The MSD Ignition - 'Exposed'

[Lorenfb]

"The Bosch puts out even less power."

The key point is not how much spark power (energy X rate) the box can make,
but if the spark energy is much more than the minimum required (about 30mj) to
ignite the fuel charge. So at about a minimum of 100mj (Bosch & MSD both) there's
more than 3X what's needed. So anymore than that is wasted. The same applies to
the spark voltage and spark rise time, i.e. a voltage to jump the dist. gaps and jump
the spark plug gap under the high pressure, e.g. for a turbo.

"If someone where wanting to twin plug, and asked your advise on ignition, what would you advise."

As mentioned, use two separate ignitions or one with separate outputs. Most all CDIs
are basically the same with some having negative issues over others as discussed.

[LJ851]

Originally Posted by carr914

Lindy, Can you explain this - it seems to me that as long as one set of Plugs is firing, you are still getting detonation. Why would your engine blow?

You want properly timed IGNITION from the spark plugs, not destructive, uncontrolled detonation.

Our engines are only capable of supporting a certain amount of compression with a given octane fuel without detonation.

If one adds a second plug, this same engine will be able to support about a point of compression MORE than the single plug setup without detonation. Say 9.5 to 1 vs 10.5 to 1 (not real #'s, just an example.)

Now if only one out of two plugs fires you have a big problem on your hands! (detonation)

[Lorenfb]

"If one adds a second plug, this same engine will be able to support about a point of compression MORE than the single plug setup without detonation."

But one can always retard the timing, right, but then what's the value of the higher compression.
As mentioned before, Porsche with 964/993 went to higher compression AND more aggressive
timing BUT added knock control. And without knock control, even with twin plugs, the timing
may still be a problem, as with any engine without knock control.

[LJ851]

Originally Posted by Lorenfb

"If one adds a second plug, this same engine will be able to support about a point of compression MORE than the single plug setup without detonation."

But one can always retard the timing, right, but then what's the value of the higher compression.
As mentioned before, Porsche with 964/993 went to higher compression AND more aggressive
timing BUT added knock control. And without knock control, even with twin plugs, the timing
may still be a problem, as with any engine without knock control.

I agree with you, i was speaking generally. The timing needs to retarded compared to single plug anyway as the burn is faster or at least maximum power with twin plugs is usually achieved at a lower timing number.

A non knock sensor equipped engine will always take a back seat (reliably) to one that has a knock sensor.

Loren, how about a knock sensor retrofit for 3.2 911engines? This would make you and us happy with maximum performance and maximum safety!!

[RWebb]

it is certainly much better to have a sensor and computer capable of knock control

I am not at all sure about the "At ANY RPM"

[wwest]

Originally Posted by LJ851

I completely disagree with this. The way the system accommodates poor quality fuel, extreme heat, etc. is by sensing knock and pulling timing out. In this era of fuel efficient engines and emissions, adding fuel is not acceptable and not very effective either. The added fuel particles actually RAISE the dynamic compression ratio and can make the problem worse.

It has been proven on many different side plug 2 valve engines (particularly air cooled engines) that adding a second plug on the opposite side

greatly increases the ability to support more compression.

Or, in the alternative, simply increases the "burn" efficiency/performance of your more "standard" compression engine.

Firing that second plug with full power is obviously very important

if your engine is built to need it.

And, quite obviously, many engines mentioned herein although having dual plugs, do not have enough compression, or are running too rich, to require that both plugs actually always fire.

Look at the voltage drop on either coil primary once the initial plug fires and then tell me where is the HV to come from to fire the second plug.

There 3 situations wherein a gasoline engine might knock or ping.

1.) Lugging the engine, the piston cannot move downward fast enough to accommodate the expanding explosive "front"....downshift.

2.) The spark is occurring to soon....retard the timing.

3.) Ignition, self-ignition, is occuring PRIOR to spark ignition.....enrich the mixture using EFI PWM.

Did Ford put dual plugs, coils, etc, in my 93 Ranger in order to improve performance...????

OF COURSE NOT....!!!

The did it to improve emissions, if performance was also improved...so what.

[LJ851]

Originally Posted by wwest

Look at the voltage drop on either coil primary once the initial plug fires and then tell me where is the HV to come from to fire the second plug.

I don't don't disagree with this, i don't like the idea of 1 box + 2 coils.

Originally Posted by wwest

There 3 situations wherein a gasoline engine might knock or ping.

1.) Lugging the engine, the piston cannot move downward fast enough to accommodate the expanding explosive "front"....downshift.

2.) The spark is occurring to soon....retard the timing.

3.) Ignition, self-ignition, is occuring PRIOR to spark ignition.....enrich the mixture using EFI PWM.

There gets a point when you cannot control ignition at a time that is appropriate for a performance engine. If your engine has a 2 valve head and reasonably large bore diameter, the next move is to add a second plug and fire it properly.

Using extra fuel to reduce detonation is a not very effective band aid fix.

[wwest]

Originally Posted by LJ851

You want properly timed IGNITION from the spark plugs, not destructive, uncontrolled detonation.

