B body k-frame different from big block to small block

[AmadeusCharger500]

Is this statement true?
I am currently working on a Gen3 hemi conversion into a 73 Charger. I come to find out all of the motor mount and exhaust conversions are designed around small block k-frames, or so I am told.

[72Charger72]

true there is a different k frame for big block

[AmadeusCharger500]

It seems like the perches on the Big block, which I have, sit about 1 inch lower and maybe 1 inch closer to the firewall. I can only surmise this as I have no small block frame to compare it to.

[Mike DC]

 
There is confusion about this issue because it depends on the year. 

For 1972 and older (solid mounted K-frame) the K-frames were the same, small block to big block.  Only the bolt-on motor mounts were different.  (The Hemis and slant-6s had different K-frames though.)

The 1973-up setup (rubber isolated K-frame) used a different K-frame between the small & big block V8s.

[AmadeusCharger500]

Thanks Mike that is interesting. I bought 2 motor mount conversion kits TTI and Schumacher, and both had similar issues, although one was easier to use.
Mike at Schumacher is the person who alerted me to this. Both manufacturers base their designs on the small block k-frame. This is true for the mounts and the headers.

[Nacho-RT74]

I have a pic at my PC where difference is being shown and is noticeable... Now I'm posting from the phone, so I can't post it.

[Nacho-RT74]

Wondering.... Does it exist Hemi kits for 73 and lates B bodies?

[AmadeusCharger500]

Yes both TTI and Schumacher sell kits for 73/74 Hemi Conversion. However they do not fit into a car with Big Block k-frame. Which, unfortunately, I am the first to tell them about it.

The mounts that are currently available will require modification to make them fit. TTI mounts I found un-workable. The Schumacher mounts also needed mod but It was not that difficult.
I had to cut the left mount, grind the right mount slightly, and add 1.25 inch height to the k-frame perches.

[Nacho-RT74]

you mean later Hemi right ? I'm wondering the big elephant one.


here VISUALLY the K member differences

[AmadeusCharger500]

Yes the 5.7 and 6.1 specifically. Thanks for that pic Nacho, very helpful. It clears up a reason why the mounts were not square on the engine. I was 1st informed about these K-frame differences by Mike from Schumachers. He did not however know all the details of  differences. I am now going with his mounts. His mounts are much easier to modify for the application.
This is what I have discovered through trying to fit these mounts(designed for small block frame) onto a big block k-frame.

Big block perches are 1 inch closer to firewall (not a problem there is plenty of room), 1.25 inch lower (I'm raising the perch on k-frame), and NOT offset like the small block (easy cut and replace on driver side mount). As your picture shows the small block perches not square to body.

[AmadeusCharger500]

Nacho, If you have any measurements.. It would be very helpful.

[Nacho-RT74]

Long time ago there was somebody who take pics and uploaded in a hosting  images service where posted similar pics with measuring tape on pics, but is not working anymore.

Pics are not mine

[AmadeusCharger500]

Thats ok, that one pic was very helpful. Thanks for looking.