After swapping in an AMG M275 into my SL600, I have been logging MAP boost pressure, both with and without a performance tune.
The max MAP values I ever see is 24 psi around 3800 RPM. That might sound like the spec, but since atmospheric pressure is 14 psi, this is only 10 psi of additional boost. If the spec is e.g. 22 PSI of boost, I would expect to log 22+14= 36 psi of MAP pressure.
I never logged the original non-AMG engine, but with a tune it had the same 0-100 mph time as my stock AMG M275; this suggested the AMG engine is running at stock power.
I'm sending log file to my tuner, but hoping someone here has logged MAP values. BTW - I'm using HP Tuner's VCM Scanner for this.
Thanks.

 

I usually see around 21psi on my stock 65. The reading is correct. Atmospheric pressure can't be considered as the boost pressure is 0 at atmosphere. Otherwise you'd be running 14lbs of boost at idle. As a matter of fact you should see negative boost at idle. During normal driving I see around 6 to 7 psi when I'm not getting on it. On rare occasions if the weather is right for it I'll hit 24psi.

 

Thanks for chiming in. I think you are referring to values seen on a "Boost Gauge" which shows pressure compared to atmospheric. However, converting the voltages on a MAP sensor to PSI will show atmospheric as 14.7 psi at sea level.
At idle I see around 3-4 psi which is equivalent to about "20 inches of vacuum" as is typical when a vacuum gauge is connected to a non-boosted engine.
I just got a good answer from Peter (the BenzNinja guy) who emailed me that he sees 36 psi of MAP pressure.
This is the first boosted engine I have made modifications to. So the difference between "Boost pressure" and "MAP pressure" had me confused for a while.
I will confirm I have the correct MAP sensor and go over the MB service steps for checking the turbo system.

 

Ah I see. That cleared it up.

 

Today I refreshed on how the turbos work. First, I removed the air filter boxes for easier access to everything; connected spare MAP sensors for the missing ones in the air filter boxes.
Next, verified that the vacuum test line has vacuum and it was perfect at close to 20" of vacuum and even held it for minutes after engine was off.
Next I connected a basic vacuum/fuel-pressure gauge to the turbo air diverter line. Taped the gauge to my windshield so I could read it while driving. Went for a drive with HP Tuners logging everything.
This line correctly shows vacuum at low throttle but goes into boost under high throttle. I think it maxed out at 10 psi boost while my logging showed only 6 psi of boost. (Again 20 psi - 14psi atmospheric).
This makes me question whether the MAP values in HP Tuners are accurate. Therefore I just ordered a Bosch mechanical boost gauge and will connect it tomorrow.(Of course hard to read a gauge when these cars are going WOT.)
If I really cannot get 20 psi of boost, I may disconnect the wastegates. (Without CATs it is easy to access the turbos from underneath; I have a hoist.)

 

OP what do you get for intake air temperatures with boost?

Engine management pulls boost with elevated intake air temps or when it senses ping.

Look there before unplugging wastegates.

 

Thanks for chiming in.
The IAT was only 90F as the engine had only been running for maybe 5 minutes on a cool day.
UPDATE - I installed a mechanical boost gauge and on a brief run it showed 18 psi of boost, so very close to the expected 20-22 psi.
Next I will figure out why my scanning/logging with HP Tuners showed such low MAP/boost values. Maybe it is reading incorrectly or my MAP sensor is off. I know it is reading the MAP sensor on the intake manifold after the throttle-body whereas my boost gauge is reading before the throttle-body, but at WOT, it should be the same. The intake manifold MAP is the correct MB part number, I might try the Bosch equivalent I have.
The BenzNinja sent me a screenshot of the TorquePro showing a max MAP value of 34.5 psi which is 20 psi of boost. Since TorquePro only runs on Android, I have a new Android tablet arriving tomorrow to try and replicate his results.

 

90 degrees F or C for IAT? If C it is time for more charge cooling or even better... Water/Methanol injection. Additional heat exchanger in front of the stack. Bigger charge cooling pump. Perhaps wrap charge coolant lines in header blanket to keep radiated heat from exhaust from adding unwanted heat to charge coolant.

 

Again, appreciate you chiming in, buy my post did say "90F", so barely warm at all. Learning to use TorquePro today.
Couldn't complete a run because I got a multi-cylinder misfire code. First time on this engine; difference is I recently installed a tune. Also a warmer day and IATs were 130F due to idling learning TorquePro.

 

130F is still pretty low. Multi cylinder misfire. Coil pack or Voltage transformer. Or both!

 

Got Torque Pro working and finally found the correct PID and settings to display "Intake Manifold Pressure" in PSI. On a short run my mechanical boost gauge showed a max of 16 psi and Torque Pro recorded a max of 30.7 psi which is an exact match. (16 + 14.7 = 30.7). So that is now working!
No idea why HP Tuners wasn't showing the expected value; perhaps I picked the wrong PID.
Tomorrow I have a new Apple Car-Play head unit arriving which also has Torque built in and I believe can download other Android apps. It will take some effort to swap the head unit, but I cannot resist the idea of having a very configurable scanner built into the car.

So far the misfire code was a single occurrence. Coil packs were brand new from dealer 3 years and 8000 miles ago. Transformer has been swapped. Don't know the gap on the spark plugs. On my original non-AMG engine, after installing a tune, I struggled with frequent misfire codes and learned a lot about them. I haven't yet double checked the LTFT on this tune, wanted to see boost numbers first. I also run without the engine covers to keep things cooler.

Thanks for everyone's support. It kept me motivated to figure this out.

 

Nice work. How does she go?

 

I am very happy with my new Head unit. I first had some glitches, but the seller provided exceptional customer service with details about "hidden" settings and had me flash an update. Literally 3-page long emails with pictures and perfect English.
The Head unit also has wireless Apple Carplay, Wifi, GPS and more. The Toque App, same as on a phone, has multiple pages of completely configurable gauges. My second page has gauges for Fuel Trims, temperatures, etc.




Between trips and now winter weather I didn't have enough time to complete any performance runs with Draggy. On a flat road with a tune the Torque app was showing a max wheel torque of 542 lb/ft and a max of 32 PSI intake (18 psi boost). But when I went back to a stock tune I got the same max torque with only 15 psi boost and my butt-dyno felt no difference. I know the AMG engine is rated at 740 lb/ft torque; no idea why the measures torque is lower; I entered the car weight as 4450 lbs. Since it has GPS, it measures the change in speed over time to estimate torque; not sure it knows what gear the trans is in though. In any case, the actual number is unimportant; I do think it is useful for comparing tunes.

Since my purchased tune didn't seem to work any better than stock, I looked for other tune sources and starting learning to use tools like WINOLS to find the tables in a binary ECU file. I also purchased an inexpensive tune from Dyno-ChipTuningFiles.com which seems to be a repository of thousands of dyno-testing tuning files for a wide variety of European cars. It is technical - you have to provide your current raw binary ECU file, select the performance options you want, pay and they send you a file. You must then have the tools to copy the file to your ECU. I'm using the Ktag tool and this requires removing the ECU, opening it, and wiring to some EPROM chips to read the existing tune. I think I can use a Galetto cable to write the new tune, or I can do that with Ktag too. I will update when done.

Sure, some might say why not just buy the tune from Renntech. For one, when I contacted them, they only provide one tune with no options. Since I run Catless and have plans for some future mods, their tune will not work for me. Also I'm very familiar with tuning GM vehicles, Holley ECU systems and want to learn more about Mercedes tuning.