Hi Roy
Your your valuable input on this subject is very much appreciated!
Regarding ignition, I have been referring to Des Hammils book on the subject of tuning distributor ignition systems. He points out that it is important to get the static idle advance correct AS WELL as the total advance. I understand that total advance is a dangerous thing to play with, but with care it should be possible to go beoynd the factory numbers. As Hammil points out, the car manufacturer had to ensure that the car would be able to run on many different kinds of conditions (including fuel octane numbers) - we can be more careful. I think you agree on this, Roy?
Macaroni had his dizzy set up for something around 35 degrees total advance with a professional tuner, which is a safe number according to Des Hammils suggestions for hemispherical combustion chambers. If we look at the ignition maps at
http://www.technikhomepage.de/kfz/elektrik/verteiler.html (which I have verified to be according to the workshop manual, whether they are according to actualy distributors I don't know of course), we will find that the total centrifugal advance on the 2.2 dizzy is 13 degrees (cam), corresponding to 26 degrees on the crank.
Thus with an unmodified dizzy, we can go up to 14 degrees static ignition and still be within the 35 degrees total advance. Whether that is safe to do with a given engine on a given fuel type will have to be carefully verified of course - Hammil discusses fast road cars as well as racers, and while pinking and even a bit of detonation may be okay on the latter (where people tend to rebuild their engines routinely), I think most Murena owners will be playing the safe game. I know, I will
Hammil gives instructions for limiting the total advance of the distributor, though. It is a relatively simple mechanical modification. The difficult part is to get the tuning right - and you will always be "on your own" when you start modifying things. It's not a thing you "just" do.
Hammil claims that a 290-300 degree cam like the Holbay should run about 12-16 degrees static advance, depending on the actual engine. The 2.2 Murena engine may require less? Increasing the idle above 1000 rpm will however increase the effecitve idle advance (by simple centrifugal advance), so it may not be necessary to advance it at all on a given setup, but that's another story.
Thanks for the tip of lubricating the distributor - that was a service item I would have missed! It is extremely valuable to have this kind of advice passed on from an experienced person like you.
As always, your input is extremely valued, Roy.
- Anders
PS: Your performance numbers on the Holbay cam with the single carburettor setup should impress a few people. With that cam, I beleive that the exhaust manifold is much more important to its performance than the inlet.