Our engines are only capable of supporting a certain amount of compression with a given octane fuel without detonation.

If one adds a second plug, this same engine will be able to support about a point of compression MORE than the single plug setup without detonation. Say 9.5 to 1 vs 10.5 to 1 (not real #'s, just an example.)

Now if only one out of two plugs fires you have a big problem on your hands! (detonation)

We should all keep closely in mind that many of the engineering design decisions made back in this ERA, carburation, were made pretty much obsolete upon the advent of EFI.

EFI, the fuel/air mixture ratio could be changed, regulated, dynamically.

Then along came, ~2000, the wideband knock/ping sensors wherein the actual moment, instant, of NORMAL mixture ignition of each cylinder could be detected.

1. During idle or cruise: Keep the A/F mixture control modulation within the proper range in accordance with the feedback from upstream oxygen sensor

2. Power mode: Keep the A/F mixture modulation within the proper range, ENRICHED (~12:1) range, in accordance with the feedback from the MAF/IAT sensors.

3. Knock/ping: The engine controlling ECU uses the crankshaft position sensor along with the knock/ping sensor to detect the timing of the fuel/air mixture ignition. If the timing is such to indicate detonation/dieseling is occuring, even ever so lightly, then the ECU will automatically enrich the mixture.

[wwest]

Originally Posted by LJ851

I don't don't disagree with this, i don't like the idea of 1 box + 2 coils.




There gets a point when you cannot control ignition at a time that is appropriate for a performance engine. If your engine has a 2 valve head and reasonably large bore diameter, the next move is to add a second plug and fire it properly.

Using extra fuel to reduce detonation is a not very effective band aid fix.

"...not a very effective band aid fix..."

Find me a Marque that is building automotive passenger engines with design criteria that REQUIRES premium fuel and I'll show you a company that is currently out of touch with reality.

Most marques now use the term "Premuin fuel RECOMMENDED" ...or "Premium fuel required for rated performance".

In 2001 I was told by the factory that my '01 C4 should only be fueled with unleaded preimum fuel but that fueling with unleaded regular, as I might be required to do during our subsequent travels, would not be harmful.

The above explanation was offered by a factory engineer when I persisted.

[LJ851]

Originally Posted by wwest

Most marques now use the term "Premuin fuel RECOMMENDED" ...or "Premium fuel required for rated performance".
The above explanation was offered by a factory engineer when I persisted.

Knock sensing ECUs remove TIMING to eliminate knock, not add fuel. This is the precise reason why you can run poor quality fuel and not have it blow up. Have you ever sat on a dyno with a fixed timing ecu and tried to eliminate knock with fuel? I have.

Do some more research, you misunderstood the engineer.



Take a look at every aftermarket knock sensing anti knock system out there, I'll give you one guess as to what they affect when knock is sensed.


..

[wwest]

Originally Posted by LJ851

Knock sensing ECUs remove TIMING to eliminate knock, not add fuel.

Okay, if detonation/dieseling is co-insident with the ignition spark then retarding the spark might likely be the cure, might....

But what about when the detonation/dieseling event occurs pre-spark, what then...?

In the latter case it should be clear to all that retarding the spark is needless, the baby has already been tossed out with the bathwater, the horse has left the barn, etc, etc.

In both cases enriching the mixture, given the ability to do so, is obviously the correct solution, even if you fueled with premium (or 100LL).

This is the precise reason why you can run poor quality fuel and not have it blow up.

Have you ever sat on a dyno with a fixed timing ecu and tried to eliminate knock with fuel? I have.

Then one of us has/have been doing something wrong. I haven't flown as PIC for many years but back then I always, as I was first taught...let's see...back in '58,...to always lean the engine(s) to peak EGT and then enrich the mixture slightly (thereby providing additional cooling) to help alleviate the possibility of detonation.

Do some more research, you misunderstood the engineer.

No chance.





..

....

[wwest]

Originally Posted by LJ851

Knock sensing ECUs remove TIMING to eliminate knock, not add fuel. This is the precise reason why you can run poor quality fuel and not have it blow up. Have you ever sat on a dyno with a fixed timing ecu and tried to eliminate knock with fuel? I have.

Do some more research, you misunderstood the engineer.



Take a look at every aftermarket knock sensing anti knock system out there, I'll give you one guess as to what they affect when knock is sensed.


..

AFTERMARKET...

????

Maybe only for carbureted engines wherein dynamic mixture changes are not possible...?? Or a "simpleton's" anti-knock system designed by someone who didn't want to bother with, or add the expense of, PWM EFI control.

[brads911sc]

What aftermarket EFI system are you using?

Can you post your tables?

Originally Posted by wwest

AFTERMARKET...

????

Maybe only for carbureted engines wherein dynamic mixture changes are not possible...?? Or a "simpleton's" anti-knock system designed by someone who didn't want to bother with, or add the expense of, PWM EFI control.

