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Interesting work- anything that improves the area under the curve wherever it is should be of interest to all 928 owners.
You can tweak the AFR a little with the resistance pot if you are running the no cat option. Interesting that you are looking for an AFR of 13.3. Stock tuning produces about 12 to 12.5 when the WOT map is engaged whereas the stock cruise map alone will give something leaner at high loads but not sure what. I presume you do not have a RRFPR? You could test for this by defeating the WOT contact switch but I suspect you would end up too lean for max power.
For folks like yourself you really need the ST2 and a dyno to optimise total gains from all the various [marginal?] improvements possible.
Loue [OTT] always used to advise many years ago that the 928 motor makes max power at around 13.5. Just shows how far ahead of the game he was. He also had dyno curves showing the impact of AFR against max power. Over enrichment does drop the power but nothing compared to a lean mix of course.
Look forward to reading more about your exploits epsecially if you can integrate your work with that being done by Professor Ken.
Regards
Fred
Thanks Fred.
My (very thin) understanding is that high rpm AFR enrichment comes from 2 sources: the basic fuel mapping and the WOT switch effect on this map.
My thinking is that temporarily defeating the WOT switch might lean the mixture from lamda 0.7 - 0.8 to 0.9 or a touch more, for one or two dyno passes.
Professor Ken: yes - I would very much like to gather the data he needs to map my manifold. Wheeee.
My (very thin) understanding is that high rpm AFR enrichment comes from 2 sources: the basic fuel mapping and the WOT switch effect on this map.
My thinking is that temporarily defeating the WOT switch might lean the mixture from lamda 0.7 - 0.8 to 0.9 or a touch more, for one or two dyno passes.
Professor Ken: yes - I would very much like to gather the data he needs to map my manifold. Wheeee.
RRFPR?
.
RRFPR= Rising rate fuel pressure regulator- tweaking this lets in more [or less] fuel by reducing the header pressure but of course it changes everything across the board fuel map wise.
The WOT throttle switch kicks in at about 2/3rd throttle and when the contact goes the LH then adds incremental fuel as per the settings of the WOT. This is a one line map [load independent] that follows the RPM cells of the cruise map.
When I purchased my ST2 the first thing I found was that it seemed the WOT swtich was not working- this is infamously prone to failure unlike the idle contact switch in the same body that appears to be bullet proof- do not ask me why or how this should be- another mystery known only to Porsche.
In ST2 I permanently disabled the WOT switch and tune the motor exclusively to the cruise map. From what I experienced it seems to makes no sense to have a WOT map given when you hit the high load cells you have to be in the high load range anyway. When giving it the berries the LH and EZ load maps invariably put the operatiing point in one of two load range cells and thus most of the sharktuning can be achieved by tweaking about 20 cells in the fuel map given what happens below 2k rpm is irrelevant for the most part. The rest of it is more about optimising fuel consumption during cruising which as I could tell Porsche did a prettty reasonable job of in the stock mapping.
Compared to stock mapping the mid range seems to benefit from a bit more fuel. At top end I was having some pinking issues so did not lean off to the 13.3 leaving it about 12.4 [0.84] so potentially I have a bit more to come.
Now that I have done my breather mods and excluded recycled oil from the intake I may be able to do better. I will shortly try Greg's tip of playing around with a colder plug heat range on the hotter cylinders to see if I can get better across the board tuning.
Ken's work looks very exciting but at the moment I understand it is not adapted to ST2- I am rather hoping Ken and John can work something out coding wise for the ST2 club members- especially as I run design 2 4-hole [allegedly] 30lb injectors [in ST2 they tuned as 28lb].
The figures I have is that at lambda 0.75 the power loss would be about 2%. But as has been pointed out, all you see at the tailpipe is the average A/F.
From around 1800 rpm to 3300rpm the WOT switch gives an enrichment of around 10%.
At 4800rpm the enrichment reduces to 5% and by 5600 ii is 1.2% and zero at 6200rpm
RRFPR= Rising rate fuel pressure regulator- tweaking this lets in more [or less] fuel by reducing the header pressure but of course it changes everything across the board fuel map wise.
The WOT throttle switch kicks in at about 2/3rd throttle and when the contact goes the LH then adds incremental fuel as per the settings of the WOT. This is a one line map [load independent] that follows the RPM cells of the cruise map.
When I purchased my ST2 the first thing I found was that it seemed the WOT swtich was not working- this is infamously prone to failure unlike the idle contact switch in the same body that appears to be bullet proof- do not ask me why or how this should be- another mystery known only to Porsche.
