Diesel Swap: Cummins VS GM 6.5

[Blake Loggins]

First off, I know this has been debated over and over and over in numerous threads. But I am looking for first hand experience with these swaps. I finally got my new shop ready and its time to dive off into this diesel swap on my 93 fzj80. After weeks of research I almost pulled the trigger this week on a GM 6.5 on craigslist. But the thought of a reliable Cummins is hard to discard. I have owned several Cummins trucks and I know its a far superior engine hands down. That's not even debatable. I originally was gonna go with the 6.5 for ease of installation, cost and engine noise. But the main reason in this swap is to gain more power and with me, I never have enough. If I am gonna spend the time and money on a swap I don't want to get it finished and then wish I still had more power. So here are my questions and concerns:

1. Main concern with a Cummins is the weight. What front springs are you guys using? Any regrets or suggestions from guys who have done this swap? I know this engine can easily produce more power and still be very very reliable. Are most of you keeping the stock 80 series transmission? Which trans are you using? I really want to keep it an automatic.

2. I feel like the 6.5 would be a easy fit into the 80 series engine bay. My concern here is power. I don't want to make this swap and end up with the same power as before. (I'd just be sick) I am a little concerned about the reliability of this engine but I feel like with a few upgrades it can be reliable. Any regrets or suggestions from guys who have done this swap?

I am strictly looking for real world experience with these 2 scenarios. If you haven't done this swap or driven a LC with these engines please keep your opinions to your self. No, I'm not doing a LS swap or a Mercedes Diesel swap. Sorry this sounds like the ending of a Craigslist ad, just trying to keep the replies relevant. Thanks!!

 

[4xFletch]

I did a NA 6.2 diesel swap with a 700r4 and it felt like more power then the stock 4.5. It went up hills much easier without having to downshift. So a turbo 6.5 (I'm assuming you're going turbo) would have tons of power over the 4.5. Trying to keep it cool would be the biggest challenge.

 

[LandCruisinMy93]

You may ask @torfab since Tor and his crew do the GM diesel swaps. @maxamillion2345, @shocktower, @Jvoight @hotwod should be able to provide insight on springs for the Cummins.

 

[DIESELJEEP]

I think you'll be hard pressed to find an owner of a 6.5 swapped cruiser.Reality of it is there are just better engines to use.That said I give you my 2 cents.

The weight of the cummins dropped my front end around a half inch on stock springs.I dont think the weight is a huge concern.

I daily drove a 6.5 swapped yj for years.Power was decent but nothing compared to the cummins and considering the weight of the jeep to be much less than the cruiser I just don't imagine the 6.5 would be any better than the stock gasser in a cruiser.I owned the 6.5 yj for 10 years and never had an issue with the motor.

The great thing about the 6.5's is they are cheap to source.If you decide to go with the 6.5 I have a chevy auto adapted to the older landcruiser transfer case that I'd sell.I had collected parts to do this swap but ultimately went with the cummins

 

[Blake Loggins]

I think you'll be hard pressed to find an owner of a 6.5 swapped cruiser.Reality of it is there are just better engines to use.That said I give you my 2 cents.

The weight of the cummins dropped my front end around a half inch on stock springs.I dont think the weight is a huge concern.

I daily drove a 6.5 swapped yj for years.Power was decent but nothing compared to the cummins and considering the weight of the jeep to be much less than the cruiser I just don't imagine the 6.5 would be any better than the stock gasser in a cruiser.I owned the 6.5 yj for 10 years and never had an issue with the motor.

The great thing about the 6.5's is they are cheap to source.If you decide to go with the 6.5 I have a chevy auto adapted to the older landcruiser transfer case that I'd sell.I had collected parts to do this swap but ultimately went with the cummins

Thanks for the feedback!
Did the 6.5 in the YJ have a turbo? Did you go with a 12v Cummins? Are you happy with it? Which trans did you go with?

 

[Kaninja]

Sorry, should have read the OP and kept opinion to myself. Mods feel free to delete this post.

 

[JeepinPete]

The GM V8 diesels are hot engines. The more power they make, the harder they are to cool. They need a lot of radiator, which will be a challenge in an 80.

 

[thatcabledude]

GM 6.5 diesel shouldn't even be an option IMO

 

[DIESELJEEP]

Thanks for the feedback!
Did the 6.5 in the YJ have a turbo? Did you go with a 12v Cummins? Are you happy with it? Which trans did you go with?

Technically it was a 6.2 with a turbo.Yes I ended up swapping a cummins in my cruiser.Couldn't be happier,went from 6-8mpg(and no power) to 14-16mpg (and tons of power) I'm on 37's also.The cruiser a pleasure to drive now.I used the stock getrag 5 speed and np205 transfercase that was mated to my 1990 model cummins engine.No expensive adapters!

 

[maxamillion2345]

Technically it was a 6.2 with a turbo.Yes I ended up swapping a cummins in my cruiser.Couldn't be happier,went from 6-8mpg(and no power) to 14-16mpg (and tons of power) I'm on 37's also.The cruiser a pleasure to drive now.I used the stock getrag 5 speed and np205 transfercase that was mated to my 1990 model cummins engine.No expensive adapters!

