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My Prestolite dizzy decided to die so I have ordered a Petronix D232800. Now I need some help choosing a timing curve for my mildly built 460.
As the motor sets it is a D1VE block with stock dished pistons and ported C8VE heads running MEI 1.8 roller rockers and Ferrea CP Valves (2.19/1.75). It runs Stealth 8012 intake, a marinized Holley 80531 (850CFM with vac secondaries), and a Comp Cams 34-251-4 (dur: 236/244 @ .050, .565/.560 lift [.598/.593 with 1.8 rockers], and 110* duration). Exhaust is unfortunately still exiting through the old stock logs. This all powers a Sidewinder 18SS with a Berkeley JC pump and an aluminum “A” impeller and Hyd Place diverter.
The Petronix D232800 has the ability to advance timing a total of 24* with advance limiters of 12*, 16*, and 20*. It can bring advance to full extent by 2000, 3500, or 5000 RPM.
I’m leaning towards a base of 10*BTDC with no advance limiter and aiming for full advance of 34* at 3500 RPM. Does this seem to be a good choice or would I be better off limiting total advance to 30*?
EDIT: Well after more reading on other BBF forums I have muddied my brain even farther. Would I be better off running 14-18* initial timing (the motor does like the more advanced base in past testing) and limiting my total to 38* max?
Thanks,
Bones
http://images25.fotki.com/v948/photo...SCN2647-vi.jpg (http://public.fotki.com/Bones/misc/r.../dscn2647.html) http://images29.fotki.com/v1015/phot...SCN3289-vi.jpg (http://public.fotki.com/Bones/misc/t.../dscn3289.html)
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Your build is similar to mine with the exception of the heads and vac sec carb. I run D3 heads with compression being a point or so lower than you. I have run up to 39*total but have backed it off to around 36*. Your initial really doesn't matter (other than being able to crank it over), so concentrate on your total. A rule of thumb is to bring it all in by 3000 rpm.
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The Petronix D232800 has the ability to advance timing a total of 24* with advance limiters of 12*, 16*, and 20*. It can bring advance to full extent by 2000, 3500, or 5000 RPM.
Im leaning towards a base of 10*BTDC with no advance limiter and aiming for full advance of 34* at 3500 RPM. Does this seem to be a good choice or would I be better off limiting total advance to 30*?
Thanks,
Bones
34*@3500 ought to be the maximum ignition advance with your 9.2:1 compression ratio engine combo, assuming 91 octane pump gas. (Even if the engine doesn't detonate with more advance, you will not likely find any more power up there in your case.) Do plug readings and jet accordingly because there is such a thing as INAUDIBLE detonation; don't ask me how I know.
Roost gets away with exploring more advance because of his lesser c/r engine combination. On the flipside, if you try dropping to 30*@3500 and there is no power loss (after optimizing the fuel metering for that timing advance), then stick there...but I suspect that 30* will generate less power in your particular combination.
Nice combo, by the way.
LO
