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Old 02-01-2013, 02:24 PM
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Timing question

It seems like everyone I know advances their timing. Why is that,I know if you advance too far you can cause detonation. What are the advantages of advancing? If it makes more power or economy,you would think the Mfg would set it ahead. Do you have to advance it on a street motor with a mild cam? I have played with mine a couple times & didn't notice any difference in how it ran,so the guys that are always turning it ahead,are they doing it for a reason,or just because maybe some race car driver did it?

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Old 02-01-2013, 03:32 PM
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You must set the timing where the engine runs best.
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Old 02-01-2013, 04:58 PM
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Timing

It depends on the engine and what its used for. Mine is advanced as well...but thats because I leave the line at 4500 RPM's. I want mine in full advance. Industry started retarding timing to keep their engines running longer. Daily driving a car with full advanced timing, with cold and hot starts, wont take long to destroy that engine. Timing was retarded to contribute to longevity...vacuum advance will still advance the timing under acceleration to provide performance. This is just a generalized statement in attempt to paint a picture for you
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Old 02-01-2013, 05:20 PM
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Best timing is determined by many things. Advancing a stock engine ay not gain enough power to warrant the longevity and drivability issues. On a hopped up non-stock engine, it can make a world of difference.

Finding the right combination can be tough and purpose specific. Drag only, Street only or street/strip.

I am at 24* at idle (1000rpms) with no vacuum advance. I am all in at 36* by 3000rpms. Vac advance adds 8* under light throttle. Works well for my cam combination. If I go any lower at idle, throttle response suffers as well as vacuum. Any higher and its hard to start. I had to not only advance timing but limit mechanical advance travel and vacuum advance travel.
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Old 02-01-2013, 05:30 PM
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I guess it can be complicated. My car is strictly street it book says 5* I have a mild cam and have it set at 10* ,the car runs really good ,but if I go from idle to wot it bogs & backfires through carb. Would more advance help that?
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Old 02-01-2013, 05:49 PM
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The shop manual indicates overly retarded initial timing advance because the factory does not know what gasoline octane rating the car owner is going to use. That is part of the factory CYA program in order to prevent engine damage and warranty issues.

If you have 9.5 to 10.5 compression ratio, set the initial advance at 12 degrees with the engine idling at the lowest RPM possible. That setting must be with the distributor vacuum temporarily disconnected and the vacuum source plugged. After the initial advance is set, reconnect the vacuum and turn up the idle to where it idles best, usually between 700 and 900 RPM for a stock or mild camshaft. It is best to set the idle as low as possible in neutral or in drive if it is an automatic transmission.
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Old 02-01-2013, 05:53 PM
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timing

Well, a vacuum advance spring kit could help, but you may have other issues causing that bog. Dont know what carb you have, but perhaps its dumping too much fuel into the secondaries upon WOT. Have it open later or check the squirters and jets to the secondaries. It couldn't hurt to advance your timing up some. Play with it a little...try advancing it 5 degrees and take it for a spin. Whats the engine and what kind of carb? whats it in?
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Old 02-01-2013, 05:57 PM
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Its a 390 Caddy,recent rebuild,mild cam, running 2 Stromberg 97's all the time (not progressive)--The one in my avatar---has 6 carbs,but only use 2
10.5 compression & uses premium gas
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Old 02-01-2013, 06:09 PM
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timing

OH....very nice! I'd run your timing between 12 and 16 degrees advanced. You should notice a definite difference. Just talked to my buddy who runs a similar engine and told me that he advanced his due to unleaded fuel. Had to be retarded back in the day to accomodate leaded fuels. Try advancing it...should notice a very nice change
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Old 02-01-2013, 06:13 PM
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Thank you---will try it,but winter time here now--probably won't have it out till next month---I'm always afraid to go too far because I run lakes style headers & can't hear if it would start pinging
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Old 02-01-2013, 10:17 PM
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Quote:
Originally Posted by yragat View Post
I guess it can be complicated. My car is strictly street it book says 5* I have a mild cam and have it set at 10* ,the car runs really good ,but if I go from idle to wot it bogs & backfires through carb. Would more advance help that?
Your problem may have nothing to do with the ignition timing, but rather the fuel mixture when the throttle is opened quickly. I think that you are not getting enough accelerator pump shot. Been there, done that!

Bill

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Old 02-02-2013, 08:49 AM
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There is a big difference between initial timing and total timing. When people advance the timing at idle they typical need to reduce the total timing curve to maintain the total timing amount.

Low timing at idle is an emissions device. Makes the exhaust hotter which makes better exhaust emissions.

A bog or back fire from the carb is caused by low timing and/or not enough accel squirter in the carb.

Even a mild engine likes more timing at idle but if you use more initial timing then you will need to reduce the timing curve in order too not over time the engine at higher rpms.

I run 20 degrees with my 454 then add another 10 with the vacuum advance connected to a manifold vacuum source. So it idles at 30 (20 + 10). Then adds another 20 of mechanical mostly all in by 3000.

The best total timing for an engine depends on a lot of factors. An engine will need more timing if the pistons are very wide, if pistons are domes or dishes, and if the heads have slow flame travel (to name a few). My 454 has all of these things and requires lots of total timing (40) to run at it's best. On the other hand, a vortec 350 with flat tops runs best with around 34 degrees of total timing.
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Old 02-02-2013, 09:22 AM
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I haven't been able to find out what total should be on the Caddy engine ----it is a 1960---390ci new rebuild with mild cam my vac advance (connected to manifold ) is 12* and I believe my centrifical is 12* also---If I remember ---have it written down some where--will have to check.
And I probably should have 4 of the carbs running instead of 2 ,but can't afford to have them rebuilt & get linkage right now plus the gas stations would eat me alive. Like I said the darn thing runs like a rabbit,except from idle to wot. And who doesn't like to blow off a tuner at the stop sign once in a while ha ha
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Old 02-02-2013, 09:22 AM
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timing

454c10 kind of hit the nail on the head. There are simply alot of factors involved in setting timing thats correct for your car. Alot of which is trial and error. Heck, even the climate you drive in will influence timing. I'm running a 383 stroker and I'm usually all in about 38 degrees total advance. I played around with a recurve kit for a day before finally settling on the advance that seemed to work best for mine. A whole day at the track and 40 passes, alot of number crunching, alot of tuning, and I'm finally happy that I've got all I can get out of her. Alot of patience and a little money and you'll work you way through what works best for your engine.
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Old 02-02-2013, 11:12 AM
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Compression ratio over 9.5:1 cannot tolerate more than 14 degrees initial timing advance. My 455 CI Pontiac had 12:1 compression ratio and it ran best at 12 degrees initial timing advance, + 12 degrees vacuum + 10 degree mechanical = 34 degrees total at 3000 RPM.

The lower the compression ratio, the more initial advance must be used to get good torque and throttle response. At the risk of over simpification, a lot of initial timing advance in a low compression engine gives the piston time to build up dynamic cylinder pressure as it approaches TDC after ignition occurs.
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