2270(or so) Build |
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2270(or so) Build |
yeahmag |
Jan 8 2021, 12:47 PM
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#1
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Advanced Member Group: Members Posts: 2,421 Joined: 18-April 05 From: Pasadena, CA Member No.: 3,946 Region Association: Southern California |
I'm starting to get the case(s) machined and inspected and parts ordered for my next generation engine. The car is mostly used for autocross.
78x96 96mm piston with 22mm wrist pin (stroker) 5.4" Type 1 Rod, 22mm wrist pin WebCam 86b/86c David Finch heads (from Len Hoffman many moons ago) 9.5:1 CR running on 91 octane pump gas CB Dry Sump (heavily modified) or Thorsten Piper dry sump pump Front mounted oil cooler There are a few crank options out there now: * DPR offset grind Type 1 journal * AA Performance Forged Type 1 journal * FAT Performance Forged Chevy journal I've read about a few 80mm DPR cranks breaking, so I was planning on staying under 80mm as I like the car to be able to rev. I was considering Chevy journals for ease of assembly, but the two cranks I've read about breaking were 80mm/Chevy journals. Is there any new information on cranks out there? Any input on the config? |
yeahmag |
Jan 21 2021, 11:24 AM
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#2
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Advanced Member Group: Members Posts: 2,421 Joined: 18-April 05 From: Pasadena, CA Member No.: 3,946 Region Association: Southern California |
Zach,
That's exactly how I ended up where I am. Built 2x 2056cc (with parts from Jake, Thanks Jake!) over time and now I'm starting to build up a 2270 that's much more aggressive. My class is all about power to weight, I want more power, and the I'm not that far off the pace of the guys who have a much lower ratio than I do. Should be interesting. I've been spending some time trying to figure out what static CR I want with both the 86b/86c and the 163/86b. The easiest design puts me at 10.8:1 static, which is way outside my normal rule of thumb of low 8:1 dynamic CR (above 9:1 dynamic). I'd need to add quite a bit of volume to the chambers or a big dish in the pistons to get down to 9.5:1 (which puts me right about where I'm comfortable with in dynamic compression). The fixed numbers I'm working with are: Bore: 96mm Stroke: 78mm (maybe 80mm, still debating) Head CC: 50cc Target Deck Height: .040" Rod Length: 5.325" Intake ABDC (86b/86c): 54 degrees Dynamic CR for the 86b/86c At 10:1 static I calculate 8.56:1 dynamic. At 9.5:1 static I calculate 8.14:1 dynamic. So, I can move around the DH a bit and add a dish to the piston, but I'd prefer to keep the quench area that a tight deck affords me. I *think* an 80mm diameter, .2mm deep dish in the piston will get me to the needed 60cc combined (piston dish + heads), but I'm still modeling. I also need to mock up the motor and see if I need valve reliefs, which will add some cc to the volume. |
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