Has anyone changed cam or done other modifications to increase low rpm torque or mpg on GM 7.4s, driving my 98 dually for over 20 years, only use it when camping and towing the drag car, at 137,000 miles it uses less that a quart of oil per 1000 while hauling 3,700-pound camper and sometimes also towing 6000-pound car/trailer. The sweet spot towing is at 62 mph at about 2100 rpm. About 400 miles ago I replaced the OEM injectors with the new Bosch 4-hole injectors, this mod improved fuel milage about 1/2 mpg.
This is apples to oranges. I had a 78 crewcab 3/4 ton that I pulled my race car with for 1 season. 454/ auto. I had a friend who owed me some money install a Comp HE260 cam and a standard 4 barrel intake with a 780 Holley. The original was a drop down intake with a q-jet. The original setup made 4 mpg and had no power. The new setup had much more power and after re-jetting gained almost 2 mpg. My truck would have been better than 2500 rpm at road speed. Your Vortec is night and day improved over the old engines so improving might be really difficult. ?????
I'm curious what your MPG numbers actually are? Both loaded/unloaded. I have flirted with finding a low mile '96-'99 454 truck. I hardly ever need a truck, so mileage isn't as big an issue to me as the $110,000 these idiots want for a new one....
Empty on a road trip 12 mpg With the camper "4000 pounds loaded" gets 8-9 mpg, wind sensitive Adding trailer and car another 6000-7000 pounds 7-8 mpg This is with some exhaust improvements, after the stock 2 3/4" cats stepped up to 3" exhaust pipes, into a 3" dynomax muffler and out the back with 3" tailpipes
I gave up on towing with big blocks...thanks for reminding me why. With the newer 1/2 ton trucks with 5.3 engines usually get mid teens towing a 6000 lb car/trailer, and low teens with pulling the Airstream. ymmv, of course. And the best bang/buck was the 2006 Tahoe that I paid $6k for with 155k miles on it, sold it a few years later for $5k with 200k miles. It pulled the trailers reasonably well. I'm thinking that I really should have ordered the 2022 tahoe with the diesel option...but they were kind of hard to get at the time.
1990 left Minnesota heading to Columbus Ohio with a 1976 Chevy 4 door dually 454/AT pulling a 26' enclosed trailer with a 1969 Plymouth Roadrunner drag car inside plus tools and spares. 90+ temp. 7 mpg with a/c off. 4 mpg with a/c on. Miserable expensive trip and the last Chevrolet tow rig. Been Dodge or Ford diesels ever since.
This all makes me feel better about my 75 Lincoln MKIV tow rig with the 460 and C6. I can get 8 or 9 pulling a car on our trailer.
Yup, just no graceful way to pull tall trailers and campers, plus always seems to be pulling against the wind. My buddy's 96 Dodge diesel pulling a similar camper/trailer set-up down to Indy got 14 mpg. I really like this truck and don't want to buy a new one for over $100,000, its old like me and I've been able to learn most repairs/maintenance, plus make improvements along the way. Never driven it in Wisconsin winters so that also makes it easier to repair Planning for when it is time to rebuild, stroke it to 496 for some more low speed torque, wondering if anyone here has done this already and what was the results.
The vortec 8.1 is pretty common around here for irrigation use. That has cathedral port heads. They seem to be a better engine than the earlier versions. Especial in oil leakage because of o ring usage. I don't think you will get better mileage than what you have now.
Look into having ECU's Reprogramming,, All BBC I have had auto's in 3500 crew 4 +4 , MPG Was 8 to 12 ish with or with out Loaded pulling 24 -30 ish box or so trailer , 1974 -1998 . My 86 stand cab roll back 9 -11 mpg , My 92 std cab 3500 10 mpg . Had a Spec order Hd 99 towtruck with 498 was like 10 , My best was a 74 crew , Played witch carbs, one carb 13 mpg No power , Another carb size plenty of power 9 mpg . I used a Tahoe 5.7 loaded with box trailer about 15 mpg with 26 box . I know others with diesels mpg about same as Gas , Problem with new Diesel & gas Issues with all electronics ,all crap since around 94 ish Ecu controls speedo, BCM ,Ac , ect , Some No issues until 300 - 400 thou , some @ 130 thou . I rather have old mechanical D , Another thing here , the actual gas prices are not that Expensive In Va Most all the local Gov / state gov have added a extra $1.00 each gallon .. This seems to started around 2007 . Growing up Diesel was always .005 - .010 scents + or - of gas . In 2000 both average $1.00 gal . My under standing the reason Diesel is so expensive is because When Formula change on How gas made change the way diesel is made causing it to be more expensive Including Kerosene, Heat , & Jet
Just because this is the HAMB, I understand forced induction helps in these matters quite a bit..... We ran a fleet of 454 powered Duallies at a past job I worked. They were often tasked with pulling 35 ft sled deck trailers around the country. Often, you only needed one hand to calculate the mileage when pulling loaded.
I have a 98 Dually 454 that I pretty much only use to tow my 24 foot enclosed or skid steers. It was a daily driver until gas prices went up and gets about 10 MPG best I recall.. I have a 2007 Suburban 1500 with 4x4 5.3 with an override for the 4 cylinder cutout that I use with my open car trailer. The 2007 gets about 14 MPG loaded at interstate speeds.
About 15 years ago I had a '93 Suburban K2500 with the 454 and 4L80. This was a 4x4 and had 33" tires. I used this to haul my 20' Challenger car hauler trailer. I noticed the transmission was hunting for the converter to lockup when in OD, and it had soft 2-3 shifts. I did a transmission flush, filter, new fluid, and installed a B&M Shift Plus to recalibrate the shifts when towing, flip it back to stock when not towing. I installed a larger transmission cooler with a dedicated electric fan, as well as a transmission fluid temperature gauge. That fixed the hunting issue and firmed up the shifts and made me more confident when towing. Later, I installed headers and a 3" single exhaust that was designed for the similar year diesel trucks because it was cheap and it was just as quiet as the stock system. I had to do some fabrication to modify it to work, but it was worth it. I added the '95+ Bosch 4-hole injectors and a Superchip, along with a home made "cold air intake". When bone stock, the rig got 14mpg by itself and about 8-9mpg when towing a standard 3500lb car on my trailer. After all of the upgrades, it got about 15mpg empty and around 9-10mpg towing. The biggest upgrade was the improved shifts. I wasn't really worried about the fuel mileage with it being a heavy big block pig. Compared to my previous truck, a '97 Dodge 3500 Cummins 12-Valve, the Suburban towed just fine, but that Dodge got over 10mpg BETTER than the Suburban both loaded and empty and was a powerhouse. 26mpg empty was my record, and 18 towing wasn't uncommon. I'd like to have another Cummins 12-valve one day. Compared to my current truck, a '17 F150 with the little 2.7 Ecoboost V6 and 4x4, this little Ford will run circles around that ol Suburban, empty and pulling. My current trailer is heavier than my old car hauler and this truck doesn't care. I get about 18-22mpg empty, and 12-15mpg when towing... not great, but not bad for a little engine in a big truck. I do miss that Suburban though, it was a solid rig.
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