Typical Conditions of Blowing the Bottom End?
Typical Conditions of Blowing the Bottom End? I was just wondering under what conditions does the bottom end usually give out? I can only think of engine speed, power, and engine weakness(which is a given). Basically I am not sure if I should start saving for a forged bottom end now to go with the soon to come Procharger. I figure if I keep it under 6000rpm, which I usually do anyways, I will be fine. My hp peaks at 5800rpm so if I stay below 6000rpm do you think I will be okay? I plan to run between 500 and 550rwhp. I hear the bottom ends on the 99's are really weak which has got me worried. Thanks!
eh, you should be ok if you stay south of 550hp, spinning south of 6200 everyday. of course its not going to last another 85k miles, but it should last you til you can save up enough for a forged stroker bottom end 
From what has happen to me and a few other road racing friends is that the rod bolts give out.....spinning a bearing. This was most likely caused by taking the car above 6200 with modified engines.
The engines don't "shell" per-se, depends on how quickly you catch it. All of us caught our cars quick enough that it was only necessary to change the crank, one rod and bolts (it can get a lot worse though)......but none of us did just the minimal
Now understand, in road racing one is mataining high RPM's for prolonged periods of time and high G turns can also cause oil starvation, in a 1/4 mile you're only seeing those RPM's for a very shot time (no oiling issues). That being said, in keeping your RPM's down, I agree with the above post of get the money in the bank but it should hold - for a while
The engines don't "shell" per-se, depends on how quickly you catch it. All of us caught our cars quick enough that it was only necessary to change the crank, one rod and bolts (it can get a lot worse though)......but none of us did just the minimal
Now understand, in road racing one is mataining high RPM's for prolonged periods of time and high G turns can also cause oil starvation, in a 1/4 mile you're only seeing those RPM's for a very shot time (no oiling issues). That being said, in keeping your RPM's down, I agree with the above post of get the money in the bank but it should hold - for a while
Launching!
Joined: Jul 2004
Posts: 200
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From: Gainesville, Florida
Rod bolts should only be loaded in tension when the crank is applying a downward force on the piston, so I don't see how power could be a factor? Most engine's will last if tuned right without any knock, seems hard to believe that the LS1 is really that weak.
TheBowtieboy,
How high were those cars being reved? 6200 is pretty damn low... I guess I'll lower my rev limit on the road course, sigh.
TheBowtieboy,
How high were those cars being reved? 6200 is pretty damn low... I guess I'll lower my rev limit on the road course, sigh.
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Launching!
Joined: Jan 2004
Posts: 273
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From: Trois-Rivières (Québec / Canada)
Originally Posted by Grant B
Rod bolts should only be loaded in tension when the crank is applying a downward force on the piston, so I don't see how power could be a factor? Most engine's will last if tuned right without any knock, seems hard to believe that the LS1 is really that weak.
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Joined: Jul 2004
Posts: 200
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From: Gainesville, Florida
Eric,
I disagree. The tension on the bolts is directly proportional to the square of the crank speed and the weight of the piston/rod assembly. Greater power could mean a greater variance in the speed of the crank over each 720 degrees of rotation, which of course could cause a variance in the tension on the rod bolts. But that doesn't really sound significant, does it?
I think the rod bolts are loaded the most when they are pulling the piston down during overlap. If they are going to fail, I believe thats when it happens.
IMO. I just don't see how greater amounts of cylinder pressure could put significantly more tension on the rod bolts.
I disagree. The tension on the bolts is directly proportional to the square of the crank speed and the weight of the piston/rod assembly. Greater power could mean a greater variance in the speed of the crank over each 720 degrees of rotation, which of course could cause a variance in the tension on the rod bolts. But that doesn't really sound significant, does it?
I think the rod bolts are loaded the most when they are pulling the piston down during overlap. If they are going to fail, I believe thats when it happens.
IMO. I just don't see how greater amounts of cylinder pressure could put significantly more tension on the rod bolts.
