Help Me Pick a Drivetrain

[bryanedp9]

Hey folks, I've currently got an '89 ton 3+3 dually after being out of the squarebody game for too long. I'd always wanted one of the crew cabs. I'll get pictures up later, but it's nothing too crazy.

Anyhow, it's got the TBI 454/400 with 4.10 gears I believe. I'm aiming to replace the standard bed with a utility bed and a slide-in camper. It is to be a travel unit, and I don't need any more power, but I'm considering economy.

The 454 as-is gets around 10mpg and I'm sure could do better with some TLC and the right conditions. However, I've been playing with the idea of a turbo 6.2 or 6.5 diesel swap. The motors can be had cheap (especially the 6.2) but needs some fortifying. As well, I'd want to avoid the electronic pump of later 6.5 motors. This is all just one avenue.

I'm thinking 15mpg is top-notch for a 454 with the right gearing, and the diesel could only do slightly better in such a loaded rig, maybe 20mpg.

So I'm thinking to focus on gearing first. NV4500, maybe even an NV5600.

Others might say to just regear the rear, but the TH400 is getting a little lazy and only has 3 speeds, ya know.

Curious what you'd do. I am perfectly happy taking the slow roads for economy as it is, but I'd like to have those extra gears, especially for lugging it up to 70mph.

So 5 or 6 speed? Diesel or gas? Can the gearing really save either one much?

[K20Detroit]

Personally, I would go with a 6.2/700r4 combo.
I used to have a truck with a rebuilt 350 and th400.
Aside from the engine+trans, they were the same rig driveline wise.
Without even considering fuel economy;
My 6.2 has a much more useful torque and power curve. Power off the line is vastly improved.
The 6.2 feels much more refined. It's easier to start in cold weather, it runs much smoother, better throttle response.

My 6.2 is an '84 K20 with Silverado package and 700r4 trans. I average 19MPG on my 285/75/16 tires, though do a decent amount of city driving.  The low end grunt really helps in the city.

[roundhouse]

A non turbo 6.2 in a six wheeler crew cab with a slide in camper is going to be dangerously underpowered




Sent from my iPhone using Tapatalk

[K20Detroit]

A non turbo 6.2 in a six wheeler crew cab with a slide in camper is going to be dangerously underpowered




Sent from my iPhone using Tapatalk

He mentioned fortifying the 6.2, which would allow performance mods at the same time.
Single plane intake, exhaust, mildly turned up pump, and you'd already have a decent amount of power.
Even with an EGR intake, restrictive mufflers, and untouched pump; my 6.2 would give my old 350 a run for its money. The 350 was rebuilt, with dual exhaust, upgraded carb (don't remember specs), and all the usual things.

[bryanedp9]

Yeah I should mention that I would hope to turbo. Not much, but just to help climb and compensate for altitude. If done mildly and I keep my foot out of it, it could be beneficial for mpg as well.

[roundhouse]

The mpg is good.   But 85 HP is not enough


Sent from my iPhone using Tapatalk

[1967KaiserM715]

The mpg is good.   But 85 HP is not enough


Sent from my iPhone using Tapatalk

What? The 6.2 had 130 to 160hp, a 350 had 160 to 210. That's at best only a 30 hp difference, which is easily overcome with choice upgrades

[bryanedp9]

The mpg is good.   But 85 HP is not enough


Sent from my iPhone using Tapatalk

What? The 6.2 had 130 to 160hp, a 350 had 160 to 210. That's at best only a 30 hp difference, which is easily overcome with choice upgrades

Yeah my Chevette can make nearly 85hp lol


Oh also, I own a Chevette :/  I don't mind slow, I suppose.

That all said, you're right about the 350, Kaiser, but I'd be giving up a 454. The numbers don't look great, but a 5mpg increase with less than a grand in the motor ain't so bad, either.

EDIT: I guess I should add that, with the 6.5 Detroit in ideal spec I should be able to make 215hp and 440ft lbs whereas the 454 in it should've been about 230hp/385ft lbs from the factory.

I'm still keeping my eyes open for a 6.5

[roundhouse]

The mpg is good.   But 85 HP is not enough


Sent from my iPhone using Tapatalk

What? The 6.2 had 130 to 160hp, a 350 had 160 to 210. That's at best only a 30 hp difference, which is easily overcome with choice upgrades

Had 130 at best when it was brand new
An old one has about 85

I feel confident in claiming that the one that's in my 82 long bed hasn't made more than about 80-85HP since Reagan was in office

[square81]

I'd give the 454 a little more power because you already have that. Either change the gears to 3.73 and keep the turbo 400 or add a good overdrive 4l80 or get a 5 speed and keep the 4.10s.

[bryanedp9]

I'd give the 454 a little more power because you already have that. Either change the gears to 3.73 and keep the turbo 400 or add a good overdrive 4l80 or get a 5 speed and keep the 4.10s.

Noted, but that's kinda the antithesis to what I'm after. I'm willing to give up a little umph for 5mpg. Seems like regardless of gearing I'd be very lucky to get 15mpg from the 454.

[bryanedp9]

So I've got a line on a '01 Dodge NV4500 2WD. Gotta see what it would take to swap behind the 454. Anybody know?

[big_al273]

you would need to swap out the input shaft and bell housing for the Chevy versions, then you would have to figure out the speedo situation as the NV4500 has no provision for a speedo cable, if you had 4wd then this would be a non-issue as the speedo cable comes from the transfer case. oh and you would have drive shaft modifications and clutch pedal assemblies to find

[bryanedp9]

you would need to swap out the input shaft and bell housing for the Chevy versions, then you would have to figure out the speedo situation as the NV4500 has no provision for a speedo cable, if you had 4wd then this would be a non-issue as the speedo cable comes from the transfer case. oh and you would have drive shaft modifications and clutch pedal assemblies to find

I knew it being a cummins meant the input shaft was too big. Am I just looking for the SM bellhousing and Chevy input shaft and retainer? I figure the Dodge shaft for gas NV's is still an inch too long for a GM bellhousing, right?

Regarding the speedo, I think there's certain Dodge units with a mechanical speedo. This will be a bit of a problem otherwise. Seems pre-97 Dodge stuff had a mechanical speedo in the tail housing. I think I can swap the VSS for that, but it will still need the right gear and cable.

[big_al273]

you would need to swap out the input shaft and bell housing for the Chevy versions, then you would have to figure out the speedo situation as the NV4500 has no provision for a speedo cable, if you had 4wd then this would be a non-issue as the speedo cable comes from the transfer case. oh and you would have drive shaft modifications and clutch pedal assemblies to find

I knew it being a cummins meant the input shaft was too big. Am I just looking for the SM bellhousing and Chevy input shaft and retainer? I figure the Dodge shaft for gas NV's is still an inch too long for a GM bellhousing, right?

Regarding the speedo, I think there's certain Dodge units with a mechanical speedo. This will be a bit of a problem otherwise. Seems pre-97 Dodge stuff had a mechanical speedo in the tail housing. I think I can swap the VSS for that, but it will still need the right gear and cable.

You need the GM NV4500 bell housing and hydraulic clutch, NOT an SM456 bell housing (SM456 bell housings can be modified to work with some NV4500s not all) and a GM NV4500 input shaft. I have never heard of, or or seen a NV4500 with a mechanical speedo cable provision. Personally i would forget the Dodge NV4500 and find a GM NV4500 for what you want to do it would be a whole lot less effort than finding the parts to convert Dodge to GM. I have no choice but too make a hybrid GM/Dodge NV4500 for my Cummins swap, Dodge input and bellhousing GM output and tail housing