Quote:
Originally Posted by Ryephile
Exactly. Undersquare is not related to rod ratio.
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Correct.
The rod asymmetrical design revving to 7k rpm with that r/s ratio is is what the topic is about.
FB20 and FB25: 90mm stroke with a rod length of 129.3. 1.44/129.3 rod to stroke ratio. You kinda want a minimum of 1.5 r/s ratio for an engine more if it high revving. 1.74 r/s ratio is an ideal r/s ratio for the street. A 2.0 r/s and above is f1 and supercar territory.
Some info for comparison. I gave the r/s ratios and 89-90mm strokes on the Hondas that had them and then the EJ stroke for comparison to FB.
EJ20 1.74/130.5 75mm stroke
EJ25 1.67/131.7 79mm stroke
Every rod to stroke ratio from Honda is better than the FB20/25 since the 80s.
K20A 1.62/139
K24A 1.54/152
B16A: 1.74/ 134MM
B17A1: 1.62/131.87MM
B18A1: 1.54/ 137MM 89mm stroke
B18B: 1.54/137MM 89mm stroke
B18C1: 1.58/137.9MM
B18C5: 1.58/137.9MM
B20A3 1.50/142.75MM
B21A1: 1.492/141.7MM
B20B: 1.539/137MM
H22A: 1.577/143MM 90mm stroke
H23A1: 1.49/141.5MM
F20C: 1.821/153MM
D17A1: /140MM
D17A2: /140MM
D16Y8: 1.52/137MM 90mm stroke
D16Y7: 1.52/137MM **
D16Z6: 1.52/137MM **
D16A1: 1.52/137MM **
D16A6: 1.52/137MM **
D15B1: 1.59/134MM **
D15B2: 1.59/134MM **
D15B7: 1.59/134MM **
D15B8: 1.59/134MM 90mm stroke
ZC: 1.52/137MM