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Old 09-28-2012, 09:05 AM
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Where do I start on timing?

I recently bought a 71 el camino with a stroked 454 (496) and have no information on the motor. It runs pretty strong and has a cam card that says it has a 640 lift and 270 duration, with both valve adjustments at .24. It has a lot of lope but the solid lifters have a couple of clackers. There is more info on the card, but I don't have it in front of me. Is there a standard place to start when it comes to timing? I'm a shade tree mechanic that knows just enough to be dangerous!

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Old 09-28-2012, 10:50 AM
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Quote:
Originally Posted by Heeb View Post
I recently bought a 71 el camino with a stroked 454 (496) and have no information on the motor. It runs pretty strong and has a cam card that says it has a 640 lift and 270 duration, with both valve adjustments at .24. It has a lot of lope but the solid lifters have a couple of clackers. There is more info on the card, but I don't have it in front of me. Is there a standard place to start when it comes to timing? I'm a shade tree mechanic that knows just enough to be dangerous!

this is for a 350 but it's the exact same process, afterall the distributors are universal.



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Old 09-28-2012, 12:47 PM
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Hard to advise in any great detail if we dont know what type of distributor you have or the complete engine/cam spec? There are basic rules of thumb however. With that much cam duration and overlap the motor will want allot of base timing at idle.

First off verify TDC

http://www.crankshaftcoalition.com/w...op_dead_center

then

Block your wheels, park brake on, vacuum advance (if you have it) disconnected and plugged, rev motor to 4000 RPM and with distributor hold down bracket loose/snug rotate the dist and set the total timing to 34 Deg BTDC, (you may need a timing tape if you dont have a dial back light) then let it idle and adjust carb to get about 800-1000 RPM in park/neutral, take another timing reading at idle and this will be your base or initial timing, what is it? if it is lower than 18 deg BTDC you may need to re configure your mechanical advance to limit it or add some idle timing with vacuum advance. This is just the beginning of the tune, there are many more steps and considerations however TDC verification and determining the maximum amount of total timing (32, 34, or 36 at 3500-4000 RPM) is critical.

A cam like that is gonna want approx 30+ Deg BTDC at idle. This can come from a high initial timing + vacuum advance (say 22 initial + 10 vac adv). In some cases you can lock tihings down and out at 34-36, run no vacuum advance or mechanical advance. Chances are you have little engine vacuum with that cam? have you checked this? what kind of vacuum is it making at idle?

Is this a mechanical roller cam? what is the duration @ 50, engine compression, induction setup etc etc etc
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