pinking at WOT.. advance question
Discussion
Need some advice in the engine tuning area...
At WOT rpm on my Megasquirted Griff 500 (72mm Plenum, 45 flared trumpets and EDIS/ Ford cold packs) I have noticed my MAP sensor shows a very unstable reading over 4K RPM.. its see-sawing between 92-96kpa when normal atmosphere (ie engine off) is 100kpa.
So I suspected the whole intake tract is not supplying enough air... but wanted to see what the MAP sensor would read without the filter/air tract connected..just the 90deg elbow connected to the plenum. As I thought, there was an improvement at WOT..at 100kpa atmosphere there was now only 1-2kpa drop.
However, the engine was pinking like crazy with out the filterover 4K RPM. At 100kpa MAP above 4K RPM, I find that I need to reduce the advance down to 18deg advance before the pinking stops.. yet with the filter connected I could run 24-26 degrees no problem (or at least I couldn't detect anything). Maybe the pinging sound wasn't muffled by the intake. I am surprised that such a small difference in MAP needs such a large decrease in advance. I did think mof air intake temp..however despite the engine sucking in engine bay air, the intake Air temp at the butterfly was 30 Deg C.. not noticably different to the outside temp when air being drawn from the filter. So I doubt whether hot intake air had a major impact.. or am I wrong?
Could anyone explain this behaviour? BTW I recall the dyno tuner reduced advance and VE at WOT (>80 MAP at above 4K rpm). Why would he do this as he didn't really eloborate why.
Many thanks..Lindsay
At WOT rpm on my Megasquirted Griff 500 (72mm Plenum, 45 flared trumpets and EDIS/ Ford cold packs) I have noticed my MAP sensor shows a very unstable reading over 4K RPM.. its see-sawing between 92-96kpa when normal atmosphere (ie engine off) is 100kpa.
So I suspected the whole intake tract is not supplying enough air... but wanted to see what the MAP sensor would read without the filter/air tract connected..just the 90deg elbow connected to the plenum. As I thought, there was an improvement at WOT..at 100kpa atmosphere there was now only 1-2kpa drop.
However, the engine was pinking like crazy with out the filterover 4K RPM. At 100kpa MAP above 4K RPM, I find that I need to reduce the advance down to 18deg advance before the pinking stops.. yet with the filter connected I could run 24-26 degrees no problem (or at least I couldn't detect anything). Maybe the pinging sound wasn't muffled by the intake. I am surprised that such a small difference in MAP needs such a large decrease in advance. I did think mof air intake temp..however despite the engine sucking in engine bay air, the intake Air temp at the butterfly was 30 Deg C.. not noticably different to the outside temp when air being drawn from the filter. So I doubt whether hot intake air had a major impact.. or am I wrong?
Could anyone explain this behaviour? BTW I recall the dyno tuner reduced advance and VE at WOT (>80 MAP at above 4K rpm). Why would he do this as he didn't really eloborate why.
Many thanks..Lindsay
That pressure loss is completely normal, the filter and air flow meter (if you still had it) both cause a pressure drop that can go up to around 15 kpa. If the filter was blocked it could be a lot more than that.
When you disconnect the filter, exactly what are you changing? Would it have any effect on anything else such as the crankcase breather?
If you have so much pinking that you have to back the timing right off to 18 deg then I think the engine must be running lean. Do you have a wideband O2 sensor? If so, what is the mixture doing under load? If not, get one! In the meantime run some logging with/without the filter and see whether the injector pulse widths are smaller without the filter.
Unless you are sure this has already been done, confirm the TDC timing reference marks using a dead stop and then use a timing strobe to confirm that the timing you're actually getting matches what MS is telling you.
When you disconnect the filter, exactly what are you changing? Would it have any effect on anything else such as the crankcase breather?
If you have so much pinking that you have to back the timing right off to 18 deg then I think the engine must be running lean. Do you have a wideband O2 sensor? If so, what is the mixture doing under load? If not, get one! In the meantime run some logging with/without the filter and see whether the injector pulse widths are smaller without the filter.
Unless you are sure this has already been done, confirm the TDC timing reference marks using a dead stop and then use a timing strobe to confirm that the timing you're actually getting matches what MS is telling you.
Here's a couple of graphs of dyno runs from my car. They are before and after the twin plenum upgrade. The "after" graph shows evidence of clutch slip too.
Before:
After:
You will note the huge pressure drop in the first graph, and very similar MAP noise to what you describe. I should still have the log files somewhere if they would help you...
I found that I was never getting in to the top line of the ignition table before the plenums were fitted, and when I did, I needed to run much less timing than when the MAP was at 90 kPa. Also, the fuelling requirements were considerably different - enough to cause lean running if there's insufficient feedback.
Before:
After:
You will note the huge pressure drop in the first graph, and very similar MAP noise to what you describe. I should still have the log files somewhere if they would help you...
I found that I was never getting in to the top line of the ignition table before the plenums were fitted, and when I did, I needed to run much less timing than when the MAP was at 90 kPa. Also, the fuelling requirements were considerably different - enough to cause lean running if there's insufficient feedback.
Thanks (and Hi) Peter and David..
Yes running TechEdge Lin WB.
