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Old 06-15-2012, 07:27 PM
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Locked timing on the street ?

What are the pro's and con's about running locked out timing vs mechanical advance on the street. engine is a 350 Sbc with 9.1:1 compression and has Msd distributor. Engine is in a 2800 lbs Chevrolet Monza.

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Old 06-15-2012, 07:43 PM
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IMO timing locked out is for mostly WOT engines and megga cams. With a 9.1:1 motor you are not in that category are U?
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Old 06-15-2012, 08:02 PM
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I've done it and it didn't suck, but it wasn't ideal. I had a 454 with an XE268. The cranking compression suggested that my heads hadn't been shaved far enough and I was a little under my target compression. After some extensive testing and checking I found that I could lock it, set it at 34 degrees, and then use ported vacuum to fill in the gaps at cruise.

When it was very hot, it sometimes kicked back a bit against the starter, and rarely at part throttle/low RPM it would ping a wee bit.

IMO, locking the mechanical is only good if you have overdone the cam, or under-done the compression. If you're going to the extra work of locking it out, its not that much more work to just re-curve it to limit the advance.
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Old 06-15-2012, 08:09 PM
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I will say one thing for locked timing, it is predictable

yeah the starter buck is a big draw back for a street machine, OP run a retard or kill switch if you have MSD box or HEI
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Old 06-15-2012, 08:18 PM
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This is only a mild engine, - 268 Comp cam. aluminum heads, dual plane intake and a dp holley carb. Transmission is th350 with 2500 stall converter and 4.11 rear gears. So it seem's to me that it would be best to run it with the mechanical advance. (there's no vacuum advance on my pro billet distributor)

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Old 06-16-2012, 01:16 AM
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locked out timing

i have a .724 lift cam and i don't have my timing locked out. plus you should have electronic start retard. also a large distributor cap as the start retard can fire backwards which is what causes kick back and will tear the teeth off the ring gear. best case scenario is destroyed starter.
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Old 06-16-2012, 04:37 AM
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Thanks for your input guys, i appreciate your help allot and it's decided, i will use my mechanical advance distributor.

Thanks again and take care !
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Old 06-16-2012, 08:43 AM
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Locked timing can work okay but its not ideal. I have a car that has locked timing for now, but that will change once I finish wiring up the megasquirt unit. Start retard is one problem, never having truely optimised timing is the other. For your application i'd probably run 18 or so degrees initial, 34ish total and the lightest springs in the tuning kit. There are a few factors that can affect that a few degrees either way but its a good start.
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Old 06-16-2012, 03:30 PM
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Locked timing is very effective on street motors that have a big cam
240+++@.050". EG: comp[ XE284H-10. 292H magnum cam.
larger comp big muthr thumpr cam.

You don;t have a big cam. You don;t need to lock out the distributor.

If you want to try locked timing get the GM starter motor brace and install it.
This is the cause of broken starter noses, not timing.

268XE cam : I suggest 18 to 24deg idle timing. 10-12-14deg advance curve

36 max at WOT. limit the mechanical advance travel stop.
then work on the vacuum advance system.
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Old 06-16-2012, 04:26 PM
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Uh, he can't work on the vacuum advance because for some unknown reason he is not running vacuum advance on a street engine. Don't know why not.
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