Air Fuel Ratios for supercharged applications

[blownbluez06]

So under boost running meth your registered AFR is 13.x:1? Really?

Yes. and with no knock at WOT. I tuned in the safety and it saved my engine and me a ton of time.

[07cobaltsupercharged]

Yes. and with no knock at WOT. I tuned in the safety and it saved my engine and me a ton of time.

And that's exactly why you blew your transmission!

I just couldnt resist....

[blownbluez06]

Thanks!

Hey, we both agree on the fact that using meth requires a richer stoich/AFR. That is what so many do not realize or care to understand.

I have quite a few in-depth writeups on determining proper stoich values I could point you all to (more on who made those in a few). For those only running one form of fuel enrichment, all one needs to do is determine this and then modify their Stoich AFR parameter within their pcm calibration, and everything else falls into place. Now, for meth, this is a different story, as one is not on meth 99% of the time, therefore they have to allow the meth to add the fuel for the most part. Yes, some tweaking can be done with the PE and/or Boost Enrichment table to add even more fuel (or even richen it up). As know, I do not recommend skewing the Load/VE calculations of the pcm. However, everyone will be different in this area, and it's hard to say which is "less wrong" or "more right", since meth takes away the perfection of proper tuning via pcm only control.

Stoich of pure gas is approx. 14.6x, as we know, 50% meth is approx. 11.8x, and 100% pure is approx. 8.9x (as you stated). On ModularFords.com, my good friend Eric (black2003cobra), who is a brilliant engineer, I believe has an article on how to determine stoich in the combustion process based on % of meth injecting. On a meth kit, naturally it's not going to be 100% perfect, as there isn't any logical means of determining the exact mixture within the combustion chamber, due to variances in meth kits and how they release the fuel. However, if I'm right in remembering that Eric did make such an article, then his data would help you get it VERY close.

All in all, as we both agree upon, one must always run richer when using alcohol based fuels, and this goes for injecting meth. The stoich is what it's all about!.

So do you agree that what you read on your gauge or HPtuners log, running even pure methanol should still read 14.7 for stoich? If your gauge reads 14.7 when running pure methanol in an engine, your actual AFR would be 6.40:1. The UEGO's we use are taking a Lambda of 1.00 and converting it to what we consider a stoich AFR for gasoline (14.7). A stoich lambda of 1.0 is achieved by the same sensor output voltage regardless of the fuel used. For instance, a lambda value of 1.0 is a sensor output voltage of 2.5volts. It takes AFR's of 14.7 for gasoline, 15.50 for LPG, 6.40 for Methanol, 14.50 for diesel, 9.765 for E85 and 9.0 for E100 to achieve that 2.5 volts on the sensor output. Since our sensors are programmed to convert that 1.0 lambda or 2.5volts to a stoich gasoline value, we read 14.7. This is why I don't try to achieve more than .1-.2 richer on my meth reliant tune (due to the extra oxygen released in the burn). If I were running E85, I would still tune for my gauge to read 11.5-6 at WOT, but the actual AFR would be much richer. I expect somewhere around 6.5:1.
I just want to be clear so that folks understand how this works. It might all be so much easier if we tuned our cars based on lambda values since it is universal.

No, what he's saying is that he adjusted his IAT vs. Spark table OFF meth to see if he would register any knock, and even ran it up very lean.

No, I would NEVER recommend anyone doing that under boost, but all he's saying is that obviously IATs skyrocketed at his boost levels when meth was off, and he used the IAT vs. Spark table to yank out a buttload of spark to remain safe.

I wouldn't recommend anyone doing that either, however I not only lost my meth but lost my secondary fuel system when a vacuum line came loose. That was the reason for such a lean condition. My safety net in the tune came in quite handy that day.

[blownbluez06]

And that's exactly why you blew your transmission!

I just couldnt resist....

I wouldn't recommend repeating that. If you run around telling everyone that I blew a tranny from running lean, you're going to get committed to a mental institution. I hope you have good insurance, because uncle Arnold certainly afford to foot that bill! An IOU maybe.

I couldn't resist either.

[5_Liter_Eater]

Blue,

I understand tuning meth for performance from a timing standpoint. I agree with that thinking and my plan was to install a remote IAT post MAF, get a meth kit and bump the timing back to stock or even more in the boost area and use the IAT retard to cut it back in case of a meth failure. But I hadn't thought about tuning towards a ~13:1 AFR. Theory of meth+gas stoich aside, I guess you're tuning it as if it's NA since the meth should take care of the detonation the boost would normally cause. So you're commanding ~13:1 in PE and BE and your boost VE table would have smaller values than the VE because of the meth.

