One howls and buzzes, and the other snorts and hammers.

In both cases, you make them sing their song by way of a deliciously mechanical manual gearbox.

These truly are two of the most exciting powertrains I've experienced in the past 12 months, and one started life in a Jaguar S-Type, the other in a Mazda 6 from a few generations back.

That probably says a lot about the dearth of interesting engines and three-pedal gearboxes in mainstream new cars, but let's not dwell on that.

Where the mainstream doesn't provide, niche operators step in to fill the void, which means there's no shortage of companies that do fun things with old cars.

In the very billionaire-friendly world of 2026, there is plenty of attention for million-pound Singer Porsches and Eagle E-Types, but you don't need to spend as much as that.

Representing the more democratic end of the professional restomod scene are Rocketeer and Frontline.

For the past few years, Rocketeer has specialised in V6 engine conversions for Mazda MX-5s.

Although the company now does a lot more than just put engines in cars, the swap kits and basic conversions are where it started and the DIY kits are still a big part of the business.

Rocketeer's 'turnkey' demonstrator keeps things sensible with a few supporting upgrades - MeisterR coilover suspension, an interior retrim, underbody strengthening and one or two other things.

A similar build would cost you around £44,000 plus a good donor car, which can be either a first-gen or second-gen MX-5.

The whole thing seems meant to be. As founder Bruce Southey explains, he didn't choose the MX-5 for its cute pop-up headlights but because it's already a fantastic platform. It was just missing a compelling engine.

Cue the Ford 3.0-litre V6 from the late 1990s and early 2000s. Porsche allegedly had some involvement in it and Cosworth did the heads for the longitudinal application in Jaguars.

It's also oversquare, has a forged crankshaft and, because the block is aluminium, this V6 weighs no more than the original Mazda four-pot. And yet it went into moochy Jags, smothered with emissions equipment and long gear ratios. When we tested the S-Type in 1999, we found it slightly unwilling.

Originally it put out 240bhp, but Rocketeer sends its engines off to be taken apart, balanced and blueprinted.

Off comes the restrictive intake and exhaust, in favour of freer-flowing (and more exotic-looking) pipework, for 280bhp.

By way of a custom adaptor plate that Rocketeer makes, it is mated to the MX-5's standard five-speed gearbox, so there's no need to source a rare manual S-Type donor car.

Any early 2000s S-Type, XF or XJ will do. Rocketeer is currently building a car destined for Hawaii. The demand from warm places means it has developed its own air-con system.

Southey says the Mazda 'box copes well with more than twice the power and torque because a six is smoother than a four. I suspect Mazda's durability engineers might disagree, but if you're not drag racing it or doing moon miles, it probably is fine.

In the light MX-5, the result is memorable. Of course it's quick, but that's not what we care about here. It sounds incredible as it fizzes towards its 7000rpm redline.

With the carbon airbox and naughty exhaust, there's something of the E46-generation BMW M3 CSL to its metallic howl. It's not quite as ferocious, but the fact that I'm making the comparison at all says a lot.

In fact, the Rocketeer has one over the CSL by having a manual gearbox. The electric throttle response makes gratuitous downshifts an absolute joy.

The shift quality itself is fine, with good weighting and feedback, but a little bit of slop and a slightly too short lever. I'm sure a kit exists to tighten it up, should you want to.

There's something incredibly freeing about a big yet revvy engine in a light car: it suddenly seems as if other cars' tyres were filled with cement.

That was Southey's philosophy: "Four cylinders are great when they're at 12,000rpm in a sports bike. Anywhere else they don't do it for me. So a screaming V6 was the answer.".

Typically I'd agree, but there's something else here to make a very strong case for the fruity four-cylinder. Although Frontline has done an MGB with a V8, its more usual build - and its demonstrator car - has a 2.5-litre four.

Ironically, given the present company, it's a Mazda engine. In the UK, it was briefly found in the Mazda 6 but was mostly used in various very dull American-market Fords.

To add life to this rather ordinary engine, Frontline takes it apart and treats it to forged and lightened internals. The engine bay doesn't look quite as impressive as the Rocketeer's, with the exception of the Jenvey throttle bodies.

They look like Weber carburettors but are actually a fuel injection system. They sound like Webers as well. In fact, this MGB is all layered gurgly noises. You can just hear the air being violently ripped apart, before being ingested and combusted.

It's harsh, but in a very exciting way.

Where the gearchange in the Rocketeer is merely good, it is perfection in the Frontline. It uses the six-speed gearbox from the current MX-5 and it's somehow even better here than it is in the Mazda.

The long lever does nothing to dampen the satisfyingly mechanical action, which has no sense of friction whatsoever. It's just a neat click-click as you flick through the gears.

This isn't a like-for-like comparison, because this particular Frontline is a higher-end specification than this particular Rocketeer.

