Centerline dizzy advance curve - Page 2 - Alfa Romeo Bulletin Board & Forums
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post #16 of 30 (permalink) Old 09-20-2009, 07:49 PM
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Quote:
Originally Posted by gigem75 View Post
I got decent driveability by doing what they said dial in 10deg BTDC timing at idle.
Michael,

Again, I am sorry for your troubles with this unit, yes we will "do the right thing" since you're not satisfied with the distributor.

But with all due respect, that is NOT what I said to do, and it is not what the instructions that come with the unit say either.

To reiterate, I said to dial in 36 degrees max advance, and not worry about where the initial advance falls. If you hear detonation, dial back the max advance a degree at a time until it goes away.
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post #17 of 30 (permalink) Old 09-21-2009, 07:50 AM Thread Starter
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I marked my pulley when I built the engine and timed the cams and know where 36 degrees is on the pulley and set it there under the light I have also set it at idle with 10 or do deg advance. Respectfully I think setting it for max is what you told me to do. As a matter of fact I've set it in just about every postition one can set a distributor in excluding the fact that there are an infinite number of places one can set a distributor between two points where it is set initially and where the max advance occurs due to the fact that any number no matter how small can still be divided by two. I get some detonation at 36 so when I dial back the low end gets even worse. If I set it for good low end I end up way past 36 degrees max advance and extreme detonation. I'm using premium fuel. In any event 36 degrees is really irrelevent because if I set it for good top end performance I don't get good low end. That statement in no way means that I haven't set it at 36, the point I'm trying to make is that I can get good top end or good low end but not both.
Thanks for working with me on this.

Last edited by gigem75; 09-21-2009 at 07:56 AM.
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post #18 of 30 (permalink) Old 09-21-2009, 09:03 AM
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Hi,
I will try it once again as Joe described and gigem75 did, and hope I will see some improvement without detonations. I think I was really near 36 degree max advance and about 10 degree BTDC at idle, but now I will check it accurately and will give it a second chance
Thanks for the hint
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post #19 of 30 (permalink) Old 09-21-2009, 09:47 AM
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Just a note on what I have mentioned before: most of the timing lights that I have seen that have the "dial back" feature where you can use the dial to check advance, are not accurate. Particularly at high rpm.

I leave the "dial" feature off and set the max advance that way, on the known factory mark or the mark I have added to the front pulley at the time I degreed the cams in.

Michael: Questions that need to be asked: Did you degree in the cams when you built the engine? Is the valve lash to specs? And have the carbs (or Spica) been properly jetted? Changing the timing can mask other settings that are not correct. For instance, advancing the timing with a rich condition will tend to lean out the mixture; and retarding the timing will make a lean mixture work, but not well. Incorrect cam timing will also change the flame front in the combustion chamber and cause poor driving characteristics.

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post #20 of 30 (permalink) Old 09-21-2009, 10:45 AM Thread Starter
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Thanks George, I set the cams at 102 and they are the spica performance cams, I also put degree marks on my crank pully when setting up the cams. I've set the pump up according to Wes's specs, done numerous plug chops and the plugs indicate a proper mixture. Valve lash is spot on. I've got about 5000 miles on this engine since rebuild and know it inside and out. I've been happiest with the stock Marelli distributor curve wise but was under the impression that I could go from better to best, unfortunatly it was the other way around. Just as much as I was looking to improve engine performance I was also wanting to get rid of the points which was why I went with the Centerline. I've driven the car from up in East Texas down to the Valley and back up through Corpus, San Antonio, Austin, then back home to Longview (1,200 miles) a couple of months ago with the Marelli and got between 28 and 30 mpg along the way depending on a head or tail wind. I checked the plugs along the way since it was a new engine and they looked fine each time. I'm planning on driving this car out to the left coast here when it cools off and I want a distributor I can depend on so I may just buy some points and condensor for the Marelli. Sure would like to find a Bosch 045 though and put a "hot spark" ignition module in it. Heck I might even really bite the bullet and go for the 123 dizzy. I want to burn film, er well fill up memory cards on this trip not engines
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post #21 of 30 (permalink) Old 09-21-2009, 03:37 PM Thread Starter
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Ok, here's the deal from my corner of the world. The bosch 006 has two springs, one elongated which does nothing at idle and another one that holds the weights back from zero rpm. This second spring is pretty stiff. I ordered a Jegs spring kit and took the lightest spring and put it in to replace the second spring that holds tension all the time. Now under the light this light spring, springs into action immediatly and gives a quick advance up to where the elongated spring comes into play. As near as i can tell under the light it's about 2200 rpm. Pretty evident under the light. When 2200 is reached both springs are holding the weights back and the marks on the pully move in a linear motion on up to and a little past the "M" mark which is where I have my max advance set. I'm getting a good jump off idle because only one spring is holding the weights back and they swing out quickly, then slow down as the second spring begins to apply it's tension on the weights. Without a distributor machine this is a close as I can come to exact but things are happening the way I want them to under the light and more importantly they are happening the way I want them to driving the car. Close enough anyway so as to be able to drive the car and enjoy it. Actually it looks pretty close to the Marelli curve where my car ran best anyway. Bottom line is that a plex unit to replace the points on my Marelli is what I really need. Anyone out there sell them?

edit, in addition the lighter spring I added gives a quicker advance even when both weights are stretching the springs past 2200 rpm. I had added the first lighter spring but stretched it some so it didn't work right, not enough intiial tension so I added the second lighter spring without any modification (they give you two of each) ,hence I have a Bosch 006 distributor V3
Thanks!

