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Old 09-14-2007, 05:55 AM   #1
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Retarding Timing?

I'd heard of it done a few times in order to increase FE.

My question is, does it work, and if so, how much should I do it? Just a couple degrees?
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Old 09-14-2007, 12:13 PM   #2
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retarding the timing wouldn't result in an increase FE. by retarding it, you are starting the burn in the cylinder later, which will result in the fuel not completely burning while in the cylinder. you'll be basically having still burning fuel go out on the exhaust stroke

so, you'd lose efficency, rather than gain it.
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Old 09-14-2007, 01:30 PM   #3
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Pyro - Remember that almost all car manufacturers run their timing advanced from TDC of the piston. I think What Biff is shooting for is changing the timing from being 16° BTDC (Before Top Dead Center) to maybe 12° BTDC. I used those specific numbers because that is the operating range on most of the Honda motors for Ignition timing.

Biff - I'd check your service manual on what is a safe ignition timing range for your car as per manufacturer specs, then set it to the low end if it isn't already and see what that does for your MPG.
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Old 09-14-2007, 07:35 PM   #4
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I've heard that you want the peak pressure in the cylinder to occur at somewhere around 14 degrees after TDC. To do this requires that the spark occurs before TDC. If you can increase the combustion efficiency and get the mixture to burn more quickly and completely, the timing will need to be retarded or the peak cylinder pressure would be reached too quickly and the engine would wind up working against itself. Also, speeding up the burn rate will reduce the NoX emissions because it won't have time to reach the temperatures necessary to produce NoX.
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Old 09-14-2007, 10:51 PM   #5
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Pyro - Remember that almost all car manufacturers run their timing advanced from TDC of the piston. I think What Biff is shooting for is changing the timing from being 16? BTDC (Before Top Dead Center) to maybe 12? BTDC. I used those specific numbers because that is the operating range on most of the Honda motors for Ignition timing.

Biff - I'd check your service manual on what is a safe ignition timing range for your car as per manufacturer specs, then set it to the low end if it isn't already and see what that does for your MPG.
I am very well aware of this. you don't want to retard your timing either way. you WILL lose power and efficiency. You want that to spark ASAP to start the burn. too soon, you'll detonate, and if you have a new enough car, the knock sensor will retard the timing to stop this. The knock sensor will crank the timing up as far as possible till you almost reach detonation, and keep it there. thats when your getting the most energy out of your fuel.

longer its burning in the cylinder, the better.
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Old 09-15-2007, 03:00 AM   #6
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I don't have a working knock sensor.

I have the timing set to the factory stock of 10* btdc.

I've noticed that turbo cars have timing far less advanced than N/A cars...
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Old 09-15-2007, 06:05 AM   #7
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the timing for the turbo cars goes back to the detonation thing. Forcing more hot air in there, is going to raise the pressures in the cylinder more, and if you spark that plug too soon, the heat and pressure will start the burn extremely quickly, and start to apply power to the piston, before it is even over TDC. then you have detonation. not good.

most turbo cars run a boost retarded ignition, so when your just crusing (no boost) it will have the timing advanced as far is it can, then when in boost it will pull timing so it doesn't detonate.
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Old 09-15-2007, 07:46 AM   #8
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Originally Posted by Pyrorocketeer View Post
most turbo cars run a boost retarded ignition, so when your just crusing (no boost) it will have the timing advanced as far is it can, then when in boost it will pull timing so it doesn't detonate.
his car is an 87 ford. i doubt it changes the ignition timing.

10 degrees btdc is pretty retarded already, no pun intended, i would NEVER retard the timing further unless the car was knocking. i know that you are not me, but if i were you i would clean out anything that would be lowering the octane level of the air fuel mixture and try to advance the timing 1 or 2 degrees for better fuel economy.

turbo cars have to retard timing for boost, thats why more modern cars that can control their ignition on the fly make a lot more power just by putting a higher octane fuel in there. they immediately advance the timing to an optimum range and can squeeze out the extra efficiency(power).

bottom line: advancing the timing within safe means is what will give you better mpg.
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Old 09-15-2007, 08:25 AM   #9
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his car is an 87 ford. i doubt it changes the ignition timing.
it probably has a mechanical advance, or vacuum advance, so yes it does. if it has vacuum advance, it can easily be made for boost.

all in all, don't retard it.
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Old 09-15-2007, 12:58 PM   #10
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it probably has a mechanical advance, or vacuum advance, so yes it does. if it has vacuum advance, it can easily be made for boost.
interesting. i didnt know that technology was employed back then...

out of curiosity what is this cars redline?
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