ignition systems euro/us

[George Willet]

Here is my two cents worth on distributor curves.

One: the curve needed is determined by the combustion pressure of the cylinder. That has to do with the static compression ratio, the cam timing, the type of induction, the type and efficiency of the exhaust system, and the torque rpm range.

Two: the two liter engins seem to give the best torque with a total advance of 33 degrees, the 1750 at 36 degrees, and the 1600 at 40 to 46 degrees. For the same reasons that some engines need more total advance, they also can run more initial.
So an advance curve of 26 degrees at the crank works out well for each of the above engines.

Three: Distributor curves were designed for the engines running on the available fuel at the time. Leaded gas requires more advance than unleaded to have the same flame front timing. But the unleaded fuel on an aluminum head needs a little more advance than a cast head, so it equals out in todays Alfas.

The best starting place for timing is setting the total at the M mark on the crank pulley, then going 2 degree increments till the car runs slower at full throttle, and then backing off two degrees. Bet it's at the M mark!

I worked with Centerline on the distributor modifications, and the advance curve for the distributors they sell, and I use them in the engines I build, along with the stock Bosch coil with the external resister. (And 8mm spiral wound plug wires) That combination shows the best torque on the track and the dyno.]

I emphesize torque, because "torque wins races, horsepower sells cars"

Hope this helps. George Willet

[John M]

Hey Todd:

Its very similar to the stock bosch unit. I think that the advance is in a little quicker than the stock unit. The RML curve is modified. And comparing to Papa's excellent graphs...that seems to be the case. Total advance on the RML unit is 36 degrees...and I believe that is all in at 3000 rpms if my memory is not failing me. They did just sell me the distributor. I actually bought the distributor w/ optical pickup and the magnacore red plug wire set for right at $300 and that included shipping. They were excellent to work with. Just some of the best service I have ran across for the Alfa owner. They took a lot of time to discuss what I have, what I need, what others are doing, the entire smash.

On you question about will it work with a stock bosch setup. Both MSD and Crane multispark boxes will work with optical, magnetic, points, and crank/flywheel timing sensors. And on another point....the RML ignition boxes are made by the same people who make the Crane boxes. So an RML Hi6 is a Crane Hi6...identical. Best thing to me about RML other than the great service is that they have the new optical output that is compatible with the points trigger lead on the MSD 6AL. The old setup people had to use to utilize an optical trigger included two ignitions boxes.....a 700 to capture the optical signal and to pass it to the multispark that fired the plugs. Not the case anymore with the new optical square wave pickup in the distributor by RML. I don't know if other suppliers have this particular type of optical trigger that can go directly to the MSD 6AL. Perhaps someone will add some clarity on triggering options.

Best Regards,
John M

[DriverJon]

Thanks for clarifing that Jim...

I was a little confused with 2 or even 3 distributors being listed with two curves.. thought one line was one dist..

I went from a S166B to a S166B... ;-)
Bought one on ebay with then external vaccum switch for the points (gives +- 3 deg) since mine didn't have one.. probably don't need it, but it was $10 and it feels tigher than my original..

I'm with todds on the "feel" of the car as the important point.. and George backs that up in that lots of torque is what we want, as well as evenly applied across the rev range.

One of the most enjoyable things about my first Alfa experience (69 1750 Berlina) was the amazingly flat torqe curve. I ran across a 69 Car and Driver, and they even made special comment on how something like 85% of full torque was available from 2500-5500, which made for an unusually responsive engine no matter where you were on the tach..

BTW.. I just got my 77 Spider started last night... after nearly a year off the road, rebuilt engine, new springs, all suspension bushings, etc, etc... Started the break in last night.. Woohoooo!!!

Uh, off to drive some more.. see ya!!

[papajam]

Todd,
I got the graphs, 9 graphs for 15 different distributors, from a fellow Alfista from down under a few years ago. I simply redrew them for an easier read.
Yes, all the stock Alfa dizzys in the '84 Euro book have vacuum advance (except for the Motronic) which provide about 9 degrees advance. Is vacuum advance desirable for an Alfa engine? Since Alfa, and virtually all other manufacturers (that I know of) have used it at one time or another, yes. But depending on the application, there are two completely different ways to apply it. One is hooking up the diaphram to manifold vacuum. This gives max vacuum advance with a closed throttle. The other is ported vacuum which provides max advance with an open throttle.

Eric,
Yes, as of the beginning of this year, I have volunteered some of my free time to be AROC-USAs tech librarian. While copies of whatever is in the library is available for the cost of copying and mailing/shipping, the service is available to anyone with a passion for Alfa, not just club members. The thought being that this could help promote new membership for the club.

[papajam]

Quote:

Originally posted by George Willet Two: the two liter engins seem to give the best torque with a total advance of 33 degrees, the 1750 at 36 degrees, and the 1600 at 40 to 46 degrees. For the same reasons that some engines need more total advance, they also can run more initial. So an advance curve of 26 degrees at the crank works out well for each of the above engines.

