Should ignition timing be locked out for drag racing? - Hot Rod Forum : Hotrodders Bulletin Board
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Old 05-03-2008, 02:04 PM
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Should ignition timing be locked out for drag racing?

I am trying to decide if the ignition timing should be locked out on a ford 347. This is in a 70 mustang with 4.11 gears and a 3000 stall converter. The engine has edelbrock victor jr. heads and intake with a comp cams 288R solid roller cam. Since the timing would generally be all in by 3000 anyway would it be beneficial to just lock the timing at the full advance? 3000 stall would mean that the engine doesn't see significant load until then right? What would be the advantages and disadvantages of doing this?

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Old 05-03-2008, 06:42 PM
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Quote:
Originally Posted by chevyv8_power
I am trying to decide if the ignition timing should be locked out on a ford 347. This is in a 70 mustang with 4.11 gears and a 3000 stall converter. The engine has edelbrock victor jr. heads and intake with a comp cams 288R solid roller cam. Since the timing would generally be all in by 3000 anyway would it be beneficial to just lock the timing at the full advance? 3000 stall would mean that the engine doesn't see significant load until then right? What would be the advantages and disadvantages of doing this?
Typically a full up drag engine uses either a locked advance or a lot of static with a small amount of centrifugal.

If you go this way, it's a good idea to put an ignition kill switch in the car, class rules may require this anyway, this lets you crank it up without spark then put the spark on after it's had a few revs. This takes a lot of load off the starter and reduces backfires when cranking.

Bogie
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Old 05-03-2008, 06:42 PM
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Engines with long duration cams need much more spark timing at idle to idle
correctly and have good throttle response. (intake reversion and Exhaust gas EGR effect slows the fuel burn time) Your cam is up there - borderline. Will need minimum 24deg at idle.
Requiring a shortand quick 10-12deg advance curve. It will probabily run fine with locked out timing. My 406 SBC has a similar duration-overlap hyd flat tappet cam XE284H-10 and runs around just fine with locked timing+ custom tailored vac advance.

Very stable. Maximum low end torque and throttle response. Clean consistent idle.
Adds strain to the starter motor when hot starting. a Spark kill switch and/or start retard box takes care of that issue.
You can still use vacuum advance but it will need custom dialing in. I use ported vacuum. I generally lock out the timing on motors with more than 250
@.050 duration.
Try it. If you find an issue you can always redo the distributor advance curve as described above. I lock out mine using common electrical tie wraps to bind the advance mechanism so it can be reversed and restored easily if nessessary.
Many aftermarket distributors (MSD etc) have the built in ability to lock out the timing advance with minor dissassembly and reconfiguration of the mechanical advance mechanism. Read the directions.
Crane sells good fully adjustable vacuum advance cans for various different distributors.

Last edited by F-BIRD'88; 05-03-2008 at 06:48 PM.
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Old 05-04-2008, 12:33 PM
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Is my thinking right then that when the stall converter is to the point where all the timing would be all in anyways that you could lock out the timing?
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Old 05-04-2008, 04:55 PM
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No really. It strickly has to do with the idle and low speed timing requirements of a motor with a long duration/high overlap camshaft.

If you run a mild cam say 214-224@.050 and a 3500 stall, you don't need to lock out the timing.
Not to say that a somewhat modified advance curve won't help acceleration and throttle response.
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