Can My 4x4 Take a MONSTROUS 1,200 lb Engine?? 

Yes actually! In fact in this case it helps my position since the explorer frame isn't as wide as the ram frame meaning the heavy cummins will have less leverage on the frame. I didn't want to get too bogged down in the details so anytime stuff like that worked in my favor I skimmed over it to get a "worst" case. Also the crossmembers would endup heavily modified to fit the new suspension so I wouldn't have been able to know exactly how to model them at the point when I made this video

@@BuildSomethingAutoyeah, not trying to trivialize setting up a more sophisticated model... But I'd love to see what happens to the model when both sides are connected, and the torsional force is limited by the compression of the cross member. Not to mention that the engine would triangulate the cross member itself. I wonder though, if the vibrations, which the Cummins is known for, lees so for the 6bt than the 4bt, would cause fatigue where the cross member joins the frame.

Its a vertical load on the crossmember, that causes a resulting torsional load on the framerail. However the exact terms dont really matter, you are correct that a crossmember will make it more rigid. It will tie the load between the rails so both rails take some of the stress, and the member itself would be in compression resisting the movement of the framerails, so overall it will be a lot stronger if you consider crossmembers. The analysis I did was a "worst case" for a lot of reasons, but no crossmembers is certainly one of them. Engineers are lazy, we like to oversimplify, so rather than do an accurate model of both frames, including all the twists and bends and crossmembers, etc, this simplification lets me get 90% of the way there with 5% of the work 😅. What matters here isnt the exact value it spit out, but rather how close it is between the two frames. In reality the total stress will be much lower, but knowing that the stress is similar between the two frames is what I was interested in. Id never use these results to design a new frame or anything, without making it much more detailed, but I would use it to say "the worst case is almost as strong as a ram 2500 frame so its gotta be good enough". I hope that makes sense, thank you for your comments!! Edit: also for the record, theres a term in engineering called "sharpening the pencil". If this simple analysis that used conservative assumptions implied that the explorer frame was way too weak, the first thing to do would be to sharpen the pencil, add more detail and see if the frame is actually too weak, or if I just oversimplified it too much and thats why it appeared too weak. Since the simplified first pass using conservative assumptions said the frame was strong enough, no need to waste effort adding detail to see "how" good enough it really is. This is what I mean when I say engineers are lazy, good enough is good enough 😅

@@BuildSomethingAuto that all makes sense. Thanks for clarifying.