MAF readings and HP estimates.

[OllieVRS]

Edit: I've realised this post is a bit of a rant, you can just look at the pictures and skip to the large text at the bottom. 

Read online that horsepower can be fairly accurately calculated by multiplying the MAF g/s reading by 1.25, as the engine aims to burn 1.25g of fuel for every 1.0g of air taken in, creating 1 horsepower. And these reading can be logged in VCDS so that's what I went about doing around the time I got my 200 cel sports cat.

Here is my reading after installing sports cat, without an additional tune, running 99 octane from one of Northern Ireland's only 99 pumps, in Newry:



187.42 at 6960 RPM, so 187.42*1.25 = 234hp. Before the sports cat I made 233hp via this same MAF HP estimation method, on 95 + a serious amount of proper octane booster. Does that sound right? Just gaining 1hp as it's not tuned in yet? Of course such a small difference could be considered negligible, and put down to small inconsistencies in the testing environment, fuel quality etc.

But why is peak power at the very redline??? When this car was dyno'd before the sports cat, running the same amount of octane booster as in my 233hp test mentioned previously, peak power was 232hp at 5833 RPM:




Redid the test yesterday, this time on just 95 octane without any booster. Ambient temp roughly the same as in the previous tests, if not a couple degrees warmer:



ON 95 OCTANE PEAK POWER HAS INCREASED???  190.53*1.25 = 238hp, also at the same redline as the previous tests.


Anyway, I'm not too concerned about the power differences and octane etc.

I'm concerned about why my peak power is at the very redline, instead of around the 5.5-6K RPM range everyone else gets on their MAF readings, just like I did on the dyno. Like in this guys post for example.

Is there something wrong or am I measuring this the wrong way? Or is just VCDS too unreliable for these kinds of reading and estimates?

Cheers 

[ROH ECHT]

The peak HP on the dyno graph always shows peak HP to be where torque drops off faster than rpm can increase; something to do with volumetric efficiency. As HP is only calculated by torque and rpm. If its torque weren't dropping so rapidly, the HP would continue to climb when nearing redline. Using the maximum mass air, to figure peak HP, always occurs at redline; when it is sucking in the most air. These are two different calculations, and using the MAF report to figure its HP isn't entirely accurate; but it has its uses. For one thing, you are relying on the accuracy of the mass air the MAF reports. The only thing I use the MAF report for is to determine the health of my MAF. I take note of what a new MAF is reporting and I replace the MAF should it begin to noticeably report a measurable amount of less air; given the air filter is clean. When all is good on mine (w/K04)...the MAF reports 270 to 280 g/s. If I see it has dropped below 250 g/s, I replace the MAF if cleaning it and the filter do not help. Also, the peak mass air report varies per gear. You might find the max mass air is different in third when compared to fourth.

[OllieVRS]

The peak HP on the dyno graph always shows peak HP to be where torque drops off faster than rpm can increase; something to do with volumetric efficiency. As HP is only calculated by torque and rpm. If its torque weren't dropping so rapidly, the HP would continue to climb when nearing redline. Using the maximum mass air, to figure peak HP, always occurs at redline; when it is sucking in the most air. These are two different calculations, and using the MAF report to figure its HP isn't entirely accurate; but it has its uses. For one thing, you are relying on the accuracy of the mass air the MAF reports. The only thing I use the MAF report for is to determine the health of my MAF. I take note of what a new MAF is reporting and I replace the MAF should it begin to noticeably report a measurable amount of air; given the air filter is clean. When all is good on mine...the MAF reports 270 to 280 g/s. If I see it has dropped below 250 g/s, I replace the MAF if cleaning it and the filter do not help. Also, the peak mass air report varies per gear. You might find the max mass air is different in third when compared to fourth.

Thanks for you reply! That's quite a lot of insight.

Run was it 4th gear, I felt that was it was more accurate that 3rd gear as the it had more chances to poll before it got to the redline.

Out of interest, what's your HP currently at? I wonder how accurate 270 to 280 g/s is if that is equivalent to 338 to 350hp (according to the estimate). And would you by any chance be able to post your log from VCDS of a 4th gear run to red line (if you already have one or you can do one without getting yourself into trouble)?


But I hear what your saying about calculating HP from RPM and Torque, so I used this handy website: https://www.electrical4u.net/calculator/torque-nm-to-horsepower-hp-conversion-calculator/

Peak power from the postcat 99 RON run is 230hp @ 6160 RPM, postcat 95 RON is 220hp @ 6440 RPM. So octane makes a difference of ~10hp, ignoring inaccuracies from the ECU torque reading.

Unfortunately I didn't record torque in my precat run, so I can't calculate what the HP was before.

Figuring that out felt like a Eureka moment though, I can't believe I've measuring it all wrong these last few weeks.

[ROH ECHT]

Here's one clip of mass air data from a log. You see mine peaked a few hundred rpm before the near 6900 redline (a bit higher due to its DSG tune). I can't remember when the HP peaked at on my old dyno runs, the graphs are packed and have no pics, but those show only wheel HP; for being done here in the states. The dyno peak HP occurred, iirc between 5600 and 6100, a good bit before the 6500 rpm mass air peak shown in the data log. So I could only guess what the BHP would be. But yeah...others have said "at least 340 BHP."

[pudding]

ROH ECT has a K04 conversion, but your 240ish hp is about right for a stage 1 K03 tune.

