Fighting Detonation - Richen Carb or Back of Timing?

[jamyers]

To keep detonation under load (especially on hot days) from happening, which is the better route:

1. Richen up the carb (assuming it's not so lean as to cause driveability issues like surging)

2. Back off the timing (either initial, or rework the curve)

 

[xctasy]

Plugs are like this?

It's fixable by

1) a more conservative vacum advance,

2) by fitting stiffer mechanical advance springs reduce the onset of total advnace


3) a combination of both above

4) or by reducing initail advance (not a good method at all).

Bump up the inital timing as high as you can, then reduce the total advance and the problem usaully goes away.

Lean misfires won't cause problems, as the car will decimate spark plug cores before it causes a hole in a piston. If its ultra lean, the spark plug will open plug gap over a very short time, and will then take the tips of the plugs


Detonation is the result of 22 characteristics of an engine/drive train /car combination, and the easiest thing to change is the ignition.

Going to a stiffer set of mechanical advance springs will reduce the growth in spark advance and a more conservative vacum advance will also reduce total advance, and make the car less likely to detonate.

In most cases, figure on less than 36 degrees total advance (mechanical, plus vac adanvance) in a car with tall gearing, any kind of heated metal intake manifold, and try to bump up the initial advance to 12 degrees on the crank.

 

[jamyers]

Nope, nobody's plugs have been beaten up that badly...yet.

What's prompting the question is an ongoing discussion (argument) here about dealing with engines that run fine in the fall/winter/spring, but once the temps get into the summer 95-plus'es, detonation becomes a problem. One camp says jet richer, the other says back off the timing.

I'm thinking it's more of a need to rework timing curves and find adjustable vacuum advances that you can tweak for summer/winter, and your comments support that argument.

 

[rickwrench]

Back off the timing.
Running rich causes carbon build up. Carbon build up causes hot spots. Hot spots cause detonation.
The other option is water injection.
Rick

 

[xctasy]

European Webers ran the variable intake air horn, with a summer /winter postiion. I'd suggest you look into that if running a non orginal air cleaner isn not important. A hose through the fire wall is fine in summer, and in winter, it can take air from the exhast manifold. You could do that manually like Ford of Europe did with all the 1600 and 2000 Capris, Escorts, 1600 Fiestas, 2 liter Granadas and Transits with the Weber carb.


Austrailan 3.3 and 4.1 Falcons with Webers from 1985 to 1993 ran what was basically a heat stove source from the exhast when cold, then fully opened to the outside air. That was a perfect set-up which never needed intervention .

The method of control was TVS switch, and a port vacum sustain switch (PVS)to advance the distributor when cold, but back off when hot.

Those are time honoured structures which work on mixture strenght and peak advance.

I'm certain Mark P discussed the factory yellow connection module used on some of the later DS11 ignitions in one of his posts.


If you run the port divider, you will hurt the cold start warm up phase in areas where its below 32 degees F, and the warm up will increase from the 4 or 5 minutes to 8 or 10 minutes. In summer, it will be fine.

The key is to focus on the spark sustain to raise advance when cold, and to whack it back when warm. There are about 12 emission devices used by Detriot engineers back in the 80's, to do this, and you can see them in my posts on the Weber Carb.


Note the common PVS juction block found on my 1980 Aussie Cortina is the same as that found on 1980 to 1984 emissions 200 Fox and X-shell Fords.


(bottom of pictures)

http://img.photobucket.com/albums/v223/ ... G_0023.jpg

http://img.photobucket.com/albums/v223/ ... ssions.jpg

It was always keyed into that dreadfull auxhilary air port on the side, made of square alloy. Heres another one of a 2.6 Cologne V6 with 5200 carb. Same set-up was used.

http://img.photobucket.com/albums/v223/ ... or5200.jpg

Not a great system, but you only need to retard the advance a little when its warm, so examine the set-up, and experiment with it on your pick-up.



The key is it rasies vacum to the advance unit to make the car run better cold, and then it backs off when warm. Its a brilliant set-up.

 

[83F150]

Well....it comes down to do you wanna lose gas mileage or power?

Why not just run 89 or 93 octane fuel? I advanced it on my old LTD II and I have to run 89 (sometimes 93) but it runs just fine.