[George Willet]

Hi Jim

Different model distributors were designed for different engines depending on the factors I mentioned earlier: more advance needed for a small-high rpm engine, IE 1300/1600, and less total for a 2 liter. Over the years, it has been pretty much agreed that having full advance at or around 3000 rpm works best for most all engines, without getting too technical.

Yes, maximum torque will be at 5250 rpm, that has nothing to do with spark advance.

There is a factor that after maximum torque, the fuel ratio will get marginaly richer as the rpm goes up, due to the volumetric efficiency going down after maximum torque. So Alfa did some curves to increase advance one degree per thousand rpm after 5000 rpm to use that richer mixture. I understand that computerized ignitions do the same for power/emissions, (read 1995 and later cars).

So putting a distributor for a 1600 cc engine in a two liter will give too much full advance if set at 2-3 degrees at idle, and will be retarded at idle when set at maximum advance at the M mark.

I have always recognized that Alfa was one of the first to give one horspower per cubic inch in a mass produced car, and they are a very highly tuned engine to begin with. So unlike early Fords/Chevys that needed hot rodding, one needs to reasearch and be careful in trying to get more out of the Alfa engine. There isn't much latent horsepower just waiting to be awakened. You can get more power, but you tend to change the comprimise to a different area. IE: more cam timing raises the rpm range, gains some horsepower, (torque times rpm equals horsepower), and lowers the torque, everything else being equal. So where do you want the comprimise to be? Every time you make a decision you have to give up something!

Sorry if I got off the distributor curve thread, but everything dealing with engines is interrelated.

Please reread what I wrote about setting timing at the M mark, and 26 crank degrees in the distributor working well for all the Alfa engines.

George

[papajam]

Thanks for the response, George. Maybe this sinus thing I've got has affected some brain cells or something but I still don't get this 26 degree thing or where it fits into, say, a stock 1600 or Euro 1750 fitted with a stock Bosch 041/044 dizzy with timing specs of 3 deg fixed and 43 deg max.
And I'd like to learn more about why no more advance is needed after 3000 rpm. This pretty much goes against everything I was taught and practiced for the past 30 years. Unless that's 3000 DISTRIBUTOR rpm.

[George Willet]

Hi Jim

If a 1300/1600 engine in "hot street/ racing tune needs 40/46 degree total advance, then it will need more initial advance to create low rpm torque because the dynamic compression ratio is lower caused by the relative cam timing needed to get the power wanted by the engine builder. Are you with this so far? ( more cam timing equals lower dynamic compression ratio, which needs more initial timing). So, the 1300/1600 needs a total of 14 degrees initial to give low end torque/response/ idle , plus 26 crank degrees, equals 40 degrees total.

A 1750 engine has need for a total of "36" degrees, so because of the longer stroke to help cylinder filling, etc, the initial doesn't need to be as much as the short stroke engine, so 10 dregrees initial works well for our stock or race engine. Oh yea, 10 plus 26 equals 36 degrees.

Same for the 2 liter: 33 degrees total seems to work out, so more displacement, long stroke, cam to displacement ratio needs less initial timing, say 7 degrees, plus 26 gives 33 degrees total.

This has worked out on the track and the dyno on the Alfa engines, and while is is not conclusive, is pretty close to what i've found if the engine is "balanced". IE: induction, cams, compression, exhaust, what did I forget?

At or about 3000 rpm, there appears to be a balance of all the factors in a combustion chamber shape in relation to things like Quench area, turbulance, or lack there of, bore size, fuel front propagation, or burn rate, that more timing is not going to make the flame front expand faster in a chamber than at a higher rpm. Increasing the timing creates " negative torque". Means piston moving up against advanced timing/flame front causes pressure against the piston moving up to be greater that the power produced by the advanced timing. Yes we can finesse spark advance. but to what benefit in an Alfa that has a "dirty hemi combustion chamber", versus, say a later design.

Certain advance curves were created for certain engines to fill a need, power, drivaibility, octane, emissions, and so on. What works for one won't fill the need for another. And if your are trying to work this into emission testing, I'll have to say " for off road use only, and not for use on public highways"!

Thanks, George

[todds]

That last post was very interesting, thanks George. I'm a little confused about initial vs. crank degrees though. By initial do you mean static-idle speed timing spec? Should we alter our timing from the F mark at idle? If that's true, then "26 crank degrees" must be everything the distributor weights (and vac advance) are adding right? So I think what you're saying is you recommend a distributor which adds 26 degrees of advance (at the crank) for all engines and simply alter the static timing spec appropriately. In other words, my stock marelli s166B, with it's max advance of only 28 or so would be perfect provided I advance the initial timing to around 7 or so and throw in some light-ish springs so it's all in around 3000rpms.

I've actually tried that on my car before, and while the engine felt smoother, the idle was way too fast with webers. I couldn't get anything below 1500rpm's with such advanced initial timing (and the webers were full closed, correct mixture/jets/etc)

I think what papajam is surprised at is that according to what you're saying, the bosch 041/044/045's are unsuitable for 2 liters, which is shocking because it's what alfa used on euro-spec models.