Your VE curves don't look wildly different to be fair, although if your MAF is peaking out at redline, it's making the power from revs rather than flow.  Any number of reasons for that, including turbo size differences. K04s pull harder up top as they're less restrictive than K03s.  ROH's VE curve is very typical. It should reduce approaching redline as the engine simply runs out of flow.  The cam profiles, valve sizing, head flow and throttle body can't get any more air in. Plus the turbo's turbine wheel and housing size become the mother of all exhaust restrictions at that point also.

4th is the right gear to do it in as it's 1:1, so takes gearing out of the equation. Shorter gears increase torque at the wheels, taller gears reduce it, but that only becomes a factor on the coast down fudging on a rolling road.  But on the highway, there's more load in 4th, so works the turbo harder and there's also enough legs to max it out without doing crazy speeds

The MAF divide by 0.8 or times by 1.25 often comes under criticism as a rubbish metric, but it's actually not far off, since MAF and fuel injection timing are directly proportional to each other. Every time I've used that method for road tuning, it was only 5% off on a rolling road.

[OllieVRS]

ROH ECT has a K04 conversion, but your 240ish hp is about right for a stage 1 K03 tune.

Your VE curves don't look wildly different to be fair, although if your MAF is peaking out at redline, it's making the power from revs rather than flow.  Any number of reasons for that, including turbo size differences. K04s pull harder up top as they're less restrictive than K03s.  ROH's VE curve is very typical. It should reduce approaching redline as the engine simply runs out of flow.  The cam profiles, valve sizing, head flow and throttle body can't get any more air in. Plus the turbo's turbine wheel and housing size become the mother of all exhaust restrictions at that point also.

4th is the right gear to do it in as it's 1:1, so takes gearing out of the equation. Shorter gears increase torque at the wheels, taller gears reduce it, but that only becomes a factor on the coast down fudging on a rolling road.  But on the highway, there's more load in 4th, so works the turbo harder and there's also enough legs to max it out without doing crazy speeds

The MAF divide by 0.8 or times by 1.25 often comes under criticism as a rubbish metric, but it's actually not far off, since MAF and fuel injection timing are directly proportional to each other. Every time I've used that method for road tuning, it was only 5% off on a rolling road.

Great insight, thanks!

MAF points to max power at nearly 7000RPM, Torque spec points to max power at ~6200RPM.

Also the '238hp' I posted earlier definitely comes up under 'rubbish metric'. I dynod at 232hp on a proper dyno, running enough octane booster to make my 95 octane equivalent to 99. But you're right, less than 5% off.

I hope to get my tune updated on the dyno in a couple weeks, but only on 95 as it would be dangerous to map for 99 in a country that doesn't sell anything it. My HP on 95 is 220-225, so hoping for 235 at least. Irish 95 is pretty depressing after all though, so can't have my hopes too high up. Allegedly Irish 95 is actually worse for mapping than Great British 95, according to online rumours.



EDIT: Forgot to include, finally learnt how to use Excel, here's a couple neat graphs from logging on just 95:





And some timing pull, to do with the lower octane or is does higher octane get this too? Haven't had a chance to retest with booster yet.

[pudding]

Oh dear, maybe move to England 

Yeah I was just looking at the timing pull and anything over 6 isn't great to be honest, but not critical. Even standard ones usually pull -4 to -5, they run pretty close to detonation from the factory.  -7.5 certainly isn't disastrous, so don't worry about that too much. If you see figures of -10+, you need better fuel or a remap of those load areas.

From memory, those aren't the actual degrees of ignition retard. It's a weird Bosch way of doing things. It retards in steps of 0.75 degrees, so it would 7.5 x 0.75 = 5.6 actual degrees of retard, which at 1700rpm isn't anything to lose hair over.

The stock TFSI timing map is pretty gnarly. At some load points there is 0 degrees advance, sometimes minus degrees. They're just all over the place, but it all works hand in hand with the VVT and other parameters, but anyway, I've not seen anything in any of your charts that rings alarm bells    You have very low timing pull from 3600 upwards, which is the danger zone.  At those rpms, excessive detonation is game over as you don't have time to back off, and you can't hear it happening.  I think the ECU's retard limit is -25KW (18 degrees), so you're well within the limit.

Obviously you want as close to zero pull as possible for power consistency and engine life span, but even with 99 RON in England I was seeing -6 on my ED30 with Stage 1.

Also bear in mind, a heat soaked intercooler will raise intake temps, which will also cause the timing pull.  45 degrees C intake temp is when the ECU starts pulling it.

[OllieVRS]

Finally, got mapped. Unfortunately no dyno as the dyno my tuner normally borrows was too busy, so just a road map for now. He says we'll get the map fine tuned when the dyno is free, but who knows when that is

Also, I've figured out that the HP conversion formula I was using was for BHP, not 'PS', or the version of HP I like. God damn you imperialists, making me think I have 3 less HP. So all numbers presented below (and previously) are all in imperial horsepower, not metric. 

Anyway. The numbers. There's some weird anomalies like high HP near redline so I've included timing pull again and intake air temp.


95 Octane



Horsepower ≈ 250BHP*


95 Octane + NF Sport Octane Booster



Horsepower ≈ 259BHP*


*To be taken with a grain of salt, as this is just VCDS logging and anomalies occur in the data. Only a dyno will reveal a more accurate number. I also just threw in the octane booster right before the second run without filling up, so may not have been mixed perfectly.


I'd like to know what you think of the timing pull, @Pudding . Tuner said he changed the timing slightly to squeeze out more power. She's hitting as much as -9KW timing pull on 95 in the peak power RPM range.

Cheers!

[pudding]

-9 is a tad high but not excessive. Personally I wouldn't want to see any more than -6, but the octane booster appears to reduce it