[Diy_efi] Ignition Timing

[Becker, Damon Damon]

Set MBT (by extapolation, I'm assuming) and let the knock sensing system
handle it?  I'm not sure that's a good way.  The reason I'm not sure is
the knock sensor requires actual knock to happen before it can sense it
and respond.  If this happens too much before the response, then the
knock might get quickly severe, right?  This would be exascerbated with
increased difference between MBT and knock-limited timing.  

As for mapping every possible combination, you could map the combo you
have that day and set the compensation maps to be conservative.  Beyond
that, you would have to rely on the knock sensor.  

Thank you for your time.  I look forward to yours and other responses!
This email list is a great internet tool!   

Damon

-----Original Message-----
From: diy_efi-bounces at diy-efi.org [mailto:diy_efi-bounces at diy-efi.org]
On Behalf Of Adam Wade
Sent: Tuesday, July 26, 2005 2:58 PM
To: diy_efi at diy-efi.org
Subject: Re: [Diy_efi] Ignition Timing

--- "Becker, Damon (Damon)" <damonb at avaya.com> wrote:

> Since I'm knock-limited, I won't hit MBT timing before I hit knock, 
> right?

AFAIK, that's what "knock-limited" means.

> I have read many books that advocate reading the plugs as a great way 
> to set the ignition timing.  I have read other places that using a 
> stethoscope against the block and listening for knock under heavy 
> loads while doing the dyno runs is the best way.  I have yet others 
> say it's best to use the stock knock sensor (unmodified internals, 
> stock
knock
> sensor still valid) to listen for knock.  

With a turbo application, I'd think it would be far easier to make an
MBT ignition map and let the stock knock sensor back off the timing as
needed.  There are a lot of variables in the operation of a turbocharged
motor, and I would expect it to be fairly time-consuming and difficult
to map ignition timing specifically for every combination of intake
temp, engine speed, throttle position, engine temp, and boost level.

You may well want to data-log the resulting ignition timing in
operation, as you may be getting so much retard that you wish to take
other steps to move the spark back closer to MBT (intercooling, piston
crown oil squirters, richer mixture, less boost).

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