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Re: what does this mod help out? Posted by Notnoel [Email] ![]() ![]() In Reply to: what does this mod help out?, Austin Underwood, Mon, 7 Jan 2008 05:16:51 Members do not see ads below this line. - Help Keep This Site Online - Signup |
This is really a two-part problem to be overcome:
1) The retard stop allows you to advance the timing to 20-22 degrees so that you will get a quicker response before the boost kicks in. At full boost you want a retard of about 9-10 degrees. Unmodified, the arm on the Vac advance capsule only swings through 26 degrees (from 16+ BTDC idling to -10 under full boost). TSo, if you just set the timing up to 20 degrees at idle (without changing the position of the stop), you will get better off-boost performance, but will only get to -5 under full boost, thereby limiting your top end. To overcome this, you can bend the stop back, or replace the stop with a cam (You can find out how to do this by searching the performance board under "retard stop mod" or something like that.
2) the next issue to overcome with the vac advance capsule is the rate at which the reard takes place as you accelerate. Unfortuantely, the spring in the stock capsule is not stiff enough. Once the boost begins to come on, the weak spring causes the arm within the capsule to move, more or less, all at once -- this results in a "flat spot" in the retardation curve, so that you suddenly gave more retard than is optimal. Under this condition, when you stomp the accelerator, the car hesitate for a moment, then surges forward as the boost pressure "catches" up to the appropriate retardation. To overcome this, people have created what is called and "AID", or Advanced Ignition Diaphragm, by placeing a stiffer spring inside the capsule -- Contact 900aero, Dave, for this mod.
I figured out how to modify the arm mechanism using the tiny springs from a discarded floppy drive. this creates a linear retardation curve that delivers a much more powerful, controlled, surge of power than the stock. Easiest way to do this is to buy one from Dave (I don't know what he charges. If you want to make one, it'll take you a couple of hours to build and calibrate it using a Mity pump. Search under my name on the performance board, there's a picture.
posted by 63.139.1...
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