Your above post about the subframe and the weight of the car held up by the springs.........it's not really about weight that the necessary strength is about...........it's all about torque. Drivetrain torque.
If your engine puts out say 500 ft lbs torque, you might have a 1st gear ratio of 4 to 1.
That will give 2000 ft lbs at the driveshaft.
Then once you go through the diff at 3.5 ish, that's 7000 fl lbs.http://www.stealth316.com/2-gears.htm
OK so 1st gear overall is 12 and a bit....so 500 at the engine becomes 6000 at the wheels.
It's a bit hard to visualise 6000 ft lbs but we should all know what 80 on a torque wrench feels like?
edit......that's not quite right because a diff splits torque....55/45 front rear or something like that so the figures are really about half of what I said but still a lot..........and that's also WHY RWD conversions break......because you've doubled the torque to the rear end.
To ramble on a bit more.......Mr ricer comes along and says I'm going to do a RWD conversion.....no , it'll break. Ricer says........stop being negative.....no, the mathematics and the physics says you're doubling the torque to the rear end.........it's NOT being negative, it's being realistic. It's only negative if you've got no fecking idea what you're talking about. Wishful thinking.
Now think about a traditional front engine RWD car........the body twists to the point where you lift the left front wheel due to torque reaction ....equal and opposite forces etc.
No different from a FWD car where the engine rolls back (or fwds depending on orientation) on a launch and when the mounts are broken in the case of a GTO it breaks the transfer case because you're putting side loading on it.
Rubber mounts are used not just for noise and vibration but to absorb peak forces and it's the peak forces that break parts. Polyurethane mounts are stronger but still flexible.
Solid engine mounts as an example.......they're just for ricers....you're going to break more parts, not IF but WHEN.
So have another think on the rear subframe and think on how much torque it needs to handle without getting twisted and putting everything out of alignment and breaking parts.
The diff head, the transfer case and the driveshaft need to be straight at all times which means no side loading.
The torque reaction from the driveshaft will be lifting the body on one side and pushing it down on the other side.
The torque reaction from the driveshafts from the rear diff to the rear wheels will be lifting the front of the rear subframe and pushing the back of it down.
That's WHY it's X shaped.
In my own case I swapped a Falcon LSD into my Zephyr, got the pinion angle a bit wrong , it went OK for a few years but broke in the end (lasted about 12 years as a DD),it was inevitable really that it broke at the rear universal......which is WHY driveshaft safety loops are now compulsory for modded cars.
OK so the total weight of the rear subframe, diff etc?
Try comparing it to say the weight of a Ford 9 inch diff....it's not a lot different....if you were doing a 9 inch seriously you'd use a 4 link, not leaf springs.
Oh and if you're interested in seeing a high performance japper that's been crashed, rolled T boned or whatever.......I used to be a regular at Turners damaged car auctions.....that's where you get to have a look at them. I never went to buy crashed ones, just ones with blown engines but you get to see whatever you want to.
quote from barryboys.
Yes, yes, yes, that might be so, but you're clearly missing the bigger picture.....