Vortec 7.4 MPG vs 5.7 on lifted truck

[kylenautique]

Plan on 10 or less, more than likely. Big tires, wind catching lift, basically the world working against you.

My '99 K2500 Suburban on 265/70R17s gets 11.5mpg back and forth to work. Best tank ever was 14mpg @ 68mph. Will run in the low to mid 13s in the low 70mph range. Gets high 11s maybe 12mpg @ 77mph. This is with no cats, BB tune, and better flowing exhaust.

Yes it will be worse than a half ton, but given the choice between a K2500 in a 5.7 or a 7.4...I'll take the big block every day.

Great information. I have a 3 mile commute to work. I mainly drive up to our lake cabin which I climb from 500ft sea level to almost 4000ft, and back down to 1500ft where the lake cabin is, so I mainly drive my truck on winding forest roads. I've never calculated the mileage but I'm sure its not amazing. And, I tow a boat there, so it makes me wonder if the 7.4 because its got more power behind it would get close to the same? I don't struggle for power with the 5.7, but more towing power would be nice sometimes.

 

[kylenautique]

Just spoke with the seller. I found out that the truck has a 4" lift with 33" tires. I'm getting the Vin and RPO codes so I can figure out what gear ration its got. Anyone out there done a Black Bear tune on these 7.4 rigs? Just curious if it really wakes the engine up or are they pretty decent from the factory? I was pretty impressed when I did the tune on my 5.7.

 

[b454rat]

Mine isn't lifted yet, and haven't driven it yet. But the 99 with 180-something and even being a lil tired, still moves. It would lite the tires up at a stand still. Was hoping to get it going before snow falls, but don't think it's gonna happen lol. Swapping to a 5-speed.....

 

[amrush2112]

My 99 K2500 7.4 454 4l80E with 4.10 gears and 33" tires gets about 12.5 on freeway. 10 around town. Bone stock with converters and smog pump. California truck originally. Has 3" lift.

 

[OutlawDrifter]

BB tune is 100% worth it. Driving experience is night and day different, they just drive better when tuned.

 

[BNielsen]

96 K2500, 454/4L80E, on 285s with 3.73 gearing, an 0411 swap and true dual exhaust; after 0411 swap and when I wasn't fighting any issues I got 10-12 running around town and driving on the interstate.

I've gotten anywhere from 8 to almost 14.5 I think, I got that on a long road trip but I think the truck was running really lean; compared to pulling my camper and dealing with a violent misfire got me 10 surprisingly cruising at 50-60 mph

Personally I would expect anything better that 10 or 11 MPG, plan for 8 and hope for higher.

 

[Dravec]

10-11 mpg average in my K3500, same in my Suburban. Both 4L80E, 4.10s

 

[Schurkey]

I'm trying to get a gauge on what to expect MPG wise from a 1999 k2500 crew cab short box with a 7.4, 4l80e, 6"lift and 35" tires vs my current 1998 k1500. I don't know what mods the k2500 has, so let's pretend its got a black bear tune and electric fans...

I have an opportunity to purchase the 1999 k2500, and I just am curious am I going get considerably worst gas MPG, or will they be somewhat close? I drive like a grandpa, and I mainly use my truck as a daily driver, tow rig for a ski boat, family hauler, and running construction materials and firewood to my cabin...

I would tune it with Black Bear and throw electric fans on it to free up as much power as possible and match the shift points to the tires/remove most of TQ management, to help with gas MPG and power.

Great information. I have a 3 mile commute to work. I mainly drive up to our lake cabin which I climb from 500ft sea level to almost 4000ft, and back down to 1500ft where the lake cabin is, so I mainly drive my truck on winding forest roads.

I found out that the truck has a 4" lift with 33" tires.

1. You're wasting time, money, effort, and enthusiasm converting to electric fans. Likely creating problems you wouldn't have with a properly-functioning stock fan system.

2. Removing torque management is a great way to screw-up a transmission.

3. I can't comment on the rest of the "Black Bear Tune".

4. Explain again, if fuel economy is important, what is the reason you're running lifted trucks. Seems to me that you're not in such a serious "off-road" situation that a lift is doing anything positive for you, but adds extra friction and wind-resistance, and makes life harder on the U-joints.

 

[L31MaxExpress]

I wouldn't touch a Black Bear tune with a 100 mile pole.

Electric fans are also a waste.

I think the 454 will perform better than the 350 towing. 8-lug truck has a much beefier driveline, better brakes, etc.

 

[Carlaisle]

I wouldn't touch a Black Bear tune with a 100 mile pole.

Would you mind offering some additional details? He seems to generally have a pretty solid reputation.