Importance of ignition advance in high boost applications?

[TTA976]

I talked to Dan at DLS 5 or so years ago... He explained the pro and cons of timing. Long story short he told me not to run more than 19* up top. .. 93/alky. I run 19* up top, 26# boost and target 11:1 a/f . No issues with knock and the turbo ta pulls smooth... Didn't pick up any mph on higher timing on MY car. Every car is different.

 

[Mr.Spool]

I've become very interested in this topic. Curious if some opinions have changed over the last four years when this was originally discussed?

Tuning strategy can be way different from combo to combo.some go low timing bigger boost some go higher levels of timing and lower boost.the fuel being used,compression,turbo inter cooler,and how good or bad of and air pump you have are all factors.in the end the motor can only move so much air.on the timing comments I have run as low as 14 degrees and as high as 32 degrees on these 109 motors it was very enlightening.dont think for a second there isn't power in higher timing with the right fuel and circumstances.

 

[TTA976]

Too much timing = high cylinder pressure is what kills motors. Generally speaking you want higher timing (down low) as you increase cylinder pressures , then you want to scale down the timing (up top) while the most load is on the motor.

 

[Mike T]

The complete understanding of tuning is not one of my strong points. A while back my car went on a dyno for a baseline. After the first pull and a review of the PL files the tuner said pulling timing would be his first move for more power. This has always puzzled me because it was contrary too what I've always thought.

Later I asked a very smart Buick guy about this and he said their is really no definitive answer. Basically said "sometimes more" and "sometimes less".
He went on to say "pick a direction" (add a degree or remove a degree) and watch the AF ratio.....if it starts to lean out your going the right way.

 

[Jerryl]

Too much timing = high cylinder pressure is what kills motors. Generally speaking you want higher timing (down low) as you increase cylinder pressures , then you want to scale down the timing (up top) while the most load is on the motor.

I agree with this.
In a perfect world, a system would independently close loop adjust each cylinder for AFR and timing for min/max cylinder pressure @ given crank angle.

 

[TurboBuRick]

Too much timing = high cylinder pressure is what kills motors. Generally speaking you want higher timing (down low) as you increase cylinder pressures , then you want to scale down the timing (up top) while the most load is on the motor.

It's my understanding engines are loaded harder at lower rpm. As rpm rises and vehicle speed increases, load decreases. Detonation is another story. Ignite fuel before the piston is on the down stroke, it will create a ton of pressure. Hence blown head gaskets and cracked pistons.

The killer is HEAT. That's why timing needs to decrease as rpm rises. Thermal meltdown can happen with no detonation.

Rick

 

[Mike T]

This is the PL screenshot at peak HP of about 450....I knew it was rich and probably power left on the table there. This was pump gas so we didn't want to push the boost any more but he really felt pulling timing would have been the way to go. Wasn't there for tuning just wanted a baseline.....looking back I wonder if it may have had 500+ in it as he suggested.

 

[bison]

That's why timing needs to decrease as rpm rises. Thermal meltdown can happen with no detonation.

Rick

I disagree. Too much timing at flash is what heats the cylinder and sets it up for disaster which is a common problem. I've seen a lot of engines hurt when the timing at flash was too much. Car usually runs it's best 330' and 660' ever and is broken by the 1000'. More timing is needed at higher rpm because there is less time for everything to happen.


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[TurboBuRick]

I disagree. Too much timing at flash is what heats the cylinder and sets it up for disaster which is a common problem. I've seen a lot of engines hurt when the timing at flash was too much. Car usually runs it's best 330' and 660' ever and is broken by the 1000'. More timing is needed at higher rpm because there is less time for everything to happen.


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Par for course. You have said it yourself never run more than 20* max timing with 93 and alky. I'm done posting

 

[Reggie West]

Bison I understand why you are a little cagey about giving away some of the info you have found.

But you cant have it both ways. If you are going to disagree with others here you gotta back it up. Come on dude.

 

[bison]

Bison I understand why you are a little cagey about giving away some of the info you have found.

But you cant have it both ways. If you are going to disagree with others here you gotta back it up. Come on dude.

It is backed up. Re-read the post


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[Mr.Spool]

.looking back I wonder if it may have had 500+ in it as he suggested.

Looking at your screenshot I'm glad you guys didn't try.pushing things on pure pump gas is the one of quickest way to torch things.keeping a fuel cushion is inmo a key ingredient to keeping the cars together octane is the other.

