Turbocharging the Nissan MR20DD Engine! Part Two, the Internal MR20DD Architecture

One of the oddest features on the cylinder head was a ring-shaped bump on the valve seats.  This probably contributes to tumble into the piston pre-chamber on the intake stroke, but we feel that this probably inhibits flow into the cylinder by quite a bit.  We are probably going to remove this, but are debating this right now.   As you can see the direct injector shoots across the combustion chamber instead of going down into it and maybe this has something to do with it.  The combustion chamber has an efficient shape with a narrow included valve angle and generous tight fitting to the piston quench pads with a low surface-to-volume ratio for good thermal efficiency.

The efficient chamber and high compression ratio is going to contribute to high NOX emissions which is another probable reason why this engine had such a high volume EGR system as discussed in our first article.

Some OEM engineering goodness is present in the valvetrain.  The valve springs are beehive in shape.  This is good because the shape is non-resonant which allows less spring tension for less friction to reduce the possibility of spring surge and valve float. The OEM springs are very low tension – which gives us some concern.  The retainers are very small and made out of thin stamped steel to reduce the weight and are hardened for a long life. We had some concerns for their long-term life, but we have found out that in racing on VQ engines they have a much longer life than any other material! We are going to look at the possibility of using the MR16DDT springs as a replacement for our turbocharged use.

The OEM cams are fine for turbocharged use and our Motec ECU is going to allow us to tune the variable intake and exhaust timing for the best response, fastest spool, and best powerband.  Notice that the base circle of the lobes is narrowed to reduce friction to a minimum.  The cam followers are DLC coated as well to minimize friction!

Now we hope you can have an internal familiarity of the MR20DD engine.  Stay tuned, in the next edition of our series, we will get a good look at the parts we are going to use and how we are going to make our engine more suitable for moderate levels of turbocharged power!

Part one on turbocharging the MR20DD



  1. I wouldnt´t worry too much about the unsupported main caps.
    AMG M139 and BMW B58 have 2-bolt main caps without any girdles and they do just fine with one being the highest specific power 4-cyl ever made and the other being capable of 1000hp with bolt-ons.
    Tiny main bolts ar a drawback though.

    Interestingly the bore/stroke numbers (84/90.1) are also quite similar to the AMG 83/92 and BMW 82/94.6.
    That goes with my understanding that a small cylinder bore with a long stroke almost always lends itself well to turbocharging. In part due to faster burn time.

    Have you looked towards the MR16DDT oil pump assembly? No balance shafts and looks to be a straight swap to the MR20DD block. Also the MR16DDT comes with a girdle, which I’m sure with some machining would fit the MR20DD.

    1. It’s not just the matter of two bolts, it’s the flimseyness of the caps and the register area of the caps. Due to the compressed time we didn’t investigate the Juke gridle but my thinking is it probably helps if it is adaptable. We just didnt have the time to have studs made and then machine and align bore the block.

      1. Mike, you mentioned tight timeframe – is this a SEMA project? Doesn’t make any difference to me one way or the other, just curious.

  2. Very cool to see all this tech in a lowly Sentra. Subaru, why can’t you even do this on your “sport” engines?

  3. I like how the piston pins are already showing slightly concerning wear patterns even at stock power level and not much mileage. I thought the connecting rods would be the real main underbuilt parts of the bottom end, but nope, turns out the whole bottom end is underbuilt. Oh, Nissan.

Leave a Reply

Your email address will not be published. Required fields are marked *