Anyone have a LS swapped 3+3?

[KnockingDiesel]

About 13 mpg so not bad. Being TBI and having that overdrive makes a world of difference.

85 K20. 1 ton axles, Nv4500, 350, Vortec heads. 15-16 mpg

What gear ratios are you running? The D70 rear has 4.10 and D60 front I’m getting is 3.73. I’m gonna assume the D60 gears are in better shape. Been considering 3.73 and LSD swap on the D70.

I’m also staying with 235/85R16 tires.

 

[SquareRoot]

What gear ratios are you running? The D70 rear has 4.10 and D60 front I’m getting is 3.73. I’m gonna assume the D60 gears are in better shape. Been considering 3.73 and LSD swap on the D70.

4:56. With the OD, my 350 would probably struggle pulling anything heavy on the highway. A higher torque engine would help that.

 

[KnockingDiesel]

4:56. With the OD, my 350 would probably struggle pulling anything heavy on the highway. A higher torque engine would help that.

That’s still a decent mpg for your setup.

 

[SquareRoot]

That’s still a decent mpg for your setup.

Agree. It only cost me about $5K in parts, a few quarts of blood, 50 gallons of sweat and two heatstrokes to up my mpg by 25%. Meanwhile, the price of fuel went up 50%.

 

[TotalyHucked]

IF it was me, I'd use the 6.0 or 6.2. I just don't think the 5.3 has the torque to move the 3+3 dually down the road real well. My dually is pretty low miles so I've got years before I have to worry about engine swaps but when the time does come I'll be going the 6.2 route.

Just my $.02 cents


Down side is using stock oem fuel injection on that kind of swap is pretty painful. So you need to use Holley, Halltech, MSD,..... whatever. Holley did just come out with Holley Sniper 2 that is SUPPOSED to be more "plug n play"

I disagree (if we're talking LS injection and not adding FI to a carb'd big block). Putting OE GM injection in is super simple and dead nuts reliable. My tuner has ripped out several Holley and FiTech setups to install either a BP or PSI harness with GM rails/injectors/computer/etc. It's also nice knowing it all will work together, rather than piecing together rails from one place with injectors from another and finding out you need spacers or adaptors and then a regulator and whoops, they won't work with the intake so now you need something else yada yada

 

[Old77]

What gear ratios are you running? The D70 rear has 4.10 and D60 front I’m getting is 3.73. I’m gonna assume the D60 gears are in better shape. Been considering 3.73 and LSD swap on the D70.

I’m also staying with 235/85R16 tires.

4.56 For me too

 

[KnockingDiesel]

I disagree (if we're talking LS injection and not adding FI to a carb'd big block). Putting OE GM injection in is super simple and dead nuts reliable. My tuner has ripped out several Holley and FiTech setups to install either a BP or PSI harness with GM rails/injectors/computer/etc. It's also nice knowing it all will work together, rather than piecing together rails from one place with injectors from another and finding out you need spacers or adaptors and then a regulator and whoops, they won't work with the intake so now you need something else yada yada

I won’t use anything but GM FI. I like the idea Of the vortec 7400 but I’m apprehensive since it’s an old platform I feel like support and parts availability might be an issue.

The LT seems like twice the cost of LS while only offering 25% more power. Although I’m still undecided I think the LS may be the route to take.

Plenty of support and new enough to still be relevant but old enough to have cheap parts available.

I found a few trucks locally and I am going to drive them. To get an idea of what I’m getting into.

2012 3500 crew cab
1996 3500 ext cab
2021 3500 crew cab

If I go LS it’s only L96/6L90E, I had the 6.2/6l80e in a 07 Escalade and while very powerful and decent mpg I just don’t think the 6.2 is built for what I want out of it. I may be wrong though, my ext was 6500lbs, the 3+3 I figure around 7,200lbs.

 

[Old77]

If I go LS it’s only L96/6L90E, I had the 6.2/6l80e in a 07 Escalade and while very powerful and decent mpg I just don’t think the 6.2 is built for what I want out of it. I may be wrong though, my ext was 6500lbs, the 3+3 I figure around 7,200lbs.

That 6L90E is what will make the most difference. It's more suited for a big truck than than the 6L80E is regardless if you go 6.0 or 6.2

 

[Frankenchevy]

If you aren’t worried about modifications, the 8.1 is another option for a higher gross vehicle.