[brads911sc]

You are never going to win an argument with wwest. doesn't matter what the topic is, he is the resident expert even if you present proof he is wrong, he will argue with you. Might as well save your breath.

Originally Posted by LJ851

Knock sensing ECUs remove TIMING to eliminate knock, not add fuel. This is the precise reason why you can run poor quality fuel and not have it blow up. Have you ever sat on a dyno with a fixed timing ecu and tried to eliminate knock with fuel? I have.

Do some more research, you misunderstood the engineer.



Take a look at every aftermarket knock sensing anti knock system out there, I'll give you one guess as to what they affect when knock is sensed.


..

[wwest]

Originally Posted by brads911sc

What aftermarket EFI system are you using?

Can you post your tables?

I don't.

[brads911sc]

I do. and you dont know what you are talking about. so stop now before you look really uneducated.. every aftermarket system i have looked at, include MS which I use, manipulates timing not fuel to address this issue. yes, you can arbitrarily richen the VE tables just as you can accel and decel and warm up and cold start tables... but it will not then be linked to knock. not an apples to apples discussion.

QUOTE=wwest;6745709]I don't.[/QUOTE]

[Lorenfb]

"The timing needs to retarded compared to single plug anyway as the burn is faster or at least maximum power with twin plugs is usually achieved at a lower timing number."

Actually that's a common misconception. Here's the logic:

1. The greater the timing, the greater will be the torque to the point of near detonation.
2. Based on #1, it's always optimal to run as much advance as possible avoiding
detonation. That's the significant benefit of knock control, i.e. the timing doesn't
need to be overly conservative compromising torque because of; poor octane,
very hot engines, unknown loading conditions, e.g. climbing a steep hill using low
octane fuel on a hot day.
3. Increasing the compression ratio will increase torque at the expense of sooner
detonation, thus requiring retarding the spark, using a much higher octane, modifying
how the fuel charge will burn, e.g. twin plugs, or a combo of the three on an engine
without knock control.

So when Porsche developed the 964/993 engine with higher compression, they wanted
to NOT lose torque by using less advance (#1 above), i.e. retard the timing, so they
twin plugged the engine AND used knock control to allow even more timing advance.
Thus they had a two fold gain in torque from BOTH the increased CR and timing.

Without knock control and a CR increase with twin plugs it might be necessary
to retard the timing (not because of "burn is faster") compared to the original
timing, but because the point of detonation wasn't reduced enough by the twin
lugging. So if retarding the spark becomes necessary, torque will be lost.

One of the easiest engine variables to modify and effect torque (performance) is
to tweak the timing. That's joke about 'performance' tuning and the ECM mods
one reads about. Once the AFRs are within 2 - 3 range (common for most stock
factory tuned engines), 'performance' tuning is nothing more that 'pushing'
the timing beyond stock, a simple process for a 911 3.2 versus an earlier 911,
hardly an effort requiring any real engine knowledge.

[LJ851]

Originally Posted by Lorenfb

Actually that's a common misconception. Here's the logic:

Have you dyno tuned a lot of engines converted to twin plugs from single? In my experience, twin plug engines always want 5-6 degrees less peak timing for max power compared to single plugs. This is on engines that can just cope with 93 octane in both respects. You can raise the timing on the twin plug engine but it wont make more power so why do it? My thought is always max power with min timing.

Originally Posted by Lorenfb

1. The greater the timing, the greater will be the torque to the point of near detonation.

It's not always that cut and dry on the dyno as i just mentioned.

[Lorenfb]

"In my experience, twin plug engines always want 5-6 degrees less peak timing for max power compared to single plugs."

That's the KEY advantage to using twin plugs, i.e. more advance timing without potential detonation
using the same timing. Porsche did NOT use twin plugged so they could use a less advance timing
curve, i.e. why add the twin plugging cost just for that. So if one is going to increase the
compression ratio, why not just retard the timing enough and also just use a higher octane fuel
and not waste money on twin plugging? That would be a solution, right? But what would happen
now with the torque at the retarded timing? So what could one now do to get the timing 'back' to
offset the loss, maybe use twin plugs?

One needs to evaluate the 964/993 timing maps versus the 911 3.2 where 964/993 engines
had more CR and more timing advance.

"It's not always that cut and dry on the dyno as i just mentioned."

Actually it is. On a 911 3.2 for every one degree change in timing 3 - 4 ft-lbs of torque change
results, where peak torque occurs (@ RPM = 5252).

[wwest]

Engine knocking - Wikipedia, the free encyclopedia

Abnormal combustion....detonation:

Detonation is charactorized by an instantaneous, explosive, ignition of at least one pocket of fuel/air outside of the flame front.


........................

So, by definition detonation can occur even after the ignition spark, especially with the ignition spark occuring before TDC wherein the compression "cycle" hasn't completed.

Now the question becomes, just how close can I get to the maximum torque arising from detonation, INSTANT ignition of the entire cylinder contents, as happens in a diesel engine, in my gasoline engine without destroying it...??

Obviously starting more than one flamefront simultaneously would be a positive design aspect.