Just an observation about something. I work for a company that builds UPS trucks. They are powered by regular old 6L GM engines but they are mated to a HD Allison Trans. I'm guessing similar to what the Duramax trucks get. It isn't a terribly HD engine.
To help meet the GVWR the intake tubing is nearly 4" in diameter. The air box is truly huge and at least double what I've ever seen in a normal pickup application including diesels.
The exhaust is huge as well. Especially considering a non turbo gasoline application. I'd guess the exhaust at 3.5"



As for the 460.....I don't have real world experience yet but have been reading a bunch. Opening up the exhaust and intake should help. Don't expect huge gains though.
One of the sites I was reading a guy gained 100rwhp and 2mpg with an engine package a guy put together for him. In two different vans. One a 4x4 the other a delivery van. I found his site looking for max effort iron head 460 heads.
Sounds like 700+dyno proven HP is possible with more common iron castings.....Even more with SCJ heads. (that's the direction of interest I'm going with my 460 build.....800hp SCJ head 545 stroker)

I believe the HP numbers are at the crank, not the wheels. Also as I said, I know for a fact it is legit because i did it myself and went from 8mpg to 14.5 mixed town/hwy and a considerable increase in hp/tq. I didn't dyno it but definitely a large increase.

If I had a EFI 460, some money, and wanted more out of it without opening it up I'd put some L&L headers on it, big exhaust, a whipple/screw type supercharger, and cowl induction.

I'd think that would net a rather good HP increase and maybe a little better MPG given the better/cooler flow and that the whipple has a bypass to reduce drag.

I wouldn't say nothing will increase MPG, but very little can be done with the engine without a rebuild to increase MPG. Synthetics, ignition upgrades, higher temp thermostat, new injectors, and cowl intake is about it, small gains but gains. But some can be done to the truck, again synthetics, the right tires, but most of all aero mods. Air damn, under pan, tonneau cover, lower front end, etc.

That is funny, because I have everything they had done BEFORE my supercharger, but I had better gears(3.55) and a factory OD trans and the best I could ever get on the highway was 13. So like I said, BS

Brad, weren't they working with a Bricknose with a C6? If they were I can see all those improvements giving some major help, especially with the first generation efi heads, although I dont know about those numbers they post.

What kind of HP/Torque increase did your Vortec Charger give you for that 460? I'm guessing at the expense of 4-5mpg

Brick nose with No OD C6 and NO lock up T/C which is HUGE

I have a .76 OD and it is 100% "lock up" since it is a stick. You can't get much better than that.

I just came back from Carlisle and got 11.5mpg 90% high-way 10% RACING around town
Before the S/C it would get 13mpg as a high with 100% highway

How much HP/Torque do you think the super added?

Right from Vortech.....
7.5L: Increase HP from 230 to 311 and torque from 385 lb./ft. to 450 lb./ft.

Damn. Ported heads and a nice exhaust and thats a pulling animal

Yeah, heads are on the list and the full header back exhaust is already done