[Healeys] 123 Tune - timing settings
WILLIAM B LAWRENCE
YNOTINK at msn.com
Sun Oct 16 18:22:14 MDT 2016
The ported vacuum takeoff is located ahead of the throttle butterflies so they are separated from manifold vacuum when the butterflies are closed. that means the vacuum advance comes into play when the throttle is opened and not at idle. Taking the signal from the manifold would mean the advance would occur when the throttle is closed, which is the opposite of what the engine needs.
From: Healeys <healeys-bounces at autox.team.net> on behalf of Roger Grace <roggrace at telus.net>
Sent: Sunday, October 16, 2016 6:29 PM
To: Healey List
Subject: [Healeys] 123 Tune - timing settings
I recently installed a 123 Tune distributor on my BJ8, replacing a Pertronix - mainly for ease of adjustments, repeatability, and to eliminate the mechanical weights springs and vacuum advance; and not be constrained by the mechanical limits of the Lucas/Pertronix; a crank fired system was appealing but too much hassle to fit the toothed wheel !
Works OK - now after realising you have to be ultra diligent about taking up the rotor drive freeplay before closing the cap.
Timing curves are set via a USB connection to a PC.
Checked with a timing light and the advance you set is what you get at the crank.
Hoping some other listers have installed a 123 Tune and would share the settings/curves that have worked best for them on AH 3000 engines and not being constrained by mechanical advance. Also vacuum settings that have worked.
My manual gives 10 deg. static advance and 15 deg strobe at 600 RPM then 34-38 deg at 6400 RPM.
I used max of 35 deg at 6400 RPM
When I use these settings the timing was too retarded.
Checked with a vacuum gauge that was very jittery at 700 RPM and way down at about 7-10 ins
To get a sensible vacuum reading (18ins) have to use around 22 deg at 600 RPM.
Did some road testing - the 123 software has a nice RPM stopwatch feature.
Around 22 deg seems to give best results. Went from 1200 RPM to 2800 RPM in 4th and 3rd gears. Interesting - reducing advance to 17 deg made a big difference - lot worse. Use 94 octane Chevron and no pinging. Believe it is a standard cam. Only mod I have is a Maniflow exhaust header. Compression is OK at 155 psi ave.
So why are these advance setting so different to what the manual gives for the Lucas 25D ?
(I find some of the manual advance data to be confusing particularly the decelerating and vacuum settings)
Unfortunately didn't take a note of the settings I used before I made the distributor change as had just set it "by ear".
Also wonder if anyone has tried manifold vacuum for advance instead of the ported take off ? With the flexibility of the 123 it sort of makes sense to deviate from the standard settings.
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