Detonation - WAS: Re: Oh yeah, Rod Bearing

[Peter Serwe]

Hmm ...

        I thought it sounded like detonation from the moment he started
talking about this
        but then, I'd wonder why it would happen under 4.5k w/ a stock
ECU.

        On a side (but definitely related) note:

        I've set my timing using the tried and true, and pretty well
documented - well, I
        use the short version, attributed to Kojima, unplug the TPS with
the car running,
        rev above 3k 3 times, letting it fall to idle in between, then
when the idle
        smooths out and drops to 950, set the timing using a dial-type
set to 15, hit just
        a hair over 0, and I see about a 1 degree fluctuation in the
timing (no big deal,
        right?)

        I've set the timing to 15-16 BTDC, and running 93 octane gas, I
get can hear what
        sounds to me like detonation, but only after 4.5k.  I originally
noticed it a month
        or so ago when I listed to you guys talk about how the stock ECU
auto-retards up to
        4.5k .. The sound of detonation, far as I can tell is when the
motor starts to
        sound like steel shot's rattling around in the head, well, that
might be an
        exaggeration of the sound, but it's somewhere near there.  Since
then, I tried
        experimenting with octane booster, after hearing something about
MMT based octane
        boosters being evil, I found the only one that doesn't contain
any MMT, dropped it
        in, and whammo, the sound of detonation disappears at ANY rpm.

        Now, I guess the real question is, and I'm a 93 octane nazi on a
stock SR20DE with
        no engine mods but a po-boy pop charger - (k&n tie-wrapped to
the upper half of the
        stock air box, lower section removed, in-piping left for some
CAI-ish action) how
        could I possibly be getting detonation?

        I'm not certain if my SR20 is US or JDM spec, I *think* JDM, but
I haven't found a
        tiny light to poke into a spark plug hole to check the pistons
yet.  Some people I
        know claim that compression of 10:1 with 93 octane street gas
will give you
        detonation on a properly timed domestic v8 (because of the high
MTBE content, BTW),
        and that you have to retard the timing to run street gas any
higher than about
        9.6:1 compression.  When I hear you guys talk around on the list
and read a bunch
        of stuff about everyone's project cars, it seems like up to
about 11:1 works on
        street gas - or does the timing get way retarded when you guys
boost hard?  Then my
        next question would be, where should I set my timing on my stock
motor to avoid
        detonation w/o having to use octane booster.

        Or to sum it all up, can anyone tell me why I'm detonating w/o
octane booster on 93
        pump gas?  Most of my 93 has been Mobil, I got some Exxon today,
dropped it in with
        another bottle of 104+..

        George Roffe wrote:

        > Steve wrote:

        > >One other thing, Pulling the spark plu wires off one by one
makes no
        > >difference at all. The only thing that changes the noise is
timing, the more
        > >you retard it, the quiter it gets...

        > Steve, that is knock, ping, detonation, etc.

        > Seems kind of odd that is would happen at 17 deg BTDC and that
you would
        > have to retard it to 10 deg BTDC.  Are you *certain* about the
timing settings?

        > It's definitely not rod bearings.  I'm 99.5% certain it's
        > knock/ping/detonation.

        > George Roffe
        > Houston, TX
        > 91 SE-R (well modded)
        > 91 G20  (well modded)
        > 84 944 SCCA ITS race car under construction
--
Peter Serwe <peter@easytree.net>
Cheaper, Faster, Better, pick any two.
finger peter@easytree.net for public pgp key