Question about semi-open loop and boost/meth

[thunder550]

I have a question about semi-open loop, I apologize if it's a stupid question but I'm new to the whole tuning thing, so be patient :)

Would there be any benefit to changing the stoich AFR in the computer to 11.5 (boosted AFR) so you have the STFT's running when you are in boost to keep the AFR's as close to 11.5 as possible? I am working on my AutoVE tuning right now without meth, but once I throw the meth into the works my AFR's will probably be affected more from one tank of meth to the next (I am running 50/50 water/meth, and if the mixture is off a little I can see it throwing the AFR's off a little). Would having STFT's compensate for the slight differences in meth/water mixture be a good idea?

[dc_justin]

Unfortunately it won't work like that because the NBO2 sensors are only good at telling you were 14.7:1 is. To have the trims work, you'd have to adjust the O2 switch point, and there really is no way to know where exactly 11.5:1 is in that range. One o2 sensor it could be 930mv, another 960mv...

[thunder550]

Ahh damn I knew there had to be a catch.....

[mmorgan24]

Just curious - why would a custom OS have LTFT and STFT at all? A standalone EMS would not have these functions.

[turboberserker]

Thunder, what you need to do is (assuming the meth is for making max power and will come on with for max boost):

1) Tune without meth to get your VE accurate,
2) Add your meth (and get to the max amount you will run)
3) Add to max boost/timing (boost is better for hp than timing, but with the radix, you either need to pulley down or add timing)
4) Retune your boost table to get back to the AFR you want (11.5 for me) WITH the meth

Then you are making max power.

You probably know from performancetrucks.net that I advocate 100% meth since water won't compress

[thunder550]

What about the cooling effect of the water? What is that worth?

[turboberserker]

It's true that water cools better than meth, but you can add more 100% meth than you can 50/50 water/meth, so the point gets lost for me. That's not to say you won't get good cooling from a 50/50 mix, or good power, you *will*, but its more limited in terms of adaptibiliy and will make less power than 100% meth (assuming you can exceed the power potential of the meth and water).

The biggest concern for me is the non-compressability of the water -- if you keep turning it up, you will reach the point where you have too much water in the system which can be extremely bad on the compression stroke. You can combat this and keep water in the mix by going to a 25/75 or 20/80 mix, but IMO, 100% is still the best option.

[thunder550]

Thanks for the info...I have heard people say that one is better than the other but have never had it explained why. The only other concern that I had with 100% meth was erosion of the S/C rotors....do you have any info about that?

[turboberserker]

Not any direct info, but on these trucks, almost everything is aluminum. I think that as long as the meth is atomized, you'd be fine, but you might wanna check with BlownChevy on PT.net.

[thunder550]

Ok thanks for the help, I really appreciate it!