Timing adjustment question
Thread Starter
Melting Slicks
Joined: Jun 2001
Posts: 2,525
Likes: 1
From: Sarasota, FL
Timing adjustment question
In my continuing quest for enough power to spin my tires from a stoplight I have recently adjusted my timing to 6* btdc (was at 8*). This was done at the same time as new cap, rotor, plugs, and plug wires so I do not know if this alone made any difference at all. I was simply trying to get my car to a good state of base tune (it was a bit neglected in that area, the plug wires were still original). My question now is since the car advances timing through the ECM, would advancing the base timing to 8* or so make any difference in the way the car performs? What advantages are there to changing the base timing? I am familiar with the theory and all as I have spent years tuning my vacuum advance cars and trucks, but I am unfamiliar with the way the spark curve, etc operates in the Vette and what effects changing base timing might have. Any input would be appreciated. Thanks
Bob
Bob
Team Owner
Joined: Mar 1999
Posts: 22,025
Likes: 192
From: At the beach in little Rhody
Re: Timing adjustment question (BobMachus)
Bob, ECM adds timing to the base value, i.e., if you add two degrees of base timing you effectively shift the entire advance curve up by two degrees. Hope that makes sense. I am currently running 8, but I have an aftermarket chip and have noticed some occasional ping if I am near a wall or something for it to reflect off of. Thinking of returning to six.
Thread Starter
Melting Slicks
Joined: Jun 2001
Posts: 2,525
Likes: 1
From: Sarasota, FL
Re: Timing adjustment question (vettenuts)
Thanks Vettenuts. ok so if by moving the base timing the entire curve shifts, iget that, but wouldn't the knock sensor etc retard from any knock regardless of base setting?
Drifting
Joined: Mar 1999
Posts: 1,931
Likes: 1
From: Norcross GA
Re: Timing adjustment question (BobMachus)
The spark curve gets updated continously for closed loop operation. (WOT is open loop.) Yes, the knock sensor will retard the ignition, if it detects the knock! Open loop operation (cold or WOT) puts the ECM into a predefined look up numbers situation.
ECM's are different, but most have full advance in by 3000 rpm. ESC module (knock sensor) will pull out 2, 4, 6 degree's depending on the ECM.
ECM's are different, but most have full advance in by 3000 rpm. ESC module (knock sensor) will pull out 2, 4, 6 degree's depending on the ECM.
Pro
Joined: Jun 2000
Posts: 686
Likes: 0
From: Crystal Lake, IL USA
Re: Timing adjustment question (BobMachus)
Knock sensor should react before you even hear a ping. ECM quickly pulls out a lot of timing at this point (10 degrees?), then adds it back over the next few seconds. Not the best for optimum performance. 2 degrees isn't all that much, but you really need to hook to a scanner to dial in base timing properly by looking at knock counts. My .02
Safety Car
Joined: Jun 2000
Posts: 4,870
Likes: 25
From: Long Island, NY
Re: Timing adjustment question (BobMachus)
I know guys that have the base timing at 10 degs, no problems what so ever.
As long as the knock sensor doesn't hear any pinging, you are ok.
What the other guys said is correct, moving the base timing will shift the entire timing curve up. The stock chip is based on 6 degs of timing.
I run at 8 degs, and no problems.
A stock L98 is good tune should be able to spin the tires very hard off the line. Are you saying that your car doesn't do this ?
Vic
As long as the knock sensor doesn't hear any pinging, you are ok.
What the other guys said is correct, moving the base timing will shift the entire timing curve up. The stock chip is based on 6 degs of timing.
I run at 8 degs, and no problems.
A stock L98 is good tune should be able to spin the tires very hard off the line. Are you saying that your car doesn't do this ?
Vic
Team Owner
Joined: Apr 2000
Posts: 27,818
Likes: 8
From: CT
Re: Timing adjustment question (Vic'89)
I know guys that have the base timing at 10 degs, no problems what so ever.
As long as the knock sensor doesn't hear any pinging, you are ok.
What the other guys said is correct, moving the base timing will shift the entire timing curve up. The stock chip is based on 6 degs of timing.
I run at 8 degs, and no problems.
A stock L98 is good tune should be able to spin the tires very hard off the line. Are you saying that your car doesn't do this ?
Vic
As long as the knock sensor doesn't hear any pinging, you are ok.
What the other guys said is correct, moving the base timing will shift the entire timing curve up. The stock chip is based on 6 degs of timing.
I run at 8 degs, and no problems.
A stock L98 is good tune should be able to spin the tires very hard off the line. Are you saying that your car doesn't do this ?
