6.0L questions, so many questions, the more I read, the more questions…

[83GMCK2500]

Truck currently: 1983 GMC K2500 400sbc/sm465/4.10 gears/33” tires.
Truck goals: ORD 2-3” lift, 6.0/NV4500/?.?? Gears/33” tires (likely 255/85R16, or 255/80R17)

For those that haven’t read my intro or did and have forgotten since I mostly lurk in the square and gmt400 sections these days: this is a forever truck, my dad is the original owner and it stays in the family. Is it possible to set this brick up (I know, aerodynamics are against me, particularly with the small lift and 33s.) to get anywhere near 20 mpg on the highway? Using an RPM calculator, in OD at 70 with those tires and 3.54 gears the RPM is ~1,819, with 3.73s RPM is ~1,917. 3.54:1 is the highest gear I can get for a Dana 60 front, so there is another limitation. I don’t want a race engine, just a bullet proof high torque truck engine, preferably on a budget. Within reason at least, I can’t just throw gobs of money at the engine. Say $4-5k tops? Is that reasonable?

I have gathered that generally speaking the cathedral port heads are best for low-end torque, but rectangular when paired with the right cam can also produce good low end torque. Either way, what is the right cam, something from TSP or a BTR Truck Cam? I see that BTR has like 5 different truck cams, 4 stage + Truck Norris…why?

For intake, I am thinking Holley dual plane ls1/2/6 intake (if cathedral port), one of their 4150 style EFI units (I do not want a front draft intake. I want the intake to look classic with original tall filter air cleaner.), electric fans, etc. Is a stroker the way to go or stay with stock bore/stroke? I assume the more cubes I add the more fuel I add, the less economy I get? Do I need to consider a range box to get a double-OD? Should I be aiming for 1,500-1,600 rpm on the highway?

If there is another thread with a similar build in mind I was unable to find it, I am open to reading through some if anyone can point a few out. I have sifted through this section, ls1tech, performancetruck, etc. As the Title says, more research = more questions.

[mongocanfly]

I'd say if you expect 20mpgs from any 6.0, your gonna be disappointed...
Like real bad..
My C30 has a similar setup, but is 2wd
I have a LQ9 backed by a nv4500, 4.10 gears, and 31 in tires..
If, and only if , I can keep my foot out of it, it gets mid 16s..
Put a trailer behind it and you can forget about mpgs.
On the dyno , the 6.0 turned 344hp and 399tq..
but it likes rpm.. based on my driving , the 6.0 sweet spot is around 2000rpm..
Only mod to this engine is headers, which I had to do to get around the clutch linkage,
Should have done hyd clutch
Manifolds will flow as good as headers I'm told

On my IH build I have a 5.3, with a stage 2 btr cam..backed by a nv4500,
I have 4.56 gears and 255/85-16 bfgs (34in tall)
Mods on this engine are btr stage 2, Holley intake and fuel rails, headers
By my calculations, the 65mph rpms should be really close between the 2 trucks..
IH isnt on road yet , so I dont know what kinda mpgs or hp numbers its gonna get

Its gonna cost big time to connect a LS to a nv4500.. unless you can find all the factory stuff..
I couldnt, had to go with all advanced adapter on both of these trucks

C30 2022rpm at 65mph
IH ..2055 at 65mph

If you want the classic look , that's gonna cost as well..
I did it on the IH, feel free to check the engine out,
And dayj1 did a superb job on his ,( I copied most of what he did) on his build called "another way to skin a cat"

[83GMCK2500]

Originally Posted by mongocanfly

I'd say if you expect 20mpgs from any 6.0, your gonna be disappointed...like real bad..
My C30 has a similar setup, but is 2wd
I have a LQ9 backed by a nv4500, 4.10 gears, and 31 in tires..
If, and only if , I can keep my foot out of it, it gets mid 16s..
Put a trailer behind it and you can forget about mpgs.
On the dyno , the 6.0 turned 344hp and 399tq.. but it likes rpm..

On my IH build I have a 5.3, with a stage 2 btr cam..backed by a nv4500,
I have 4.56 gears and 255/85-16 bfgs (34in tall)
By my calculations, the 65mph rpms should be really close between the 2 trucks..
IH isnt on road yet , so I dont know what kinda mpgs or hp numbers its gonna get

Its gonna cost big time to connect a LS to a nv4500.. unless you can find all the factory stuff..
I couldnt, had to go with all advanced adapter on both of these trucks

C30 2022rpm at 65mph
IH ..2055 at 65mph

If you want the classic look , that's gonna cost as well..
I did it on the IH, feel free to check the engine out,
And dayj1 did a superb job on his ,( I copied most of what he did) on his build called "another way to skin a cat"

In all my research, I discovered that 99-00 LQ4s have a standard length crank flange, can use earlier trans on them without spending a fortune. I thought I would need to find a gmt800 nv4500 too, then I found this: https://www.tickperformance.com/mcle...8-part-460535/

That looks to accomplish the same as the early crank, no?

Great info, thank you, I will sift through your builds. What is your 60-70 cruising RPM in the C30?

[mongocanfly]

65mph --2022rpms..
Itll run 80-85mph all day..did a turn and burn to Colorado last fall..avg mph was 80+..over 3000miles
Got around 13mpgs on that trip

My LQ9 is a 2002..and my nv is a 96+ y model..dont really know about the early 6.0s

[mongocanfly]

Heres a couple of pics of the 5.3 in the IH