Why capacity is the key to real street power

Why capacity is the key to real street power

People often say turbos are the replacement for displacement, but if you have both then you really are on easy street to making a properly fast car. Look at the ease turbo V8s make four-digit power figures, for instance.

This week Marty and MOOG put the EJ25 STI-swapped Levorg up against MCM's original heavy-hitting battlewagon: Supergramps (CLICK HERE). Supergramps represented the best bits from the Subaru catalogue all marmaladed together into the best-looking Subaru wagon*

Watch the whole Gramps and Supergramps builds (23 episodes!) HERE to get a refresher on why SG is one of the best true street daily drivers in Sydney. One of the keys to Supergramp's appeal is the 3.6-litre flat-six and full-frame Garrett turbo at its heart, even though the internals of the EZ36 have been left alone. 

There are plenty of mega-power EJ20 and EJ25 four-cylinder engines, but they have to work much harder to produce that 700, 800 or 900hp. With all other parts the same a larger engine with more cylinders will make more power, and it won't have to be spun as hard as the smaller engine. 

Sure, the EZ36 has its own challenges like con rods with a bent knee that are weaker than a straight rod. However, in an engine that primarily lives on the street and doesn't get taken to the redline every spare moment (right, Marty? RIGHT?) these weaknesses simply don't matter. 

Supergramps is one of the most responsive turbo street cars I've driven in my 20 years as a motoring journalist. This family wagon is legitimately as rapid and responsive as a Porsche 911 Turbo S (one of the fastest real-street production cars I've driven), and any time you twitch your foot near the throttle the 300kW (at the wheels) hits like the EZ has 8L of capacity not 3.6-litres.

What gives this epic performance is capacity. 

The EJ can be set-up to be a 9000rpm screaming track weapon, sure. But engines, no matter the layout or piston count, are just air pumps and bigger engines can pump more air, so they have an advantage over smaller engines when it comes to making power.

Traditionally the big versus small argument pitches little, efficient overhead cam four-cylinders against huge, lumbering pushrod V8s, but when both engines have the same basic technological layout (camshaft location, etc) the large engine will always have the wood over the smaller. 

Where the Supergramps combo falls down is inherent weakness in the standard pistons and con-rods, as the EZ36 was never designed for a boosted application. As replacement forged parts aren't available this limits the amount of boost and timing Marty can put into his big-block Subaru.

So, in an all-out maximum-effort combo, a slightly smaller capacity engine that can use better designed forged pistons and con rods capable of handling serious boost and lots of ignition timing will make far more peak power without sacrificing a lot of low-end power, as with a 500kW EZ six compared to a 500kW EJ four-cylinder.


*The fourth-generation Liberty wagon is the best looking wagon Subaru has ever made and anyone who disagrees can hand-deliver their sternly worded letter of complaint to 123 You're Wrong Street, Wrongsville. 

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