Many large gasoline powered motorhomes are fitted with a Chevrolet 454 "big block" V-8 engine. You will find them on many older Class A's based on the Chevrolet P-30 chassis and on the mor recent Workhorse Chassis. They are generally quite powerful and reliable, but not particularly stingy when it comes to fuel economy. I've owned several 454 powered Class As, ranging from 28' to 35' and they all pretty much got about 6-7 mpg -- up hill, down hill, head wind, tail wind, towing a trailer, driving solo, sitting in a parking lot! A popular saying is that a 454 can pass anything but a gas station. I like the power of the big block engine in a motorhome, especially when towing my enclosed motorcycle trailer. I have tried motorhomes and pickups with the smaller 350 engine and found fuel economy was often even worse (especially when towing), while lacking the pulling power of the 454. By the way, the newer fuel-injetected Vortec engines are quite a bit more fuel efficient than the older carburated models. I got 16 mpg on my 4WD pickup on a 20 hour winter trip even driving in 4WD through the snow about half the time!
Over the years the 454s have developed a reputation for a few specific issues you may want to watch for if your RV is thus equipped. For starters, they tend to generate a lot of heat. The typical solution is to improve the exhaust system, replacing the stock manifolds with headers, enlarging the exhaust pipes, and installing free flow mufflers. I've seen the stock manifolds on more than one motorhome glowing cherry red after climbing a steep hill. That kind of heating contributes to warped manifolds causing noisy and dangerous exhaust leaks. Upgrading the exhaust system will have other benefits beyond getting rid of heat. A more open exhaust reduces back pressure and lets the engine "breath" better. I experienced a very dramatic demonstration of the affects of a restricted exhaust system when I blew out the "donut" gasket between the manifold and the exhaust down pipe on one of my 454s. I was climbing a gentle hill at the time and the motorhome jumped forward like it had been kicked in the butt when that gasket blew out. A better exhaust is one of the key features of the famous "Banks Powerpack". Another major component of the Banks upgrade is an improved air input system. Together these two changes typically deliver both improved performance and better gas mileage, which is a pretty good deal since most performance modifications improve power at the cost of fuel economy or fuel economy at the cost of power.
That heat also translates into well known starter problems. The starter is necessarily tucked in right under the right exhaust manifold where it is exposed to very high temperatures. The most common symptom is hard starting when the engine is hot. The starter binds up inside and can't overcome the internal resistance with enough force to turn the engine over. Over time, the problem further damages the starter so it doesn't work well anytime. After market high performance and geared starters are available and are said to help mitigate common 454 starter problems. Another common heat related problem is melting of wiring on the starter. You may also be able to install a heat shield to keep some of the heat from the exhaust manifold from impacting the starter directly. There are at least two kinds of heat shields. One is a metal plate that helps reflect heat from the manifolds away from the starter. Another is foil wrapped, insulated blanket that wraps around the starter.
There is another problem that is often mistaken for a starter problem. The symptoms are much the same. The starter will turn over once or twice and then stall. This is often due to a faulty ground strap between the engine and the vehicle frame instead of a dead battery or worn out starter. Over time the connection between the ground strap terminal and the frame can become rusted, weakened by flexing or vibration, or corroded so it doesn't make a good connection. If you experience starting problems that would be one of the first things to check. Many times it can be corrected simply by cleaning the terminal and the spot where it attaches to the frame. Or you may want to replace the entire ground strap, especially if it is small or flimsy to start with. And old fashioned braided steel battery ground strap about an inch wide is a good choice if you have to upgrade. I've even heard of at least one RVer who added a second ground strap on the right side of the engine. Perhaps he has a "Valley Girl" mentality ("For sure, for sure."). A second strap shouldn't be necessary, but it certainly won't hurt.
You may find folks who recommend an oversize oil filter to increase oil capacity. They will often claim it will even help dissipate engine heat, especially if the filter is equipped with cooling fins. I tried the oversize filters on a couple of my rigs and can't say that I noticed any perceptible difference. However, having nearly an extra quart of oil in the system certainly won't hurt anything (except a small pain in your wallet for an extra quart at each oil change and the extra cost of the oversized filter). The extra filter area may also be more efficient at removing contaminates. It could reduce contamination and prevent unnecessary wear. Anything that helps keep the oil cleaner longer is a good thing. The impact of these factors is difficult to measure. The oversize oil filter is usually available as a direct replacement for the regular spin-on filter, but will be a lot taller. The consensus I found in my most recent research is that over sized oil filters probably aren't worth the extra cost, but if it gives you peace of mind, it certainly won't hurt anything. I put it in the "good to have", not the "must have" category.
On the subject of filters, there is another filter worth thinking about: the air filter. First of all, you always want to keep your air filter clean. A clogged air filter will significantly reduce mileage and performance. I like to use a K&N re-ususable air filter. They generally allow greater air flow than standard paper elements and can be cleaned and reused over and over. They are a bit pricey to buy, but since they don't have to be replaced frequently, they pay for themselves over a few change intervals. The improved air flow gives better power and better fuel economy. Regular cleaning consists mostly of knocking off loose dirt; scheduled in depth cleaning calls for washing the filter in an approved solvent and re-oiling it with K&N filter oil.
Most 454s are equipped with fan clutches that engage and disengage the fan depending on the temperature. You can usually hear when the fan kicks in or off from inside the coach. The sound can be quite dramatic. Many drivers mistake it for downshifting when the fan kicks in. If the fan is always engaged or never engages, the clutch may be faulty. The purpose of the clutch is to engage the fan when it is needed for cooling. If it is on when it isn't need, it puts some additional drag on the engine, which could have a slight affect on fuel economy and performance, and it may prevent the engine from reaching proper operating temperature by over cooling the radiator. If it never engages, the fan will never operate, resulting in overheating.
Speaking of radiators, I've seen some motorhomes equipped with what I would consider to be undersized radiators. I'm not talking about the square inches of surface or height and width, I'm talking about the number of rows of cores inside. The more rows, the better it will cool. If you have consistent overheating problems you should have the radiator checked. First of all, there can be internal deposits that restrict flow and significantly reduce cooling capacity. This can be tested with an optical sensing thermometer. If there are places the radiator that are hotter than in other places, there is something restricting the flow, most likely some kind of internal blockage. Secondly, you might have a radiator with only a few rows of tubes in the core. If boiling out and rodding out the radiator to get rid of deposits doesn't solve your problem, check with your radiator shop about upgrading to a heavier duty radiator with more core tubes. Unless the extra thickness pushes the radiator back into the fan or interferes with something out front, a heavier duty radiator should bolt right in where the original was without any modifications required. Of course the heavy duty radiator will be more expensive than an OEM replacement, but the improved performance is well worth it. I once had a radiator "rodded out" and it still didn't perform well. When I finally had it replaced I found the previous mechanic had only "rodded out" the area he could reach under the filler cap instead of removing the tank and rodding out the entire radiator.
I have personally owned several motorhomes and pickups powered by 454s. I have experience some of the manifold and starter problems described above but I have always appreciated the raw power they deliver. I've heard it said a 454 can pass anything but a gas station. Newer fuel injected and computer controlled engines deliver far better mileage than their older carbureted predecessors. I have a Chevrolet K3500 with the Vortec 454 that delivered about 16 mpg on a round trip from Salt Lake City to Denver Colorado one winter when we were in 4wd much of the way! My motorhomes typically got around 6-7 mpg. I now have over 300,000 miles on that K3500 and, although compression has been dropping, it is still running strong.
Big blocks rock!