Nuances of dwell... any input? Options

[detoxcowboy]

74 2.0 Stock

I just replaced my electroninc ignition for points and am learning a bit.. I noticed the dwell range is 44-50deg.. Currently I am at 47.8.. What is the difference in runing a lower dwell vs. a higher dwell #??

[john rogers]

Why did you do that? Generally electronic points replacement will have several advantages such as no dwell change, no points bounce, no points sticking and probably others as well. If dwell changes then the timing will change so performance will change accordingly.

[SLITS]

Dwell is the amount of time the points are closed allowing saturation of the charge to the ignition coil before the points open and the field collapses (sparks).

Shorter dwell = less time for saturation = weaker spark

Longer dwell = well, you know.

[ArtechnikA]

Dwell is the amount of time the points are closed allowing saturation of the charge to the ignition coil before the points open and the field collapses (sparks).
...
Longer dwell = well, you know.

Since it also affects the amount the points open, for completeness, let's mention that if the dwell is _too_ long - i.e. the points do not open enough - the points can sustain an arc across the very narrow gap and burn quickly. This is bad.

The factory spec (0.016" or 0,4mm) is an excellent balance and provides enough charge time for the rev ranges the average street-driver 4-cylinder engine needs.

[detoxcowboy]

Dwell is the amount of time the points are closed allowing saturation of the charge to the ignition coil before the points open and the field collapses (sparks).
...
Longer dwell = well, you know.

Since it also affects the amount the points open, for completeness, let's mention that if the dwell is _too_ long - i.e. the points do not open enough - the points can sustain an arc across the very narrow gap and burn quickly. This is bad.

The factory spec (0.016" or 0,4mm) is an excellent balance and provides enough charge time for the rev ranges the average street-driver 4-cylinder engine needs.

good , excellent.. that is what i did.. .4 mm just thought there were finer resoulutions that could be advantages on either the low end or top end but not both, you said balance and I like that idea..

[detoxcowboy]

Why did you do that? Generally electronic points replacement will have several advantages such as no dwell change, no points bounce, no points sticking and probably others as well. If dwell changes then the timing will change so performance will change accordingly.

I had 2 problems in 2 years with electronic ignition, both times the issues masked itself as potentially other issue, I mean wierd but consistent issues like extreme hihg idle until warmed up then normal this time (barely rubbing shutter that apparently would beat itself away from rubbing about the time the car warmed up) or surging pulses to near failure at idle the other time (not visiblely nor feeling it but losse moplex conection).. I take long roads trips in my 914, electronic ignition can be difficult if not impossible to repair on the road, points I can do anywhere, also I mantain my car so often that setting points, replacing points, or even pulling the distributor out is not really a huge project anymore than adjusting the valves..

In short this time the crane xr700 pissed me off for the last time..

[Elliot Cannon]

Switching from electronic ignition to points is like, switching from DSL to dial-up!! Like switching from transistors to vacuum tubes. (IMG:style_emoticons/default/lol-2.gif)

[detoxcowboy]

Switching from electronic ignition to points is like, switching from DSL to dial-up!! Like switching from transistors to vacuum tubes. (IMG:style_emoticons/default/lol-2.gif)

pm sent

[Elliot Cannon]

Switching from electronic ignition to points is like, switching from DSL to dial-up!! Like switching from transistors to vacuum tubes. (IMG:style_emoticons/default/lol-2.gif)

pm sent

pm sent back (IMG:style_emoticons/default/lol-2.gif)

[realred914]

if the electronic ignition is installed such that the shutter does rub, then of course you will have problems keeping timing correct, a rubbing component will alter the advance or retard of the distributor. I have seen this happen before. there can be no rubing, the advacne/retard plate must move freely. tight wires to teh electronic ignition will also alter timing, they must have enough free length to allow travel of the advance/retard plate.

never had a probelm with a Pertronix so long as the install has no rubbing (had to modify one once, when i put a Bug one in a 914 (different sixed unit, did rub, but a little file work made it fit in the distributor just fine)


