Hot Rod Forum : Hotrodders Bulletin Board - View Single Post - locked out timing or timing curve?
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Old 07-06-2011, 07:21 PM
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Originally Posted by z-adamson
I figured a curve with vacuum advance would work best.

No experience with locked out timing though so I figured I would ask.

Couple more more questions though:

1) If high gearing as commonly found in street cars causes low rpm / high load conditions, and droping compression could keep this from being a problem when using locked timing, couldent lowering the gear ratio make this work as well? If so, would the gearing have to be so extreem that it wouldent even be streetable? I imagine that low gearing in conjunction with a high stall or a manual trans would be plausable, but then we are getting into a high rpm / high powerband application again. But hypothetically speaking, what about a low stall, low gear combo such as 1500-4500 powerband, th350 auto w/ 2krpm stall, 29" tires and 4.56:1 gears?

2) How could 20 degrees of retard be too much? Total timing would normally around 35* in most applications as far as I have seen. If the timing were locked in those same applications that are 35* total w/ a curve then it would be locked at about 35*right? With a 20* cranking retard that would mean 15* while cranking and 15* till 800rpm. I don't see how 20* retard would be problematic.
Steeper gears help a lot to let you get away with higher compression. But your ending up laying with the whole machine, which I thought you said was a street machine.

The 20 degree retard leaves only 15 degrees out of 35. The amount of advance is sensitive to RPM, throttle position and load on the crankshaft. while 15 degrees might be fine for idle it will be insufficient in the mid RPM range where most street vehicles spend most of their time. The trade to stiff gears puts a pretty heavy load on your wallet for gas. There are solid reasons why cars have gone to high ratio rear axles with overdrive transmissions that include a really deep low gear combined with electronic fuel injection. The same approach will work with a carb it just takes more upkeep to stay on tune than injection does.

But I'm pulling straws here as I really don't understand what it is you're trying to do. For the engine you described and the use of the vehicle locked out timing just doesn't make sense. So what's really going on?

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