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Smart quod bastardus
 
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question on AFR and water meth injection

I installed water meth injection in my 79 930 and am in the process of tuning it now.
Question: Should I disconnect the system to tune the AFR without the meth injecting and then retune it with it hooked up?
Main question:
If the engine at high load (4th gear) and high boost (0.7bar) were running out of fueling but the meth injection was injecting at full flow, what should I expect to happen to the AF ratio? Meaning if the gas was lean but I were over fueling with water/meth fluid, would the AF ratio show rich or lean?
Right now I am running in the low 11's to even 10.9 to 1 AFR under high boost, high gear and am experiencing slight hesitation which tells me I am injecting too much water/meth and quenching the combustion. I just dont know if I am still getting too much gasoline and truelly rich or if the AF ratio would show 11 to 1 with a lean gas mix and too much water/meth. Its hard for me to believe that my stock WUR is able to get to a rich condition at these engine conditions when everything on the forum says it should be way lean.
hope I asked the question clearly.
Thanks,
Fred

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1979 930 Turbo....3.4L, 7.5to1 comp, SC cams, B&B intercooler, Snow Perf water/meth injection, Rarlyl8 headers, Garret GTX turbo, 36mm ported intakes, Innovate Auxbox/LM-1, custom Manually Adjustable wastegate housing (0.8-1.1bar),--running 0.7bar max
---"When you're racing it's life! Anything else either before or after, is just waiting"
Old 07-22-2011, 11:25 AM
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beancounter
 
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Hey Fred...

Just curious how long you've been running the wideband sensor. I ask because mine was in the car for a couple years and finally crapped out on me. When I plugged in a new one it read leaner than the old one, but also more in line with what I saw from the Dyno shop's high end equipment. I think that they lose accuracy over time
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Past: 2009 997 Turbo Cab / 1979 930
Old 07-22-2011, 12:10 PM
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I'll be honest. I think meth injection is a bandage. But!
What system are you using?
You should always have an established base map, or adjustment typically on the safe side a little rich. Are you tuning EFI or Jetro + digital WUR? It's possible to damage or cook an oxygen sensor. Also as a rule of thumb you should service your oil more frequently with meth.

Usually, I'll tune the initial base map, then tune the parameters more aggressive but not quite at the limit and then add increments of meth as required. I spend more hours on a dyno testing more variables. Hot / Cold, different loads. I also have monitoring equipment and have clients go free range and watch city and highway driving. But it's all about hours and time/budget.
Old 07-22-2011, 12:28 PM
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PS, don't guess with meth.
Base map it, see what your values are at a safe conservative tune, then tune the areas " you need " and add meth, and slowly and tune further but once satisfied give a small buffer zone as driving conditions, fuel, temp etc all will change in dynamic conditions.
Old 07-22-2011, 12:32 PM
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A 50/50 mix changed my A/F by 1/2 a point. If you tune car without the meth and then put the meth system on you should see about a 1/2 point richer conditions at 50/50 mix. Unless you run less meth and more water. Meth works great for me but I dont track my car. My intake temps are much cooler with the meth system. I have not had long term exsperience yet, about 4 months. My engine has never ran better.
Old 07-22-2011, 01:32 PM
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I am leaving mine on the richer side too.. 11.2-11.8
Old 07-22-2011, 01:33 PM
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Hey Fred

What mixture are you running for your meth injection? I started with wiper fluid, but after a while I found I couldn't source a steady supply of one particular brand. Here in Canada we have four seasons, which are all catered to differently. Different brands would give me diff. results and actually change the AFR readings. I now mix my own, Methanol Hydrate/distilled water, at 50/50%. This give me a very rich at boost afr. 10.5-1. I also wondered about the air pump which I am running? Think that makes a difference? Philip
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Old 07-22-2011, 02:28 PM
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I use boost juice by Snow Performance. I can get it for a good price thru one of my distributors. I dont want to mess around with inconsistance of wiper fluid. I know some guys use it.
You should be able to get methanol easy and cheap up in canada. Here in NY it is hard for me to find locally and exspensive to ship so it pays for me to use the boost juice, I also like using a fuel that is designed for the product I am using.
With the meth working I adjusted my WUR to get my A/Fs were I wanted them. I am in the lower to mid 11s up to 6800. I dont really rev it higher than that. Before the meth I was at 11.8-12.4 with less boost. Since I did increase my boost for safety I now run lower A/Fs.