Running stock rear axle and fuel tank?

 

[DIESELJEEP]

Running stock rear axle and fuel tank?

Yes still rocking the stock axle.2500 miles on the swap so far being pretty rough on it.No issues.But I did have to swap out the stock fuel tank and relocate one to the rear.Used a yj tank cause its what I had

 

[maxamillion2345]

Ahhh, I wondered about driveline clearance. I run a getrag/205 and 14 bolt and pulled factory tank in favor of a grand cherokee tank mounted behind the axle.

 

[cjmoon]

i think your spring question comes back to how much lift. any of the heavies 220-250 spring rate will be great. 6bt all the way if i did it again i'd jump to 6bt. turbophil has Heavy ARB, winch 6bt combo it drives very nice with the HD TJM 3.5-4" lift (about 2.5-3" with his set up added 1" spacers to clear the 35" Tires better

 

[Blake Loggins]

Thanks for all of the feedback. Looks like the 6.5 is out!

 

[JaketheSSnake]

Other than my love for Toyota, I'm a die hard gm Homer. If gm had something to compete or come close to the cruisers, I'd have it instead. That being said, I'd never consider a 6.5 diesel, ever! Cummins all the way in this scenario.

 

[Bisonthecruiser]

I hate to ruin your party, but I wouldn't consider either. I think you'd be way better off with a V8 petrol than you would be with a diesel. This is coming from someone who owns both the 1FZE and a 1HDT. There's a reason you see so many Cummins swaps for sale.

 

[Bisonthecruiser]

I hate to ruin your party, but I wouldn't consider either. I think you'd be way better off with a V8 petrol than you would be with a diesel. This is coming from someone who owns both the 1FZE and a 1HDT. There's a reason you see so many Cummins swaps for sale.

Shoot, just read your first post the whole way. Didn't realize you were closed minded on this. GL.

 

[Blake Loggins]

Shoot, just read your first post the whole way. Didn't realize you were closed minded on this. GL.

Im not closed minded. Just looking for real experience and evaluations instead of opinions. You just made a suggestion and discouraged another with absolutely zero experience with either, a gas v8 or cummins/GM6.5.

 

[shocktower]

First off, I know this has been debated over and over and over in numerous threads. But I am looking for first hand experience with these swaps. I finally got my new shop ready and its time to dive off into this diesel swap on my 93 fzj80. After weeks of research I almost pulled the trigger this week on a GM 6.5 on craigslist. But the thought of a reliable Cummins is hard to discard. I have owned several Cummins trucks and I know its a far superior engine hands down. That's not even debatable. I originally was gonna go with the 6.5 for ease of installation, cost and engine noise. But the main reason in this swap is to gain more power and with me, I never have enough. If I am gonna spend the time and money on a swap I don't want to get it finished and then wish I still had more power. So here are my questions and concerns:

1. Main concern with a Cummins is the weight. What front springs are you guys using? Any regrets or suggestions from guys who have done this swap? I know this engine can easily produce more power and still be very very reliable. Are most of you keeping the stock 80 series transmission? Which trans are you using? I really want to keep it an automatic.

2. I feel like the 6.5 would be a easy fit into the 80 series engine bay. My concern here is power. I don't want to make this swap and end up with the same power as before. (I'd just be sick) I am a little concerned about the reliability of this engine but I feel like with a few upgrades it can be reliable. Any regrets or suggestions from guys who have done this swap?

I am strictly looking for real world experience with these 2 scenarios. If you haven't done this swap or driven a LC with these engines please keep your opinions to your self. No, I'm not doing a LS swap or a Mercedes Diesel swap. Sorry this sounds like the ending of a Craigslist ad, just trying to keep the replies relevant. Thanks!!

I have done a few, 6bt swaps never a GM ( I hate GM and their diesel is crap ) the Cummins is proven by you and others, I use the 343 stock tranny, front springs are 3" OME it does have the stink bug look, I am going to put some 30mm spacers to try and level it it up, and eventually, I am going with 4" slee's, I used a complete kit, so I did not have to fab stuff, I also put a 1" body lift, to make a little more room, I have a 12 valve VE pump simple and mechanical, I would do one again in a second. I have 2K miles on my swap and still excited when I drive it every day, the only thing is I have yet to get the full potential of the tranny with the new stand alone. The 6BT fits better the the stock motor

 

[shocktower]

I hate to ruin your party, but I wouldn't consider either. I think you'd be way better off with a V8 petrol than you would be with a diesel. This is coming from someone who owns both the 1FZE and a 1HDT. There's a reason you see so many Cummins swaps for sale.

The reason most people want to sell them, is to make money, if I let you drive mine you, would change your mind, and now there is a better stand alone for it, so it shifts much better, I have worked on several 6 bt swaps and yes I am biased, but I know this I got 22.86 MPG and I can walk all over people with a huge smile, and my 80 has never been so much fun