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TTQS
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« on: May 22, 2011, 10:13:09 AM »
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Hi guys.
Bazaa and I were recently discussing the Revo Technik stage 2 remap for the 225 & 240 PS Audi 1.8T engine variants so I suggested I post up my VAG-COM logs during WOT runs in 3rd and 4th gear for general interest/discussion. I included a sub-set of these results in my 'beginner's guide to ECU remapping' document.
The background to these logging runs was my general disbelief of the rolling road dynamometer results obtained before and after the remap. The agent estimates transmission losses during a run down from peak engine speed and adds this on to the wheel output which gave peak outputs of 256 bhp & 350+ lbft. I felt the bhp was maybe 8-10% too low and the torque far too high, so I sought some alternative ways of estimating or calculating this from engine parameters.
BHP is estimated from the tried and tested expression BHP = MAF/0.8 for 1.8T motors, but I have also logged block 120 which has some measurement of torque and then back-calculated BHP from this. I don't know how this figure is measured/calculated and would be grateful for advice on that. Suffice to say that it is much lower than the dyno figures. The data in blue type are all calculated from the logged parameters.
Bazaa commented that there was some general dissatisfaction with Revo remaps on forums relating to rich running, etc., but the view on the forum I was previously a member of was that the outputs were highly optimised and very satisfactory with little evidence of undesirable side effects. However, you can see some rather high IDCs (up to 148%) on the 4th gear run compared to maximum of 98% on the 3rd gear run. I would like to credit Morgan Evans of Vagcheck in Staines, U.K. for his advice on this.
There was also a great deal of discussion about the supposed benefits/advantages of higher octane super or premium unleaded fuels in terms of peak outputs and greater fuel economy, but nobody ever investigated it or obtained any objective data so all arguments were based on hearsay, opinion and the good ol' butt dyno only. Most TT owners, whether remapped or not slavishly stuck to the premium or super unleaded products with Shell V-Power 99 RON being the most popular. I grew rather tired of this and sought to find out whether the standard supermarket 95 RON fuels were significantly worse in terms of fuel economy and require greater individual cylinder timing corrections during WOT runs to cope with more knock events from fuel of higher calorific value.
I have not repeated the WOT runs with supermarket 95 RON fuel yet, but am currently nearing the end of my second tankful of the cheaper fuel during which I have deployed 'hypermiling' techniques including gentle acceleration and cruising at 60 mph on the highway. All my mileage nowadays consists of 36 mile round trips, of which, 95%+ is cruising in relatively light traffic two lane highway (dual carriageway in the UK) giving a consistent baseline for comparison. So far, I have been able to EASILY add 50 miles to my range and 3-4 mpg by driving carefully.
Continued in second post due to character limitation..
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« Last Edit: July 17, 2011, 02:03:41 AM by TTQS »
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TTQS
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« Reply #1 on: May 22, 2011, 10:20:58 AM »
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My working hypothesis is that the higher octane 99 RON super unleaded fuels are not worth the 5 to 8 pence per liter premium over 95 RON standard fuel because:
(a) Any small improvement in fuel economy is likely to be greatly outweighed by variation in driving technique/style and traffic/weather conditions
(b) There won't be significantly more knock events at high loads with the lower RON/higher calorific value fuel such that the ECU will pull sufficient individual cylinder timing correction for there to be a noticeable reduction in peak output.
However, I'll see in due course...
Doug
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« Last Edit: May 22, 2011, 12:57:54 PM by TTQS »
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bazaa
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« Reply #2 on: May 22, 2011, 12:20:33 PM »
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Hi Doug
Thanks for posting your logs
Those IDC's are extremely high are they standard injectors and fuel pump your running,
As an injector can only really be 100% max/open all the time i guess that's got to be a commanded value opposed to real injector value,but i notice they are only exceeding this at very high revs so probably exceeding the IPW .Might be time for some larger injectors with those figures .lol
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« Last Edit: May 22, 2011, 12:31:22 PM by bazaa »
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TTQS
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« Reply #3 on: May 22, 2011, 01:10:03 PM »
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Hi Bazaa.
Yep, stock 3 barg fuel pump and stock 386 cc injectors. The injector pulse width values are real, measured values and the IDC is just calculated from them in the normal way using the expression
100 x (IPW/((2 x 60 x1000)/RPM))
Such high IDCs are unexpected and such a big difference between the two runs is a bit of a mystery. Clearly, actual EGT will be higher for longer under sustained full load therefore the ECU is trying to enrich to reduce it. My understanding is that the stock Bosch injectors have a maximum pulse width of 25 ms and at 7160 rpm on the 4th gear WOT run it is practically maxed out at 24.82 ms. But duty cycle takes into account engine speed too, so for any given on-time, the higher the engine speed, the less time is available for injection/ignition events. The only way to go, as you say, is a higher flow rate to get the required fuel injected in the available cycle time. :-/ Hmm.
I sort of justified or excused this 'feature' of the Revo map with the view that sustained full loads like that are rare, even in sporty or enthusiatic driving and on European roads where sports cars like the TT come into their own, you're only maxing out like that briefly for overtaking, powering out of slow bends, etc. Therefore, it is reasonable to push the boundaries of the ECU fuelling regimes to extract big headline output figures.
Doug
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« Last Edit: May 22, 2011, 01:11:52 PM by TTQS »
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carlossus
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« Reply #4 on: May 22, 2011, 01:17:17 PM »
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Doug,
As a 1.8t owner your approach is exactly what I wanted to hear. Forums are usually breeding grounds for nonsense so an evidence based approach is so refreshing.
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TTQS
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« Reply #5 on: May 22, 2011, 01:18:43 PM »
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Doug,
As a 1.8t owner your approach is exactly what I wanted to hear. Forums are usually breeding grounds for nonsense so an evidence based approach is so refreshing.
