J&S safeguard, individual cyl knock detection and timing retard?
30 May 2003, 04:03 PM
#2
perhaps, it listens to the knock sensor in time with the cylinder firing so gives individual igniion timing for each cyclinder. the problems comes when it doesn't see the knock or retards when there isn't any, although I think the J&S is very advanced (techically) in this respect).
In theory it means more power, but there is so much that can be done before that.
paul
In theory it means more power, but there is so much that can be done before that.
paul
30 May 2003, 05:06 PM
#3
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hmm would it be superior to a knocklink ? instead of just indicating knock it also seems to try and reduce it just wondering if it was worth getting instead...
Cheers
Cheers
30 May 2003, 05:12 PM
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The factory ECU already does this quite well until its upper RPM threshold - at least on a fairly standard car.
However, ignition retard is not always the best way to reduce knock. Extra fuel is a good idea with the retard to quench the higher temps you might get from the retard which can set up vicious cycles. Ideally you might control excessive boost as well in these circumstances.
You can make a car slower by retarding the ignition and throwing in fuel than you could be dropping the boost back to a more sensible level.
However, ignition retard is not always the best way to reduce knock. Extra fuel is a good idea with the retard to quench the higher temps you might get from the retard which can set up vicious cycles. Ideally you might control excessive boost as well in these circumstances.
You can make a car slower by retarding the ignition and throwing in fuel than you could be dropping the boost back to a more sensible level.
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31 May 2003, 01:56 PM
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True enough. However, if you retard a cylinders timing it will only get hotter? It seems that Scoobies blow a variety of cylinders and number three is notorious unfairly?
31 May 2003, 11:43 PM
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I thought that EGT (as a proxy for average temperature over time at the exhaust port) was supposed to drop at the start of detonation because the intense vibrations speed up heat transfer? I've not let my engine detonate long enough to find out, but when I've been monitoring EGT and there is no detonation on a given fuel then advancing the ignition appears to keep things cooler and helps keep it to a minimum over 900C which I feel happier about with cast pistons. So if I can't keep it that low through timing advance I usually richen things until I can and/or drop the boost.
I'm aware that with EGT with respect to AFR that it peaks towards stoich and then declines again on the lean side of stoich (hence needing to know which side you are) but I didn't know there was a similar effect with advance.
I'm aware that with EGT with respect to AFR that it peaks towards stoich and then declines again on the lean side of stoich (hence needing to know which side you are) but I didn't know there was a similar effect with advance.
31 May 2003, 11:50 PM
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Here's a little snippet I had filed away on the subject, I can't find the source though....
Having just spent the day on a chassis dyno watching exhaust gas
temperature while measuring torque, I'd like to point out the
sensitivity of EGT to spark advance. Retarding spark will increase
EGT. Naturally, this has an effect on torque output, too, but
that's not to imply that you'll find the same EGT at all operating
points that have the same torque and RPM. So, one suggestion I have
(of which Sven-Erik is probably already aware) is to account for spark
advance, too, at least relative to maximum brake torque timing. Some
engines may run retarded from MBT for various reasons, so data both at
and below MBT timing could be interesting.
Heywood, of course, discusses the relationship between EGT and A/F
ratio. He shows predicted and measured results that indicate that
EGT reaches a maximum at 14.7:1 and falls off as you go rich or lean
(holding RPM and IMEP constant) ("Internal Combustion Engine
Fundamentals", p. 770; data from "A Fundmental Model for Predicting
Fuel Consumption, NOx, and HC Emissions of the Conventional Spark-
Ignited Engine" by Lavoie and Blumberg, printed in Combustion
Science and Technology, Vol. 21, pp. 225-258, 1980). These results
also show how retarding spark increases EGT.
temperature while measuring torque, I'd like to point out the
sensitivity of EGT to spark advance. Retarding spark will increase
EGT. Naturally, this has an effect on torque output, too, but
that's not to imply that you'll find the same EGT at all operating
points that have the same torque and RPM. So, one suggestion I have
(of which Sven-Erik is probably already aware) is to account for spark
advance, too, at least relative to maximum brake torque timing. Some
engines may run retarded from MBT for various reasons, so data both at
and below MBT timing could be interesting.
Heywood, of course, discusses the relationship between EGT and A/F
ratio. He shows predicted and measured results that indicate that
EGT reaches a maximum at 14.7:1 and falls off as you go rich or lean
(holding RPM and IMEP constant) ("Internal Combustion Engine
Fundamentals", p. 770; data from "A Fundmental Model for Predicting
Fuel Consumption, NOx, and HC Emissions of the Conventional Spark-
Ignited Engine" by Lavoie and Blumberg, printed in Combustion
Science and Technology, Vol. 21, pp. 225-258, 1980). These results
also show how retarding spark increases EGT.
