Quick question: Will a 5 to 6 degree driveline angle "work"? We're got a bit of a situation where it's going to be really complicated to get it much better.

The long story: 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 a 8 10 [Edit: Remeasured] 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 4+ 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 has slightly more clearance between the mount and the bracket than the clamshell mount. The tube holding the poly bushing is basically welded to the mounting plate. It's about as tight as you can get for putting the engine mount through bolt to the block without using a solid mount. All assembled, the mount has maybe 1.1" 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 2.4" or so. Stock, the fourth gen mount is about 3.5" height.

The beauty of it on most muscle car frames is that you get quite a bit more at the motor than the amount you lower the bolt holes in the mount tabs. The crossmember is at 45 degrees. So, this is a triangle formed by a right angle triangle with two equal sides. When the mount height drops, the engine drops by the hypotenuse of the triangle. So, if the mount height goes down just over an inch, the engine drops around 1.56 inches. That will put any oil pan into the crossmember. So, use the Holley 302-3 or a knock off. There is exactly one exact knock off of this pan, but I'm not going to promote it, even though I admittedly bought it. [Side rant: Note to Holley--Make your stuff in the USA or stop pricing it like it is, and I wouldn't. A price different of almost 200% between a "generic" and the real deal is ridiculous.] The 302-3 is the max clearance pan without breaking the bank. But, it only gains 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 7.7 degrees. [But if you just need 2 degrees, this is a magic ticket with zero cutting.] 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 clearance. That half inch will allow raising the mount/tail shaft by slightly more, which improves things by another degree to around 6.8 degrees. If banging out the tunnel gets another half inch or so, it gets to 5.7 degrees. Not perfect, but not bad.

Important thing here is that the header collector actually moves *up* a small amount. Dropping the engine over an inch and raising the trans mount does not end up dragging the headers. Yes, it will end up lowering where the headers turn from vertical to horizontal, but this shouldn't matter because the angle is simply getting closer to zero, i.e. level with the ground and in line with the collector. 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 10 degree driveline angle after a swap, but if you do... hopefully this helps. But even if it's only two degrees you need to fix, this is still a fairly easy fix compared to cutting or removing crossmembers to lower mounts. Two degrees of drop can come from just modifying the mount itself. And if you're starting with a mount that stacks up to over 3.5 inches, the gains are even more. 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. For example, after dropping the mount holes 1.15" and clearancing the tunnel an extra .5 inches, the front of the intake will come down 2.25 inches, the collector will go up .35 inches, the front of the pan down 1.62 inches, and the trans mount will go up 1.3 inches.

Now the question: If we can only get it down to 5 degrees, leave it or try harder? If we leave it there, what to do with the diff angle? Leave it neutral or make it 3 degrees?

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

 

Front and rear operating angles should be equal and opposite and less than 3 degrees for smooth high speed operation.

Andrew