Agreed, but this forum is much better than the usual! Besides, as a ex-scientist (of sorts) and an engineer in training, there can be no other way than objective evidence. B.S. has never cut it anywhere I've ever worked, so I don't see why I should lapse into it on internet forums. It's disrespectful and irritating to the peer group. Doug |
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« Last Edit: May 22, 2011, 01:22:22 PM by TTQS »
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bazaa
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« Reply #6 on: May 22, 2011, 01:27:13 PM »
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I agree 148.1%  where in the uk can you really sustain full load and drive at high rpm for any time and the expence upgrading would as you say will be uneconomical for minimal gain .I know i couldn't jusify it. Bazaa |
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julex
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« Reply #7 on: May 22, 2011, 05:02:34 PM »
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I will comment on few things that caught my eyes:
Fuel octane rating: for normal driving it doesn't absolutely matter how low octane the fuel is, it only matters when you step and you WOT. At cruising load levels there won't be any knock (octane rating is really a resistance to pre-detenonation which is really the purity of fuel) and hence no improvement in economy.
IDC: now that one is a mystery, kind of, until you realize what IDC really is. 100% of IDC is basically a term that describes an injector being open for 100% of its OPTIMAL (capitalized on purpose) injection time where intake valves are open.
If injector is lacking flow though and ECU knows about it, the ECU can pre-inject fuel before the valves are open and that's when 100%+ IDC shwos up. Since the air is moving so fast at that time, that pre-injection and fuel stalling for few ms in the manifold don't really matter and you don't get weird AFRs etc so it all works out.
The problem is that injctors relay on sub 100% IDC since they use the fuel to cool them so you are stepping beyond design envelope here.
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TTQS
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« Reply #8 on: May 23, 2011, 12:04:13 AM »
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Hi Julex. A good contribution, thanks.
Although I failed to mention it, I think I realised intuitively that for economical cruising and hardly any/no full load acceleration, knock events will be limited so there is no advantage yo using the premium fuel as you say.
I had also rationalized >100% IDC as pre-injection based on the odd fuelling regimes I read about in the lean burn type strategies deployed in the FSi engines. I'd rather it was <100% but EGT seems to be under control so I don't worry.
Doug
Doug
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Rick
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« Reply #9 on: May 23, 2011, 03:25:31 PM »
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Julex,
are you sure that's correct re IDC's?! It certainly isn't when talking in traditional ECU language. Nearly all engines will become pseudo batch fire as you describe at high loads. 100%+ duty cycle is where the injector needs to be held open longer than the time for one complete engine cycle.
Rick
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nyet
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« Reply #10 on: May 23, 2011, 03:28:11 PM »
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Julex,
are you sure that's correct re IDC's?! It certainly isn't when talking in traditional ECU language. Nearly all engines will become pseudo batch fire as you describe at high loads. 100%+ duty cycle is where the injector needs to be held open longer than the time for one complete engine cycle.
Reminder: a FULL cycle is two rotations! So yea, rick, I agree. 100% is static, as in, fully open for two full crank rotations. |
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Rick
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« Reply #11 on: May 23, 2011, 03:56:19 PM »
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yea, one cycle = 720 degrees.
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TTQS
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« Reply #12 on: May 28, 2011, 02:44:41 PM »
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Incidentally, the 'hypermiling' experiments extend to my wife's car, a MY2005 E12 model Toyota Corolla 2.0 D4-D 5-door hatchback with a 55 litre (12.1 imperial gallon) fuel tank. Specs here: http://www.toyota.co.uk/vs2/oldpdf/05/CO6_63_spec.pdfMy previous best range was 508 miles from a brimmed tank to the low fuel warning light illuminating but my wife typically gets maybe 400-420 miles before she is near the bottom of the fuel gauge and has to refill (not to LFW though). We recently took a week long break with the car carrying two adults and a full load of stuff which involved 160 miles of motorway driving. I drove economically at all times and stuck to 60 mph on the motorway. The low fuel warning light came on at 549 miles. I think 575 is possible but my wife had driven the first 74 miles at an indicated average 47 mpg so I was on the back foot from the start. It's not much use talking about indicated fuel consumption because the offset appears to be large (maybe 25%) and highly variable, but indicated fuel consumption when I refuelled was 63.2 mpg. When I refuelled and drove the remaining 17 miles home, the displayed mpg was showing 76 mpg and was as high as 84 mpg at one point. So irrespective of the actual numbers, there are big gains to be had by driving sensibly. Doug |
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nyet
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« Reply #13 on: May 28, 2011, 06:35:34 PM »
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there are big gains to be had by driving sensibly.
Which usually cause nothing but frustration to cars around you, such as anybody stuck behind 4 prius's running abreast on the freeway at 54 mph. |
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julex
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« Reply #14 on: May 28, 2011, 11:52:23 PM »
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But that's only typical of stupid (yes I mean it) US drivers who have exactly ZERO driving education and even less courtesy ending in asshole(s)/(lettes) (yes I mean it again) driving in left lane at or below speed limit. When I see priuses I just shiver and basically absolutely rudely cut in front of them once I manage to pass one after that ass blocking fast lane for the last 5 minutes. Every european driver is told and enforced by law to sit in right lane unless he/she is passing which implies going far above speed limit. I central europe/east europe you're guaranteed to have somebody riding your ass/flashing lights/etc if you anything below 2x speed limit on the left lane. Cops will give you a ticket for violating law b/c you drove left lane constantly without intent to pass. In US I noticed that having 3k HIDs in fog lights and having them on 24/7 (by re-wiring the harness) gets peoples' attention to GTFO of your way.  . I get lots of "V"s from audi/VW folks too. Sorry for rude post but the post above just struck some nerves there. |
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