I suggest you give electronic points a try again, with close attention to freedom of movement of the advacne/retard plate.


if you run points, middle of the specification would suit you fine for dwell. just remember that the points will drift in timing so you have to stay on it.


just a thought, if you dont trust the electronic ignition, you can always keep spare points in the glove box for a emergency field service. but honestly if they are set up with no rubbing, you should be ok with them. the pertronix uses a magnetic pick up rather than a light and shutter wheel, that might fit better???

good luck

[john rogers]

Have you considered a CompuFire points replacement unit or even replacing the distributor with their solid state system? We had one of their setups in our 1974 D-Jet 2L car and it lasted for about 10 years or so and I used on in the 2.8L four cylinder race car engine until I switched to a six. They are pretty good units as far as I remember.

[charliew]

As with any mechanical device the installation is critical. Farmers liked tractors with points because they could use a matchbook cover to gap the points about once a month. I never not even on off road stuff had a desire to use points. The light and shutter wheel is susceptable to dirt and the magnetic pickup is not.

[avidfanjpl]

Some people tell me 50 dwell is ideal.

I am at about 47 like you and the car is pulling strong.

I set it at .017 not .016, but that may be splitting hairs.

The big thing for me was the wrong CHTS. 012's cannot replace 017's, and cause havoc instantly.

I can set points almost by sight. But I always carry a gauge and a screwdriver. Takes me 2 minutes flat.

I prefer points. Simple for stupid me.

All my mechanics have warned me away from electronic since they came out. This is my 6th 2.0L. I don't know everything, but Bosch points, the right ones, are brainless.

But I always have to remember the lube! I forgot it last fall and they wore out in 500 miles.

John

[ME733]

....Detoxcowboy..........To be realistic about setting dwell, /or to say point gap...at least two other factors come into play.......The first is the condition of the distributor, or to say , the amount of "wobble" in the cam , the points are mechanically operating from.....naturally the more "wobble" the greater the variation in the point gap you set when the distributor is turning.( you might set .016 ths inch....but due to wobble of the shaft,the net effect of the point gap could be .014 to .018 ths., or more., Additionally this wobble will also contribute to POINT BOUNCE at high rpm,s...and you can chase your tail around hunting an elusive misfire at high rpm,s..or just ...not having the H.P.....you know should be there....it,s all about the coil saturation TIME. The other factors are , having points with a "stiff" spring which will help the rubbing block "track" the distributor cam lobe.(much like increasing valve spring tension in a higher than stock performance engine). lubrication of the cam is critical.expect some immediate point gap change until the rubbing block is "seated". lubrication of the cam is critical. Finding a slight point gap change until the rubbing block seats is no big deal. A distributor shaft that wobbles also affects the rotor and cap clearances., increasing resistance, again affecting the net net voltage/ amperage to the spark plugs.(and some other stuff)........A distributors condition, overall condition,is vital to having a good running engine........My personal preferance is to use a MAGNETO, which are built to aviation standards, and has roller bearings to to ensure the shaft does not "wobble."(they do not have bushings for shaft support). I do not recommend this for everyone, and they are expensive.

[76-914]

I'd have to agree w/ John, Elliot and Charlie. I've run Petronix in my Karmann Ghia (type 1) for 8 yr's and in my 914 for 1 yr w/o any problems. I'm careful to not leave the ign switch in the on position if not running, though.

[Drums66]

I'd have to agree w/ John, Elliot and Charlie. I've run Petronix in my Karmann Ghia (type 1) for 8 yr's and in my 914 for 1 yr w/o any problems. I'm careful to not leave the ign switch in the on position if not running, though.

..I'd really consider anything but points?...maybe keep a set in the trunk for
an emergency! .....I prefer the pertronix,I love the longevity..over 10 yrs (IMG:style_emoticons/default/wub.gif)
(IMG:style_emoticons/default/idea.gif) ......here we go again! (IMG:style_emoticons/default/popcorn[1].gif)