Have been playing with the adjustable cam sprockets on a B18C1 here, and I am realizing that I may have been overly aggressive with my dialing in. Even on cool gray overcast days, going up hill at low RPMs produces a steady faint tinking of detonation. It's not loud, but it's constant, so I assume that the ECU is getting the word from the knock sensor and is pulling spark timing back as far as it can.

Part of this problem is that I'm in California, where $2.50/gal buys you an absolute maximum of 91 octane. Effing dishwater. Don't get me started on bitching about our crappy fuel. Anyway, I'm stuck with 91 until I decide to move to a saner place, and the engine isn't happy with that.

Whenever someone asks me about detonation, I always tell them they have a few options:

(a) switch to higher octane, if available;
(b) detune the engine by retarding timing, etc;
(c) cool the intake charge if possible.

I can't do (a) easily without spending a fortune (100-octane unleaded is available but for $6/gal, and nowhere close to me). I don't want to do (b); the engine is right at a sweet spot for the powerband right now.

That leaves (c). The engine compartment is pretty well cooled and I have no real signs of heat dissipation being a problem. But the underhood air that the stock intake is pulling in is still warm, to say the least.

I am wondering if a CAI like an Icebox would give enough of an improvement on intake temperatures as to hold back this last annoying bit of rattle. Has anybody got any anecdotes, or better yet, real data?

 

What sort of advance are you running? Cooler intake air will help a little, but you are likely running a little too much advance. Unless you plan on moving to Texas where you can get 93 octane for about 50 cents less a gallon. I ran more advance(18, which is the max) without a problem, here I run 16 and have no problems, but I don't have cam gears either. YOu could always get some octane booster, or put some toluene in there, though I don't know how happy your cat would be with that stuff, probably all right, but I would not want to find out the hard way

 

I would strongly recommend detuning the engine. California just sucks like that.

You could also try running richer, but that would basically be the same as detuning and you'll get worse gas milage.