I forgot to mention that at 14 lbs they were running a 50/50 race fuel mix. They were using 110 octane race fuel.
Mountaintech
TY 4 Stroke God
Gee, I guess 15 lbs. is not the max.
Run 100 pounds if you want. I'm telling you I have it on good authority the motor in stock form isn't strong enought to run on plus 15 pounds for a long period of time. You may get away with it but when it fails it will be really bad. I'm tlaking Rods through the case!!!!!!!!!!!!!
I'd have to agree with Jason on this one. The tensile load on the rod is the limiter in engine design (ie. the load on the rod during an exhaust stroke). At about double the HP of the stock engine, the compressive load on the rod will start to be greater than the tensile load (assuming RPM has remained constant). 15 lbs boost would put the HP right in this range. You might be able to get away with exceeding this a bit, but you are now definitely asking the motor to do things it was not designed to withstand.
The load on the rod during an exhaust stroke? I could maybe understand the power stroke, but what is so harsh about the exhaust stroke?
Tensile = pulling force. At +10k RPM, the piston has to decellerate to a dead stop a few thousand times every minute with nothing pushing back against it (like compression).
Ok, if tensile = pulling force then where is the pulling force in the exhaust stroke? Are you talking about when the piston stops at the top of the exhaust stroke? Why would this not also be a problem during the intake stroke?
I know a person who claims that he ran 17lbs. The only problem he claimed was signs of detination from a lack of octane. Maybe he didn't tell the whole truth?
I know a person who claims that he ran 17lbs. The only problem he claimed was signs of detination from a lack of octane. Maybe he didn't tell the whole truth?
The short answer would be inertia.
The long answer I'll paraphrase from one of the turbo books that I think explains the topic quite well:
An inertial load results from an object's resistance to motion. To examine the inertial loads, it is convenient to divide a cylinder assembly into an upper half and a lower half. Imagine the two halves seperated by an imaginary line called the center stroke.
The piston always accelerates toward the center stroke, even when travelling away from the center stroke. In other words, when the piston is above the center stroke, it will always be accelerating downward. When it is below the center stroke, even at bottom dead center, it will be accelerating upward. Acceleration is greatest at top dead center and bottom dead center, when the piston is actually sitting still. When acceleration is greatest, the loads will be highest. Similarily, acceleration is zero and velocity is greatest as the piston passes the center stroke.
the size of the loads generated by these motions is proportional to the RPM of the engine squared. For example, if the engine speed is increased threefold, the inertial load will be nine times as great. The action of the piston's being pulled (forced to accelerate) to a stop at top dead center and then pulled down the bore toward the center stroke will put a tensile inertial load into the con-rod/piston assembly. Similarily, as the piston is pushed to a stop at bottom dead center and then pushed back up the bore toward the center stroke, the inertial load will be compressive. Thus, any time the piston is above the center stroke the inertial load will be tensile, and below the center stroke, it will be compressive. The largest tensile load induced into a con-rod is at top dead center on the exhaust stroke (because at top dead center on the compression stroke, the gas is already burning and creating combustion pressure to oppose the inertial load). The largest compressive load is generally at bottom dead center after either the intake or power stroke.
These inertial loads are huge. A large displacement engine running 7000 rpm can develop con-rod inertial loads greater than 4000lbs. (That's like a Caddilac sitting on your rod bearing).
The long answer I'll paraphrase from one of the turbo books that I think explains the topic quite well:
An inertial load results from an object's resistance to motion. To examine the inertial loads, it is convenient to divide a cylinder assembly into an upper half and a lower half. Imagine the two halves seperated by an imaginary line called the center stroke.
The piston always accelerates toward the center stroke, even when travelling away from the center stroke. In other words, when the piston is above the center stroke, it will always be accelerating downward. When it is below the center stroke, even at bottom dead center, it will be accelerating upward. Acceleration is greatest at top dead center and bottom dead center, when the piston is actually sitting still. When acceleration is greatest, the loads will be highest. Similarily, acceleration is zero and velocity is greatest as the piston passes the center stroke.
the size of the loads generated by these motions is proportional to the RPM of the engine squared. For example, if the engine speed is increased threefold, the inertial load will be nine times as great. The action of the piston's being pulled (forced to accelerate) to a stop at top dead center and then pulled down the bore toward the center stroke will put a tensile inertial load into the con-rod/piston assembly. Similarily, as the piston is pushed to a stop at bottom dead center and then pushed back up the bore toward the center stroke, the inertial load will be compressive. Thus, any time the piston is above the center stroke the inertial load will be tensile, and below the center stroke, it will be compressive. The largest tensile load induced into a con-rod is at top dead center on the exhaust stroke (because at top dead center on the compression stroke, the gas is already burning and creating combustion pressure to oppose the inertial load). The largest compressive load is generally at bottom dead center after either the intake or power stroke.
These inertial loads are huge. A large displacement engine running 7000 rpm can develop con-rod inertial loads greater than 4000lbs. (That's like a Caddilac sitting on your rod bearing).
Sorry, forgot to give credit - those are the words of Corky Bell, from his book titled "Maximum Boost".
Although I had to read it twice that seems to make some sense.
BTW keep those cadilacs off of my sled!! I'm trying shed weight!!
BTW keep those cadilacs off of my sled!! I'm trying shed weight!!
Google Newton's laws of motion (if they're not fresh in your mind) and re-read it again with laws #1 & 2 in mind. Or you could just put in stronger rods if you plan on running boost in the mid to upper 'teens. 
If you've eve had a Stock rod in your hand and then a corrlla You'd see why it needs to be updated.
So what is the strength of the rod? That is the question of the day......
I don't have the equipment to do that type of test.
There also seems to be a question as to the octane needed.......
I don't have the equipment to do that type of test.
There also seems to be a question as to the octane needed.......
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Spray25, you have the perfect equipment to find the strength of a rod! Put in straight race gas, crank it to 15 lbs of boost and keep going up until you bend a rod, then back off a pound! You just found the strength of a stock rod! 
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