 

[Old77]

I disagree...

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[TotalyHucked]

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[Bextreme04]

I won’t use anything but GM FI. I like the idea Of the vortec 7400 but I’m apprehensive since it’s an old platform I feel like support and parts availability might be an issue.

The LT seems like twice the cost of LS while only offering 25% more power. Although I’m still undecided I think the LS may be the route to take.

Plenty of support and new enough to still be relevant but old enough to have cheap parts available.

I found a few trucks locally and I am going to drive them. To get an idea of what I’m getting into.

2012 3500 crew cab
1996 3500 ext cab
2021 3500 crew cab

If I go LS it’s only L96/6L90E, I had the 6.2/6l80e in a 07 Escalade and while very powerful and decent mpg I just don’t think the 6.2 is built for what I want out of it. I may be wrong though, my ext was 6500lbs, the 3+3 I figure around 7,200lbs.

We use our 2011 Suburban with the aluminum LC9 5.3/6L80e to tow our 6500lb travel trailer regularly. It does ok, but definitely not great. I have 4.10's and 33" tires on it, so a little better ratio than the stock 3.07 that it came with. I sourced an L9H aluminum flex fuel 6.2L from a 2009 Denali that is currently being rebuilt and will go in to the suburban by the end of the year. Unloaded, the suburban easily cruises at 75-80mph and knocks down 15-20mpg while doing it. It will likely go down some with the 6.2L, but not likely to be by much. I would expect the 3+3 to be about the same weight as a GMT-900 Suburban. The 6.2L, with a TSP L92 VVT Stage 1 cam, should be knocking down about 100-150 more hp/tq than the stock AFM/VVT 5.3L did just about everywhere.

Here's a dyno run with their Stage one L99VVT cam, which is very similar to the older L92 truck grind, but with a bit more lift and duration that shifts the HP curve up a bit higher RPM than the L92 one has. You can see the VVT 6.2L has a basically flat torque curve(at 400ft/lbs+) from ~2k rpm to 6800 rpm and makes 550hp while its doing it.

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I also have a Vortec 7400/4L80 combo going into my 1980 K25 pickup. It was a 350/TH400/NP205 truck stock and will likely be getting the 454 swapped in in the next few weeks. I am using a 2002 LS computer and the original wiring harness from the 97 K2500 Suburban that I pulled the engine and trans from. I converted it to CNP with an EFI connection 24x reluctor and had the factory cam reground by Delta Camshaft in Tacoma. Updated the fuel system to use an external adjustable FPR and bosch D3 injectors. Adjustable valvetrain update. Otherwise left stock. I rebuilt the transmission for ~$1k including a reman converter. Its been dual fed, sonnex no-walk roller output, Sonnex line to lube PR valve, Transgo TCC and AFL valve updates, and sepaerator plate drilled for mild firm shifts. You can also use the factory cruise controller from the GMT-400 truck you get the engine/trans from and use your choice of the factory cruise stalk or an aftermarket one.

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[KnockingDiesel]

The more I look at figures and dollar to hp the L96 and 6l90e look like the way I’m gonna go. The support and aftermarket are there it’s a lighter more efficient package with good power and decent fuel economy. The only mods would be a tune, ceramic coated headers and electric fans possibly.

 

[Camar068]

What gear ratios are you running? The D70 rear has 4.10 and D60 front I’m getting is 3.73. I’m gonna assume the D60 gears are in better shape. Been considering 3.73 and LSD swap on the D70.

I’m also staying with 235/85R16 tires.

I went with 3.73. I regret not going 3.90 or 4.10 in mine. 4th has absolutley no power. I lose speed going up hill. Part of it's because it's not dyno tuned, but I still wish I'd gone 4.10 or 3.90.

You have to change one or the other. Think about it, google it, look around here, before you make up your mind. I wish I'd listened to others here @HotRodPC

 

[KnockingDiesel]

I went with 3.73. I regret not going 3.90 or 4.10 in mine. 4th has absolutley no power. I lose speed going up hill. Part of it's because it's not dyno tuned, but I still wish I'd gone 4.10 or 3.90.

You have to change one or the other. Think about it, google it, look around here, before you make up your mind. I wish I'd listened to others here @HotRodPC

What engine/trans/gear/tire are you running?