Techtalk/Guide: HR12DDR - DIG-S

Hi Everyone,

since there is not much info on the dig-s engine, i want to have a info/disussion thread about what we know and what we want to know. about the Engine. Maybe some of you found ot something, which will be interessting for others too.

Technical Roundup (source: wikipedia)
The HR12DDR is a 1.2 L supercharged straight-3 engine. It produces 72 kW (97 hp) and 143 N·m (105 ft·lbf).
Some of the pertinent features are:
  • Compression ratio of 13:1 (see article about compression bellow)
  • Continuous Variable Valve Timing Control System (CVTCS)
  • Direct Injection Gasoline (DIG)
  • Miller cycle
  • Supercharged
  • Variable capacity oil pump
  • Hydrogen-free diamond like carbon(DLC) coated valve lifters and piston rings
  • Sodium filled exhaust valves
  • High efficiency
It is fitted to the following vehicles:
Engine Facts
  • A high-compression ratio of 13:1 is quoted; however, it is really the Miller cycle’s expansion ratio that is comparable to a +9:1 compression ratio in a conventional engine.
  • Bore: 78mm
  • Stroke: 83.6mm
  • Displacement: 1198ccm
The MillerCycle


The Supercharger
  • The Supercharger is an Eaton R410 [flow chart]
  • Stock pulley size is: 62mm (diameter)
  • Nissan used an Eaton Roots-type supercharger with twin 4-lobe rotors, with a revolution of 2.4:1 compared to engine revolution.
    Although the supercharger already has low-rotating friction under a non-boosting condition, Nissan adopted the electromagnetic clutch—driven directly by the ECU—for further friction reduction.
    For boost pressure control, the engine uses a bypass valve upstream of the throttle valve.
  • An air-cooled intercooler is downstream of the supercharger.
    Nissan said that this is important to maintain knock quality using Miller cycle on the boost condition.
    It also makes it easy to control the charged air volume along with recirculation under partial boost conditions.
User Facts
  • Fitted a Boost Gauge, before the Magnetic Purge Valve
  • Pressure while driving
  • ~.6bar / 8.7psi vacuum
  • ~.45bar / 6.5psi boost
  • the car`s top-speed is limited to 195km/h (approx: 121mp/h)
  • after fitting my boost gauge, i realised that the boost is falling to ~.2bar at top speed.
Unknown/to find out
  • SC Pulley Calculations/Combinations
  • how to override/exploid the bypass-valve, in order to achieve more boost.
  • ...
Lets get some light into our new Machines :)

Sources/further read:
Just having a nosey through the Thai forums using Google Translate to see if I can gleam any info from there that would be useful for us. Found no DIG-S related stuff yet though :(


yeah tried to registry on the thai forums and got banned because i didnt get the anti spam measurment right haha :D


i know the fb too. they do loads of exterior mods, but actually never saw some engine mods/pics there. anyone knows why they always write 5555 as comments?
i know the fb too. they do loads of exterior mods, but actually never saw some engine mods/pics there. anyone knows why they always write 5555 as comments?

Except the unichips, they didn't made any engine mods... :( maybe more to come later... we'll see...
5 in thai sounds as HA, therefore, 5555=HAHAHAHAHA <=> LOL
For what its worth the dig-s engine is not a true miller cycle engine. The original miller cycle engine design from 70 years ago used an unusual double cranking mechanism to allow the piston to take a shorter compression stroke than expansion stroke. Unfortunately the crank arrangement introduced more inefficiency than was gained from the long expansion stroke. Some time in the 90s Mazda introduced a 3 litre V6 with what they called esoteric valve timing to achieve the miller cycle. Press referred to engine as 5 stroke. The engine was only available as an expensive optional extra on the not so popular Zedos 9. Think they may have called it Millertime? Mazda also quoted the engine as 2.3 l not 3 l measuring the compression stroke only with valves closed. Without variable valve timing the engine needed forced induction at all revs only achievable with a lysholm compressor (think dig-s supercharger is lysholm type) This engine was very good but not a sales success. Move forwards to today and latest prius and yaris hybrid engines are 1.8 and 1.5 engines which run a valve timing based miller cycle. No supercharger is needed as the electric motor attached to the engine replaces the need preventing the engine stalling at low revs. Also we have the dig-s engine and the Fiat twin-air engines which can run miller cycle. In case of the Fiat the engine which has non mechanically actuated inlet valves operates in 5 different modes involving lean burn, miller and stoichiometric - I.e. conventional perfect air fuel ratio. Unfortunately where the Fiat engine on paper is an absolute work of genius - in reality its just not that good needin revved hard to get any power which is never that much and returning about 35mpg. I'm not sure whether the dig-s works like the Mazda constant miller cycle or the Fiat. I believe Nissan system is like the Fiats using constantly variable timing to operate in different modes which should be better. The dig-s is certainly a very refined engine with good mid range power but fuel economy has been a bit of a disappointment.

Sent from BlackBerry 9790 using Tapatalk


updated top speed "issue"

after reaching the speed limiter the boost gauge swings at from about ~.1bar to ~.2bar reducing the speed to maintain its 195km/h.
the fiat twin-air engines are massively clever. Fiat have managed to reduce a huge amount of rotating weight from within the engine.

Fiat decided that instead of using camshafts to open and close the valves, they could use hydraulic actuators instead. the the actuator timing is set by an ECU, reading from a crank position sensor and other sensors (throttle position etc). this cut the best part of 15Kgs from the engine.

sorry to be pedantic, but every engine requires revving for power.

power = torque X angular velocity (revs) in radians.
Sorry to be pedantic, but every engine requires revving for power.

power = torque X angular velocity (revs) in radians.

... think I said HARD revving!

Interesting formula may be relevant to steam engines and some turbines where power is in near linear relation to rpm but when considering forced induction internal combustion engines....well think about it.
PS Fiat engine still has a cam for the exhaust valves.
Given that DIG-S is direct injection only, I am a bit surprised that almost never heard of any case of excessive carbon buildup on intake valves, except this mild one:

Probably a stupid thought from a newbie, but could that be because of Miller Cycle which allows some fuel to slip through intake valves?
Or it is just simply because we don't have many DIG-S engines out there, compared to VW or BMW?
Probably because the people who drive them generally done know/care.

I would expect the injector to only fire once the intake valve is shut otherwise you are putting fuel into the intake and it would become un-measured.

I have considered using sea foam or something in the past, however at 75k, but i'm probably at the point of 'no return'. From new and as a preventative measure maybe, however using it on an older engine maybe asking for trouble if chunks full off which could damage the cylinder walls/valves. At least in our case we dont have a turbo in the way as well but IMHO.
My Note got nearly 50K which seems risky to use Sea Foam. But I am more worry about damaging the catalytic converter.
If the issue ever arise and couldn't be ignored, I might go to a walnut blasting service (if there exist one could deal with our engines) which is safest and most effective I think.