Toyota GR Yaris packs a 3-cylinder engine that can…until it can’t
The Toyota Yaris is best described as a frugal subcompact and was hardly a model sought out by enthusiasts unless a fuel-sipping daily was required to keep the enthusiast car progressing. That all changed with the announcement of the GR Yaris which packs a 1618cc three-cylinder pressure-fed by a turbocharger. Enthusiast eyebrows were raised the world over.
“No replacement for displacement” is a saying I haven’t heard in years. I chalk that up to the fact that just about everyone has seen the light on what modern tuning can do with forced induction. Cylinder head design, ignition control, and fueling consistency all add up to the ability to create highly potent little engines once they are no longer pulling their own air into the cylinder. The GR Yaris was tuned to a humbling 257 horsepower and 266 pound-feet of torque straight from the factory, but that doesn’t mean there isn’t room to improve.
Just how hot was that little trio of pistons tuned though? The only way to find out is to tune it to 11 and see what breaks. That’s exactly what Motive Video did, and here’s what failed.
Motive Video went about hotting up the hot hatch immediately upon taking delivery and it eventually spun up to fitting a larger aftermarket turbo kit to replace the factory-fit turbocharger. The final form reached nearly 500 horsepower but it wasn’t long before the coolant became pressurized and it was time to tear open the stock engine.
They expected to find stretched head studs, which is actually fairly common with high-boost situations where cylinder pressures are far beyond what a naturally aspirated engine would typically see. The studs can stretch or deform, even just momentarily, and it allows the cylinder head to lift and combustion pressure to escape into the water jackets of the block. In this case, the heads inspected fine, but the head gasket showed that it failed and was allowing that pressure to leak into the coolant.
Interestingly, the team knew there was coolant pressure beyond the typical amount created by heat but the engine passed a compression and leakdown test with flying colors. It might have been a situation where the engine needed to be under extra pressure to force the issue to appear. Even more intriguing is the design of the head gasket that prevents using a copper ring around each cylinder due to reliefs cut for each of the four valves. For now, the factory head gasket is the best and only option.
For those thinking of the simplest solution to the problem, it’s not that simple. It sounds so easy to “just tighten the head stud a little tighter. Surely that will solve the problem!” Not so fast. As with most modern engine hardware, those head studs are likely torque-to-yield, and thus giving them an extra ugga-dugga with the torque wrench will not necessarily result in more clamping force. In fact, it might invite failure to happen even sooner. It seems this engine is going back together soon and we will see if new camshafts with different profiles will help solve the problem by managing cylinder pressure better. Sometimes this aftermarket stuff is truly trial and error.