Vic
Thread Starter
Melting Slicks
Joined: Jun 2001
Posts: 2,525
Likes: 1
From: Sarasota, FL
Re: Timing adjustment question (Vic'89)
Yes Vic that is what I am saying. I cannot spin my tires at all off the line, hard or otherwise. I have an 88 Roadster with a 770R4. I have so far:
New NGKs
Taylor SpiroPro Wires
Cut Air lid
Premium Dist Cap and Rotor
New Fuel filter
Adjusted TPS to .64v
Cut MAF Screens
Removed and Cleaned TB
Adjusted timing to 6* BTDC
The idle is very smooth now and the mileage is much better than when I got it, but it still wo't spin 'em. Seems to pull hard above 2000 rpm or so, but no smoky burnouts. When I mash the throttle off the line the car just kinda meanders of the line and then at about 2200 or so gets a kick like a light NOS shot, or a turbo coming on. I am baffled and frustrated to say the least. I am beginning to think it may be transmission related, only because I have done so much to tune up the car. Any thoughts or input would be very appreciated.
Bob
New NGKs
Taylor SpiroPro Wires
Cut Air lid
Premium Dist Cap and Rotor
New Fuel filter
Adjusted TPS to .64v
Cut MAF Screens
Removed and Cleaned TB
Adjusted timing to 6* BTDC
The idle is very smooth now and the mileage is much better than when I got it, but it still wo't spin 'em. Seems to pull hard above 2000 rpm or so, but no smoky burnouts. When I mash the throttle off the line the car just kinda meanders of the line and then at about 2200 or so gets a kick like a light NOS shot, or a turbo coming on. I am baffled and frustrated to say the least. I am beginning to think it may be transmission related, only because I have done so much to tune up the car. Any thoughts or input would be very appreciated.
Bob
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Burning Brakes
Joined: Feb 2000
Posts: 958
Likes: 1
From: SF Bay area, CA USA
Re: Timing adjustment question (BobMachus)
Is it possible your transmission is not starting in first gear? Maybe kickdown linkage needs to be adjusted. The tires are pretty wide so it may just not break them loose on dry ground. I know with my 4+3 I really have to try to spin the tires. On wet ground it is a different story, those wide tires break loose with no effort at all.
Advanced
Joined: Aug 2001
Posts: 75
Likes: 0
From: Pueblo Co
Re: Timing adjustment question (BobMachus)
Part of the problem is your altitude in Ft Collins (apprx. 6000'). You are not getting enough air. You will loose significant power when in hogher altitude. I live in Pueblo Colorado (5000' elev.). I bought my 85 in NY and drove it out to Co., it had some upgrades (exhaust, injectors, etc.) and I could really light them up in NY but not in Co. I recently put 30 lbs injectors and a BBK 58mm throttle body for more air. Now it rips the tires off. :eek:
Melting Slicks
Joined: May 1999
Posts: 2,037
Likes: 0
From: Sarasota FL
Re: Timing adjustment question (ZylaRace)
Be careful using 50s hot rodding techniques on a modern car. The spark advance is curved for many rpm and load situations, with adders and subtractors for other situations. The knock sensor has to react to knock, which is harder to stop once it's started. There's also a maximum amount of spark that can be pulled out due to knock. Plus, max power is usually well before knock threshold. Detonation is very bad for your motor.
Unless your dampener has slipped and you're getting a false reading, leave it at 6 and find out what the real problems (if any) are.
Unless your dampener has slipped and you're getting a false reading, leave it at 6 and find out what the real problems (if any) are.
Team Owner
Joined: Mar 1999
Posts: 22,025
Likes: 192
From: At the beach in little Rhody
Re: Timing adjustment question (Aaron's 87)
One other note, just because you can't "hear" a ping doesn't mean that it is not taking place, the knock sensor is reacting and timing is being pulled. 10 degrees is a lot of base advance. You need a scanner to find out what is being removed by the knock sensor.
Pro
Joined: Jun 2000
Posts: 686
Likes: 0
From: Crystal Lake, IL USA
Re: Timing adjustment question (Aaron's 87)
But....
GM's 6 degree specification is based on using 87 octane gas, at least for MY '86. So, if you run premium, there should be room to bump up the timing a bit. A scanner will tell you how *much* room is available.
Then again....
Advance curves in the PROM also assume 87 octane and are conservative compared to 92 octane gas. To completely unleash the potential, chip burning and scanner reading are what you need to get into.
My .02
GM's 6 degree specification is based on using 87 octane gas, at least for MY '86. So, if you run premium, there should be room to bump up the timing a bit. A scanner will tell you how *much* room is available.
Then again....
Advance curves in the PROM also assume 87 octane and are conservative compared to 92 octane gas. To completely unleash the potential, chip burning and scanner reading are what you need to get into.
My .02