Im a programmer but I work on a solar powered race car for my university so I know a little about aerodynamics since we do a cross the country race using the power of a hair dryer at 70mph. The problem in calculating these values is that getting a good front area calculation is difficult from the angles and requires loooots of fluid dynamics to find the coefficient of drag and then apply that to an accurate reading of the cross section area. OR..you google it!

To calculate aero loss, F = .5*(Cd*A)*r*V^2
Cd = Coefficient of drag
A = cross section area of front of car or wind profile
r = rho = density of air
v = velocity (ft/sec)

for the H3..Google (Track & Driver Magazine) says
A*Cd = 16.8 ft² (1.56 m²)

To calculate rho, air is 79% nitrogen and 21% oxygen. nitrogens molecular weight is 28 and oxygens is 32. so
r = ((.79*28)+(.21*32))/22.4(molecular weight volume)
r = 28.84g/22.4l = 1.29g/l

Converting this to pounds per cubic foot,
r = .0801

So...

F = .5*16.8*.0801*v² ² (in ft/sec)

Cleaning this up to make it for MPH, you're left with..

F = .986832*V² (in mph)

Which gives you a unit of pound mass..which isnt even a "real" unit so lets make it HP loss for better understanding...

F = (.986832/32.1)*V² in pounds of force..much better but not HP.

P = ((.986832/32.1)/550)*(22/15)*V^3

And theres your HP loss formula..just plug in V in mph and do the math. (You can copy that formula into google with your speed in V and it will compute it for you.

h

 

"It would seem to me that all you would need to do is determine the difference in manifold pressure from an idle to WOT. Then, based on standard atmospheric conditions of 59F deg and a barrometric pressure of 29.92" hg @ sea level, you could determine any power setting and fuel consumption between the minimum manifold pressure at an idle all the way to maximum manifold pressure at max RPM."

You can get the manifold pressure from the MAP sensor.

"In a basic aerodynamics class I learned about coefficient of drag. Coefficientof drag is equal to drag divided by dynamic pressure times area, or: Cd=D/q*A.

So it would be possible to find the coefficient of drag for the vehicle, and determine how much power is required to maintain a given speed. Then take this drag information and determine what power setting, or throttle position, would be required to maintain it, or to accelerate to it. When drag equals the power being produced, then you have a constant speed. Any more power than this will be used for acceleration. Using this power requirement as the BHP in the fuel consumption formula and figuring the lbs fuel used to produce that power from the air/fuel ratio will give you the specific fuel consumption for that power setting, and thus be able to figure the fuel consumption for that speed."

You can measure CdA with a simple test or you can find it here in a Car and Driver article (http://www.caranddriver.com/roadtest...-h3-page4.html) (Drag area, Cd (0.51) x frontal area (32.9 sq ft): 16.8 sq ft)

"My question is, why couldn't you figure all of this stuff at your desk instead of driving around and trying different things to determine the best comprimise between fuel economy and power? Wouldn't it be chaper? I know nothing about programming a computer, so maybe I am missing something here. I do realise that on paper things would be figured for the specific conditions given, such as the standard atmosphere, but shouldn't the basic program of the PCM compensate for the differences of the actual conditions compared to the standard?"

Its gets complicated pretty quickly. For fuel economy the engine has more parasitics at high RPMS, the unlocked torque converter is more efficient at high RPMs, as you move away from a 1:1 gear ratio efficiency drops, at high PRMs the tranny pumping losses increase, ... When you start modeling all the individual parts of the system it gets hairy. So, that's why I decided just to measure the efficiency and treat the H3 as a black box instead of predicting the system efficiency.

 

The last answer is what I was looking for. The classes that I was refering to are part of a commercial aviation degree, so all of the stuff about rho and airspeed vs ground speed are nothing new to me. Our test mule in class was an aircraft we are all familiar with and did some of these calculations in it to show what we already knew from flying it. I am aware that sitting at a desk and crunching numbers gives you a theoretical apsect to things, but when the engineers are designing something, this is where they start. I was just curious why this same principal wouldn't work to get the tune you are looking for, that's all.
Google is a great friend when it comes to making things simple, but we had to do it the old fasioned way, you know, with a pencil and paper.

Thanks to both of you for your responses.

 

I don't think I have ever felt more intimidated (in a good way) in my life as I do right now reading this stuff Now I understand how the attorneys I work for feel when I'm fixing their computers!

Well, I'm going to relax tonight, but so far, here are my findings:

First and foremost, there is no low-end dragging stalling pickup like there was before. When shifting into first off a stop, even if you floored it, sometimes it would take a while to get going before you felt the acceleration kick in. Now, it's very quick right when you take your foot off the clutch. It doesnt start off slow then get faster as you go (as far as the speed the acceleration picks up). It now seems like there is more low-end torque before you hit mid-range on the tach then less low-end torque like before. This is a HUGE deal to me, because I always felt like the engine was being sufficated and didn't have enough gas or air to get going. Now, it's awsome.

