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Old 09-07-2007, 01:53 PM
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Timing woes on SBC 350 with bigger cam.

Ok so basically i wan't to set the timing on the 350 i have. I know how to adjust the timing i just dont know at what rpm should i adjust it at. The block i am using is a 350 SBC Block #14093638 350 87-95 from a earlie 90's truck i think. I swapped a bigger cam in it and dont really know what to set the distributer at. This is the information i have about the new and old cam.
New Cam Intake .300 Exhaust.300
Old Cam Intake .251 Exhaust .265
The engine is running now and seems pretty good with the newer cam and the timing is set at +8 degree advanced at about 850-900 rpm is this correct and if not any ideas about what would be best for this specific situation any information is appreciated.

Thanks...

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Last edited by Brawler; 09-07-2007 at 02:21 PM.
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Old 09-07-2007, 02:45 PM
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Static timing is not near so important as total timing and the RPM at which it is all in. Perhaps your cam manufacturer can provide a starting point as to a recommendation for this. Are you using a distributor with mechanical advance? If so, a recurve kit with various weights and springs should be purchased. From there, in lieu of a dyno, ETs or even SOTP can be your guide. You want total advance in much earlier than a stock distributor's set-up. Depending, you may want to eliminate the vacuum advance altogether, if so equipped. With a timing light, you should be able to see when total timing is all in and how much total advance there is. Knowing basically nothing of your combination, start with a total advance of 32 degrees and play from there. Sometimes more advance can help in the low and mid ranges but hurt you at higher RPMs. Again, there are so many variables depending on your package and it's end use.
As a starting point, advance timing until spark knock occurs, then retard it slightly. Initial timing is irrelevant in a performance engine, as long as the engine turns over well when restarting hot. In extreme cases, even this can be dealt with by having a separate switch to activate the ignition once the engine is spinning. This shouldn't be necessary in a well tuned street engine though.
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Old 09-07-2007, 02:57 PM
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Thanks for a quick reply but i am a n00b to this whole thing and dont understand what you mean by total advance i only knew of turning the distributer wich is HEI on this motor i put the cam in and did all lash everything is pretty smooth.
i dont know much about the cam expect for what iv'e posted.
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Old 09-07-2007, 03:34 PM
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Quote:
Originally Posted by Brawler
Ok so basically i wan't to set the timing on the 350 i have. I know how to adjust the timing i just dont know at what rpm should i adjust it at. The block i am using is a 350 SBC Block #14093638 350 87-95 from a earlie 90's truck i think. I swapped a bigger cam in it and dont really know what to set the distributer at. This is the information i have about the new and old cam.
New Cam Intake .300 Exhaust.300
Old Cam Intake .251 Exhaust .265
The engine is running now and seems pretty good with the newer cam and the timing is set at +8 degree advanced at about 850-900 rpm is this correct and if not any ideas about what would be best for this specific situation any information is appreciated.

Thanks...
What about the rest of the engine and what is it in, if originally an 87-95 truck motor it was a computer controlled TBI injection system so knowing what it is now is really important because if the computer is still driving things what you need to do is different from if this is some modification using a carb.

Bogie
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Old 09-07-2007, 03:49 PM
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sorry abou that it is in a 1980 camaro fuel injection is all gone i put an carter carb 600/650, edlebrock preformer intake manifold, holly fuel pump 0-3000, cam, lifters and a hypertec electronic ingnition the rest is stock. I just want a rough idea of where i might want it set up anything is better than me just playing around.

Last edited by Brawler; 09-07-2007 at 03:54 PM.
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Old 09-07-2007, 04:33 PM
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Timing woes

For someone to say "set your initial timing at X degrees and it'll run great" they'd have to know your distributor curve etc. Not knowing that, here's how I would proceed, set your initial advance so that your total advance is in the neighborhood of 32 to 38 degrees. We can argue all day about which number is the best, but we don't know that without putting the car on a dyno or running at the track etc. Just for the sake of discussion let's say we want 35 degrees total advance. I would buy an adjustable timing light and set the dial at 35. Then I would disconnect any vacuum advance from the distributor and plug the hose. Rev the engine until the timing stops advancing, hopefully under 3500 rpm so you don't wake the neighbors. If the timing mark on the engine isn't aligned with 0 degrees on the engine balancer adjust the distributor so it does. I would let the engine idle down before I moved the distributor, then rev it up and see where the mark lines up. Repeat as needed until your total advance is 35 degrees. (Total advance for our purposes is initial advance plus mechanical advance. Disregard vacuum advance for now.) When that's done read your timing mark at 800 rpm and that's your initial timing setting. Then reconnect the vacuum advance, if you have one, and make your final idle adjustments. We'll say the initial timing is 12 degrees BTDC, if you want to see if your car performs better with 32 degrees total advance retard the initial setting 3 degrees and give it a try. Repeat as needed until your car gives you the best performance.
There's lots of ways to skin a cat, but that's how I'd do it.
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