Minecraft 1.6.4,
Other Mods:
Tekkit Pack 1.2.9e, only change I made was update BigReactors from 0.3.0A to 0.3.4A2.
BigReactors Version: Phenomenon observed in Bigreactors 0.3.0A and 0.3.4A2 Hotfix (I didn't test the intermediate Versions.)

Height, width and depth: 11x11x5

I have build two absolutely identical turbines and therefore expected them to behave exactly identical as well, but one of them never reaches more than 300 RPM, while the other one is at 900, both at the same flow rate (435). The set up is absolutely identical so the problem shouldn't be the steam input. I have checked the turbines block for block and even experimented with creative steam generator but to no avail. The only discernable difference I have discovered, that the left turbine, which is the one behaving strangely, is positioned across a chunk border. Turbines though don't seem to have problems with chunk burders. Could it maybe be the very short rotor shaft (3 blocks) of my set up compared to the great width (11 blocks)?

Am I missing something obvious here?

Also: Holy moley! Supplying a sizeable Reactor with water is quite a challenge, even in creative!

I'm seeing two different turbine designs here. Are you testing between the long-and-narrow (center) v. the short-and-fat turbines (far-left/far-right), or between two turbines identical in layout?

I am testing between the two short and fat turbines to the left and to the right. Disregard the two small ones between them.

Hmm. Just conjecture here, but does this happen with freshly-built turbines, or only those which have gone through a chunkload?

You don't need to build a turbine from scratch to check this - simply breaking a single block on each turbine, then replacing the blocks and running your experiment should be sufficient.

I hope that break-and-reassemble bit doesn't fix things, as that'd point towards a nasty bug down in the core code somewhere.

I have already tried breaking and replacing a block and it did not fix the problem so I tried building a new turbine above the defective turbine, copying it block by bloxk, except that I nudged it by one block to the left so that it did not cross a chunk border and voila, the turbine now behaves as expected!

The lower turbine is the errant one and the top turbine is the new test build, which is identical to the other one. Note that I nudged it by one block so that it fits into the chunk.

Without the chunk highlight:

Here we see the interface of the top turbine that is completely within the chunk. For comparison to the errant turbine, just look at the screenshot from my opening post.

So from what I can make out, building a (short & fat?) turbine across a chunk border causes weird behavious. I'll test longer turbines if I get around to do so, but I'll be writing a lot of exams for university over the course of the next weeks.

Ugh. Well, at least it happens in freshly-assembled turbines, so it should be easy to reproduce. I'll take a look at this. It's probably a bug with the post-validation operational constants calculation code, which looks over the rotor's structure to determine runtime-invariant performance parameters.

Thanks for the info.

I have been testing large turbines (16 blocks in length (z axis) , and 5x5 width and height (x and y axes)) that cross chunk borders and those behave normally, at least if the chunk border is just crossing the turbine along the langth axis z. Note that the xyz axis here are just examples denoting the dimensions of the turbine and not the in game axes of minecraft. I have yet to test crossing large turbines on the y and x axes.

When you say 'z axis', do you mean the vertical axis? The vertical axis has no chunk boundaries - chunks are entirely on the horizontal plane.

With z axis I mean the length of the turbine. The turbine rotor shaft is the z axis.

Would you mind repeating these tests in 0.4.0rc5+ and using the new debug tool to check the operating parameters of the turbines?

I had a similar bug in 1.6.4. 3 identical turbines and suddenly 2 of them spinned at a lower speed than they originally were without changing anything to them or the system that filled them with steam.

It's nothing to do with chunk borders. The iron which was surrounding the turbines in the first picture was acting as part of the coil. Replace the iron with a different material not conductive inside the turbine or use carpenters blocks.