There is also a noticable difference in high-end torque, specifically once you hit 4500 RPMs. It's almost like a turbo-charger kicks in and pulls you back in your seat. It's not as noticable obviously in 3rd 4th and 5th gears as it is in 1rs and 2nd, but it's there.

Since I have a stick, I don't notice much of a power increase in passing, unless I downshift, but it's there. The throttle definitely seems more responsive when you punch it just casually driving down the street. Again, it seems like alot of the delays that were there between pressing the accelerator and the engine actually moving has almost dissappeared. It could just be me, but I notice it.

Obviously I don't know if my MPG has gone up since I've been driving so spuratically, but I'll figure that out after I burn off this first tank of gas. So far though, as much as I've been punching it, I am getting about the same mileage as I did just with casual driving, so that seems like a good sign.

The engine idles very smoothly. I am running 93 octane so that might have something to do with it (I'm still learning all about that from you guys). There is absolutely no vibration when in idle and you can't hear the engine at all. The engine seems a little quieter then it was before with the same gas. There was a VERY slight backfiring when I revved the engine the first time I started the engine after I replaced the PCM, but that seems to have dissappeared.

Also, there has been NO stuck throttle problem. THANK YOU! It started doing it again yesterday before I swapped the PCM's, but with this new tune, it hasn't happened once and I have driving about 200 miles already. It may just be a coincidence, but so far, it hasn't been stuck once. We'll see how that goes.

So, overall, I know nothing about the drag coefficient and dingle dongle doohickees but I can tell you to me it was worth it. It remedied the problems I had with lacking acceleration off the line, and I can actually accelerate in 5th gear on the expressway at more then a 1 MPH every 2 seconds rate! (That is MY scientific calculation)

I'm very please with the results. I'm sure things will start working better and I'll notice more little things that I haven't so far. I have only been able to floor it off the line 2 or 3 times because A) my wife has been in the car the entire time and B) Every FREAKIN stop light or sign I have been up to I have been stuck behind slow people. BLAH.

As soon as I figure out if I'm getting better mileage, I'll let you guys know, but overall, I'm happy with it. I have no complaints. No security relearn or check engine lights came on. It started right away with absolutely no problems. I'm going to recomment Alvin to a couple of my Chevy vette owner friends and see if he can tune them. I think it was definitely worth it. I can't wait to really drive this thing this week to work and back and see what it can do.

 

I am so glad everything turned out great for you Mike..especially the over revs on clutching....!

I'd like to give their tune a shot just like the one you got..and compare it to the tune I got earlier this year,..sounds to me like what Kelly was saying..Alvin's tune make it more driveable in the day to day city driving...Which is where it should be, snappier..Oh well I burnt that bridge..so to speak

 

I think people with Automatics are going to see a bigger difference then with a stick, just because I don't have the new shifting tables and all that like you guys with the automatics do, but like I said, I can tell a difference. Because I don't have a CAI kit or exhaust, I probably won't notice it as much as you, but if it makes a difference for me with no mods, I'm sure it would make a difference for you. I'll see how it feels through this week with my daily driving.

 

The H3 will feel even stronger in a couple days. The PCM needs to learn things.

 

OK I'm a bit confused being new at this. People on here say the PCM doesn't learn anything. It only adapts from the time you start the car to the time you stop, and then over again the next time. What exactly does the PCM learn? I'm just curious. I might just be missing something, but from my perspective, everybody seems to have their own theory as to whether or not the PCM actually learns and retains anything. Someone from GM said it doesn't, others say it does. Maybe I'm just stupid Please explain. Thank you!!!

 

I think and Im not totally positive but from what I have figured out, the PCM doesnt retain information like a data aquisition system would from a "black box" sense by logging MPH, RPM's, Temp, etc... but the engine basically has 2 operating modes, long term and short term. Short term is kind of like the 10% of your driving habits and is like when you pass a car or pull a trailer. The short term doesnt change much and can adapt the fuel trim quickly to what the system needs at that moment. Long term is more about how the engine runs under normal conditions and is what it reverts to once it decides its in for the long haul like on a highway. This long term is adaptive to your driving style though as its sort of a moving average of tuning the engine to how you use the pedal. If you take off from stoplights slow every time, it will probably give you a little more torque in the low end and die out sooner because it knows the engine rarely gets into its upper RPM's. However if you take off quick all the time, you will probably notice that your engine runs happily at higher RPM's. I did a little experiment with this and after a week of driving like a grandma leaving a stop light, I definately noticed that it was NOT happy to be at higher RPMs. But after a few days of leaving the line like a top fuel dragster, it accelerated smoother and quicker but my low end was a little shaky.
but these are all seat of my pants tests so who knows but in my attempt to understand long term fuel trim and short term fuel trim, that is what I concluded.

 

Glad you are enjoying it!

As soon as you start driving the truck like you normally do the gas mileage will start to increase. Most of our customers report about 2mpg better (if not more) on thier second or third tank of gas. There is a good bit of learning that has to go on and it does take a few hundred miles or so.

We did do some things to tweak the idle including spark changes and such. Thats probally where your noticing the smoother idle. We really give these tunes a thorough going over and change quite a few parameters