In ST2 I permanently disabled the WOT switch and tune the motor exclusively to the cruise map. From what I experienced it seems to makes no sense to have a WOT map given when you hit the high load cells you have to be in the high load range anyway. When giving it the berries the LH and EZ load maps invariably put the operatiing point in one of two load range cells and thus most of the sharktuning can be achieved by tweaking about 20 cells in the fuel map given what happens below 2k rpm is irrelevant for the most part. The rest of it is more about optimising fuel consumption during cruising which as I could tell Porsche did a prettty reasonable job of in the stock mapping.
Compared to stock mapping the mid range seems to benefit from a bit more fuel. At top end I was having some pinking issues so did not lean off to the 13.3 leaving it about 12.4 [0.84] so potentially I have a bit more to come.
Now that I have done my breather mods and excluded recycled oil from the intake I may be able to do better. I will shortly try Greg's tip of playing around with a colder plug heat range on the hotter cylinders to see if I can get better across the board tuning.
Ken's work looks very exciting but at the moment I understand it is not adapted to ST2- I am rather hoping Ken and John can work something out coding wise for the ST2 club members- especially as I run design 2 4-hole [allegedly] 30lb injectors [in ST2 they tuned as 28lb].
Regards
Fred
Thanks for all that effort.
When giving it the berries... LOL.
What a giveaway of your country of origin.
Also "giving it the wellie" "putting the boot in".
Can I ask a question as a non technical person in a technical post thread.
Why is the S4 inlet manifold regarded as being so compromised? I've read this previously and that the S3 manifold is 'better' I've never read the explanation as to why.
Brave stuff! I'd scare me sh!@less to take a grinder to the manifold!
Richard
But Richard, it's only a little teeny grinder.
I'll soon be posting info about air flow into bellmouths. It should go some way to answering your query.
Thanks Upfixen, for the pictures and analysis. That is JFB. However, intuitively it looks to me like that large bell shoulder just in front of the cross-thru where the flappy is, needs to come out of there. Why don't you cut it out and round that area/transition out just like the one on the other side of that opening. It will end up a lopsided bell, but I can't see why that would make a difference.
Hey Jerry
Good question
I'll soon be posting info that will clarify the pro's and con's of that.
Very high performance sports bike engines use something similar to produce a bellmouth with a wider range of resonant frequencies in the intake runner.
This is from a ZX600 Kawasaki. (135bhp @ 13,500 rpm. Street version).
At those rpm's the wavelength of fundamental frequency is proportionately shorter than that of a 928 intake runner @ 6000 rpm, so it turns out to be very compact solution to broadening the powerband of the ZX600.
Interesting work- anything that improves the area under the curve wherever it is should be of interest to all 928 owners.
You can tweak the AFR a little with the resistance pot if you are running the no cat option. Interesting that you are looking for an AFR of 13.3. Stock tuning produces about 12 to 12.5 when the WOT map is engaged whereas the stock cruise map alone will give something leaner at high loads but not sure what. I presume you do not have a RRFPR? You could test for this by defeating the WOT contact switch but I suspect you would end up too lean for max power.
For folks like yourself you really need the ST2 and a dyno to optimise total gains from all the various [marginal?] improvements possible.
Loue [OTT] always used to advise many years ago that the 928 motor makes max power at around 13.5. Just shows how far ahead of the game he was. He also had dyno curves showing the impact of AFR against max power. Over enrichment does drop the power but nothing compared to a lean mix of course.
Look forward to reading more about your exploits epsecially if you can integrate your work with that being done by Professor Ken.
Regards
Fred
that's not always true... I have a lot of dyno runs that showed the power gains going from 13.5 with no mods to 12.5:1 on 928 engines. I think its very unusual to see 13.5 as a peak HP mixture with most any V8. PLUS, if you are at 13.5, that is a pure average..... this means that some cylinders might be 14 and others 13........... very dangerous for those with changing operating conditions that can lead to one cylinder to have a lean enough mixture that can detonate! this might be one of the reasons I have had the sucesss that I have had racing the 928 engine continuously for 15 years now...... I might (and I say might because there are a lot of factors) be losing 1.5% hp by not being optimal in AFR, but ill pay that price if the engine is safer....... 12.5 is a very safe and usually the most powerful range to operate the engine.... AKA .85 Lamda
If you disable the throttle position switch WOT function, then you'll only not impact the fueling but also ignition. Your car goes on a special load-independent ignition map at WOT. Whatever power losses or gains you get from disabling the WOT position of the switch can't be unambiguously attributed to either fuel or ignition. You have to get a ST2 to test this.
I noticed you've cut the tab above cylinder five runner:
However, I think that this modification only works with a permanently mounted spacer if you want to use the factory gasket to seal the plenum. You don't get the full benefits of cutting of the tabs without a spacer anyway. Just my opinion.