Re vac advances: I think manifold vac simply gives high advance at idle and less as the throttle is opened, whereas port vacuum, which is what most people recommend, gives none at idle, most at low-mid throttle, and none at wide open throttle. And that most closely follows engine requirements. I think "port" vacuum is simply taken earlier in the carb's throat so the throttle doesn't get to it until you've opened it a bit. At least, that's how it works on chebbys :-)

Didn't alfa use vac advances in the 60's as well? I wonder why they ditched them for the 70's, and used them again in the 80's.

___
/<>/>/>

[papajam]

Thanks, again, George. NOW I understand; the 26 degrees is max advance minus initial advance. Must have had (another) Homer moment. D'oh! But as Todd said, and I have seen, carbed street engines with an initial advance of anything more than like 6 or 7 degrees will idle at double the recommended idle speed with no chance of going any lower. And a street engine will ping like a sumb*tch with initial advance in the teens. Is this 26 degree thing for race engines only?
My understanding of this more advance at higher rpm thing is not that additional advance is needed so the flame front expands faster but that the flame front needs to be established before (or about) TDC. Since establishing the flame front takes a (reletively) fixed amount of time, the faster the piston speed, there's less time available for this to happen so ignition needs to occur earlier. Is this incorrect?
Please don't take my questions/comments as a challenge to your knowledge and experience. They are not. I'd simply like to learn more about why your findings differ from what I was taught was the 'industry standard' about advance curves as applied to street engines.

[George Willet]

Hi Jim

In respomse to the total advance at xxx rpm, I'll quote David Vizard, (engineer, engine builder, writes books and tech articles): "Fortunately. flame speed often increases nearly proportional with engine speed-primarily due to the increase in chamber turbulance as engine speed rises. This means that the crank angle though which combustion takes place can remain relatively constant. This relationship is well established, principally from direct measurements and from observation that higher speed engines require no more , or slightly more, advance as those running at normal or lower speeds."

I recommend three books on the subject, (out of many): How to build and power tune distributor type ignition systems by Des Hammill; The doctors step by step guide to optimizing your ignition, by c.a.Jacobs, phd & EE. He is the developer of the Jaclbs ignition system. This book is VERY heavy, but tells how to do it, RGHT!; And How to build horsepower, volume one, by David Vizard.
These books are available at motorbooks.com

High idle on carburated engines: I was shown by a WEBER guru that this is nearly always caused by the throttle plates not being completly closed. I learned to pull the aux. ventury and the choke out and hlod the carb up to the light. If there is any more than a tiny bit of light, then align the plates, (save that for another discussion on How Toos.) The other thing, afetr the carbs are mounted, is to pull the plugs from over the progression holes and set the throttle stops by viewing the plates thru the holes, don't need a monometer or the air flow testers. Also the idle screws should turned out to be in the range of one and onehalf turns on carbs with single or double digit suffexes,IE xx dcoe 2, or xx dcoe 32. Newer models with three digits, IE 45dcoe152, should be in the two and onehalf turns to be in the proper distance off the seat. There is a difference in thread pitch. If the turns out are more than 1'2 turn in or out, then the jetting needs to be adjusted, cause the idle screw is letting in too much air.

On stock, or 190 horsepower engines, I'm able to get 750 rpm idles with the steps above, and with the initial advances I mentioned earlier. Like everything else, it all has to be done just right, to gt the right result.

Thanks, George

[todds]

ok.. last question..

Does anyone sell tape or some sort of guide for the alfa front pulleys that makes timing a bit easier to see and quantify? As charming as the rusty faded Fisso, Punto, and Massimo marks are, I'd like to have some numbers on there...

[papajam]

Thanks for the references. Seems there could be a little reading in my future.

Quote:

Originally posted by George Willet High idle on carburated engines: I was shown by a WEBER guru that this is nearly always caused by the throttle plates not being completly closed.

[CarlosSpider]

Hello.

I don´t know if it is of your interest, but I have an Alfa Spider 2.0 (from Europe) with a Magneti Marelli distributor (I don´t know if it is a 103B, 103BA…). It has not vacuum advance, only mechanical advance.

In the owner´s manual appear these data:

anticipo fisso : 6º - 8º prima del P.M.S. a 800 – 900 giri/min (rifirimento F sulla puleggia dell´albero motore)
anticipo max.: 35º - 38º a 5100 giri/min (rifirimento M sulla puleggia dell´albero motore).


Its means that advance at idle is 6º-8º BTDC and 35º - 38º BTDC at 5.100 rpm (marks F and M at pulley)

Naturally is carburated (non spica).

Recommended Sparkplug: Lodge 2HL

Valve timing

Intake: opens 40º 34´ BTDC
closes 64º 34´ ABDC
Exhaust opens 63º 54´ BTDC
closes 27º 54´ ABDC

Regards



My distributor (before cleaned)

[sono veL.O.ce]

I have an AR Ricambi electronic unit, and I have no idea about the curve on this thing. I have been trying to dig up info on it to no avail.
Anyone have advice on setting the timing with this setup?

2 liter, Ported head, weber 40s, otherwise stock, street gas 91 oct.


Thanks,