The higher the rpm, the shorter the time a rod is under compressive stress. The lower the rpm, the longer it is under compressive stress. If I put 500lbs on your shoulders, you might be able to take it for 2 seconds, but could you take it for 4 or 8? 600lbs? 700lbs? At some force, the stress becomes too much for the period of time, and at lower rpm, that's more time for the same stress. Then failure occurs.

Then things get much worse when some form of non-spark ignition happens. Throwing a ton of air and gas in at lower rpm gives more time for such unhappiness to occur.

This makes sense and is definately a big part of the concern from what I gather. However, I am trying to quantify these limits somewhat.

Preventing knock and pre-ignition is a part of the puzzle, but is that really all of it though? The issue I keep getting hung up on is that without knowing the cyclic stress curve of the rods and the bearing capacities for cyclic loading how can one come to a torque/rpm number that is safe? How are tuners doing this? From an engineering standpoint you would design the rods and bearings to accept the desired maximum force for the number of cycles the engine should last plus a safety margin. Since adding boost to the engine we are now eating into that safety margin and some of the cycles the engine is built for, how do we come up with a number for low RPM that is safe? Is it all subjective and done by feel? Surely there must be some general consensus on how far one can push this.

As a side question, are the bearings used in the FA20T engine the same as in the FA20?

I think you might be looking at this from a fatigue standpoint and I don't believe that this is how they are failing. It is exceeding the critical buckling load of the connecting rod. When it does fail it is not under "normal" load. Something else (knock/early ignition) is causing the overload if the connecting rod. The problem with Superchargers is they they can build large amounts of boost early. Like jsimon7777 said. There is more load on the con rods at lower rpm. The gas/air charge doesn't expand instantly. It takes time for the reaction to take place. If you hold that charge longer it has more time for it to expand building more pressure in a smaller volume. This I believe is the problem in lower rpm. Expansion of the explosion vs expansion/release of the combustion chamber and exhaust valve opening

Yeah, I suppose I am focusing too much on the fatigue aspect and less on the yield strength. I'm trying to learn some of these details and it is hard to find information on these topics.

So, trying to understand things here, is it fair to say it is the knock and pre-ignition, especially at low rpms is bending the rods? And excessive torque at any rpm will be responsible for wrecking bearings moreso than bending rods?

They are interrelated. I am no expert but most bearing failures I have seen are due to oiling issues. I am not sure if the rod bearings will fail before the con rod due to load alone. Any load that the bearing sees the the con rod sees. The wrist pin is also much smaller than the rod bearing so if a bearing load were to fail first I think it would happen at the wrist pin between con rod and piston. Torque is just the output force of the direct load on the piston. Please correct me if I am wrong.

I believe there are quite a few variables. Ignition timing, valve timing, intake temperature, exhaust gas temperature, heat soak, air pressure, boost, oil temperature, oil pressure, lubrication qualities, rpm, humidity, back pressure, age of components, component choice, and driver behavior all play roles. I doubt there's a simple number. A lot of fudge factor. If you really want a torque beast, you need to build an engine. Even then, there are no guarantees. Tuning isn't just a table each for ignition and fueling.

That's why I'm waiting to see how things turn out for people. I'm hearing about issues with AVO, which scares me away from them. I'm not hearing about many problems with Vortech and Innovate, though I'm not paying much attention to Vortech. I suppose one big advantage of Vortech is how delivering torque at high rpm is easier on the rods, at least in compression.

There's not been a lot of attention paid to EGT in any thread I've read here. That worries me. EGT tells a lot about what's going on. There's also been a lot of aggression on timing, especially with E85. That can beat on the bottom end. People are focusing on numbers more than reliability. A bad tune can blow an engine on stock power. A good tune can get a lot more from an engine.

I agree about the lack of EGT data on here and I would love to see some numbers here and get an idea of what is safe.

Hummmm

OK so here's the scoop from SEMA

Spent about 10 minutes chatting with the guys from sprintex, and the big blower will be coming out pretty soon. When Innovate sells it will be decided by Innovate, but target date is very early 2014.

The big blower will be good for 400whp, and it will be mostly the same kit except the rear piece.

It will bolt up to the current manifold, same casting.

It will NOT be worthwhile to upgrade because you will be left with an 210 blower with no plenum. This is a bigger hit than resale loss. If you do not have the IC kit especially. But the big blower kit will be quite a bit more expensive than the current...so it will make sense for people who are planning on building motors. Current users don't sweat it; the original kit will carry plenty of resale just by that fact alone.

Some additional pictures:

http://www.moto-east.com/images/sema2013/sprintex-1.jpg
http://www.moto-east.com/images/sema2013/sprintex-2.jpg
http://www.moto-east.com/images/sema2013/sprintex-3.jpg
http://www.moto-east.com/images/sema2013/sprintex-4.jpg
http://www.moto-east.com/images/sema2013/sprintex-5.jpg

Mike, when they say motor build, I'm curious if you were able to get any more details of what they mine. Is there a specific compression ratio they're recommending for the bigger blower?

9:1-10:1 would be a reasonable starting point, if you want to run pump fuel.

My concern would be whether or not going through all that effort with a motor build and upgraded blower, if the car would still be able to reach that unholy 400hp mark with the lower compression. I guess timing advance up the wazoo?

Maybe. It'll probably be a challenge on pump fuel. E85 probably no issue. Also depends if you're talking about crank or wheel power. Big difference!

400 whp on pump. Probably not. Maybe on a unicorn dyno.

This car/engine is a bit of a challenge when it comes to making big power. I'm too lazy to bother. I'd buy a GTR instead!

Can't wait to get that big blower. Good things do come to those who wait!