Is it just an optical illusion, or do you have epoxy also on the outside of the manifold on the cylinder 5 runner?
Your air guide inside the throttle body element is potentially a good idea. I say potentially because there are so many changes in your system that we don't know if any individual change is helping or hurting:
However, a word of caution. If it vibrates at all in the air flow, it can disintegrate into unpredictably small pieces. It's aluminum and it fatigues very quickly from any cycling.
I think you have a lot of good ideas there. You are probably not getting a full credit from the group here because your work does not appear detailed and neat. Your work might be appreciated more if you say this is only for testing and you'll, scout's honor, redo it all by welding and not epoxy and a CNC mill and not an electric grinder, powder coating and dry-film lubricant instead spray-can paint, etc.
that's not always true... I have a lot of dyno runs that showed the power gains going from 13.5 with no mods to 12.5:1 on 928 engines. I think its very unusual to see 13.5 as a peak HP mixture with most any V8. PLUS, if you are at 13.5, that is a pure average..... this means that some cylinders might be 14 and others 13........... very dangerous for those with changing operating conditions that can lead to one cylinder to have a lean enough mixture that can detonate! this might be one of the reasons I have had the sucesss that I have had racing the 928 engine continuously for 15 years now...... I might (and I say might because there are a lot of factors) be losing 1.5% hp by not being optimal in AFR, but ill pay that price if the engine is safer....... 12.5 is a very safe and usually the most powerful range to operate the engine.... AKA .85 Lamda
Mark,
I agree with the principal of what you are saying- I have to run at 12.5 for the very reasons you mention. However you have to look at what I have written in the context of this post. There can only be one point of optimal efficiency if we are talking specific power delivery and having an unnecessarily rich mixture is a compromise to offset the individual differences of air flow to the cylinders.
What our friend in Austrailia is doing is trying to bring more balance to the air flow- what Ken is doing is to very cleverly rework the engine management code to permit better management of the inherent cylinder to cylinder differences.
I raised a thread some time ago querying why our motors were seemingly so down on power relative to the engine capacity and technology deployed. We are starting to see in more depth some of the reasons why.
When sharktuning Jim's excellent sharkplotter programme computes the statistical difference in AFR for any given cell on the map and I was concerned as to why the AFR spread it was was intimating occurred. Thus for a high load/rpm cell I typically see a calculated AFR deviation of 0.4 which tells me my AFR's are fluctuating between a range 12.1 to 12.9 when the "average" is 12.5.
Given the inevitable resonance fluctuations and the analysis of the pulses Tuomo so cleverly talks about, it would seem very clear to me that there is in fact quite some scope to optimise what we have- in other words do what Porsche did not. Pinging on 2 and 6 limited my top end timing-possibly caused by more air flow at high rpms but I now have a tip from Greg to fit those cylinders with colder plugs.
When folks fit trick exhaust headers what they are doing is improving the engine breathing- whether this evens out the air flows or simply permits more flow across the board do we really know? All we do know is that more mass air flow= more power but trying to average out the fuelling to suit when you may have a cylinder flow spread of 10%[?] is clearly going to leave something on the table somewhere. Thus I can well imagine that if the air flow is evened out then an optimal AFR for power delivery may well be in the region of 13.5.
For sure modern technology is permitting more real time data gathering and with it more analysis. Louie managed to eek some 340 rwhp out of the GT Jim now owns. With different cams Jim may well have even more these days. Superimpose Ken's work and possibly our Aussie friends efforts on top of these and you may well have a 5 litre motor that is turning out well over 400 crank BHP.
Thus why I am impressed by the OP's efforts here and indeed what Ken is doing to optimise the legacy design. As Greg astutely points out the stock design is a very elegant package design wise even if it has flaws.
Does any vee configuration motor past or present have a lower bonnet line than a 928 even today? I doubt there is any front engined motor today that has a lower bonnet line than the 928 and thus why it looks so sleek/elegant.
Dude, nice work. Looks great and it sounds like you not only learned a lot, but you're having a great time doing it. Win-win. That's why I futz with my car too.
Originally Posted by ptuomov
Some more comments:
<Snip>
I think you have a lot of good ideas there. You are probably not getting a full credit from the group here because your work does not appear detailed and neat. Your work might be appreciated more if you say this is only for testing and you'll, scout's honor, redo it all by welding and not epoxy and a CNC mill and not an electric grinder, powder coating and dry-film lubricant instead spray-can paint, etc.
Wait wait. I haven't seen anyone mention the Venturi effect. What's going on here? I don't even know you guys anymore.
love the inlet guide vane!!
it does wonders for flow around bends and curves and efficienctly distributing flow. BUT, I would worry about material and It coming apart.
01-08-2015, 04:22 AM