Frontline has been in the restomod game for a while - probably from before the word restomod was a thing. Its subject of choice is the MGB, though it has recently branched out into the MGA as well.

Like with Rocketeer, you can take it as far - or not as you like. You can order some wheels from its web shop to bolt onto your own car, or you can 'commission' a bespoke car, like its demonstrator, which would cost you around £170,000.

Because MGBs are a few decades older than MX-5s, they tend to need a lot more resto before there's any mod.

As such, Frontline likes to start with a brand-new shell from British Motor Heritage for its full builds. That itself costs about as much as an entire Dacia Sandero but it does give you, in effect, a factory-fresh MGB. The whole body is de-seamed as well.

Open the deliciously clicky door and you can immediately see where the money has gone. The Rocketeer demo is just an MX-5 retrimmed in leather, with an updated instrument cluster and a Nardi steering wheel.

It's nicely done, but the switches, air vents and fundamental shapes were made to a budget in the 1990s and there's only so much you can do to take that to the next level. Rocketeer will try, and it has some high-end projects in build.

Even a standard MGB, particularly a fairly early one like this, with its metal dash and chrome trim, is already a more charming place to be than an MX-5. Cars from the 1960s might crack your skull and take your eye out in a crash, but they'll do it in style.

Frontline then adds in its own bucket seats, which are works of art in their own right, and trims everything in the most sumptuous vintage-looking leather. The boot area looks like an antique drinks cabinet.

This is all Bentley-grade stuff, but done in period-correct style. At first glance, the casual observer might not guess that any of it wasn't original. Look very closely and you might spot that there's a neatly integrated Bluetooth sound system and air conditioning, which lift the usability without killing the retro vibe.

All of it is bespoke, so you can have any colour you like, and you don't have to have the seat harnesses or the roll-cage. Having said that, it is possible that the cage does contribute to the way the Frontline drives.

Unexpectedly, given it's 30 years older than the MX-5 and runs on a live rear axle, this MGB feels like the more modern car to drive.

Although the MX-5 doesn't feel excessively floppy for an old convertible, the MGB GT coupe is clearly the much more rigid car, so while the suspension (by British specialist Nitron) is firmer, it rides with more composure and comfort because every bump is dealt with in a one-and-done movement, whereas there's a bit more shake and shimmy in the Rocketeer.

The Frontline also has more grip. This car's Bridgestone Turanza T005s aren't at all an aggressive tyre but they yield a more safe-and-steady balance than the classic Michelin Pilot Sport 3s on the Rocketeer.

I personally prefer the Rocketeer, which can be deliciously steered on the throttle at very reasonable speeds. Your right foot precisely decides with how much yaw angle you come out of a corner. It's a lot like a Toyota GT86, but with a proper engine.

The Frontline fundamentally has quite a similar balance, but you just have to work a bit harder for it, and the retrofitted electric power steering isn't quite as communicative as the Mazda's original hydraulic system.

Mind you, the Frontline is still an enormous amount of fun. Light weight, small dimensions, rear-drive balance and that raucous engine add up to a pretty beguiling package.

In less than perfect conditions, the additional grip and traction will surely be welcome, and I don't doubt that a more playful demeanour is just some anti-roll bar settings and a set of classic-style tyres away.

This isn't the sort of test where there's a winner. With these sorts of largely bespoke cars, they are what the customer wants them to be. And anyway, both of them are utterly delightful.

They are pure joy to just have around, walk up to, potter around in and, yes, go for a thrash. You get the sort of sights, sounds and smells of yesteryear, but with modern performance and quality.

As new driver's cars get choked with emissions and safety gear, or fall prey to the temptations of excessive power and grip, more of these specialist companies will undoubtedly spring up.

Both cars' driving positions are of their time: quite low and with the steering column and pedals very offset. In either case, you quickly get used to it.

Which gets you thinking, what could be next? If someone's dropping a six-cylinder engine in a Porsche 944, give me a call.

A quick guide to Rocketeer

Rocketeer is based in an unassuming industrial unit in the countryside. It was started by Bruce Southey, an industrial designer who's spent time at Ford, Bristol and Overfinch.

During his time at McLaren, he decided to build his own ideal sports car out of an MX-5 and the Ford/Jaguar V6 engine.

It wasn't intended to be a business until YouTuber Alex Kersten made a video about it and generated significant demand. Today, the company is working on a 400bhp version weighing less than 850kg and a V6 conversion for the NC-generation MX-5.

Who is Frontline?

Frontline came into existence after founder Tim Fenna broke several gearboxes while racing and decided to modify a Toyota gearbox for the job instead.

Three decades later, the team operates from an Abingdon base. Frontline is perhaps still best known for the LE50, an uprated MGB GT produced between 2012 and 2021. Having mastered the MGB, it recently added an MGA to the line-up.