Is all of that correct?

Another question is how do you know your meth ramp rate is set "correctly"?

[blownbluez06]

Blue,

I understand tuning meth for performance from a timing standpoint. I agree with that thinking and my plan was to install a remote IAT post MAF, get a meth kit and bump the timing back to stock or even more in the boost area and use the IAT retard to cut it back in case of a meth failure. But I hadn't thought about tuning towards a ~13:1 AFR. Theory of meth+gas stoich aside, I guess you're tuning it as if it's NA since the meth should take care of the detonation the boost would normally cause. So you're commanding ~13:1 in PE and BE and your boost VE table would have smaller values than the VE because of the meth.

Is all of that correct?

Another question is how do you know your meth ramp rate is set "correctly"?

Oh, I wasn't tuning for 13:1. I was tuned for ~11.6:1, including meth and everything. I lost my meth and secondary fuel system, so I was left on the stock fuel pump with 79lb injectors at WOT and 18psi boost. All because I didn't zip tie the most important vacuum/boost line in my entire car at one connection, losing the reference for the hobbs switch that triggers the secondary fuel system as well as the reference for the methanol system. All a stupid ass accident.
I only share my stupid mistake to help others learn that it is possible to produce a tune that has the proper AFR's and not be too concerned with losing the meth and eventually the motor.

I honestly installed the methanol system without making adjustments and tuned around it in the VE table to achieve reasonable fueling. I am still running a bit rich at low boost levels, but never seem to get around to setting aside some time to clean it up.

My PE and BE is set for my desired AFR's so I don't get scolded for raping them.

[RWTD]

First, I made some statements about the stoich content of various fuels. I accidentally typed meth for ethanol. I corrected that above, which I'll retype here:

Stoich of pure gas is approx. 14.6x, as we know, 50% ethanol is approx. 11.8x, and 100% pure ethonal is approx. 8.9x, and 100% pure meth is approx. 6.47. A 50/50 of pure gas with meth would produce a stoich of approx. 10.4.

Personally, I feel a potential safe WOT AFR for any forced induction vehicle would be at most 0.82 multiplier of stoich and lower (some vehicles need even richer, depending on boost, compression, etc). i.e. 14.64 stoich * 0.82 = 12.0x. 14.1 (E10) * 0.82 = 11.562. 8.9 stoich * 0.82 = 7.298. FYI, Ford uses values that are "% of stoich" on their main fuel tables, as well a 14.64 as stoich, therefore the equivalence value for the PE table on a GM would be 1.22 (however, many GM vehicles use slightly different stoich values for pure gas, so keep that in mind).

So do you agree that what you read on your gauge or HPtuners log, running even pure methanol should still read 14.7 for stoich?

One should set stoich content in the pcm if you're running any type of alcohol based fuel in the tank (such as ethanol). This shouldn't be an arguable point, as that is just simple proper tuning. As you alluded to, narrowband sensors are blind to the type of fuel being used - however, provided they are not degraded, they will switch at the proper point, regardless. This is why GM has fuel composition sensors on their Flex Fuel based vehicles. Having the pcm recognize the stoich value of the fuel being used allows all the fueling tables to fall into place properly, so to speak, and allows the adaptive strategy for those that are using such (I'd wager 99% still use it in the aftermarket world), and helps to prevent one from raping the tune.

The difference is meth injection - one is only running meth generally less than 1% of their driving (provided it's not a race car only), and unfortunately we aren't able to alter the stoich value of the pcm for just PE mode (too bad that wasn't an option in the calibration from the factory). What do you do in this case? The only logical answer is to continue to leave the stoich scalar of the fuel that is within the tank, leave the PE (and BE if custom OS, and using such table), and then allow the meth to do the job of enrichment for you (this is what I've stated all along). However, those on meth who wish to "tune" the WOT non-meth portion of the fueling on a load bearing dyno, so to determine if additional power can be had by enriching or leaning out, then the only logical option is to either use the PE or BE table. There's obvious caution and care that need to be taken here if one does such, however. As we know, not everyone uses the BE table on boosted setups running the custom OS, and not everyone uses the PE table either (some do it all through the VE tables). However, the VE and MAF tables should represent exactly what they were meant for (calculating exact volumetric efficiency).

As for wideband sensors, one should set it to the stoich value of the fuel they're using, OR, as you stated, set it for Lambda mode ONLY (especially in the case of meth), that way there won't be any ultimate confusion. Of course this requires a high quality wideband sensor, like the ECM setups, or the NGK (which is an ECM in disguise) with the NTK sensor.

