75 roadrunner k frame/ subframe

is the f frame/subframe the same on a 75 roadrunner between small block and big block?

You are going to get some people saying they are the same, and some saying they are different.
From what I understand they are different.
And interchangeable from any 73-79 B body and 79-81 R body.
Got a 75 Road Runner? I happen to love those. I have one.

The only thing I can tell you is we pulled a 400/727 out of a 75 Road Runner and installed a 360/727 and didn't have any issues. Both motor/trans were swapped as complete units. The 360 came out of a 73 or 74 Challenger, but it may not have been original to the Challenger either. The 400 ended up in that 73 or 74 Challenger, and that was a bolt in as well. Both car owners were happy, as was I, I got paid by both to swap out the motor combos. Gene

No, they change. Engine mount locations changes. Have the pics somewhere.

They can fit.. yes, but engine will be out of alignment by a tad, making a tight fit on all drivetrain mounts and could get some linkages issues

The 74 parts book shows different part numbers. I assume 75 would be the same.

Not the same.

While you can get the other type engine to bolt in, it's cockeyed.

Back in my sailor days we swapped a 400/727/driveshaft and the entire front suspension out of an 78 Cordoba into what was a 318 75 Coronet. Tedious but everything bolted right up like factory, because it essentially was.

I know its not the same but when I put a 440 in place off a 318 in a 71 B k-frame it fit good but it seemed to sit a tad high

75 and 76 factory part number books do list different part numbers for small block vs big block b-body k frames. Suspect other years will as well. As for what's actually different between them, couldn't tell ya and if there is in fact something different betting it would take meticulous measurement to figure out.

I've used boneyard donors from 73, 78 and 81 (original engines unknown) in to 75 and 76 small blocks. I've also dropped 440s in to 75s that I yanked the 318 out of. Even with keeping the original C body motor mounts they dropped in after swapping oil pans. If it's tweaked front/back side/side or diagonally I sure can't notice. As in: dropped right in to place like it was made for it and no fighting to get the holes lined up. Hood clears fine with OEM style intake / carb / filter, 440 fan fit in the 318 shroud, etc, etc.

Recall the same experience when putting the 318/904 in the C-body that was headed to the scrap yard after donating the 440/727. Dropped right in. Looked wrong as hell because of how small it was but again, no kinds of fighting to get the mount bolts in.

I've never done a small to big block swap, but, one other thing that is different (on '73's anyway) is the sway bar mount. Where the end links attach to the K. The mount for the link is welded in place. No sway bar? No mount.

I'm just curious if this is why two part #'s are shown. If not, there should be three (or four?) part #'s then, correct?

(the only factory V8 cars I've seen without a sway bar are small block cars).

They are definitely different.

Here is a pic showing the difference.

https://board.moparts.org/ubbthreads/ubbt...3-74k-frame.jpg

A link to this topic

https://board.moparts.org/ubbthreads/ubbt...ck-k-frame.html

This is Moparts. We can't let real life experiences over ride the book and part number thumpers. Every vehicle built has + and - tolerances. That would mean that anything may fit somewhere else, if the production shift is in your favor, or it may not fit if the production shift was not in your favor. The issue that has always been consistent when dealing with swapping a Mopar big block where a small block used to sit has always been an oil pan or an oil pump/filter clearance issue. My guess is that 9 out of 10 times, the big block clears everything, but if your writing a book, you have to cover your butt for that 1. Gene

Hacks gotta be hacking

Asking will it fit or is it the same are two different things.

That photos tells it.
Anyone remember the small block to big block swap mods on 73-76 A body K frames?
I remember it required cutting the mount off the K frame, and moving it back about an inch on the left. Looks to me like the same principal applies here.

If it's like my 74 satellite, the k-frames are different. The motor mount perches are different and the engine will fit wrong. When I bought mine, the previous owner put in a 440 out of a 76 chrysler and used the spool type mounts that were on the engine. Yes, the engine fit, however it was too high in the front and it was too far forward. The previous owner had to bash in the oil pan with a hammer to get the front of the sump to clear the k-frame. I later bought the schumacher conversion mounts and the difference in fit was night and day better.