General Motors has produced a lot of incredible engines in its 115 years as a company, but I can bet you’ve never even heard of their craziest and coolest engines!

#1 CERV III Corvette

Alright, getting straight into this, let’s take a look at the Corvette that almost made it to production, the CERV III.

Now this barely qualifies as a secret engine because it was never a production car. That being said, of all the mid-engine Corvette prototypes, the CERV III was arguably the closest one to reaching that full-scale production reality.

What we’re here for, though, is the engine under the hood, which is actually an engine you might already know of. That’s the 32-valve dual overhead cam 5.7L found in the C4 ZR1.

And for those who don’t know, this was an engine designed almost entirely by Lotus after GM had commissioned them to help with designing the ZR1.

Ordinarily, this 5.7L V8 output 385 horsepower, which is already very impressive for a 1990s naturally aspirated engine, but it wasn’t good enough for the CERV III.

GM wanted this mid-engined Corvette design to really be something special, and in order to do that, it needed significantly more power.

To achieve this, GM slapped two GarretT T3 turbos on it to bump the power all the way up to 650hp and 655lb-ft of torque, which ironically is almost the exact same power output of the LT4 in the C7 ZR1 they put together a few decades later.

At this power level, the CERV III ran the 0 to 60 in just 3.9 seconds and could pull upwards of 1.1g on the skidpad, which quite literally meant it had all the performance specs of a true supercar.

Unfortunately, though, the CERV III never made it to production, mostly because the amount of technology and innovation would’ve priced the car around $300 to $400,000, which is about 10x the price of the base Corvette from the same time frame, and about 5x the price of the ZR1.

I know Corvette guys are normally retired and have money, but seriously, no one would pay $400 grand for a Corvette in the 90s. And GM didn’t think so either, so the CERV III ended there.

Still, though, the fact that GM had a 650hp twin-turbo dual-overhead cam V8 engine all the way back then is pretty impressive.

#2 LS V10

Next up on the list, we have something which I can almost promise you’ve never heard of, and that’s a V10 LS. And you might be thinking, how have I never heard of this? And I thought the exact same thing.

I’ve bought and sold LS engines, I’ve built a handful, and yet I’ve still never heard anyone ever say anything about a V10 engine with the Gen III and Gen IV architecture, but it’s very real.

The discovery of this engine happened back in 2016 when a performance shop bought the engine from a supplier who works with GM and had purchased it from GM.

This means that at some point, GM, whether official or not did research and development to create an LS-based V10 engine.

The engine, as shown in the video below, was sold as scrap and spare parts, and when it came to the performance shop that purchased it, it was missing an exhaust manifold, and it had some minor damage but was otherwise complete from the top down.

The block for this engine uses the 4-inch bore, which is shared with several other LS engines, and a 3.7-inch stroke, which is also shared with other LS engines, but with the addition of two cylinders, that brings total displacement up to 465ci or 7.6L.

On the heads, the port configuration is identical to the D-shaped ports of an LS7, but obviously with an extra set of ports for the extra cylinders.

As to why GM was testing a V10 LS, there’s no clear answer, but it was likely as some sort of larger displacement engine for trucks after GM had stopped offering the 8.1L Vortec.

Either way, it’s a very cool engine that just about no one knows about.

#3 427 Mystery Engine

This next engine on the list is an important yet strangely secret part of GM’s history, and that’s the Chevy 427 Mystery engine.

And we’re not talking about the Z11 427 engine, but rather the engine that was produced alongside it in 1963.

While the Z11 was developed for drag racing, the true mystery motor, aka the Chevy 427 Mark II, was intended exclusively for NASCAR.

And on the outside, it looks a lot like the later big-block Mark IV engines. As a matter of fact, a lot of people regard the 427 Mark II engine as effectively a prototype version of the big block.

And yes, they do look physically similar, but just about none of the important parts interchange, so realistically, it’s not a living prototype of the later big block engines but rather its own special engine entirely.

The heads feature pretty large 2.19-inch intake valves with 1.72-inch exhaust valves. The main bearings were also increased in size. Essentially, this engine had all the part changes needed to survive Nascar racing, which is lots of high-RPM usage with minimal downtime in the pits.

When it first hit the track, the Mark II engine was an absolute beast, although it was a rocky start for the cars equipped with this engine, and it was claimed to be around 600hp.

Not only is that a pretty good power output for a naturally aspirated 7.0L engine by today’s standards, but that was also very impressive by early 1960s standards.

That being said, the general consensus seems to peg the true power output around 540hp, which is still very impressive, regardless.

Supposedly GM built anywhere from 16 to 50 of these engines, with very few in circulation now. Most of them are in museums or show cars. So if one pops up for sale, definitely grab it as fast as you can because it’s a very special and very rare racing engine.

#4 Oldsmobile Jet-Fire

Now this next engine I must applaud for its innovation because it is quite literally the world’s first ever turbocharged production car, and that’s the Oldsmobile Jetfire.

And I mean just look at this thing. It’s crazy to see what a 1960s turbo looks like compared to today.

The whole reason behind GM producing this engine under their Oldsmobile brand is that the Americans wanted smaller and more fuel-efficient cars in the very early 1960s.

Sure, muscle cars were awesome, fast, and fun, but they were also expensive on gas.

So rather than developing a smaller car with a smaller engine, Oldsmobile came up with the idea of using a turbocharger as a means of improving fuel mileage while still using a V8.

