[DMCForum] Re: Andrew's "Knocking"

["content22207" <brobertson@xxxxxxxxxxxx>]

Most performance engines are timed closer to TDC, not advanced. Moving
spark earlier in stroke lowers power. That's one reason HP killed in
domestic blocks throughout 1970's: 1969 Ford 460 timed 10 degrees
BTDC. By 1977 moved to 17 degrees. 1978 (last year 460 in automobiles)
timed 20 degrees BTDC.

If you're "knocking" are two different potential problems:
pre-ignition and pre-detonation. 

Pre-ignition:
Spark ignites fuel mixture too soon
Sounds like constant drumming of diesel engine
Worst at higher RPM's, accelerating, under load, etc
May be unaffected by octane

Pre-detonation:
Fuel mixture spontaneously combusts before spark
Is random, like popcorn
Worst when cruising
Usually improves with octane

Pre-ignition can be a timing issue. Lots of higher mileage engines
have never been re-timed. 

Pre-detonation usually indicates something wrong inside combustion
chamber. Can be as simple as carbon buildup (glows red hot, and also
reduces chamber volume -- increases compression). I suppose a weak
coil could cause as well (little or no spark).

If you're knocking on 93 octane, suspect ignition time. Even the 11:1
engine in one of my Lincolns can be timed to run on 93 alone (no
octane boost). Interestingly do so by ADVANCING time just a little
from factory spec.

Is your car difficult to start cold? One thing I've noticed about over
advanced cars is engine has to spin much longer than normal before it
will catch.

Bill Robertson
#5939

>--- In DMCForum@xxxxxxxxxxxxxxx, Andrew <aos+yahoo@xxxx> wrote:
> > Better gas. We have no knock sensor to control this. The new ignition
> > system may also help.  What are you going to do for a coil. His
package
> > didn't include one. Is it extra and how much.
> 
> I've got no reason to believe I have bad gas.  I'm using 93 octane, and 
> only buy major brand names, and not always at the same station. 
I've got 
> a couple of jugs of Sunoco 104 in the garage (for fun weekends with the 
> other car).  Maybe I should toss a few gallons in the DMC and see if it 
> manages to knock with that.  That is, if it can even ignite it at
all.  :)
> 
> I'm not expecting much, if anything, from the ignition upgrade stuff.  I
> know a lot of people claim it's snake oil, but since I enjoy tinkering
> with things, and it's fairly easy for me to get over to DMCH to pick up
> the parts, I figured I'd give it an unbiased opinion.  Hopefully I'll 
> finish the install tomorrow.  I ran out of light today.
> 
> Right now I'm still on the stock coil, which I assume is 20 years
old.  I 
> don't believe it was replaced when the performance engine was put
in.  I 
> plan to leave it as it is for the time being, at least until I've
had the 
> opportunity to determine what, if any, is gained by adding the
performance 
> ignition package.  After that point, I may well upgrade it.
> 
> Since I have the performance engine, this may well just be a case of 
> slightly too aggressive timing, so backing it off a little may also
be of 
> some help.
> 
> -andrew



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