I'm going to drop this in here just in case it's useful for anyone else, since it took a lot of time to figure some of this stuff out, and hopefully it will save someone some time if not now, perhaps years from now when they need it. Input on whether the driveline angle we can achieve might work would also be appreciated. Backstory is I decided to rid out a leaky LT1 and put in an LS3. The car has a 2nd gen Camaro subframe, so this should have been a very simple swap. No. Got everything in for the test fit and the engine is sitting at around an 8 degree angle, possible a bit more. Trans was on the tunnel. Huh? Well, as it turns out, according to an old article from the early '90s in Hot Rod Magazine, it was a "great trick" to just weld your subframe in a few inches high since that would lower the car. My guess is that's exactly what happened. Subframe went in 3+ inches high, or even angled, and this was the result.

How to fix it, and how much "fixing" was needed? We are using UMI 2406 mounts. These move the mounting location backward to the standard 4th gen camaro location using a huge plate. If you're trying to fix something like this, those extra inches turn out to matter. So does the 4th gen f-body motor mount. Effectively, the trans mount, engine mount, and amount the engine is raised from neutral form a triangle. From that triangle, everything else can be calculated--where various bits and pieces will end up, how much clearance will be gained at the hood (another problem this caused), and what angle you end up with after moving some part "X" inches. First, forget the factory engine mount holes. They're dead to you. Second, forget the "stock height" risers for the mount tabs. You're cutting them down. And I'm pretty sure that in an extreme lowering situation, these are perhaps the best mounts to have. Why? UMI also sells a 4th gen engine-side tubular poly mount that is (still waiting for it and have to measure exactly) but around 1/2" shorter than the clamshell mount. The 4th gen mounts are basically welded to the mounting plate. It's about as tight as you can get for putting the bolt to the block without using a solid mount. Combine that with the roughly .6 clearance from 2406 to the "bump outs" on the factory clams, and the mount has around 1.15" or so to give. We're going to clearance the mount for the "ribs" that help hold on the circular mount. All in, you can get a really low stack height modifying this setup. It should come in at 2.5" or so. I think. Doesn't figure into the calcs, but maybe helpful to compare.

The beauty of it on most muscle car frames is that you get quite a bit more than 1.15" lower at the motor. This is also a triangle formed by a right angle triangle with two equal sides. The crossmember is at 45 degrees. When the mount height drops, the engine drops by the hypotenuse of the triangle. So, if the mount height goes down an inch, the engine drops around 1.6 inches. That will put any oil pan into the crossmember. First, use the Holley 302-3 or a knock off. There is one, but I'm not going to promote it, even though I admittedly bought it. The 302-3 is the max clearance pan without breaking the bank. But, it only gain an inch. So, you're looking at cutting an inch out of the cross member to clearance the pan.

What do you get for all this effort? About a 2.5 degree improvement. Puts me at 5.5. But there's more... This assumes the engine drops, and the trans mount stays fixed. But, as the front of the engine lowers, it opens up some room in the tunnel. The interference point is about 10" forward of the transmission mount. That spot will drop gain around a half inch. That half inch will allow raising the mount/tail shaft by slightly more, which improves things by another degree to around 4.5 degrees. If banging out the tunnel gets another half inch or so, it gets to 3.5 degrees. Not perfect, but not bad.

Important thing here is that the header collector only moves down by a tenth of an inch, and we should end up going from 8 degrees to 4.5 without touching the tunnel. Collector, surprisingly, does not move any meaningful amount at all. And moving the mount location backward to the LS position improves things by about a half a degree that might not be possible using the SBC mount location. There may be another way to do this, but this is probably the easiest. I doubt hardly anyone will ever have an 8 degree driveline angle after a swap, but if you do... hopefully this helps. I built a spreadsheet to figure it out to make sure it would work and figure out what to cut out of the crossmember, which I think was a better idea than crossing fingers, guessing, and hoping.

Now the question: If we can only get it down to 4 degrees, leave it or try harder? Worth matching up the diff, or just go somewhere less?

And if you ever thought not putting a subframe where it should go so you could "lower" the car was a good idea... I hate you.