To do this, they teamed up with Garrett, who, at the time, only produced industrial turbochargers that weren’t meant for cars and had never been used for cars.

Unfortunately, there were two major problems with the whole idea.

For one, the suspension was left unaltered and was woefully equipped to handle any decent amount of power without feeling like it would lose control any second you were driving it, and the car quite literally required a special fuel additive in order for it to run without detonation.

Oldsmobile did this by using a tank filled with what they called “rocket fluid,” which is a mix of methyl alcohol and water. It then sprayed it into the intake stream and worked its magic to keep the engine from exploding.

But unfortunately, a large majority of the owners never kept the rocket fluid tank full, resulting in loads of these cars having massive issues and ultimately turning Americans off the idea of a turbocharged car for quite some time.

Regardless, it’s this engine is very important to automotive history, and being the first turbocharged production engine ever really helped cement GM as an innovative automaker, even back in the 1960s.

#5 Pontiac Pegasus

What if I told you that in the 1970s, Pontiac put together a Firebird with a V12 engine under the hood? And not just any V12 engine, for that matter, a Ferrari V12. Yup, that’s the Pontiac Pegasus, aka the Ferrari Firebird.

The story of the Pegasus starts in 1970 with Chevy designer Jerry Palmer. He’s the madman that wanted to take design elements from the old Ferrari 250 Testa Rossa and implement them on the new Camaro.

But supposedly, the design didn’t look enough like a “Chevy,” so it somehow ended up being a Pontiac.

Regardless, this concept car ended up with a Ferrari-style gauge cluster and interior, as well as a Ferrari-sourced exhaust. And the best part of all? It was powered by Ferrari’s venerable 4.4-liter V12 producing somewhere around 350 horsepower.

Supposedly, the car was tuned by Luigi Chinetti’s North American Racing Team, who were known for endurance racing Ferraris in the U.S., to promote the brand.

Reportedly the Pegasus went through a few transmissions as well, probably because GM just kept a three-speed automatic slushbox of the transmission behind a high-revving V12 engine, which later on GM realized this issue and sourced a five-speed manual transmission from Ferrari and installed it in the Pegasus.

Sure, it’s just a concept car, but the fact that GM spent significant chunks of money to put a Ferrari V12 behind the Firebird is absolutely crazy.

Think about what would’ve happened if that project had bloomed into a working partnership between Ferrari and Pontiac. Maybe Pontiac would still be around today.

#6 V16 Suburban

Earlier in the video, we talked about the V10 LS prototype engine that Chevy had designed and built, although it’s not exactly clear why. But what if I told you they didn’t stop there and in fact, plopped a V16 engine in the front of the GMC Yukon?

Think about that, it’s the length of two V8 engines, and they shoved it into an SUV.

The only reason anyone even knows about this engine is that photos of it ended up leaking, but the real reason behind putting this behemoth of an engine into a Yukon isn’t exactly clear, as a production V16-powered SUV sounds entirely impractical and something that GM likely would never do.

What is known about this V16 Yukon is that it shares the same engine as the 2003 Cadillac Sixteen concept, which was Caddy’s final attempt at bringing back the V16 engine design.

The development of this engine was fully detailed in the summer of 2003, thanks to Hot Rod Magazine. And the best part of all? This massive 13.6L engine is based on GM’s Gen III and Gen IV small-block V8 architecture, but it didn’t reuse any large parts from the LS. Rather, those were custom-made.

Allegedly, the block was completely custom, and on top, the cylinder heads were supposedly one-piece LS6-derived heads, meaning they were LS6 copies but with a lot more cylinders per head.

The rest of the valvetrain and rotating assembly were built with pretty much all top-dollar stuff, including a dry-sump oil system.

Of course, this engine was physically massive, so to even fit it into a Yukon, GM lengthened the nose by quite a bit, and the entire front axle was borrowed from GM’s one-ton trucks.

All of this added up to a hilariously impressive 1000hp and 980lb-ft of torque naturally aspirated.

#7 Four-Rotor Corvette

You and I know the rotary engine design for its use in a handful of Mazda cars, but what if I told you in the 1970s, Chevy designed and built a mid-engined Corvette prototype with a 9.6L four-rotor engine?

This whole car came to be as an evolution of the mid-engined XP-882 prototype car.

Around this time, GM president, Ed Cole, was particularly interested in the Wankel design and pretty easily said “yes” to designing this rotary-powered rocket ship of a Corvette.

And what makes this engine configuration particularly interesting is that it contains two separate two-rotor engines.

This works by using one engine on each side of a shaft that ran back to the transmission. Each engine was offset by 90 degrees to smooth out the vibrations.

The ignition, alternator, and fuel pump were run by a toothed belt, and a standard V-belt was used to run all the accessories.

The combined size of the two engines was 585 cubic inches which come out to roughly 9.6L, and with that massive displacement, power was rather underwhelming at 370 horsepower, although it has been noted by individuals involved with this project that the engine was definitely capable of making upwards of 480 horsepower with a few changes.

Both the Two-Rotor and Four-Rotor Corvettes made a big splash at the 1973 Paris auto show but, unfortunately, got mixed reviews.

Ultimately the project stalled when GM decided to scrap the Wankel project altogether.

Because of this, the four-rotor Corvette prototype never really ran great and was definitely nowhere close to production, but I’d still argue it to be the most interesting Corvette prototype that GM has ever built.