Geoffrey

It has been my experience that these engines need about 12.0-12.2:1 afr under 1 bar of boost to keep the cylinder head temps in line. At 10:1 the car will will be so rich it won't run...

K24madness

I know its hard to believe but I have seen some run off the scale over 10:1 on the dyno and still run pretty well down the road.

I will be shooting for about 11:5 to 1 at peak tourque and 12:1 at peak HP.

Geoffrey

I don't think you need to run that rich at peak torque.

K24madness

Even at 1.2 bar??

Geoffrey

even at 1.2bar. I know from experience that at 1.1bar on a racing engine in an endurance environment 12.6:1 will melt an engine after prolonged running. I've not had any issues with 12.0:1 at 1.2bar. A street engine should be no problem and that is the range I've run all of the ones I've done. No meltdowns.

K24madness

Geoffery... When do I need to be concerned with lifting the heads or bending the rods. Some say its boost releated while other think its HP related.

I feel it must have to do with peak torque regardless of HP or boost levels. What are your thoughts?

Geoffrey

I'm not really the expert on this subject as I've never bent a rod (I deal with racing engines with steel aftermarket rods) nor have I really seen much of the head lifting issue (I deal with racing engines with sealing rings).

As far as what bends rods. Look at the forces applied to the rod - tensile load and compressive load. The acceleration rate of the rod is highest when the piston velocity is lowest, at TDC or BDC and lowest when the piston is at center stoke where the acceleration rate is 0 and the velocity is highest. The largest tensile force on a rod occurs at TDC on the exhaust stroke and is the most destructive loads. This is where most rod bolts break and is the force that is the greatest. Compressive loads occur as the piston passes its peak velocity and nears BDC. An interesting point occurs when compressive and tensile loads are working in opposite direction, as the piston is in the upper half of the power stroke. Remember F=MA? Since HP is torque x RPM / 5252, the factors that contribute to rod failure are BOTH torque and RPM, or cylinder pressure and RPM. The engines I've seen with bent rods tend to be above 600hp engines, but there could have been any number of reasons for the failure.

Since I don't know, and I tend to be conservative in my recommendations, I usually won't push a engine with stock rods past about 550hp.

K24madness

I appreciate the non BS answer.

I should be safe with my current setup. I will get back on the dyno ASAP to check power levels. Last check at 1.1 bar was 461whp& 474wtq. I have since fixed some minor things (leaky IC hose, cleaned injectors and CDI ignition). It feels a lot stronger now.