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Old 02-04-2013, 01:29 PM
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Originally Posted by damanx View Post
It's just the stock cam in the engine.

I would love to get this truck on a dyno, but I'd love to get the basics in the ball park first.
The mechanical traditionally wants to be all in at or before 3000 rpm. In your case, seeing the 40-plus degrees at light throttle cruise if fine. I do not know what is the best max power timing (initial plus mechanical, w/o vacuum advance added in), but once you find this by track testing or from others who have done this, you can tailor the curve as it needs to be.

The vacuum advance is dropping a lot of timing- looks like 20 degrees. You can use a limiter to limit the amount of vacuum advance to around 12 degrees or so, then add the 8 degrees or so back to either the initial or mechanical timing- or a little of both.

I like to use as much initial as I can. This tends to make the idle better and the off idle response is also usually better. You know you've found the limit when it gets balky to start hot. With a stock cam there's no need to go so far w/initial timing that the starter starts to drag hot, so keep it below that level.

Once you've found the limit to the initial, the rest comes from mechanical. You can start trying lighter springs to bring in the mechanical as early as it'll allow. How early this will be will depend on the fuel, vehicle weight, gearing, etc. and you'll be doing some trial and retrial to get it right.

You prollably don't want the mechanical all in at 2000 rpm, though. I think this would be too low and you'll have problems w/it pinging. When you get on it, the transmission should downshift (passing gear), or you can manually drop it back a gear. This will accelerate the vehicle a lot better than leaving it in a higher gear and pulling from 2000 rpm.

There might be something to be said for an adjustable vacuum advance if one's available for the distributor you're using.
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