Robert,

The PCM uses signals from the MAF that are directly referenced to the properties of atmospheric "air." Nitrous is far from a split hair's difference in specific heat capacity, as compared with air. Generally, gaseous air, or vapor, will absorb more heat than gaseous nitrous oxide, or vapor (in terms of kJ per kgK).

For your information, specific heat capacity is the thermal energy required to raise the temperature, of one kilogram of said substance, one degree (K in our instance). Specific heat capacity is not the measure of the temperature of a substance.

I think your attempt at mastering nitrous has, while apparently proven accurate and precise, brought you to numerous, rather self-serving and utterly oafish conclusions about the intricate workings you dabble with. I do not take pleasure in insulting you, but nothing you have written about is as simple as you portray!

AG

 

Your statement on "what is slightly off" really makes no sense.

Actually, it makes a lot of sense if you understand that nitrous is not the same compound as the mixture of air in the atmosphere. Again, the simple route is to ignore this and chalk any discprencies up to...?

Think about the cars up in Alaska, their MAFs read sub 0* temps fine, then go to the Texas desert, once again, the MAF reads/works fine. To many people want something, somehow, to be wrong with the MAF, but the facts speak for themselves. We all depend everday that our MAFs will do what they were designed to do, and adding a dry hit is really noe different.

Really—as in, in reality—"adding a dry hit is really" different. I think you are getting stuck on temperature. Tell me this: how do the MAF and PCM go about calculating the mass, or volume (you pick), of the air being consumed? From the logic you have presented thus far, you seem to assert that the MAF sensor is simply a large IAT sensor. Oh, how contraire, mon freur.

 

Actually, your the one who called "BS" on my post, not the other way around. And, I never said you were "full of it", only that you seemed to lack knowledge about how the MAF sensor actually works. If you consider what I said to be "double talk and over top tech jargon", you're simply confirming your lack of knowledge. I'm not looking for "confrontation", only "accuracy".

And, if you read the whole thread, you'll see that I'm actually a strong supporter of dry nitrous systems, and have complete respect for the dry systems in the LS1 setups. I also respect the empirical data you have accumulated, but you have to understand that there's a lot of "tech" behind the workings of the control system, and that the more you understand about how the system works, the better you will be able to use it to your advantage.

No disrepect intended.

 

So what the hell are you saying. Can you speak in terms that the hobbiest, average Joe can understand? That's what I do. You guys are implying that temp of nitrous has nothing to do with how the MAF works, please give me a break. Plain and simple, it is the temp difference of the nitrous that allows the increase in injector duty cycle. You try to imply that some mystical force is behind this. Temp equals density, so an easy way for us non geeks to understand what's going on is to make it simple. Have you ever heard the statement "Keep it simple stupid", well that's my motto. If ya want to flaunt your implied greatness and all known knowledge of nitrous, I invite you to join us over at the largest nitrous site in the world, at ls1tech, please do so.
I do not take pleasure in insulting you, but nothing you have written about is as COMPLICATED as you portray! The average guy can comprehend the workings of the MAF and the dry hit, not just the over the top geeks. Now is this meant as a personal jab, naw, not my style. I never have claimed to be a know it all, and am not, but it is really hard to follow a post like yours, please spell it out better so we can all join in.
Robert

 

Ok fair enough. Yea I had been away from the post for some time. I thought you were taking a poke at the dry hit, sorry. Seems that most sites the dry hit does not get it's due respect, and am glad your on the dry band wagon. I am allways open to learn, but like the above post try to keep it simple. Yes I know there is mucho working going on behind the scenes concerning tuning/computer and feel I have a pretty good grasp on it by actually using/tuning/racing the dry and going pretty big-current hit 285rwhp. I have tlked with so many guys in the industry and end users that are very knowledgable, but never had anyone debate the MAF reading temp/density before. I can see on my logs the effect that temp has on the MAF and corresponding fueling, some day to next day fueling can change by 10% or more. It does this based on ambient air ie: temp/density. You guys may be detailing exactly how the MAF uses/converts this info, but all in all I think we are on the same page.

