I've been having a hard time deciding where to go with a motor build. My current motor runs great for street duty and has survived countless dyno pulls and runs down the drag strip and 50,000 miles under pressure, but...... you always want more.

The QR is a good motor, but design "features" limit potential w/o going broke either in the wallet or the motor. It has the lowest rod to stroke ratio os any production motor ever as far as I know. Piston speeds, rod angle, and side loading, all work together to keep the motor fairly RPM limited. Nissan redesigned the half counterweight crank and made a 8- counter weight version, been there done that (not on my car), pretty happy with the results, but it still thrashes around pretty good at high RPMs.

So the SR20DE and the QR share the same bore spacing and main journal size, so the 86mm stroke crank will drop into the QR block where the 100mm stroke crank used to sit. The factory QR rod is 143.03mm long and the pistons have a 32mm compression height. W/ and SR20 crank in the block there is a 14mm reduction in stroke, half of 14mm is 7mm, 143+7=150mm. That's the rod length the motor would need to keep the 32mm compression height.

The SR20 has a 48mm rod journal, I'll tie that in in a minute, you'll like where it goes. So if I were to spec out a custom rod it would be a c to c of 150mm, a wrist pin of 20mm, a big end diameter of 2.008mm, and big end and pin end widths of  22.81mm, and that would let me use a QR piston, or spec a custom piston based on QR deminsioins. I allways poke around what's available first to see if there is something else I can use. I came up with options besides customs: a Mitsu 4G63 rod is 150mm c to c, runs on a 45mm journal, BE width of 28.32mm or 26.37mm depending on 1g or 2g application, and pin diameters of 21mm or 22mm.

It depends on how much I can cut down the big end width and/or how much width I can add to the rod journal on the crank as to wether or not it'll work by cutting the journal on the crank from 48mm down to 45mm. Seems like a lot of machine work and that custom rods would be the better bet. BUT, there are 147mm 4g63 rod for stroker motors. But then the rod would be too short..... right? Except that the length the rod is missing is the same as the difference in the diameter of the crank journal and the journal the rod is sized for. To get the 3mm back in rod length and cut the crank journal down to fit the rod big end diameter you could kill 2 birds with 1 stone and offset grind the crank 3mm . That's really 3 birds because the stroke would change from 86mm to 92mm, sweet, destroked and stroked at the same time. One route would get a 1.7:1 rod/stroke ratio, the other would get a 1.58:1 r/s ratio.

I'm going to be having some long talks with my machinist coming up soon. Chances are it's not going to work w/o getting custom rods at a minium, but I'm really digging the idea of a 92mm stroke. Widening the journals and off set grinding will require a little welding because of the way the filet radius is cut into the crank, and cutting 4-5mm width out of the big end of the rod is probably going to pose some problems with bearing width, or require new tang slots to run different bearings. The pin ends would need to be re-bushed to take a 20mm pin also.

I figure I'd kick the idea around here to see what input you guys might have.

Posted By Big J on 10-09-2009 01:11 PM
It looks like Eagle makes a rod that will be much easier to fit than the EVO rods. BE width 23.75, c to c 148.894, 18mm pin, 1.771 journal way closer. That'd put it at an 88.2mm stroke. They also make a 151.5mm rod with the same specs but a 21mm pin. That'd be a 83mm stroke, just over 2 liters displacement.

There's no real quench area in the head, so I could play with a negative deck height and and use the longer rod, not lose stroke and get away with a factory piston. The Frontier piston has a built in quench or squish area and a thicker ring land, but I don't want to start playing with trying to get that clerence right, although the benifits might be worth it.

I'm going to keep the intake manifold simple this go around..... modified B16 manifold adapter and a plenum bolted to it............ way easy to replicate

http://www.rossmachineracing.com/plenumextrusions.html



or

total drag race manifold

I figured I could update this now because the custom bits are done. Rods took a little longer than expected. Pistons were done months ago because I get special service from JE

86mm SR20 crank next to 100mm stroke QR25 crankshaft


 

SR20 crankshaft in QR25 block. Thrust area needs to be widened up, or thrust washers narrowed, or custom thrust washers. Block (or crankshaft) needs a touch a clearnce work due to forging line on crank causing some rubbing. Snout diameter needs to be reduced to accept timing gears, and the register is 8 bolt vs 6 bolt. JWT has a flywheel for this application.

Nice.... can't wait to see this thing come together!