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Yeah I’ve already resigned myself to using 93 octane after this. (In Virginia, our pumps have 87, 89, and 93. You can also get 89 or 90 non ethanol in many places.). I know some places have 91 octane premium.
The combustion chamber volume in a P07 head is a tiny 25.x cc, compared to 34ish for other heads. There are a couple head gasket choices, and the thickest one brings compression from the stock 9.2 up to 10.73:1 I think. The thinner one is closer to 11:1. Pretty standard for higher performance honda engines in stock form, so I’m not too worried about it, but I don’t plan on using 87 octane anymore.
My stock transmission has final drive of 4.25, but the D15z1 transmission (forget the code now) is more like 3.4. One of the other trim levels has something like 3.77, which I think would put my engine speed in an acceptable range at 70mph. Right now I’m at about 2500 at 70mph, which is the crossover point for Vtec in the D15z1. I didn’t realize it was dependent on load though. I remember having a 98 civic ex and on the highway (cruising faster than I should have, but I was young), vtec crossed over when I accidentally sped up by only a couple mph. I could feel it and hear it and all of a sudden I was going about 98mph. So I do think it will cross over even if cruising at a reasonable speed if I don’t do something about it. I’m hoping a 3.77 fd will keep the car somewhat drivable and allow me to cruise up to maybe 76-78mph before vtec crosses. I try to stay around 70-75 on our 70mph highways. 80+mph is a wreckless driving ticket in VA. I had a stock VX once and I thought it was virtually undriveable. It made no power and the gearing just sucked. But I was 21 and only had it because my GSR had just been stolen, so going from the GSR to the VX was quite a difference. That was a long time ago and I’m looking for something different now, but I still want the car to be somewhat fun to drive.
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