This graph shows WOT with filter and intake connected. There is a lot of fluctuation at WOT. Running abt 12.90 AFR..and didn't hear any pinking
This graph shows WOT without filter and intake.. just the plenum. There is less spiking at WOT.. but pinging
. Acceleration enrichment dipped the ARF to 11.8 then returned to 12.9.
As far as crankcase pressure, I think nothing I have done would have changed that..
Is 12.9 OK as far as AFR. I haven't tried going lower..
David. What Advance are you runing at WOT above 4K RPM?
Yes running TechEdge Lin WB.
This graph shows WOT with filter and intake connected. There is a lot of fluctuation at WOT. Running abt 12.90 AFR..and didn't hear any pinking
This graph shows WOT without filter and intake.. just the plenum. There is less spiking at WOT.. but pinging
. Acceleration enrichment dipped the ARF to 11.8 then returned to 12.9.As far as crankcase pressure, I think nothing I have done would have changed that..
Is 12.9 OK as far as AFR. I haven't tried going lower..
David. What Advance are you runing at WOT above 4K RPM?
All the signals look very jittery to me. What is the sampling frequency?
Also I noticed that in the second plot the AFR plot shows it going slightly more lean towards the end of that acceleration run. Doesn't seem like much of a change, but worth richening it up anyway and see if that helps. Aim for about 12:1 at WOT as a starting point, you can always lean it out later if you want.
Also I noticed that in the second plot the AFR plot shows it going slightly more lean towards the end of that acceleration run. Doesn't seem like much of a change, but worth richening it up anyway and see if that helps. Aim for about 12:1 at WOT as a starting point, you can always lean it out later if you want.
Edited by GreenV8S on Sunday 9th November 21:54
I use MAP as my load axis (as opposed to TP)
The top line (104kPa) from 4000RPM to 6800RPM is 23 degrees to 26 degrees.
I can't help but notice there is a lean spike on your 2nd chart at high RPM. Acceleration enrichment will have played out by the time you get to high RPM. It's only there for transients.
I run an AFR of about 13:1 on full throttle. It seems to work for me.
The top line (104kPa) from 4000RPM to 6800RPM is 23 degrees to 26 degrees.
I can't help but notice there is a lean spike on your 2nd chart at high RPM. Acceleration enrichment will have played out by the time you get to high RPM. It's only there for transients.
I run an AFR of about 13:1 on full throttle. It seems to work for me.
It's not a lean spot really... It's just not as rich as the rest of the WOT section of the log. It's probably OK, just me being picky... 
And I think the accel enrichment is a little on the large side. All it's trying to do is compensate for the engine removing the fuel film from the port walls. Not quite the same thing as the acceleration pump on a carb.
And I think the accel enrichment is a little on the large side. All it's trying to do is compensate for the engine removing the fuel film from the port walls. Not quite the same thing as the acceleration pump on a carb.
Hi Lindsay - Eliot here, we met at Euston with Matt.
Have you looked at your intake temps? - with just the elbow on the plenum, you will be drawing hot air from the exhaust manifold. With it fitted, presumably you are drawing it from the front. Hot intake temps are more prone to pinking.
With it flowing more air, you will likely need to adjust the ve (richen it up) in that area also.
Have you looked at your intake temps? - with just the elbow on the plenum, you will be drawing hot air from the exhaust manifold. With it fitted, presumably you are drawing it from the front. Hot intake temps are more prone to pinking.
With it flowing more air, you will likely need to adjust the ve (richen it up) in that area also.
Eliots right I reckon, managing the induction in that area is tricky. You may also be getting into some Rolling v Open Road discrepancies, as the 'stagnant' hot air created on the RR may exacerbate the problem compared to tests you may have tried driving around? Its a challenge to have a short induction & cool air, lets see who comes up with the best solution 
Eliot..
Good point.. I will re connect the air intake and leave the air filter end disconnected.. this was I will get fresh cool air from the front of the car.. without the kpa drop of the filter and see what happens.
BTW.. I often think of Matt..I wonder how he's getting on??
Thanks Adrian and Spend..
Good point.. I will re connect the air intake and leave the air filter end disconnected.. this was I will get fresh cool air from the front of the car.. without the kpa drop of the filter and see what happens.
BTW.. I often think of Matt..I wonder how he's getting on??
Thanks Adrian and Spend..
Could someone suggest some settings for the amount of advance I should retard given the increase in IAT.
I am thinking that for every 10 degrees over 40deg C IAT, advance would be retarded 3 degrees.
so at:
5000 RPM at 40deg advance is 28
5000 RPM at 50deg advance is 25
5000 RPM at 60deg advance is 22
How does this sound.. too aggresive??
I am thinking that for every 10 degrees over 40deg C IAT, advance would be retarded 3 degrees.
so at:
5000 RPM at 40deg advance is 28
5000 RPM at 50deg advance is 25
5000 RPM at 60deg advance is 22
How does this sound.. too aggresive??
dnb said:
That looks like a reasonable curve to me.On MS, I pull 1 degree out every 6'c when the IAT is above 62'c - this mainly as a fail-safe in-case my chargecooler pump packed up.
Its also worth noting that MS1-v29 has a habbit of leaning out the mixture with high IAT's (40-50'c) because the air densiity calculation isn't quite right. Its usally more apparent during lean cruise. Not sure if they sorted it out in MS2.
In MS1, there is a seperate table to correct for this, for example at 50'c increase fuel by 8% - this also solved my hot restart problems.
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