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MAF readings and HP estimates.

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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.  :happy2:

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???  :confused: 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  :happy2:

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:

--- Quote from: ROH ECHT on July 25, 2023, 03:39:03 pm ---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.

--- End quote ---

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 :happy2:

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.

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