Originally Posted by JuntiusVT
any knowledge on gas motors for busses? they all seem to be diesel?
Originally Posted by WIbluebird
Probably not the greatest idea in a full size full length but in a shorter full size they're a decent option, especially the 454 GM V8s and the later 8.1 V8 that was offered for a few years until GM stopped becoming a chassis supplier for school bus mfgs around 2003.
*** WARNING – LONG, BUT INFORMATIVE ***
It really depends on the bus in question, which is dependent upon the era it was built. Until recent years, most school buses as we know them were simply bus bodies fitted to incomplete medium-duty truck chassis. And many still are, I think mostly due to budget constraints. The modern flat-nose / rear-engine pushers are likely more expensive.
It also sort of came with the territory that for a long time, there just weren't many feasible diesel options for these buses. For a long time, diesel options were too few and too costly. Prior to the late 80s / early 90s, gas engines were just overall cheaper to buy, maintain and operate. Crowns were about the only buses even offering diesel options, and I suspect that was only because the Detroit 2-stroke was pretty standard in these. Even the flat-nose Blue Birds of that time exclusively used Ford's Super Duty gas V-8 (514 CID if memory serves), only offering a diesel option with the Caterpillar 3208's arrival on the market.
Until then, the 2-stroke was about the only widely available diesel option in sizes suitable for use in typical skoolies, and most school districts simply could not afford the extra cost. This is evident when looking at an older bus from the 70s, as you'll not likely find this vintage with a diesel. They're hard to find even from 80s-vintage buses.
The Caterpillar 3208 was soon rivaled by the debut of the 6.9 Navistar, but for many school districts, diesel engines were still too costly and did not make financial sense just yet. Even though the 9.0 had been available for years, even school buses using International chassis still used gas V8 power more widely until well into the 80s.
So although diesel has been the norm for quite awhile now (and I have a theory on how all this came to pass), gas power is far from unheard of in school buses, and for a long time, it was the standard. In fact, the 290-square-mile county I grew up in had 45 gas buses, all 2+ ton and largely (if not all) 64-passenger.
Most were Ford and GM built before each manufacturer's respective nose-style changes in 1980 and 1973, with a few Dodges of the same vintage and type when I started school in 1982. A family friend at the time was a mechanic at the county bus garage, so I knew more than most did about them.
It was common with Ford back then to offer their gas FT block V8 engines, the 330, 361, 389, and 391, in the incomplete F-chassis used by upfitters such as Blue Bird, Ward, Carpenter, and Thomas. These FT-block engines were later replaced by the 370 and 429 gas V-8s in the 1980-up nose style.
I recall the county buying maybe five new buses from around 1988-1992, and I remember one diesel, an early-90s Ford that likely had the 6.6L New Holland, cheaper than the 5.9, I imagine. The bus I rode my senior year, 1994, was an old familiar gas Chevrolet C60 that couldn't have been any newer than 1972, still in use and little the worse for wear, aside from slightly worn valve seals. That should speak volumes for these old gas models.
However, there were no factory 454s in these. GM's 2+ ton C40-C70 chassis used a truck-specific tall-deck version of their gas big-block V8, in 366 CID and 427 CID, dating back to at least the early 70s, if not the late 60s. It was specifically built for higher-torque / lower-RPM applications.
If memory serves, this engine was still in production as late as 1985, some sources indicate the late 90s (likely dependent on the displacement in question). It was replaced with the 8.1 Vortec, though I'm not sure what year this came about.
Essentially, the Mark IV 454 and tall-deck 366/427 engines were put out of production in favor of the new Gen V model, which had its own version of one of the performance goodies favored by drag racers who had used the Mark IV -- a stroker crankshaft, which gave the Mark IV 496 CID, and the Gen V 502 CID. 8.0L, and 8.1L, respectively.
The 8.2L Detroit was an option when it became available, around 1980. Still, most districts clung to their gas engines due to budget constraints. It just didn't make financial sense to embrace diesel power just yet -- and let's face it, the 8.2 was far from a shining example of the benefits of diesel power. Interestingly, the Detroit 8.2 displaced 500 CID, so I'm not sure why the 502 was dubbed the 8.1 and the 500 CID Detroit was dubbed the 8.2. But I digress.
Smaller buses on GM's P-chassis (later dubbed WorkHorse) were indeed gas 350s and 454s, with a diesel option, mostly 6.2 / 6.5, some may have have even gotten the 5.7 Oldsmodiesel, available prior to 1982 in some GM pickups. Some of the P30 step vans got 4BT Cummins, but they're not that common and I think most of the P-chassis were strictly gas-powered. And most larger ones were as well until the late 80s / early 90s.
454s were not common in even these though, you'll see 454s much more widely used in RVs built on the P-chassis. The WorkHorse / P-chassis buses are identifiable by either a completely custom-built body by the coachwork manufacturer, or a cutaway Express / Savana / G-van cab with a fiberglass or steel bus body. But gas power is still quite common with these as well.
So, you see, it really depends on the era and type of bus you're talking about, because gas power is far from unheard of in a skoolie, even the larger ones.
As to how decades of skoolie gas power gave way to diesel, this is just a theory, but historically, gas engines were just cheaper to buy, maintain and repair. However, that would be soon be changing, as emissions controls were quickly becoming mandatory even on some commercial gas engines by the mid-80s. Before fuel-injection became standard on gas engines, this was achieved partially by using solenoids and servos to adjust fuel mixture and idle speed on electronic-controlled carburetors, which worked fine until they didn't.
I imagine dismantling and rebuilding a $500 carburetor to replace a $5 solenoid didn't make financial sense when servo and solenoid failures were common at 5-10 years old. And fuel-injection would not be available on many large commercial gas engines until well into the 90s. So presumably, rising maintenance and repair costs, the increasing relative and comparative simplicity of a mechanically-injected diesel at the time, and exemption from emission controls are why many school districts began asking for diesel power in the late 80s to early 90s.
Diesels and some larger commercial vehicles were still exempt from emissions requirements back then, so many school districts began asking for diesel power. As an added bonus, diesel fuel was still cheap at the time because (as sources indicate) it was nothing more than a waste by-product of refining other petroleum products that just happened to be useful as diesel fuel.
So, at the time, diesels were beginning to make more sense because they lasted longer, they were more efficient, and the fuel was cheaper. So by the early-to-mid-90s, a lot of school buses were being built with diesel engines, whether on incomplete chassis or purpose-built.
That changed again in the mid-2000s when emissions control became mandatory. And emissions-formulated diesel fuel became mandatory. And unfortunately, emissions controls have proven to be far more of an issue on diesels than they ever were on gasoline engines. Having been an over-the-road tractor-trailer driver for a few years, I've experienced these problems more than most.
I saw a brand-new 2019 Blue Bird Vision on the block at CoPart that had been damaged in transit prior to delivery. 2+ ton chassis, 54-64 passenger, Ford V-10 gas powered. So school districts are obviously starting to review their options. Don't be surprised to see more gasoline-powered buses in the future.
In summary, the same maintenance issues and rising costs of emission control systems that would seemingly appear to have caused the switch from gas power to diesel power in the first place, now appear to be causing a reversal. I think it's safe to say you can expect gas power to make a comeback in the years to come, if DPF and DEF systems continue to prove as troublesome as they have in recent years.
I suspect Ford and GM have seen this coming, and that may be the reason that production of Ford's V-10 continues after publicly 'de-emphasizing' V8s. Likely the reason GM spent the money to upgrade and improve their gas V8s to create the Gen V family. I don't think gas power ever really went anywhere, we've just seen periodic shifts from one to the other due to dollars and sense, and budget constraints.