Ignition retard knock sensor.

[d houlton x0710]

Charles  Brooks wrote:
> 
> What type of ignition and what Compression are you running? If you're running a relatively high compression ratio you may have to live with premium fuel. Adding an intercooler will reduce charge temps and help with the knock problem. If you have an MSD ignition I would suggest purchasing the MSD BTM (Boost Timing Master) module. The BTM retards timing as boost comes on. I'm in the planning stages of Turbocharging a small block Chevy. Actually I'm $1500 inot the planning stage :) I have the manifolds, turbo, wastegate, oil lines, and various little stuff. I just have to convince my wife that it's an excuse to buy a beater now!


I've looked at the BTM as well.  It's still about $300 I think.  The only
thing I don't like is that it's a passive device, retarding ignition
solely on boost level and doing it all the time.

In the last few months, I've found that detonation is *not* directly 
related to boost.  On 89 octane and no water injection for instance, if
I whack the throttle open above about 2000 rpm, boost jumps almost
instantly to 5 - 6 psi.  Detonation is almost instant as well.  However,
if I ease into the throttle and let boost come up over 2 or 3 seconds, it
can go to 7 or 8 psi with no detonation.

Also, if I'm in a situation where I want to accelerate and I'm at say
3000 rpm in a high gear.  I can press the throttle up to a certain point
(probably about 3/4) and get say 6 or 7 psi with no detonation.  If I 
then floor it, boost doesn't increase very quickly until the rpms come
up a bit (takes longer in high gear) and the mixture isn't going lean
according to the A/F meter, but detonation happens pretty much instantly.
Still can't figure that one out.  Boost and A/F don't change very quickly,
but detonation seems to be tied directly to the gas pedal.

It seems that unless you can factor in rpm (at the very least) in addition
to boost to more accurately predict knock, you have to *really* retard 
ignition to cover the worst case, which makes you suffer a power loss most
of the time.  That's why I figured the active J & S system would be much
better.

Although the MSD also has the advantage of a much hotter spark and
is something I want to upgrade eventually anyways I'm not sure how much
I want to retard ignition across the board based only on boost level.


-Dan
houlster at inficad.com
http://www.inficad.com/~houlster/amigo.htm