My sleeper

[hammer]

The topsides from mainbearing 2-5 are fine

[jsol]

I found this helpful regarding clearances etc.

http://theprojectpad.com/viewtopic.php?f=32&t=1370

[Error404]

0.05 is quite right for this kind of build, IMHO.
I think you need to check main tunnel alignment, and crank check for problems with journal and pin with parallel / eccentricity

[hammer]

0.05 is quite right for this kind of build, IMHO.
I think you need to check main tunnel alignment, and crank check for problems with journal and pin with parallel / eccentricity

Measure more than everything

[gnutz2]

Do a search but I'm pretty sure jp at jnl racing had a similar problem, the bearings would let go but only at low rpm and high torque, eventually they came to the conclusion the bearings didn't have enough support and the crank would deform and touch.

[diesel des]

Too much timing advance at low rpm? The engine may not ping but the very high combustion pressures damaged the bottom bearings? If it was torque causing a twist in the crank, main bearings top and bottom would be marked. I don't think too high torque on Its own will do this within reason. The crank is exposed to a lot of forces and only some are the torque it's carrying. Even a stock Tdi with over twice the compression of a 20vt engine and some reasonable boost numbers will generate high compression forces pushing the crank down on those bearings. Even if it's power and torque generated are lower than yours they can have higher forces maybe. So as it's only the bottom main bearings then i think excessive compression forces cause this. So that is likely to be excessive timing. What's your timing map look like?

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[hammer]

Dont no it, i have to look how many degree. But i fix them to highest torque

[diesel des]

Dont no it, i have to look how many degree. But i fix them to highest torque

Sure I understand. But for example if you reduces timing 2 degrees did torque only fall of a few nm? Sometimes you need to stop advancing timing just before the very top of the torque curve as you may be causing too high cylinder pressure. Only a cylinder pressure sensor can tell for sure.

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[hammer]

Yes if i reduces 2° torque is falling. But maybe this is the Problem. Better i go 2° back up to 5500rmp

[Majorcina]

I just read the whole threat.Great project mate!Hope you find your problem soon

[diesel des]

Yes if i reduces 2° torque is falling. But maybe this is the Problem. Better i go 2° back up to 5500rmp

That is exactly what I mean. But how much does it fall? If it's only a slight amount of torque reduction than your perhaps still too advanced. You want to reduce timing until torque falls of sharply than advance slightly again.

Minimum best torque settings don't work well on very high octane fuels. You can have slightly more torque with more advance but the cylinder pressures are way too high.

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[hammer]

That is exactly what I mean. But how much does it fall? If it's only a slight amount of torque reduction than your perhaps still too advanced. You want to reduce timing until torque falls of sharply than advance slightly again.

Minimum best torque settings don't work well on very high octane fuels. You can have slightly more torque with more advance but the cylinder pressures are way too high.

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But can there be a detonation and highest torque at the same time?

[diesel des]

Yes. There are circumstances with uncontrolled combustion were torque can increase slightly but pressures go through the roof. It's not full detonation but if say the spark lights the fuel and 90% burns normally. 10% of the remaining charge then has been heated up and burns in one big bang. This fast combusion will give good torque but a big pressure spike.

Ideally a cylinder pressure sensor is used to look for spikes but theses are expensive.

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[mushasho!]

Minimum best torque settings don't work well on very high octane fuels. You can have slightly more torque with more advance but the cylinder pressures are way too high.

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So you mean with lower octane fuel(pump) it would be easier to know where that ceiling is and back off timing from there. I think I follow what you mean...

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[diesel des]

So you mean with lower octane fuel(pump) it would be easier to know where that ceiling is and back off timing from there. I think I follow what you mean...

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Yes pump fuel is easy as you will get to detonation very early. Because you can run say 10 deg more timing doesn't mean you should. I run on Lpg gas which is high octane and it's almost impossible to get it to ping. But to be safe I stay close to pump timing.

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