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Spark curve for turbo engine.
https://www.slantsix.org/forum/viewtopic.php?t=10679		 Page 1 of 1
Author:  Dartvader [ Sun Oct 17, 2004 10:16 pm ]
Post subject:  Spark curve for turbo engine.
Much thanks to Dart270 for serious help on tuning the turbo Dart. Seems the spark was way too advanced, and the fuel too rich. Retarded the spark about 10 degrees to 2+ and leaned the entire fuel map out. It now runs pretty well during power runs except get pre-ignition at BOOST in high gear and low RPMs (1500-2500). What is needed is centrifigal advance that comes in later, and vacuum advance with more degrees of advance. Lou and I talked about using a V-8 canister, and heavier springs on the centrifigal. I have a local shop that can curve the distributor for me, but I need to tell them what to do. Otherwise it is just a crap shoot. Any ideas out there. Any experience that dictates where to go here. Bobd, what are you doing in that regard? How about Charlie S and the Drakes?Others? Maybe we can generate some talk here about this. Thanks in advance.
Author:  Tom Drake [ Mon Oct 18, 2004 5:01 am ]
Post subject: 
Cant really help you here. Our EFI system allows us to add/remove timing and fuel where needed. I have a few books at home and I will read tonight and see if they have any good suggestions.


Tom
Author:  Charrlie_S [ Mon Oct 18, 2004 5:13 am ]
Post subject: 
I can't really help you out. When I built my turbo, there was no such thing as electronic fuel managment, or boost controled timing. I used a Holley 4412 2bbl carb, in a draw thru system. I had a points distributor, msd 7, msd "ping" control, and a msd rpm based retard, that was turned on by a pressure sw at 5 psi boost. When I put my turbo on the Cuda last year for Bristol, I used a msd boost timing master, and a new waste gate. I had problems with both, and removed the turbo, and reinstalled the nitrous system, at the track. Now that the racing season is over, I'm going to install the turbo back on the Cuda, and see if I can resolve the problems. The Cuda is a street car, so I will be able to put some miles on it. I am still working on the body of the Valiant, and it is not road/track ready at this time.
Author:  Dart270 [ Mon Oct 18, 2004 7:06 am ]
Post subject: 
Vader,

Did you try retarding total advance to 22 or so yet? What was it when we left it?

Lou
Author:  Dartvader [ Mon Oct 18, 2004 3:03 pm ]
Post subject: 
Good question Lou. I found an 11 degree vacuum advance pot in my drawers of junk. It leaks some, but I figure on an EFI engine that won;t really matter. It holds the advance stable on the engine, but bleeds down some with a vacuum pump. Anyway, I installed that, and discovered two things in the process: the centrifigal is already kicking 2.5 degrees of advance at 900 RPM, which I believe is way too early for this set up, and with the way the plate on the bottom of the distributor is set right now, I cannot set the timing any more retarded than 2.5 BTDC. I was running out of time, so I just left it at that, after a short test drive to make sure it was going to get me to work tomorrow. The engine idles at 30 BTDC with 2.5 initial, 2.5 centrifigal and an honest 25 in the vacuum advance, even though it says 11 (times 2 should be 22, right?) on the pot arm. That means if the total advance, minus vacuum is 25, it would cruise at 50 BTDC, probably not a bad fit for economy. I will check out where it sits at full centrifigal soon. Any of you racers out there got total advance figures to throw my way.

So, Tom, do you have any numbers from your spark map you can enlighten me with? You should know more than anyone what spark advance a turbo slant wants, and have hard numbers to back it up. I realize your cam is huge campared to mine, but I will take that into consideration. A smaller cam wants less advance on naturaly aspirated engines.
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