Last week, we learned a great deal about why Mellors Elliot Motorsport (MEM) chose the Proton Iriz as its R5 rallying machine. As it turns out, the Iriz platform was exactly what the famed racing team was looking for, and the Iriz R5 proved its mettle in almost every rally championship it’s involved in.

As for the engine, it’s powered by a 4B11T engine plucked from the Mitsubishi Lancer Evolution X, but downsized from a 2.0 litre block to the mandated 1.6 litre capacity. If FIA ruling was the dominant factor with which engine displacement was determined, why did MEM not use Proton’s Campro S4PH 1.6 litre engine as a starting point? Chris broke it down for us.

Now, according to the ex-rally champion, there’s no hard FIA ruling stipulating that an R5 race car should be powered by the same engine as the road-going car. In fact, every other participating R5 rally car doesn’t use their respective factory-fitted engine. What’s important, though, was that the engines must not exceed 1,600 cc, and there should be an FIA-approved air restrictor fitted onto the turbocharger system. This is basically a 32 mm tube which limits air flow (thus levelling the playing field), and it’s used by every other competing car.

In theory, MEM could use the Campro S4PH engine and have it modified to the same output and reliability as the 4B11T engine. That’s because the internal components, such as the pistons, camshaft, cylinder sleeves are all manufactured by MEM using race-grade materials.

As proof of concept, Proton R3 took the Campro S4PH engine and had it rebuilt to race specification, then shoehorned it into the Iriz, Saga, and Suprima S during the course of the Malaysia Championship Series (MCS) and Sepang 1000 km (S1K). That engine made over 200 hp without forced induction, and the piston dimensions were identical to that of the actual production unit. As race engines go, it was pretty reliable, too.

Again, theoretically, MEM could do with the Campro S4PH engine, but why not? Well, it all had to do with the position of the exhaust valves and ports, which in the case of the S4PH unit, are located aft of the block. This would mean that the turbocharger would have to be installed up front, which causes a series of compromises.

First, a more complicated exhaust system would have to be fabricated, and this adds unnecessary length and weight to the entire car. The pipe would also have to bypass the gearbox (which in itself is larger than the factory unit) before reaching the back, and this is where it would run into bulky hardware such as the transfer case.

The complexities don’t end there, because ideally a rally car’s engine has to be tilted by about 25 degrees backwards, a seemingly simple modification that yields better weight distribution and driveshaft alignment. These two factors are way too crucial to overlook, hence the decision to go with Mitsubishi’s all-aluminium 4B11T engine.

With the turbocharger mounted behind the 4B11T engine, MEM could fabricate a simpler exhaust system that’s significantly shorter and lighter than it would be otherwise. As a matter of fact, the heat generated from the turbo can easily be directed rearwards without the hot air coming into contact with the engine, thus creating a more stable engine operating temperature over longer periods of time.

According to Chris, the downsizing necessitated the use of smaller cylinder sleeves, resulting in the strengthening of the smaller pistons. With this reinforced 1.6 litre 4B11T engine, not only is it FIA R5 compliant, it also harks back to the production Iriz which was once available with the 1.6 litre engine.

That sorts it, then. Now, would you like to know whether MEM built the Iriz R5 independently, or if Proton had a hand or two in developing the race car? Stay tuned to find out!

This piece has been translated from the original story written by our BM counterpart.