Atomic Motors (Merged Topic).

[GOLDIE]

Back to where all this started you need to do rods,while you have it that far apart put better pistons in,new engine bearings aswell.

This is the minium that should be done.

Ian

PS rods and pistons should be some where between 3000 and 4000.

[ms700]

will a comp test help a possible early diagnosis of any pending problems??

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Not really, a compression test will only show a problem once that problem has arisen.

It will only confirm a problem, not early diagnose it for prevention. Once a rod or a ring or a piston has let go, that is the only time generally when a compression test will show a problem.

Bottom line is this: If you play, be prepared to pay.

[Nizpro]

I have only seen one rod bolt failure, it was in a new vehicle and had simple been left loose. The car had 15 kms on the clock and was been unloaded from the transporters. This was simply a slip up. All ended well.

The most common form of failure is a compression failure of the conrod beam. This is due to high cylinder pressure loads generated from a number reasons.

The first is simply having too much torque generated from boost pressure. Typically in standard set ups failures will occur if too much boost in applied early in the rpm range as this is where torque will be the highest. The reason that we teach tuners to hold a lower but flatter torque curve by better tuning techniques and hold power later on in the rpm range is that peak torque will still be lower and this gives by far the safest alternative, than the wack all the boost in early approach, sure this does give a big surge on acceleration on the road but the trade off is both engine and drive train longevity. It also does not give as good a total acceleration rate as a long flat torque curve, even if there is slightly less peak torque available.

The second reason for high cylinder pressure can be cause from a number of events, these included engine detonation and engine misfire. Detonation causes cylinder pressure to skyrocket at times depending on how badly it is detonating, cylinder pressure will double. Putting this into perspective your 200rwkw T can now be putting the same compression load onto the connecting rod as a well tuned 400 rwkw vehicle. At this point once this is under stood it become clear why you all see failures at different power levels.

The same goes for a misfiring engine, due to erratic combustion events this too generates excessive cylinder pressure. A misfiring engine due to something as simply as spark plug gaps at relatively low power figures can cause peak cylinder pressure to rise well beyond the strength of the connecting rod again resulting in failure.

Lean mixtures on there on will not cause this type of failure due to the fact that cylinder pressure will be reduce due to the lack of combustible mixture. This is one of the key point I have shown on the engine dyno to all who have attending our training seminars. I am usually looked at with discussed when first explaining this, as people are very reluctant to believe that in some cases a richer mixture will actually cause the onset of detonation . Mind due once shown people are simple amazed.

So the reason for normal conrod failure in the Barra engine is cylinder pressure, normally caused by too much torque, not too many Kilowatts. Our rule of thumb is a maximum of 650 foot pounds of torque at the engine is our limit. Rod bolt failure is normally due to excessive rpm.

Hope this sheds some light on the problem

[ms700]

Great post Mr Nizpro.

[JimmyXR6T04]

excellent post Nizpro thanks for that.

[illusionzzz]

Cheers Nizpro

[turbotom]

That's an excellent post from Nizpro..... thanks.

Could I get you to clarify whether 650 lbft peak torque is for stock rods, or for an aftermarket rod.

I can see a lot of guys are going to be checking their dyno charts to see where they sit.....

Here are some conversion factors which might help.....

650 lbft equates to about 880 Nm, based on a conversion factor I found in a text....

1 Nm = 0.73756 lbft.

For those that want to get an indication of the torque from their power charts...

Nm = (kW x 9549) / rpm

so, if you have 220 kW at 3000 rpm, then that equates to 700 Nm @ 3000 rpm

That also equates to 516 lbft of torque in the old imperial measurements.

But if you have 200 kW at 2000 rpm, then that's over 954 Nm @ 2000 rpm

which is equivalent to 704 lbft of torque...

As Nizpro have stated, it's all well and good to get a big kick in the pants with a huge torque peak at launch, but it's much safer to control the peak torque down low, and aim for a flatter torque curve across a wider bandwidth for good reliable street use.

Some guys are finding their ET's at the track are better by early shifting to take advantage of the higher torque at lower rpm...... This is fine IF the motor and driveline can take up the stress due to the huge increase in peak torque.

tom

[Nizpro]

Yes Tom this is with the standard BA Turbo connecting rod. What you are now working out at various RPM points is correct and gives a better indication of how stressed your engine is compared to saying, at how many Kilowatts do they break at.

If you have the turbo system sorted so thay continue to make 650 ft pounds at 6000rpm that would translate in to 450 rwkws ,it simply takes intelligent thinking in regards to tuning and the turbo system rather than the smash it with a hammer approach.

Now getting back to the original point, do believe in upgrading the internals of engines if chasing numbers beyond 330 rwkws and have done since we started developing these engine in early 2003. As most people out there only have the standard turbocharger and manifolding. When using those components the flow characteristic of the engine simply will not allow the engine to maintain 650 ft p at high rpm, so torque number will be high in the mid range. Also anyone chasing numbers bigger than 330 should be realistic about the money needed to do that reliable, and this would include an engine rebuild.

The thing you all need to be aware of if that it is difficult in some cases to get correct torque reading for the engine using a chassis dyno. In a auto car the torque converter will be influencing the number, in the case of a ZF trans there is no 1 to 1 gear, you also need to calculate the diff ratio and the roller diameter vs. wheel diameter. The easiest way is to look at your dyno graph, KW vs RPM and then backward calculate the torque figure. Keep in mind you also need to look at the difference between rear wheel kws and engine kws. We see approximately 22% difference between our engine and chassis dyno.

Edited 25/10/06 03:58 AM by Nizpro

[turbotrana]

Nispro,

Whats your experience with stock pistons,FPV rods and even aftermarket forged pistons regarding piston slap.

[ELA-747]

Isn't this thread about Atomic motors?