31 May 2003, 11:59 PM
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Just remembered as well - the factory ECU (for better or worse) actually throws in fuel before retarding the ignition timing and later drops the boost in response to excessive knock sensor activity.
Back to the J&S, could the 4 channel version be used as the instructions list for a NA Subaru using a 2 channel model - are they working with retard for each half of the engine V6 style?
Back to the J&S, could the 4 channel version be used as the instructions list for a NA Subaru using a 2 channel model - are they working with retard for each half of the engine V6 style?
11 January 2004, 09:15 AM
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Depends on the MY - in general, it seems it's 2 channel for newer, 4 channel for older, but I'm not 100% sure where the switch is...92-96 for 4-channel? More info in the group-buy here 
.
[Edited by nom - 1/11/2004 9:16:47 AM]
.[Edited by nom - 1/11/2004 9:16:47 AM]
11 January 2004, 05:30 PM
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JB: So glad you were open minded enough to plunk your money down. What tipped the scales?
Regarding your recent tests, what is the factory knock controller doing, while the J&S is active? Does it retard a lot, some, or none?
Regarding your recent tests, what is the factory knock controller doing, while the J&S is active? Does it retard a lot, some, or none?
11 January 2004, 05:45 PM
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Factory knock sensor makes a token inappropriate 1 degree retard now and then.
What convinced me was the need for a display on a slappy engine where a knocklink would never have worked, but it is very useful on a non-slappy engine too.
What convinced me was the need for a display on a slappy engine where a knocklink would never have worked, but it is very useful on a non-slappy engine too.
11 January 2004, 05:57 PM
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JB
if they both feed from the same bosch sensor on the same location, I can't see why the J&S unit would work on these "slappy" blocks when Knocklinks can't, unless there's some sophisticated 'interpretation' involved. Also by "where knocklink would never have worked" what do you mean exactly, not sensitive enough or full-time christmas tree?
Robert
if they both feed from the same bosch sensor on the same location, I can't see why the J&S unit would work on these "slappy" blocks when Knocklinks can't, unless there's some sophisticated 'interpretation' involved. Also by "where knocklink would never have worked" what do you mean exactly, not sensitive enough or full-time christmas tree?
Robert
11 January 2004, 06:30 PM
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I never had chance to test the J&S on the piston slappy built engines. Using the knocklink on engines #1 and #2, it went to constant big red on the knocklink from about 3500 RPM with no boost used, I did not see engine #3 running. Turning down the sensitivity would have killed any chance of seeing anything but horrendous detonation.
The J&S signal acquisition is gated to the timing of expected knock and uses an integrative system for spotting detonation spikes. This would be expected to work better than a simple filtered level meter like the knocklink on a slappy engine.
The J&S signal acquisition is gated to the timing of expected knock and uses an integrative system for spotting detonation spikes. This would be expected to work better than a simple filtered level meter like the knocklink on a slappy engine.
13 January 2004, 08:39 PM
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Hmm, if the standard ECUs response to knock is (in order):
1. Increase fueling
2. Decrease timing
3. Reduce boost
Surely, if the J&S unit is reducing the timing at the onset of knock, then the ECU won't be doing it's bit by increasing the fueling - is this a good or a bad thing?
1. Increase fueling
2. Decrease timing
3. Reduce boost
Surely, if the J&S unit is reducing the timing at the onset of knock, then the ECU won't be doing it's bit by increasing the fueling - is this a good or a bad thing?
13 January 2004, 09:09 PM
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Throwing fuel in is not always the best technique either. Reducing boost can be a bit slow to get a response unless you drop it like a stone.
The factory ECUs tend to respond to knock quite badly once the engine is heavily modified.
The factory ECUs tend to respond to knock quite badly once the engine is heavily modified.
13 January 2004, 09:16 PM
#23
Ecu Specialist
Actually not quite as true as we may have thought, they do respond very quickly (assume MY99-00 thinking), the sensitivity to knock is the thing that needs adjusting. On the new age ecu's the sensitivity can be adjusted of course.
factory ecu responds in the order
reduce ignition
add fuel
drop boost (if you let it)
cheers
bob
factory ecu responds in the order
reduce ignition
add fuel
drop boost (if you let it)
cheers
bob
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