Ethics on shortening project in grant application to raise chances of success I am currently writing a PhD grant application, and I completed the first draft. The project is ambitious, but I and my advisors think feasible, but my advisors told me that it is quite dense and could be daunting for the grant reviewers, who may label it as unrealistic (which is a criterion of admission) and thus they may reject it.

I have no problem in working on simplifying my research project's description to make it more concise and readable, but my advisors suggested to strip half of the project, in order to raise the chances for it to be accepted. But they told me that of course, I can do the rest of the project too with the grant I will get, I just shouldn't mention that in the application.

Is it ethical and honest to "sell" a research project based on only half of its description and goals? Not only that, but also the logical reasoning and the bigger goal get totally lost, so are these worth losing against displaying a more realistic target? To me, it seems like reasoning that the end justifies the means...

I should mention that almost all the ideas for the research project are mine (the advisors helped me with naming the methods I will use, but the concepts, bibliography and goals are my own), and I was really motivated by the original whole project.
Yes, of course this should not be a problem.  The funding agencies want to see projects that are on a realistic scale.  If it will probably not be possible for you to achieve your main goals, given the time and money allotted to the project, that certainly makes it seem like a poor investment.  Conversely, the funders know that if you reach your projected goals early, you are going to use the remainder of your funding to extend the research further.  So you should try to set achievable goals in your proposal, but if you manage to exceed them, nobody is going to be unhappy.

Naturally, cutting major tasks out of your proposal is going to require some rethinking of the justification.  If the projects you think do have time to complete are less interesting by themselves than the later projects you will need to cut, they you still need to explain why they are important stepping stones toward the ultimately most important work (even if you won't be getting to that work yet).  It can be subtle to get this right, but think you would be wise to trust your advisor's judgement about how much to include in your proposal.