I threw this together - combination of the cam profile image + timing info. If anyone has the specs for the ??? boxes - let me know & I'll update my image.




Ok, my question:
Why such a variance between the US cars when it comes to ignition advance? All US 16V cars have the same ignition system. The distributor diaphragm changed from 83-84 (dropped the vacuum retard line).

Just curious if this is due to cam changes (if so, what are the EuroS ignition specs?).
Or, in the overall interest of fuel economy to spec the cars for 87 octane (leaving some performance at the door when running high octane - could crank up the timing).

My uneducated mind tells me with a weaker cam profile (80-84) you could / should run more advance, not less. So why with a weaker cam did timing go down? My money is on fuel economy / setting the motor for low octane fuel.

Yes I started a thread over a year ago with the same question - went way off topic.

Yes I am aware many 16V owners have gained performance by increasing ignition timing. I'm simply looking to discuss why the factory specs these cars where they do.

 

Bueller?

 

you membership expired?

 

> Bueller?

He's sick, I know this guy who knows...

 

Yea, sent in my payment a little late.

 

iirc the CR on 84-85 euro was 10.5:1 could be the same on post 1980 euros as well

 

If I have time, I can pull the euro cam specs from my tech spec book at home later today. IIRC.

 

ROW S '80-83 CR is 10.0:1 and '84-86 is 10.4:1. '80-82 ROW 4.5L is also 10.0:1.

 

Differ in EMS. L-Jet and LH.

 

And CIS (78-79, and all Euro's up to 84)

I'm just trying to make a one sheet list for timing & cam data.

I'm also still trying to figure out or come up with some theory why ignition timing varies so much over the years when bascially the ignition systems did not change, at lest until 84-85. All 16V 928's from 78-83, CIS and L-Jet have the same ignition system.

I'm also wondering, if you lined up all the cams, how do the cam timings compare? Meaning, is the key way in the same location in respect to when the valves open?

 

I believe emissions play a significant role.

 

That's my theory. See, what I'm trying to do here is help the owners of US cars understand (including myself) how far we can push the US 16V motors. If the Euro engines are sitting at 32+ degrees advance where the US cars are at 20 - then you take into account there is a cushion for bad fuel, or low octane on even the Euro's. We have a lot of room to go on the US cars.

Not to mention those of us running boost need to have a base timing map to follow. A common theory I've read on many boosted sites is once you have the max timing figured out N/A - you need to retard 1/2 - 1 degree per pound of boost, as a basic formula. The baseline for these cars is all over the place when you compare every 16V car.

Anyone following me here?

 

Yep, I'm with ya. FWIW, my 78 set at spec will on rare occasions, ping just a little on very hot days at WOT -- maybe on one or two occasions on a long, "spirited" drive. That's why I haven't fooled with advancing the timing any. It would be interesting to take a 80-84 car, put 76 premium in it, and advance the timing a degree or two at a time and see how close to the 78 spec you can manage. Before & after dyno(or even g-tech) would be extra-interesting.

 

Shark,
What kind / rating gas to you run? My 79 is set to stock specs, even using 87 octane on the track (don't ask) I've never heard any knock / poing from my motor.

How stock is your car? Cats, manifolds, plugs, wires etc......? My 79 is running wide open exhaust after the headers, that might / should make it run a bit cooler. The back pressure from the original manifolds is huge.

 

I use '76 91. It's using spec copper plugs, Beru wires, all stock exhaust as far as the cat(single) -- then a Borla cat-back from there. The last time the timing was checked was during my 2004 smog check. I seriously doubt that it's moved. The more I think about it, the more certain I am that the only time I hear pinging is on hot days while running "winter-formula" fuel.

Are you sure you would be able to hear any pinging above that exhaust?