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Date: Sun, 06 Feb 2000 22:37:13 -0800 From: Bill Dacat <blldacat@san.rr.com> Subject: rods and crankshafts and decisions oh my!Hey everyone,
I had sort of a question for anyone out there that may know. I had been hoarding a bunch of L series bottom end parts for some time now and have suddenly come up with a use for them. My Z18T cracked a ring land, (DON'T try 20 psi of boost on pump gas) Anyway I am at sort of a dilemma. Upon taking measurements of an L20B crank I have had sitting I came to the conclusion that it was NOT an L20B crank at all but rather a 92mm stroke Z22 crank! Cool right? Well, I have mixed feelings about it. I like the longer stroke, sure, who wouldn't? but this crank is not fully counterweighted like my real L20B crank (got one of those too) to make matters even more interesting is this; Z22 crank with L20B rod gives me a 1.586 rod to stroke ratio. Some might say this is too low. I've heard you want to be as close to 1.75 as possible in the rod to stroke dept. But here's my take on it. My original plan was to try to duplicate as close as I could the SR20 internal dimensions (86mm bore 86mm stroke). No problem, L20B block, with a 1mm overbore (86mm) and the L20B crank (86mm stroke) and figure out which rod to use to make the ratio as close as possible to the SR20. I figure this way I'm benefiting from some of Nissans R+D in designing the SR20 without actually running one. So I get ahold of some numbers for the motors that are relevant:
Motor Stroke Rod length Stock rod to stroke Ratio
Sr20Dxx 86mm 136.3mm 1.584
L20B 86mm 146mm 1.697
Z22E 92mm 148.6mm 1.615
L16 73.7mm 133mm 1.804
Option #1
Using the Z22 crank with the L20B rods gives me a rod to stroke ratio of 1.586. Note that this is almost identical to that of the SR20. But is this number actually good? One would think the numbers from nissans best offering in the 4 cyl dept. would be pretty damn good, but you never know. Also there's the nagging in the back of my head about using another non fully counterweighted crank (the Z18T isn't either) I want to have a motor that's happy to go to 7k or even higher and I have doubts about this Z22 crank doing that. Am I way off? is this Z22 crank just fine for higher rpms and I'm just being too picky? Anyone running a Z22 crank want to comment on how your motor acts? Another bonus to going this route is displacement goes to 130.447 Cubic inches/ 2137.643 Cubic Centimeters.Option #2
Using the L20B crank and the Z22E rod gives me a 1.727 rod to stroke ratio. Almost "perfect" if you listen to the honda guys. (you gotta give them a little credit guys, they make some fantastic motors. Check this page out for a neat little write up on the subject.) This and the benefit of a fully counterweighted crank which ought to spin up to 7k + no problem. Displacement ends up at 121.939 CI/ 1998.222 CC'sOption #3
Use L20B crank with L16 rods and custom pistons. This puts my rod to stroke ratio pretty close to the SR20 at 1.546. Displacement also ends up at 121.939 CI/ 1998.222 CC'sI have a set of 86mm forged pistons with the correct pin height (34.69mm) for combo #1 or #2.
Option #1 yields 226.69mm reciprocating stuff assembled height. This leaves my pistons 0.02992126 in./ .76mm below deck. Fine by me, lower compression ratio means more boost.
Option #2 yields 226.29mm reciprocating stuff assembled height. This leaves my pistons 0.04566929 in./ 1.16mm below deck. Yet even lower compression ratio.
Option #3 yields an assembled height of whatever I want but is gonna cost me at least 500 more bucks to do. That and the piston would need approximately a 51.45mm pin height. Seems kinda funky to me. Does that sound too tall/heavy to you guys? Of course there's the custom rod option too but then you're talkin kind of out of the budget.
Obviously I need to CC my combustion chambers to see where I'm at exactly in the C/R area but either way I go I'm sure it'll be acceptable by turbo standards. What are your thoughts guys? Which way do you think I should go? Displacement, Rpm, or copy the SR20?
Thanks for your time.
Jake Sweeney
69 2Dr ZxxET to be
San Diego, CA
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