some general "?" again. And in a hurry ...

[landybehr]

Hi,

so far (I thought) I learned several things. And .. this is to PLEASE be corrected !!


!) go lean in cruising areas of the map saves fuel. An AFR of 15.5 will not do any harm because combustion temperatures are not highest (highest at about 14.1 and lower towards lean. Maybe near as hot at WOT but then there´s a lack of O2 so the piston will not suffer). A lean mixture needs more advance, because it is less dense. So landybehr added a little advance If high EGT were measured in this condition (unfortunately I have no sond to do so) then that is because there is not enough advance and combustion is not finished as the exhaust valve opens, thus a flame escapes into the exhaust.

??) I have AFR´s that are leaner than 15.0 at the AFR-table below the 60kPA row. Advance starts at 22° at idle because until 25° the idle-RPM rose and then started to fall. Today I faced an emission test, just to know. The guy said that the exhaust was relatively hot (When he put his hand on the tailpipe to close it in order to detect leaks) and he couldn´t touch it for very long. What could be the reason ?
They said that they usually notice colder exhaust gasses when ignition is retarded. Most cars they dealt with behaved like that. .. which stands in contradiction to what I summarized above.

??) The distributor of the engine (now EDIS) has a vacuum advance (details here: viewtopic.php?f=89&t=33966 ) which adds up to 15°. IF my calculations are correct the 15° are in at 50kPa. What puzzles me is that the advance of the dizzy is 6° and testet with vacuum pipe disconnected as usual. But doing so at idle changed nothing (same on a friends car with completely different engine). Why does the vac.advance do nothing at idle, where MAP ought to be rather low, WHEN does it advance anything ?. If my friend disconnects the vac.pipe to that unit at higher RPM´s that DOES have an effect.

If I manage I´ll add the AFR and advance table in a few hours to let you decide ( ). Point is I´ll do a long trip tomorrow to license the

[landybehr]

so here´s the AFR:



and that´s the advance



as said, main concern is the fear to do any harm to the pistons +/ exhaust valves. I felt somewhat save until the guy mentioned that with the relatively hot exhaust.

[devastator]

They said that they usually notice colder exhaust gasses when ignition is retarded.

I think your emissions guy was mistaken. Maybe your exhaust is hotter because your tailpipe is shorter, you do not run a catalytic converter, you have a different muffler, etc. Either way, your advance numbers look good to me and I assume you do not get any backfires right? When I first installed MS2 on my engine, I had the advance in the 16 BTDC, , area and it would backfire long blue flames and turned the exhaust super hot. I increased the advance before I burned a valve. Currently, I idle at 27 deg BTDC and cruise at 32.

What puzzles me is that the advance of the dizzy is 6° and testet with vacuum pipe disconnected as usual. But doing so at idle changed nothing (same on a friends car with completely different engine). Why does the vac.advance do nothing at idle, where MAP ought to be rather low, WHEN does it advance anything ?. If my friend disconnects the vac.pipe to that unit at higher RPM´s that DOES have an effect.

Are you certain you are hooked to the proper port from the intake manifold? Maybe you have a stop in the dizzy that limits the advance, and you are up against it without the vacuum line plugged in? Are the springs and weights still on your advance "breaker plate"? I have seen pressure activated diaphragms on dizzy's before that will retard the timing, but these were only on turbocharged applications.

[landybehr]

Many thanks for dealing with my question!

One thing I did was to wrap this keep-heat-away tissue around the manifold. Maybe that it does a better job than I could have imagined in not letting the manifold radiate heat away. It is true that if you hold the hand behind the tailpipe it is comfortable for 2sec, then becomes noticeably hot and after 5-6sec you will want to take the hand away.

I need to check the former connected of the vacuum pipe to the vac-advance mechanism. Could be that it is put upstream the throttle disc. Which would explain the effect I described.

No, no backfire. Runs reasonably well. Could be smoother, slightly. PW´s oszillate around a amplitude of 0.3ms. AFR bounces in the same manner on some parts of the fuel map from 14.5-15,4 f.i.
Knock sensor gives no signal unless from 3000RPM where it is on regardless of load. Maybe noise. And I think I haven´t bothered about torque to mount it - which might be important (not to squeeze the piezo element by too much torque) and I will loosen and retighten it correctly. Still, no knock I think.

I think it is more difficult to determine the optimum advance than people say. It is easy for me at idle because there´s a steady condition and I can clearly see when RPM rises with no other change. At any other condition there´s so much more influence like wind, hills etc. so that I think it´s near hopeless to try. I don´t think I could rely on the knock sensor to guide me. Best advance would be which gives me most power for that bin of the map. Which needn´t be the point nearest to knock. Pity I don´t know someone with a rolling road.