Robert

 

I typed a long piece for you but have decided to lead the horse to the answer, instead:

For the record, no one said the temperature of nitrous has nothing to do with it's effects. As a matter of fact, it has very much to do with it's effects. You can continue to put your head in the sand on what is being argued, but I would recommend some simple, "average," research on this at your local library. You could even do research on this on the internet; I am sure their are many sites. Type in "specific heat". With regard to your "I am allways open to learn," you are sending exactly the opposite message. If you want to convince me I am talking out of my ****, disprove everything I say—don't just say, What you say isn't so because I say so, these guys appear to agree with me, and we all agree with each other (including the ignorant dyno)! That type of self-serving logic is quite a blunder and presents a viable answer to why aliens aren't talking to us.

We might be on the same page, but it seems like you read the headline and graduated straight to a research facility. I'm still fooling around in the index and appendices.

 

First, I never said you were talking out your azz. You may in fact be offering something legit. It's just that it's hard to follow and in a context for which we are talking. I understand that there are advanced logirithmic formulas at work concerning the MAF, however, I doubt that you or I understand these, not being advanced engineers on the subject. These algorthms are in fact what make the LSx platform computer so compatable with dry hits, compared to prior computers. If you can give the formula used to convert temp/density, from the heated wire to injectors, this may well give a better route for our talk.

Ok lets disect something from your earler post.

I am sure your correct here, but what is the point. Gaseous air will absorb heat better (remember guys the heated MAF wire) than gasesous nitrous. Ok, I can agree and prove it with actual real world testing. If we all think we are trying to cool a wire that is continually trying to re heat and maintain a constant temp it will make this easier. Ok, the nuts and bolts of it all concerning nozzle placement. Generally placing a nozzle far from maf will produce a leaner condition. The reason being, distribution. By the time the spray gets to the maf it has been mixed with incoming air and the pattern has spread to a point where only a fraction of the spray, in a diluted form, crosses the actual MAF wire. This results in a smaller increase in duty cycle and thus a leaner a/f. Now take the same size/hp shot and move it close to MAF wire, aimed directly at said wire, and now we will have a much richer mix and tunability. So in conclusion, what you say is likely correct, (proved by the fact that nitrous is read better in a more compact stream, whereas, air can do the job better and can pass around the MAF as well as onto the wire in equal amounts) but my point of contention was the info was used to somehow make my input seem invalid. In reality, it was just additional information used out of context, allthough valuable.

I really enjoy this type of talk, and will try better at not offending. Sometimes we get a little opinionated, but we are new on this site so I will give the respect you guys deserve.
Robert

 

The system measures the current draw of the Wheatstone bridge with the variable resistor being the heated wire. As the wire cools (a cooler substance—air and or nitrous—absorbs the heat of the wire), resistance is reduced and current flow is increased. The system then looks at the corresponding values between X current draw to maintain resistance and known mass of the air flow required to produce X current draw. This is a calibration based on the ability of air to absorb heat. This calibration is researched and not a simple formula; it is "tuned" from the factory, if you will. By extension, the engine is deciding how much oxygen is coming in to cylinder. The expression is air-fuel ratio, but air does not create combustion, oxygen in the air does. Air, for our concern, is a rather homogeneous mixture, consistently having the same mass percentage of oxygen. Because of this, and only because of this, would the MAF system, alone, work (since this—among other things—is not the case, we have oxygen sensors) When you add nitrous oxide at WOT, you are doing two things the system is not equipped to analyze: the difference in mass composition of oxygen in nitrous oxide (more oxygen) vice air (less oxygen), and the difference in specific heat capacity.

So not only does the system not know, exactly, what mass of air/nitrous mixture (because the two have difference specific heats, reference the heated wire circuitry) the engine is consuming, it has no idea of the mass composition (specifically regarding oxygen) of what it is consuming. A solution to either one of these would likely be complimentary, and each system would likely share components.

With so many other variables, it is easy to tune out these discrepancies. But, one certainly cannot deny the existence of what has been outlined for you. For someone looking to extract the maximum performance through maximum understanding of the tools and instruments at their disposal, the aforementioned is nothing short of necessary. Perhaps you will have greater understanding, now, of a variance in results when a seemingly small change is made. That is my point.