As far as air-pump goes. I dont even no if I have one on my car. If it is a part that could have been takin off it probably was. I bought the motor and put it in my car. I never had it when it was bone stock.
Old 07-22-2011, 03:43 PM
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Quote:
Originally Posted by jwasbury View Post
Hey Fred...

Just curious how long you've been running the wideband sensor. I ask because mine was in the car for a couple years and finally crapped out on me. When I plugged in a new one it read leaner than the old one, but also more in line with what I saw from the Dyno shop's high end equipment. I think that they lose accuracy over time
O2 sensor is only 2 months old, so it should be fine. I think the sensor is accurate, but the WUR has me suspicious. Is it possible that the stock euro injectors, fuel head and WUR would run that rich under boost with my engine mods?
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1979 930 Turbo....3.4L, 7.5to1 comp, SC cams, B&B intercooler, Snow Perf water/meth injection, Rarlyl8 headers, Garret GTX turbo, 36mm ported intakes, Innovate Auxbox/LM-1, custom Manually Adjustable wastegate housing (0.8-1.1bar),--running 0.7bar max
---"When you're racing it's life! Anything else either before or after, is just waiting"
Old 07-22-2011, 08:27 PM
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.7 bar is about 10psi. I think you could be seeing 11s with your set up.

Here's a set of datalog charts from my car. Its a composite of 4 20 minute session on track at NJMP. The top chart shows average AFRs vs. RPM and MAP. I'm a bit leaner than your readings at 10psi, but then I have larger displacement and my intake ports are opened up 5mm so given the same indicated boost level, I should be flowing a bit more air than you.

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Old 07-22-2011, 09:09 PM
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Smart quod bastardus
 
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Thanks Jacob.
The top chart is an average of all 4 runs? Your AF ratio were in the mid 11's to low 12's, that is pretty good.
I noticed the bottom chart some of your AF ratio dipped into the 9's! Is this chart a bad run or something or was there some sort of bad calibration on your O2 sensor?
Just trying to get more detail info from your charts.


I do have SC cams and larger 36mm ports as well, so my airflow should be pretty close to yours at the same boost levels, dont know if I mentioned that in my earlier engine mod description.
I would be amazed if my stock WUR without any modifications which I am running is getting me to the low 11's under 0.7bar boost like I am seeing.
I checked control pressures and they are all within OEM spec for my engine.
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1979 930 Turbo....3.4L, 7.5to1 comp, SC cams, B&B intercooler, Snow Perf water/meth injection, Rarlyl8 headers, Garret GTX turbo, 36mm ported intakes, Innovate Auxbox/LM-1, custom Manually Adjustable wastegate housing (0.8-1.1bar),--running 0.7bar max
---"When you're racing it's life! Anything else either before or after, is just waiting"
Old 07-25-2011, 10:34 AM
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beancounter
 
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Fred,

I didn't realize you had your heads ported too. That bottom AFR chart is showing the minimum readings over the same dataset (vs. the upper chart being average). The minimum and maximum readings are really not that meaningful in this case. For example, the AFR spikes very rich for a second just after you close the throttle post a full boost acceleration and then spikes very lean before normalizing. This is pretty obvious when you look at the raw data over time...would be really obvious too if I had a way to log throttle position. I do have a log of acceleration and braking G's and I can tell when I lifted off the throttle because the G's drop.

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Current: 1983 911 GT4 Race Car / 1999 Spec Miata / 2000 MB SL500 / 1998 MB E300TD / 1998 BMW R1100RT / 2016 KTM Duke 690
Past: 2009 997 Turbo Cab / 1979 930
Old 07-25-2011, 02:08 PM
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