 

[MCH86GN]

...a very good question. As somebody who studied internal combustion engines a lot in college many years ago (yes, I'm one of "those guys"), I'll try to give the answer to the original question. I'll try to keep this from becoming too much of a scientific paper.

There are primarily two reasons why the guys who run small engines with 4-valve heads generally run lower timing than we do...

1. Their spark plug is located in the center of the cylinder. All other factors being equal, it will take less time for the flame to travel across the cylinder when the spark plug is in the center of the cylinder (the case for most small four-valve engines) than when the spark plug is located on one side of the cylinder (like our Buick engines). The flame front only has to travel half as far after the spark plug ignites it.

2. Most four valve engines introduce a lot of air and fuel tumbling into the air that is flowing into the cylinder. That air is still tumbling around even after the piston comes back up towards TDC and the spark plug fires. The more vigorously the air is tumbling (and/or swirling) at the point of ignition, the better mixed the air and fuel will be, the more rapid the combustion will be, and the air and fuel will burn more quickly. You can do some research on the internet to learn more about "tumble" and "swirl" in engines. Generally speaking, newer engines are designed to introduce more tumble and swirl into the air charge as it enters the cylinder than older engines like ours. More tumble and swirl = more rapid combustion = less spark timing needed to get best torque. Ever wonder why newer, naturally aspirated engines make more torque and power per cubic inch than older engines? More attention to tumble and swirl are part of the reason why.

One other possible factor is simply that they are getting more cylinder filling than we are - they run more boost, and their engines breathe better than ours. So, on each intake stroke, they are cramming more air and fuel into the cylinder than we are. All other factors being equal, the more dense the air mixture is in the cylinder, the more rapid the combustion, and the less timing you need to reach best torque. Ever wonder why you need a lot less timing at WOT than you do at part throttle? The increase in the speed of combustion as the amount of air filling the cylinder increases is the primary reason.

We did some studies back in the day, and we found something very interesting about gasoline engines. An engine will make the best torque (i.e. produce the most "oomph" on the piston) when the peak cylinder pressure occurs at about 17 degrees after top dead center. This was proven over a wide range of gasoline engines, and it's a testament to the fact that the geometry of most gasoline engines (bore to stroke ratios, bore to rod length ratios, etc.) are actually pretty similar. Whatever spark timing results in combustion that produces peak cylinder pressure at about 17 degrees after TDC will result in best torque, assuming you can run that spark timing without knock. Strange, but true. Note: I'm typing 17 degrees from memory, because I don't have my old college books handy, but I'm pretty sure I remember that number correctly.

Hopefully this helps answer the original question.

I thought the location of peak pressure to get the best mechanical advantage, was 14* after TDC.


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[DR BOOST]

It's my understanding engines are loaded harder at lower rpm. As rpm rises and vehicle speed increases, load decreases. Detonation is another story. Ignite fuel before the piston is on the down stroke, it will create a ton of pressure. Hence blown head gaskets and cracked pistons.

The killer is HEAT. That's why timing needs to decrease as rpm rises. Thermal meltdown can happen with no detonation.

Rick

it is my understanding that the spark always occurs before the downstroke.....0 deg. would be TDC and 14 deg would be 14 deg before TDC. things happen fast in an engine.

 

[DR BOOST]

or is it 14 degrees before base timing?

 

[TurboBuRick]

it is my understanding that the spark always occurs before the downstroke.....0 deg. would be TDC and 14 deg would be 14 deg before TDC. things happen fast in an engine.

You are correct, spark occurs before tdc but the fuel burns after tdc.

 

[Mike T]

Thought this was interesting. Check out the timing on the lower rt side of the screen. Could be on nitrous IDK?

 

[Mr.Spool]

Thought this was interesting. Check out the timing on the lower rt side of the screen. Could be on nitrous IDK?

Seen that plenty of times on forced induction with no spray.plenty of guys depending on motor compression and fuel being used keep the timing low even on race fuel.nice vid

 

[Mr.Spool]

I'd like to add you can still break motors for sure on low timing.

 

[20psiofevil]

Thought this was interesting. Check out the timing on the lower rt side of the screen. Could be on nitrous IDK?

Turbo ls engine doesn't use a lot of timing or so I've read. That is crazy low imo but the car makes a lot of power from what I've seen on fb.