Ciao

 

Good write up. I see nothing we disagree on, only things we agree on and of course additional information. It's the exact understanding I had and do have, however, your eloquent writng style does surpass my own.

I do see what your were getting at on the different mass/oxygen content, and this is very true. That's why a staring point of close nozzle placement (which some companys have been missing) is needed for a good starting a/f; to be able to add enough fuel for added oxygen that the computer is not calibrated for. It's really the principal that dry hits work off of, and why they work, and often refered to as tricking.

On the wheatstone and variable resistance, can't current be converted to actual voltage, and thus my reference voltage. Kind of like Ohm's law "It takes one amp to push one volt through one ohm of resistance". Correct me if I am wrong (of course I am not an electrical engineer), isn't current part of this basic concept/fact? Isn't current just flow measurement of Ohm's law?

Additionally, our air is comprised of about 80% nitrogen and 20% oxygen. Whereas, nitrous is 66% nitrogen and 33% oxygen. (To release the added oxygen in the nitrous it must get to 575* in the clyinder). This info can help show why/how the pcm is calibrated different for air compared to n2o.

Robert

 

Robert:

Is very difficult to "speak in terms that the hobbiest, average Joe can understand?" when you're talking about a fairly technical issue. Alan is obviously well educated in the issues we are discussing. I'm a mechanical engineer with an MS, a professional engineering license, and 40 years of design experience involving, in part, instrumentation systems for controlling complex chemical and mechanical processes. I've also been involved with the design of spray and aerosol systems, and with flow modeling gaseous and 2-phase flow through ductwork. Its not easy to explain a lot of these technical concepts to a layman.

No one is saying nitrous through the MAF sensor doesn't work. Its been proven that it does. It might acutally be said that it works in spite of itself. The introduction of extreme temperatures and a molecular mix that the MAF was NEVER designed to accomodate means the output signal is suspect. You need to understand that you can't simply write off the differences to "temperature"... its a lot more complex than that. The more you know about what affects the sensor, the better you will understand why you need to adjust the "tune" to accomodate the inconsistancies.

I notice that you attribute the inability of the LT1 system to the lack of the advanced algorithms used in the LS1 PCM. I'd like to learn more about the LS1 algorithms. All my experience is with the LT1 PCM. I've seen people make "through the MAF dry" systems work with the LT1 PCM. But in all honesty, I've never tried it, since I spray my 300 dry shot using speed-density and an aftermarket ECU. The success of the system is fairly well demonstrated with a 127.7 MPH pass on a 125-shot.... and increase of 12MPH over a corresponding NA pass.

As far as trying to reduce things to a level everyone can understand, my online writeup on scanning the LT1 PCM is probably the reference that most people here and on several other forums use. It simplifies the operation to a level that most people can understand, without giving up technical accuracy.

 

Robert

 

Click on "Mod's List" in my signature.

 

are we sure that the LTx problem with through MAF dry shots is just the fact that they dont have integrated IATs? This might point out that the LSx dry method atually alters the A/F delivery by cooling the IAT very low... why else would the N2O nozle placement and position have such an impact on the final a/f? I've read this entire thread and the one over at ls1tech for information about dry setups as I just purchased one. I am looking for the answer on this mystery why LSx platforms respond better than LTx. Also, I dislike the idea of using spike FP as a means to add fuel.. pretty much makes my 42# injectors a waste if the PCM cant have its hand in the fuel delivery when usning nitrous

 

Your LT1 MAF has an internal air temp sensor. It has to have one in order for the MAF sensor to regulate the current through the hot wires. It does that by controlling the wire temperature at a fixed number of degrees above tthe incoming air temp. But its only used for internal purposes in the MAF. With the later MAF sensors, they realized that there was a duplication, eliminated the stand-alone IAT sensor, and tapped into the one that is already in the MAF sensor.

 

LSx MAFs have two extra wires connected to a thermistor correct? What I'm trying to get at though is the dry shots that work on the LSx applications and that have to be positioned close to the MAFs may only be supercooling the IAT sensor and richening the mixture that way. what other methods could be used to add fuel? resistor on the PCMs CTS input ?