For those of you who have been around the channel for a while might remember an article we put out in early 2021 that went over the Neutron Honda K24-based V8 engine and I spoke with Craig directly, who is the madman behind the project. While I found that engine very interesting, there haven’t been any custom engines that have caught my interest since then, up until recently when I heard about Synergy and more specifically, the JUN Auto Subaru BRZ from 2015.
This engine is actually very similar in terms of how it’s put together compared to the Neutron Honda-based V8, except this engine isn’t based on a Honda engine, rather it’s based on the Kawasaki ZX12r engine. So, sit back, get your popcorn, and let’s take a deep dive into the Synergy Power 2.4L V8 engine.
Synergy Auto’s Engine Options
Before we start I’d like to clarify that for this specific article, we’re looking at the Kawasaki-based 2.4L V8 engine from Synergy that was used in the JUN Auto Subaru BRZ. Synergy makes other engines and from their website, it looks like they might not be offering this specific engine anymore and may have moved on to the S1000RR, as it’s a superior cylinder as compared to the ZX12r’s cylinder head.
So, the engine itself is actually pretty simple on paper. It uses two ZX12r cylinder heads bolted up to one custom-made CNC machined 6060-T6 billet aluminum block. It’s configured as a 90-degree V8, which normally would take up a massive amount of space, but considering the final displacement is just 2.4L, the engine itself is actually quite small.
Understandably, the crankshaft is custom made, as it has twice as many pistons to deal with as compared to the standard ZX12r crankshaft, and because the standard ZX12r crankshaft is a flatplane crankshaft, that carries over to this engine as well. For those that don’t already know:
The flat-plane crankshaft uses a 180-degree configuration where opposing rod journals are opposite of each other, instead 90-degrees from each other as they would be on a cross-plane crankshaft. When one piston is at the top dead center, its opposing piston is at the bottom dead center. This design usually results in a lighter rotating assembly, as less counterweight is needed to balance the crankshaft.
That takes up the rotating assembly where we have forged connecting rods and forged pistons. Everything is held together with ARP bolts and keeping everything well lubricated is a 5-stage dry pump system with a separate oil tank. And it’s all topped off with eight individual throttle bodies.
That all equals out to 367hp at 10,600RPM, 200lb-ft of torque at 8000RPM, with the redline all the way up at 11,600RPM. As a company, Synergy does a lot of things, from engine design and development, simulation, engine testing, parts prototyping, and a lot more. Sure, they’re not a massive powerhouse of a company, but they’re incredibly smart and good at what they do.
Why Does This Engine Exist?
The engines that they develop are pretty much all designed for motorsports. They’re not a Toyota or a Honda focused on designing and building cheap engines that last an incredibly long time. Synergy’s focus is really on lightweight engines that produce a ton of power, and when I say their engines are lightweight, I really mean it.
In the JUN BRZ that features the ZX12r-based engine, that engine swap ultimately saved 66lbs as compared to the FA20, on top of improving the center of gravity even further. So not only is it lighter than the FA20, but it also produces nearly twice the power, all without the need for forced induction.
The ZX12r-based engine was initially developed for midget car speedway racing in New Zealand where Synergy is based, but they always wanted to drop it into a streetcar, because you know, why not? And that’s actually where the JUN Auto BRZ comes into play, as Synergy actually developed a full package specifically for that platform, although it’s incredibly expensive at around $70,000. But to be fair, that’s not that bad for a custom engine that bolts right up to your stock transmission and isn’t hard to get to work with all your factory electronics.
One Head Backward
What I find very interesting with this engine is the fact that it uses two ZX12r cylinders head, but they’re not modified for reverse flow. What I mean by this is that if Synergy put both the cylinder heads facing forward with the cam gear up front, one head would have the exhaust in the V of the engine and one head wouldn’t.
To get around this, they actually mount one of the heads backward, at least as far as I can tell with the ZX12r engine. Maybe they do it differently with the S1000RR-based engines. The whole reason for doing this is to eliminate the need for proprietary cylinder heads, which makes the engine cheaper to manufacture and allows the end-user to buy OEM parts.
This is actually the same thing Craig from Neutron engines is doing with his Honda based V8 engine and he’s doing it for the exact same reasons, which eliminating as many custom parts as possible to reduce the overall cost of the engine and make it easier for the end-user to source parts if needed.
For most of this article, we were looking at the JUN Auto car, but I’d also like to highlight that there are other BRZs with Synergy engines, and some of them are even more powerful.
Of course, a high revving, low-displacement, flatplane crank V8 does have some drawbacks, most notably a lack of low-end power. You have to remember that horsepower is just a function of torque X rpm. So, if your engine revs super high, you can make more peak power, but you’ll still be missing power on the low-end.
For a track car, this isn’t as much of an issue because the car stays at pretty high RPMs while on track, but for a street car it can be a little annoying, as you’ll have to downshift any time you want to quickly accelerate, especially compared to newer turbocharged engines which have insane amounts of low-end torque.
Overall though, I think this Synergy engine is incredibly interesting and very cool. It’s a little specific in the sense that it’s super expensive and not exactly ideal for a street car, but it’s crazy what a small V8 can do when paired with motorcycle engine technology and design.