and other block prepping in lieu of a rebuild.
But when you detonate them hard enough at high rpm when racing. This is what leads to a major engine failure. The piston doesn’t just break a little or crack. They scatter completely, leaving the connecting rod with only its little end and the piston pin to swing around and do nothing but slice through the block and put a bunch of wholes in it, and the oil pan. Some times the crank will actually survive this mess but most of the time they don’t.
Guys will tear down a 4.6L motor that’s had a major piston failure and not find much of the piston left and think that the rod failed first. But in a supercharged 4.6L nearly every time I’ve torn one down with this type of breakage. In the end it can be surmised that it was detonated and shattered the piston first.
I’ve posted a piston and rod from a good friends ’02 Mustang Saleen that had the all original 2-Valve motor and all we did was add some exhaust stuff and a Kenne Bell blower making about 12psi of boost, intercooled and ran it on pump 94 octane. The car made stout low and mid range TQ and was a blast to drive under all conditions and RPM’s. It was driving this way for months with no detonation or any problems at all. Then the greed and need for greater speed set it and he caved-in to trying to step it up even more. We bumped the boost to 17psi and switched to locally available “Turbo Blue”
110 octane leaded race fuel. A little over kill as far as octane to some, but we wanted the absolute in safety from detonation as we could. And I assured him that it was in no way detonating with that fuel in his application with my tune.
Well after making the switch to the big boost and the race fuel, the motor only lasted about one day! We made a bunch of dyno pulls with it and when he took it home that night after some drive time and abuse, the engine developed a knock that I had a hard time deciphering what it was or where it was coming from in the lower end of the motor. The funny thing was the engine did not shake or act like it had a dead cylinder like most 4.6’s and 5.0’s do when they drop a cylinder or two… it still ran and sounded perfect except for the knocking from the bottom end. At that time I knew that since it still ran good and had no apparent misfire that we didn’t detonate it and cause a piston problem. We simply might have made so much low end TQ that initially I thought we squished a bearing right out of it.
When we tore it down I couldn’t believe what we found had happened to the cylinder number #1 connecting rod. As can be seen in the PIX I’ve posted, we literally just bent it from to much low end torque. This thing made over 540ft lbs of TQ at less then 2800 rpm at the rear wheels. If it where an automatic trans it probably would have survived a lot longer, but because he had a stick and was able to lug it around at 1500 to 2500 rpms in 3rd or 4th or even 5th gear, because it did feel very good down there. He simply lugged it down to hard and loaded the rod to hard. An auto trans and its torque converter would not have let this happen as easily because it would down shift and the stall speed of a torque converter simply would'nt let it stay that low in the revs.
Take a look at the PIX, the only damage to the piston is the bottom of the skirt area because when the rod bent, it obviously becomes shorter thus bringing the piston closer to the counter weights of the crankshaft on the down stroke. This is what made the ticking noise we heard and hurt the piston bottom. You can see the top of the piston has no damage at all, the rings and the lands all fit together nice and loose like they should. Usually when a piston has been severely abused the rings wont move around correctly because the lands get distorted from det. With good gas and a proper tune, this piston would have and could have lasted a very long time in this application believe it or not. On this one the extreme low end of the KB blower and the lugging of a manual trans did him in. Of course it now has Eagle Rods and forged Diamond pistons in the new motor with the same tune and no problems for several months now.
Just some stuff for general consumption
Thanks
The only real problem I’ve found over the years with the modern connecting rod in the 4.6L is its ability to stay conformed on the big end where the rod bearing is. We’ve seen more 4.6’s spin rod bearings then any other Ford motors we’ve ever worked with. The old 302’s or 5.0’s almost never had rod bearing issues. We’ve had 4.6L’s come to us with spun rod bearing with almost no MOD’s done to the car other then maybe a gear change and some exhaust work. Certainly not some thing big like a blower or a NOS system.