My PE and BE is set for my desired AFR's so I don't get scolded for raping them.

Didn't you say that you modified your VE while on meth? I'm just picking.

[RWTD]

Okay everyone, here's the data I said I had. I'm just going to copy/paste Eric's (black2003cobra) post:

http://www.modularfords.com/forums/s...ad.php?t=71048

I had promised oldbones that I’d try to find him a graph of how the stoichiometric air-to-fuel ratio (AFRs) is affected by the addition of methanol for his new setup. Although there is published data available for a blended fuel of gasoline + ethanol, I couldn’t find anything similar for a blend with methanol. So I had to balance the equation myself, (shown below). I also did the same thing for the ethanol blend as a check, and found my results agreed with the published data, so the results for meth should be OK. I’m also including a graph of AFRs vs %meth (or ethanol) by volume. I decided to post this thinking others might be interested in the results, as well.

As with ethanol, AFRs drops with a higher percentage of methanol. The decrease in AFRs is more dramatic simply because the stoich ratio of pure meth is less than that of pure ethanol (6.47 vs 9.0). Therefore, to maintain a given equivalence ratio, (φ = FAR/FARs = AFRs/AFR), one would need to run a richer (lower) AFR, depending on how much meth is injected. For reference, for just “plain” gasoline most seem run an equivalence ratio of φ ≈ 1.25, (which translates to AFR ≈ 11.7). So if one were to run a mix of, say, 20% methanol whereby AFRs drops to ~12.9, to maintain the same equivalence ratio of 1.25, the required AFR would be 12.9/1.25 = 10.3. If one runs a leaner AFR than that, it pushes one closer to the knock limit, (which IMO, tends to defeat the purpose from the safety point of view of running methanol). On the other hand, I don’t think most do this. Perhaps that is because the higher octane that results by adding methanol, allows one to run a slightly lower equivalence ratio. However, it is worth noting that the literature suggests that although the RON increases nearly linearly in proportion to the concentration of methanol added, that the MON (the more important number) only increases up to about 15%, after which point it levels off. As a result, the fuel sensitivity (RON-MON) increases with an increasing percentage of methanol. In other words, the PON isn’t increasing as fast as the RON. I’m also attaching a graph of this (ref OEC 2002). In a private communication, James (RWTD) pointed out that if the vehicle has knock sensors, that helps get around the issue. From the power point of view, the equivalence ratio at which the (laminar) burn velocity is a maximum is slightly lower for methanol than it is for gasoline, (~1.1 vs ~1.2), so that also suggests that a slightly lower equiv ratio could/should be used, too. Nonetheless, I would highly recommend checking w/ guys like Ed or James or Jerry, et al., on this aspect of it, (i.e., what equivalence ratio to run). I know there are other members here that have some experience with alcohols, too, and they might also have some input on this aspect of it. I invite their comments. That all said, the biggest impact on knock reduction comes from any reduction in IAT2 due to the high latent heat of evaporation of the alcohols, any way. Since oldbones setup injects the meth past the intercooler, I think he may see some advantage there.

Perhaps I haven’t posted this in the right forum, but I hope some of you find this useful. (Mods…feel free to move this thread if you think it should go somewhere else. Thanks.) :beerchug:

[07cobaltsupercharged]

Well dang all I asked was a simple straight forward question on peoples afr's and lookey what all we got tech wise to read up on.

Some good reading up above for sure so some day when i might run meth (i seriously doubt i ever will) i can refer back to all this.

[blownbluez06]

Impressive work. Now my head hurts.

[Ironmancan]

Damn I've got alot to learn Still never going back to carburation this is fun

[smcstevesmc]

So leave the pe table at 11.7 on a supercharged engine for safety,

and it seems that 30% meth injection at 250cc will show a .4 drop in afr 500cc drops it aprox .7 afr

running e10 91octane (unfortunately)

What are your experiences with meth versus water mixture and iat?

[kingtal0n]

Thats an easy calc
By hand
IMG-6051.jpg

Verified online calc
VERIFIED-CALC.png

The calculation is for an engine with 440hp using 175cc/min of methanol,
showing that the temperature drop using 100% methanol (best possible IAT drop in theory from 100% meth)

is about 21*F different to IAT for sea level dry air.

Remember that air is rarely dry, the water in the air dampens the affect, and also keep in mind that some of the temperature drop is absorbed by the plumbing.
So in reality there is more likely a 10 or 15*F drop to IAT for every 175cc/min meth applied to every 440hp engine airflow rate.
i.e. 350cc/min applied to 880hp would yield the same drop I would think