The rod bearings are pretty small in diameter and width for low friction. This isn’t the best for making tons of turbo power, but they are about the same size as the turbocharged MR16DDT. Once again, if time and budget allowed for it, we would go with a custom crank and rod combo in order to run Honda K Series bearings. This would allow us to get more bearing area and to have a wide choice of performance bearings.
The OEM connecting rod is designed for low mass first and strength second, which is fine for the stock application. The rod is very minimalistic in construction with tiny rod bolts. This is one of the lightest OEM rods that we have ever had our hands on. For turbocharging, replacing the rods with something stronger is going to be a must.
For some reason, the OEM rod has a tapered end, probably to save weight, and reduce friction, however, this greatly reduces strength in the most critical part of the rod. It also reduces the bearing area to support the pin. You can see the odd wear pattern developing on the stock piston pin. The pin also exhibited to us, excessive clearance in the pin bore. This would be noisy and contribute to pin and small end busing wear which you can see is starting to happen here. Our new rod is going to have conventional dimensions here for strength and piston pin support under boost and higher rpm.
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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.
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.
Mike, you mentioned tight timeframe – is this a SEMA project? Doesn’t make any difference to me one way or the other, just curious.
stick around and find out!
Will do!
Very cool to see all this tech in a lowly Sentra. Subaru, why can’t you even do this on your “sport” engines?
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.