# FAQ - How much boost can I run?



## tekstepvr6 (Aug 15, 2001)

*****DISCLAIMER****
Please use at your own risk!! I will not be held responsible for any damage caused to your vehicle by following the steps listed in the guide below. The steps listed within will give you a better understanding of how your car is reacting to its current tune.* 
*This FAQ applies to obd2 cars with a modified stock ecu. The steps listed below were performed on a MK4 VR6 turbo. Most of the steps should apply to MK3 based cars as well.*

*What You Need*
1) VAG-COM Cable
2) Laptop w/ VAG-COM software loaded & good battery life
3) Nice stretch of highway (Please obey all posted speed limits)
4) Friend to log (Optional but highly recommended for safety)
*Start Testing*
1) Start the car and boot up the laptop
2) Connect the VAG-COM cable to the OBD2 port and launch VAG-COM
3) Navigate to *Engine -> Measuring Blocks*
4) Load measuring blocks 002, 020 and 030
****a) 002 lists RPM, Engine Load, Injector Period (ms) and Air Mass
****b) 020 lists knock on cylinders 1-4
****c) 031 lists actual and requested air/fuel ratio
5) Start off by performing a full throttle run in 3rd gear from roughly 2500 rpm to redline or your usual shift point. If this is the 1st time you are boosting the car start with a safe boost pressure of around 6 psi.
*NOTE: If you notice that the data capture is slow while logging all 3 blocks then perform a run with only one or two measuring blocks to increase the sample capture rate.*
6) After the run has been logged make sure your A/F ratio in boost is between *11.7-12.5* by checking your wideband (If you have one) or by checking block 031 and using the lamda to gasoline conversion table listed below.
*Conversion Table*








7) Next check the amount of engine knock you are seeing on cylinder 1-4 by viewing your log for block 020. Generally I don't push mine past ~6 degs of timing pull but the ME7 ecu can pull a max of ~12 degs of timing (I don't recommend pushing it that far). If you are seeing a lot of timing being pulled then turn the boost down or remove timing (MK4 cars only) via Lemmiwinks or UniSettings
8) After getting some baseline logs you will need to calculate your duty cycle on the injectors. Take the data you logged in block 002 and use the formula below to calculate the duty cycle on your injectors.
*(Pulse in ms) / (120,000/rpm) = 0-1*
A general rule of thumb is to not go over 80%-85% duty cycle on the injectors. I pushed the Bosch 440cc green tops to 88% duty cycle @ 7200 rpms with 20 psi when I was running them.
9) After logging a few runs of your A/F ratio, timing retard and duty cycle on the injectors you can begin adding boost if you are not seeing any lean or rich A/F conditions, large amounts of timing retard or 90%+ duty cycle on the injectors.
*Additional Notes*
Please keep in mind that ambient tempatures, compression ratio, timing and fuel octane will play a big role when selecting a safe boost pressure to run.
*Example Log*
Here's an example of a log I did with 630cc injectors:








Duty cycle on the 630cc injectors @ 3 bar w/ 24 psi:
57% @ 4800
62% @ 5480
69% @ 6320
70% @ 7080
A/F ratios look to go from 11.7-12.0.
If you have any questions or concerns regarding this FAQ please let me know so I can answer them to the best of my knowledge or make changes to this FAQ.


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## DMehalko(DM) (Nov 1, 2004)

*Re: FAQ - How much boost can I run? (tekstepvr6)*

Awesome! i need vag-com..and got to hook up my wideband


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## VR6rocks (Jun 5, 2004)

*Re: FAQ - How much boost can I run? (DMehalko(DM))*

Had come across this info earlier in one of your posts and saved it, good thing you finally compiled this into one thread for everyone to benefit from it http://****************.com/smile/emthup.gif 
I vote for a sticky
Too bad timing can't be adjusted on the M2.9


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## phatvw (Aug 29, 2001)

*Re: FAQ - How much boost can I run? (tekstepvr6)*

Nice writeup http://****************.com/smile/emthup.gif


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## 7165eurospec (Jun 18, 2006)

*Re: FAQ - How much boost can I run? (tekstepvr6)*

I have VAG-com . Can I do this on a 93 Corrado VRT ???????? Its not OBD2 but maybe there's some valuable info I can get?????????


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## Sosl0w (Aug 21, 2003)

Tagged for later use. Great info.


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## moacur (Sep 22, 2006)

*Re: (Sosl0w)*

Great write up man http://****************.com/smile/emthup.gif Logging runs is key to getting the max out of your tune and car.


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## jhayesvw (Oct 3, 2001)

*Re: FAQ - How much boost can I run? (DMehalko(DM))*


_Quote, originally posted by *DMehalko(DM)* »_Awesome! i need vag-com..and got to hook up my wideband

a4 vws have wideband o2s from the factory. no need for an additional WB to log this stuff
a3 vws are not so lucky


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## maxslug (May 22, 2005)

*Re: FAQ - How much boost can I run? (jhayesvw)*

Great post tekstep! http://****************.com/smile/emthup.gif 

_Quote, originally posted by *jhayesvw* »_a3 vws are not so lucky

In other words, if you have a MK3 OBD-II or any OBD-i motor (eg. Corrado), *you need a wideband* to get the lambda reading. The stock ones are narrowband and only read around lamba=1.
Another good note is that you should only log ONE THING at a time. The OBD-II port and the ECU are slow and the sampling rate is seriously affected if you log more than one channel at a time. So only look at one channel at a time when you're doing your pulls or you might miss spikes/dips.
-m


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## radoman57 (Jan 16, 2007)

*Re: FAQ - How much boost can I run? (maxslug)*

Awesome writeup, 
How did you calculate your duty cycle from the spreadsheet?


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## Jefnes3 (Aug 17, 2001)

*Re: FAQ - How much boost can I run? (radoman57)*


_Quote, originally posted by *radoman57* »_Awesome writeup, 
How did you calculate your duty cycle from the spreadsheet?


Read step #8.

-Jeffrey Atwood


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## Noobercorn (Aug 17, 2007)

*Re: FAQ - How much boost can I run? (7165eurospec)*


_Quote, originally posted by *7165eurospec* »_I have VAG-com . Can I do this on a 93 Corrado VRT ???????? Its not OBD2 but maybe there's some valuable info I can get?????????

no jimmy, we do not have that ability on our caars. 
great write up homie!!! when are we gonna do some logs on 309 with the 630 file?


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## vdub1998 (Aug 1, 2007)

*Re: FAQ - How much boost can I run? (Noobercorn)*

i have a c2 software chip with 42lbs injectors and when i'm in 6psi my wideband o2 is reading 15.7 to 17.0 can someone give me advice mk3 golf 2.0L 8V


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## FaelinGL (Nov 28, 2004)

*Re: FAQ - How much boost can I run? (vdub1998)*

Good post. Added to watched.
Mike


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## jhayesvw (Oct 3, 2001)

*Re: FAQ - How much boost can I run? (vdub1998)*


_Quote, originally posted by *vdub1998* »_i have a c2 software chip with 42lbs injectors and when i'm in 6psi my wideband o2 is reading 15.7 to 17.0 can someone give me advice mk3 golf 2.0L 8V

stop driving the car!!!
honestly though. recalibrate your wideband and make sure you dont have massive boost leaks letting lots of air out of your system.


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## vdub1998 (Aug 1, 2007)

*Re: FAQ - How much boost can I run? (jhayesvw)*

i don't have a boost leak thats the weird thing and i am lowering the compression to 9:1 but i have no idea on the fuel psi i have it now at 50


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