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Re: advance unit tweak
Posted by MS (more from MS) on Tue, 20 Jul 2004 10:38:41
In Reply to: Thanks guys, Cessna Pilot, Mon, 19 Jul 2004 17:35:57
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I found it much easier to drill out the rivet bolt/stop, then replace that with a small bolt and nut combo that's ground down in a curved angle so as to offer a range of stop positions depending on where the nut is tightened. It really works. The idea being to add that much more retard to the timing under boost to compensate for the 2 degree advanced set timing. But, when you do that you open up a "dead spot" in the boost curve when the advance unit suddenly goes from it's set advance position to the boost position. I believe that's somewhere around 4 psi. Where the added timing retard is really needed is past 8 psi. See the problem? So what is needed is to slow down, or delay, the mechanical transition from set advance to full retard by using a restriction in the vacuum hose that connects to the advance unit. It's a simple trick that a lot of boost tweakers use. Some use a small piece of tubing and slip it inside the vac hose, others use a specially made component called a Dawes Device, which is designed so you can change the restriction rate. This mechanical means to control the timing is basically what the electronic ignition control systems do - remap the timing advance and retard based on your performance specifications. A simple restriction in the vacuum hose connected to the advance unit can never achieve the precise control levels of the electronic units, but it's better than nothing.
posted by 205.188.11...
Posts in this Thread:
- What should engine timing be on 88 900T with mods, Cessna Pilot, Mon, 19 Jul 2004 12:54:18
- Thanks guys, Cessna Pilot, Mon, 19 Jul 2004 17:35:57
- Re: What should engine timing be on 88 900T with mods, aalto, Mon, 19 Jul 2004 14:02:11
- 16, JJ, Mon, 19 Jul 2004 13:31:07
- Re: 16, aalto, Mon, 19 Jul 2004 14:04:49
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