7.4 info request

[1-8-4-3-6-5-7-2]

Hey guys, I've never had a BBC motor before and don't know much about them. I'm looking at getting a dually truck to pull our 30' camper and most of them have the 7.4 in them. Is it still a reliable motor as it nears 200,000 miles? What is the typical MPG I should expect?

I read the specs and it's real close in HP and torque to the 6.8 V10 in our Excursion which hauls the camper nicely, so I know the 7.4 should have plenty of grunt. It would really be nice to have a truck to haul the camper though!

 

[454cid]

Hey guys, I've never had a BBC motor before and don't know much about them. I'm looking at getting a dually truck to pull our 30' camper and most of them have the 7.4 in them. Is it still a reliable motor as it nears 200,000 miles? What is the typical MPG I should expect?

I have over 280K miles on mine, but I have never worked it hard. I used to get 12.6mpg unloaded on the highway regulary. I haven't checked the mileage in forever since I stopped driving it long distances. It was 10/11 in town. My truck is a SRW 4x4 with 4.10s.

I read the specs and it's real close in HP and torque to the 6.8 V10 in our Excursion which hauls the camper nicely, so I know the 7.4 should have plenty of grunt. It would really be nice to have a truck to haul the camper though!

Well the 454 won't be having timing chain and phaser problems.

 

[Supercharged111]

Won't be shooting plugs out either. Whether this is a good one really depends on the life it lived.

 

[1-8-4-3-6-5-7-2]

I have over 280K miles on mine, but I have never worked it hard. I used to get 12.6mpg unloaded on the highway regulary. I haven't checked the mileage in forever since I stopped driving it long distances. It was 10/11 in town. My truck is a SRW 4x4 with 4.10s.



Well the 454 won't be having timing chain and phaser problems.

Ouch! Luckily I haven't had those problems with mine yet! I like both Chevy and Ford (hate Dodge) but give a slight edge to the Chevy as a better overall truck.

The truck I'm looking at is a 96 crew cab dually 2wd with an auto. I'm not sure on the gear ratio though.

 

[1-8-4-3-6-5-7-2]

Won't be shooting plugs out either. Whether this is a good one really depends on the life it lived.

Ouch again! You guys are killin me! I recently changed plugs on mine and 1 of them, the hardest one to get to, was an oddball so I'm guessing it was a lot older than the rest. The one in front of it was loose! Yeah, I have no idea what they were thinking about (or what were they smoking?) when they dreamt up some of the ideas for the mod motors.

Hopefully the 7.4 in the Chevy I'm looking at is in good shape and I can keep it that way. I'm usually pretty easy on the gas anyway.

 

[vr1967]

On the 96 up, check the injectors. If they haven’t been changed I would check them for leaking. The originals were prone to it. 5-0 Motorsports sells a decent set of replacements.

A tune wakes these engines up, along with freer flowing exhaust.

If you go into the engine, the long block is pretty decent (4 bolt, roller cam, flat top pistons, decent flowing 100cc chamber heads, etc) but the cam is on the mild/lazy end.

 

[Schurkey]

The '96-newer L29 "Vortec" 7.4L is much superior to the "Gen 5" TBI 7.4L. Even so, mileage won't be anything to write home about. 200K miles shouldn't be an immediate problem, but if you're towing long distances, I'd absolutely inspect the timing chain slop by turning the crank while watching the distributor rotor. I'd be looking at HOT IDLE oil pressure using a real, "mechanical" oil pressure gauge. Check for leaks at the engine oil-cooler hoses. Verify that the Power Steering cooler doesn't leak--my PS cooler is nothing more than some formed tubing looped back and forth INSIDE the front of the left frame-rail. It vibrated, wore through, and puked fluid.

Even so, the Vortec L29 heads are NOT that great. Fine for low-rpm use in a pickup. Don't expect to get anywhere at high RPM, they're done at 5K.

Distributors have been a problem. The gear at the bottom wears; the bushings wear. In stock form, the 7.4L distributor is different from the 5.0 and 5.7 engine distributors because the 7.4L uses a "Thermal Washer" above the distributor gear that the others don't have. I'm not sure that aftermarket distributors use the washer, but then they're generally not PLASTIC HOUSINGS, either. Problem with the aftermarket replacements is that they're Chinese knockoffs and have their own design failures.

Overall, a far-better engine than the Ford V-10.

The transmission should be a 4L80E; the overdrive version of the TH400. Not as strong as the Allison in later trucks, but pretty stout.

I'd expect a 10.5" full-float rear axle. Again, pretty stout.

I bought a 7.4L in a '97 K2500 just over a year ago. I haven't put many miles on it, I bought it to plow my driveway with.

 

[454cid]

...my PS cooler is nothing more than some formed tubing looped back and forth INSIDE the front of the left frame-rail. It vibrated, wore through, and puked fluid.

GM also used a real heat exchanger. I'm not sure what determined what a truck, got.... RPO or year. My 99 has a vertically oriented power steering cooler right next to the driver's side headlight.

Distributors have been a problem. The gear at the bottom wears; the bushings wear.

I haven't had any troubles with my distrubutor, but I have gone through a few ICMs right next to it, that are difficult to access.

The transmission should be a 4L80E; the overdrive version of the TH400.

Have you been inside both? A guy I used to work with had a side business rebuilding transmissions, and he told me they're really quite different inside.

 

[b454rat]

I bought a 97 2500HD that had the 454/4l80/4.10s. Bought in late 01 with 57k IIRC. Was 100% stock except had 265/75s on it. I put duals on it, made sound good but doubt did anything for performance. I found out by accident it would light the tires up, at a dead stop just hitting the gas, both tires to boot. I was shocked and impressed lol. When I left the military I had this truck and a 90 GMC RCSB that I built. I towed that on a tow dolly, I also had 2 big blocks in the bed, a set of 1 ton axles, a welder, oxy/acetylene tanks, tools, don't remember what else. The way to NYS from the DC has some decent hills, especially on 81 north of Harrisburg. Ravine I think the town is, tractor trailers with any type of load are always going slow as **** up that hill. I had the cruise set at 70, it pulled the hill and never slowed down. I don't think it even dropped a gear. With the exhaust that was on it, was pretty loud when it was under load. That what the nicest truck I ever owned, would love to find it or another one, but I have yet to see another one like it. Only used the color for 2 years.

 

[454cid]

...Only used the color for 2 years.

Which was what?