I'm interested in swapping a 6.9 diesel into my 76 highboy 360 c6. I love driving my old truck but 10 mpg I can't afford to daily drive it like I want to. I've done some research on the 6.9 and it sounds like a bullet proof motor just underpowered in stock form. What I'm trying to find out next is what do you have to do to get the 6.9 bolted into the highboy? I absolutely refuse to cut and weld different crossmembers and engine towers on the frame. I would only do this swap if I could just bolt and swap different parts together to make it work. Call me weird but I just hate doing permanent mods on a vehicle. I want it to be able to go back stock if I ever wanted to.

 

Tons of guys have done it.....but it's not, nor ever will be, a direct bolt-in swap.

 

I just recently finished putting a 86 6.9 idi backed by a 4 speed manual into my 79 Short bed 4x4 F150. First off, it's not underpowered. It's definitely got WAY more guts than the 351/C6 that came out of it... If you go with a C6 with the 6.9, yeah it probably will feel underpowered.

Secondly, it is NOWHERE close to a bolt in swap. You need to weld in the towers from the 6.9. I also bolted mine down, through the frame to be safe. I was able to leave the stock cross-members alone though.

That being said, it's not that bad to do... I would HIGHLY recommend doing it, it's a ton of work but you will be happy when all is said and done. The one thing I would do differently is mate the engine to a ZF5. Other than that, I'm pleased, and truth be told the 4 speed isn't terrible at highway speeds. I'm seeing around 16-17 mpg with 3.50 gearing and 33"x12.5" tires, which I think is very good.

 

Here's a video I seen on Youtube. In the comments it sound like you can used a motor mount that lets you bolt the engine in place with the stock towers. IDK if it would work on the 360 tower though. I wonder if it would be easier to put the diesel in a f150 then a highboy?

 

I'm not sure if it's possible to use the stock towers. I'm also not familiar with the frame differences between a highboy and an F150... I recall reading that a F250 highboy has a narrower frame, but I'm not sure if that means it's narrower than an F150. I would think it would be the same amount of work. Honestly though, I don't think that putting the towers from the 6.9 in has to be a "permanent" thing. Yes, you need to weld and bolt them in, but I know if I really wanted to that I could take the diesel out and go back to gas. But I'd never do that because I love it.

 

Will a 6.9 work with any of the drive line in a 79 351m c6 4x4? If I got a 6.9 with a desiel c6 would it bolt up to the original t-case? I'm interested I'm doing a 6.9 or possible 7.3 swap as well.

 

 

i seen a few cummins conversions around here but aint seen a 6.9 yet

 

Maybe there's a reason....

 

Go check out Oilburners. They wont laugh at you there.

 

I did My 67 two wheel drive by fabricating front engine mounts that bolted in. The C6 with GV are sitting on the stock cross member in the stock location. I'm sure You can do the same in a 4x4 I'm also sure a 4x4 would work out much better as You don't have to work around the steering. Power from a well tuned 6.9 is good in stock form they are lame. Power from one with a Banks turbo is soooo nice. You can swap the tail shaft from Your existing C6 into one that has the engine bolt pattern You want in order to bolt up the transfer case. I would strongly suggest an overdrive of some kind .

 

I have a divorced T case on my highboy so no worry there. I'd like to use a overdrive auto though the c6 with 4.10 runs 2600rpm at 55mph. My 360 stock is rated at higher hp and tq then the 6.9 is stock but a few mods and I could prolly be happy with the power on the 6.9. Mileage, alt fuel choices, and of course awesome diesel smoke are my reasons for wanting to swap.

 

I had a 6.9L in my 79 F250 for two years before I put a Cummins in. It did OK on power, not great but OK...and turning 38.5 super swampers. If you are not dead set on huge amounts of power the 6.9L will suit you just fine.

The frame widths are the same in the 73-79 in the front. The frame width in the rear is what changes.

I partly used my stock engine mounts for the 400M...but I did move and weld the passenger side one up a few inches so you could get the starter in and out if ever need be. I then made adapter brackets that bolted between the block and the mounts on the frame. Don't be worried about welding. You can cut things back off if you want to go back to original.

If you use a C6 it must be for the diesel. It has its own bell housing pattern. Any of the manual transmissions from 73-79 will bolt right up to the 6.9L bell housing and the input shaft will mate up to the clutch disc.

 

Same amount of work for a weaker engine.

 

No it's not the same amount of work the cummins is very hard to get fit in and You have to fab everything to do it the 6.9 just need front mounts