Last edited by gigem75; 09-21-2009 at 03:58 PM.
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post #22 of 30 (permalink) Old 09-21-2009, 04:28 PM
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I think that it is probably impractical to convert a points Marelli to a 'plex. The rotor on the distributor shaft is different.

The Bosch 045 was fitted to European 1750 & 2L motors with carbs. I had one but I let it go with a 1750 engine that I sold.

There were some electronic Bosch distributors fitted to European 4 cylinder cars but I don't know the models and years. Ebay seller Alfa1750 (the guy who sells Webers) had some of them for sale a couple of years ago. Jim Spackman (MoundDawg?) may know something about them.

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post #23 of 30 (permalink) Old 09-22-2009, 04:33 AM
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It seems strange that you experienced detonation at 6000+ rpm. Whenever I have been experimenting with ignition advance, I have first experienced knocking in the 3000 - 4000 rpm range at large throttle openings. It is often possible to avoid it by using light throttle to get through this range. I don't remember experiencing noticable detonation at high rpm. My understanding is that there is usually insufficient time for detonation to occur at high rpms.

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post #24 of 30 (permalink) Old 09-22-2009, 08:20 AM Thread Starter
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Does seem strange doesn't it, you would think that with the combustion chamber pressures under load being what the are at a lower rpm would be where detonation would first occur.
All I can think of is that the curve of that distributor was such that when set for good driveability the advance was fine at those low rpms but when the advance went way past the "M" mark at higher rpms there was definite detonation. Now if I set it back and got the right max advance there was no detonation, but then the timing was so retarded the driveabilty was terrible.
With the combination of springs I now have in my 006 V3 Bosch distributor I can drive on the lake road from my house to the highway, a distance of about 2 miles on a curvy rolling hills road at 35 mph in fourth gear at 2000 rpm with no sweat, don't have to down shift for every little hill on the road like I was having to do. When I hit the highway both springs are giving me a nice ramp up to max advance and the engine happily revs right on up. So by spending two days fiddling with different springs in the 006 I now have a good curve for my engine and a distributor with no points which was the initial goal of this project that turned into a quest. I will admit I learned a hellva lot on the way and my car is fun to drive so i'm a happy camper.
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post #25 of 30 (permalink) Old 12-17-2018, 06:33 PM
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NAPA part number BK735-4448 is a distributor recurve kit. There are six springs included. The silver spring replaces the light spring in the Marelli perfectly. You want no slack in that spring, unlike the slack found in the secondary spring or you could have idle and/or low speed pinging issues.

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post #26 of 30 (permalink) Old 12-18-2018, 02:17 AM
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Given Centreline are being especially helpful, why not send it back and ask for a.... 123.
Then you can program whatever curve you desire, it’s a great product

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post #27 of 30 (permalink) Old 12-18-2018, 05:39 AM Thread Starter
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Playing around with different springs is ok but without a distributor machine it's poke and hope at best. Robert at Shadetree Enginetrics has one and can recurve and he has the experience to do it right.
I thought my motor ran pretty good until I put a bluetooth 123 in. I tried a Centerline and was puzzled when I only found one spring in the advance. The other side had the weights but no spring? I never got a satisfactory answer from Centerline but they did take it back. I used RMLs on the Berlina and GTV for years until a couple of months ago I got the bluetooth for the Bertone.

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post #28 of 30 (permalink) Old 12-18-2018, 07:44 AM
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Many advance curves have two different slopes, an early steeper one and a later flatter one. The "D" curve in the old 123 that works so well on my motors has only one slope. It is a copy of a modified Bosch distributor with only one spring that is described in Jim Kartamalakis's book.
I was given data points from the owner of a Centerline distributor and it is similar to the "D" curve in that it has a single slope but it has a bigger range and a steeper slope.
If you were to set up a 123 "D" and this Centerline for the same max advance, then the CL would have less advance at idle and up to about 2500 rpm and it would have more between 2500 and 4000 rpm.

Ed Prytherch
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post #29 of 30 (permalink) Old 12-18-2018, 04:11 PM
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Quote:
Originally Posted by gigem75 View Post
Playing around with different springs is ok but without a distributor machine it's poke and hope at best. Robert at Shadetree Enginetrics has one and can recurve and he has the experience to do it right.
I thought my motor ran pretty good until I put a bluetooth 123 in. I tried a Centerline and was puzzled when I only found one spring in the advance. The other side had the weights but no spring? I never got a satisfactory answer from Centerline but they did take it back. I used RMLs on the Berlina and GTV for years until a couple of months ago I got the bluetooth for the Bertone.
I have a fancy schmancy Snap On timing light which can be used as a dizzy machine in a pinch. MT2261.

It's Giuseppe's giubos, not Guido's guibos, on my 78 Alfas
REFRESH CONNECTIONS BEFORE REPLACING COMPONENTS

Last edited by slowcreek; 12-18-2018 at 06:55 PM.
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post #30 of 30 (permalink) Old 12-18-2018, 06:25 PM Thread Starter
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cool beans!

The passenger seat is 15 miles an hour faster than the drivers seat.

currently
2017 Giulia Q4
74 GTV restored daily driver
71 Berlina in 2L restored driver
the ones that got away:
1959 750 series Giulietta Spider Veloce
1962 Giulietta Spider normale
1965 Giulia Sprint normale
1972 GTV
1974 GTV
1974 GTV
1977 Spider
1974 Spider
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