Found better technique just before publishing old, but still good technique – can the old one still be published? In our lab, we hypothesized that a technique T1 should be able to solve some problem with high performance. As per our hypothesis, we got an excellent result. We started writing a short paper to be submitted to a conference for the last date is due in four days. The paper is complete except for some proof-reading. We have not yet submitted the results.

Yesterday, just for fun, I was applying a different technique T2 to the same problem. Surprisingly it achieved an even better performance than T1.

We were wondering, is it okay to write a “failure” paper stating the hypothesis failed because of so and so [which is tough to analyze given the time constraint on deadline.]? Some of my colleague suggested to not disclose the performance of T2 until T1 is published, so that later I could do a comparative study between T1 and T2. Will it be okay?

Note: T1 and T2 are very different and it does not make any sense to write on both techniques in the same paper. Plus, rewriting the paper now is also difficult.

Update After going through answers, comments and suggestions, we are submitting T1 paper. Thank you very much all the learned academicians here on academia.SE.
Publish T1. Later, when you have time to write a whole new paper, publish T2. Doing a comparative study between the two sounds like an excellent follow-up decision as well. I'm not sure why you classify T1 as a failure... it sounds like both work and one works better.

That said, yes, it is okay to publish "failure papers." Depending on the field it might be harder to get it approved by a journal because it's less sexy to find a negative result than to find a result. This causes a measurable bias in some fields and depending on the field can be a major problem, because failed research is just as important as successful research epistemically speaking.