USB or pre-programmed 123 distributor?

Which is better, the programmable B18/20 123 distributor or the preprogrammed?

My motor will definitely not be stock by the time I am done. I've also got a copy of the Volvo service bulletin with the different B20 distributor advance curves on it. Would it be worth the extra cash to get the programmable distributor and program it with a stock curve as a starting point?

Just trying to budget out the next round of stuff I am going to do.

My understanding is the preprogrammed ones have a dip switch with different curves. If the specs on those are good for your application then I would chose the preprogrammed one. If you are going to want more choices than the dip switch. Then it's worth the money for the usb one.

The Tune version is the only one really worth bothering with. The pre programmed ones you would be just as well doing a breakerless conversion on your original

The programmable 123s also have a switch to choose between 2 curves, but you can set your own curves.

dl242gt said:

My understanding is the preprogrammed ones have a dip switch with different curves. If the specs on those are good for your application then I would chose the preprogrammed one. If you are going to want more choices than the dip switch. Then it's worth the money for the usb one.

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My idea is to just program it with a stock curve to start from that service bulletin chart. Then start tuning it from there. I know more aggressive cams (like my D cam) like more initial timing and and advance that comes on quicker. Kind of tricky to mess with that without an old school distributor tester if I was to keep a fully mechanical system.

Maybe also have different curves I can switch between. I sort of had that setup on my 240 by setting up memory bank switching in the EZK. One curve for 87 and another for 91/93.

I am just debating whether it is worth the added complexity and the extra $100.

I did one 122S with K-cam, 2x HS6, 4-2-1 header.

Worked nicely with 123 and 085 curve and about 12 deg base timing.

I got a programmable some years ago that I used in a 242.
I had the same ideas/ponderings.
But, the engine went from stock B21 to lightly worked 160 head, camshaft and 2xDCOE (a-ok),
not long after I got a b230 block,
then I got my hands on a b230+16v and at that point the 123Tune wont clear the head/intake.
And for that I got a hall-distributor (240) with databox, cut the distributor to shorten it and put a "crab" distributor lid from a saab 900 on.
Should have just got the hall+databox from the start, cost was around 800 sek in total vs 123Tune for 5000 sek.

Then again, after all that I got really tired of carbs and got a megasquirt, and so on.
But I had a lot of fun doing all the above.

I now have the 123Tune in my amazon, that has the B21 I started with, stock head.
It just makes me question what settings I have, probably end up getting a converted stock distributor and selling the 123Tune at a loss.

spock345 said:

My idea is to just program it with a stock curve to start from that service bulletin chart. Then start tuning it from there. I know more aggressive cams (like my D cam) like more initial timing and and advance that comes on quicker. Kind of tricky to mess with that without an old school distributor tester if I was to keep a fully mechanical system.

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That is a starting point if you are talking about replicating just the RPM based (centrifugal) advance function. The RPM based advance profile used in the B20E engine would be a suitable start.

If you are planning on using MAP advance, I would not use any of the later B20 profiles since I believe that they are all vacuum retard. Also, the vacuum signal on the later B20s (both carb and D jet) is taken from a 'ported' vacuum port at the edge of the throttle plate which is not the same as a true MAP signal. It is possible that early B20s might have used a true manifold vacuum signal. I have no information on the early B20B engines.

Your engine will probably run just fine with pure RPM based advance. You can experiment with adding in advance at lower MAP values to see if that improves part throttle performance. The theory is that less dense fuel mixtures take longer to burn which is why they benefit from more advance. However, without a lot of time on a dyno its going to be hard to determine optimum settings or quantify the benefits. In the Tuning section of the Megasquirt Mega Manual there is a discussion of the process for populating an ignition timing table which includes some pretty course guidelines for ignition timing versus MAP.

I think the primary up side to programable timing is that with a fixed advance curve or mechanical advance mechanism the typical problem is having to dial back total advance to avoid detonation. That usually means mechanically adjusting the distributor which shifts the complete advance curve which is not optimum. With programable timing advance I have found that the ignition map area that is most detonation prone on my B20E is around 2700 - 3000 RPM / 70 - 80 kPa. By retarding timing slightly in that area I tuned out detonation without affecting ignition timing in other operating areas.

I only briefly looked at the 123 programable distributors. My recollection is that they do not use a timing map. Rather they have individual 10 point curves for RPM and MAP advance. That makes them look exactly like a programable version of separate mechanical and MAP advance mechanisms. The down side to that is that you get exactly the same MAP advance profile at 1000 RPM as at 5000 RPM. That would not allow you to do what I did which is just tweak the MAP profile just around 2700 - 3000 RPM.

So what did you decide?

FrankBooth said:

So what did you decide?

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Well, the decision came down to whatever was most convenient. I needed a new door lock cylinder for my S70 (the little tabs where it goes into the lock actuator broke). The cheapest place for that was Skandix even when taking into account the 125 euro shipping. It just so happened that they had the non-programmable one on sale. It was cheap enough that I just got that.

It was probably good that I did because my B20 became quite a bit easier to tune with that thing installed. I guess the old distributor was more tired than I thought.