There are some who believe that the current rods in our MM will not break or have a problem with to much load and can really only break apart in the event of an over rev or high rpm condition where the piston actually rips the rod in half. I do believe this can happen and probably has happen to quite a few people. But I assure you that what most people think is a stock rod failure on a 4.6L that’s had a substantial power-adder installed was most likely a piston failure first that lead to a major rod failure afterwards instantly.
What I’ve learned is that the single, weakest part on the inside of our MM’s and many other 4.6L engines is that with out a doubt it’s the piston hands down! If you detonate them a little bit for a little while, your OK for the most part and of course fix the tune. If you detonate them a little harder and don’t catch or hear it, you will eventually break the top of the piston around the ring land. When this happens all you loose is compression in the 4.6’s and other then a hurt piston, the block and crank end up typically being completely reusable of course with a proper bore/hone job and other block prepping in lieu of a rebuild.
But when you detonate them hard enough at high rpm when racing. This is what leads to a major engine failure. The piston doesn’t just break a little or crack. They scatter completely, leaving the connecting rod with only its little end and the piston pin to swing around and do nothing but slice through the block and put a bunch of wholes in it, and the oil pan. Some times the crank will actually survive this mess but most of the time they don’t.
Guys will tear down a 4.6L motor that’s had a major piston failure and not find much of the piston left and think that the rod failed first. But in a supercharged 4.6L nearly every time I’ve torn one down with this type of breakage. In the end it can be surmised that it was detonated and shattered the piston first.
I’ve posted a piston and rod from a good friends ’02 Mustang Saleen that had the all original 2-Valve motor and all we did was add some exhaust stuff and a Kenne Bell blower making about 12psi of boost, intercooled and ran it on pump 94 octane. The car made stout low and mid range TQ and was a blast to drive under all conditions and RPM’s. It was driving this way for months with no detonation or any problems at all. Then the greed and need for greater speed set it and he caved-in to trying to step it up even more. We bumped the boost to 17psi and switched to locally available “Turbo Blue”
110 octane leaded race fuel. A little over kill as far as octane to some, but we wanted the absolute in safety from detonation as we could. And I assured him that it was in no way detonating with that fuel in his application with my tune.
Well after making the switch to the big boost and the race fuel, the motor only lasted about one day! We made a bunch of dyno pulls with it and when he took it home that night after some drive time and abuse, the engine developed a knock that I had a hard time deciphering what it was or where it was coming from in the lower end of the motor. The funny thing was the engine did not shake or act like it had a dead cylinder like most 4.6’s and 5.0’s do when they drop a cylinder or two… it still ran and sounded perfect except for the knocking from the bottom end. At that time I knew that since it still ran good and had no apparent misfire that we didn’t detonate it and cause a piston problem. We simply might have made so much low end TQ that initially I thought we squished a bearing right out of it.
When we tore it down I couldn’t believe what we found had happened to the cylinder number #1 connecting rod. As can be seen in the PIX I’ve posted, we literally just bent it from to much low end torque. This thing made over 540ft lbs of TQ at less then 2800 rpm at the rear wheels. If it where an automatic trans it probably would have survived a lot longer, but because he had a stick and was able to lug it around at 1500 to 2500 rpms in 3rd or 4th or even 5th gear, because it did feel very good down there. He simply lugged it down to hard and loaded the rod to hard. An auto trans and its torque converter would not have let this happen as easily because it would down shift and the stall speed of a torque converter simply would'nt let it stay that low in the revs.
Take a look at the PIX, the only damage to the piston is the bottom of the skirt area because when the rod bent, it obviously becomes shorter thus bringing the piston closer to the counter weights of the crankshaft on the down stroke. This is what made the ticking noise we heard and hurt the piston bottom. You can see the top of the piston has no damage at all, the rings and the lands all fit together nice and loose like they should. Usually when a piston has been severely abused the rings wont move around correctly because the lands get distorted from det. With good gas and a proper tune, this piston would have and could have lasted a very long time in this application believe it or not. On this one the extreme low end of the KB blower and the lugging of a manual trans did him in. Of course it now has Eagle Rods and forged Diamond pistons in the new motor with the same tune and no problems for several months now.
Just some stuff for general consumption
Thanks