123 ignition gains?

[Steve121]

Yep, though mine doesn't.. wish I had told them to incorporate the vacuum advance in hindsight! would get a bit more fuel economy!

[Marijn]

Hi all,
I was just reading through the forums looking for more background knowledge on the set up of different ignition curves. I would like to understand the rationale behind the different distributors in order to choose what advance curve suits my engine best. While reading, I noticed that you guys have quite some experience on the subject! Adam made a few comments in the past that I didnt understand completely, so I hope you can help me out!

First of all, it was mentioned a few times that above 2500 rpm all ignition curves flat out and are pritty much similar. However, I found an overview from the 123 ignition that suggests otherwise:

http://www.123ignition.nl/pdf/123SWITCH4.pdf

If you look at page 38 of this manual, you'll see that the max advance is almost always at a higher rpm, ranging from 2600 for a B18 penta (curve D) till 5800 for a B20B (curve 7). Can you explain this?

Also, I noticed you have recommended the 003 B18B distributor and 123 curve in the past as it has a good advance for tuned engines and doesnt have vacuum advance/retard. However, looking at the same info sheet from 123 I see that this curve (nr 2) actually does have vacuum advance of up to 10 degrees. Would you then still recommend this curve? If so, how should I use the vacuum advance, as ported or as manifold vacuum? Or is the B20B with capped off vacuum connection the better choice? (curve 7)

Last question I hope you can help me with: I noticed there are 2 different curves for the B20A: curve 4 for the standard 077 distributor, and curve 5 for the 085 distributor with alu body. I believe the last one was found on the 242's in '75 and '76 that came with a B20A. Can you explain the difference between these curves? Why would the latter have its max advance sooner (3600 instead of 4800 rpm) and have a different startingpoint (1200 instead of 800)?

My engine is a rebuild B20A, with compression increased to 9.6:1, slightly flowed head, a TT3 cam (a newly developed cam from tinustuning.nl, should give better low rpm performance then a D/K cam), a Weber 38/38 DGMS carb running on LPG. And a 123 ignition on which I'm still trying to figure out which setting will give me the best results :-)

Hope you can help, looking forward to your replies!
Marijn

[Marijn]

Nobody?
I was hoping for a reply from swedishandgerman!

[swedishandgerman]

Oh I missed this one

Yes, the curves are matches of the original distributor curves with a couple of exceptions, notably what happens when the engine is at full revs. Some drop back a bit and others have a little peak again right up there like that B20B one there at 5,800

It's all to do with optimising the spark in combination with the fuel to air mixture inside the chamber. This can be affected by cam - how widely open the valves are - and fuel delivery. Weak mixture needs more advance. Strong mixture need less advance.

Dunno what is going on there with the B18b curve. Very few B18b's even had vacuum advance, so nothing to hook up to!

With regards to your set up, I don't know how to advise you. Had you just gone for the twin carbs and cam I would say go for the B18b curve based on it is now not a B20a can. However, no Amazon came with Webers and you're on LPG which I have no knowledge on what happens with the strength of the weakness. This is where a 123 tune set up on a rolling road would quickly sort out a most suitable curve.

[Derek UK]

Marijn, what setting are you using now? Does it seem to suit the engine? Have you tried any other of the settings, perhaps ones which are close to yours numerically?
Might be an idea to talk to TT as I'm sure they have used the 123 unit.
There is apparently, a 123 forum but I've not done a search for it.

[Marijn]

Thanks for the replies!
So far I have tried the nr 6 curve (the late B20A, alu dizzy) with is for LPG. I had a fairly good fuel efficiency with that one and the car ran fine. It's hard to judge if it was optimal or not but I had no complaints. Problem is our cars will pretty much run no matter what you do with the timing :-)

Now I have switched to the nr 4 curve for normal B20A's, based on the advice from Tinustuning. He also experimented with the 123 tune and came to a curve that turned out to be pretty much similar to the standard B20A curve for his own (tuned) car. Also, he mentioned that the curve nr 5/6 is less suited as it has a more simple (singular) advance mechanism, altough I'm not sure what he meant with that. Car is again running fine, can't say I noticed much difference although I still have to check the fuel efficiency.

I'm also still tempted to try the b18b or b20b, based on that it seems to me the most similar to my current setup: increased compression, faster cam, faster carb. However, with the B20B the vacuum mechanism becomes useless, and with the B18B i'm unsure how to connect it: using ported or manifold vacuum?

[amazon69]

I found the best answer was to just go through most of them and drive the car, noting differences if any, then settle on the best one. I can't even remember what it's set to now, but I like it :)

[emeka]

Hot and burning coils once the vihicle is in motion

I use a 2005 Volvo xc90 after changing the engine too much current started coming to the coils any time i drive up to a kilometer what i do to stop it, because it has really cost me a lot of money.

[classicswede]

you would be better starting a new thread in teh right section