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Old 08-20-2009, 04:42 AM   #1 (permalink)
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Exclamation Touchy subject - Big Bang Theory (not the religious argument)

Big Big theory


On the forum there seems to be two schools of though of how to improve economy.

Firstly what I’m calling hot camp. The concept as I grasp it is that warmer air is less dense so the is less 02 hitting the lambda sensor in the exhaust – ECU thinks the car is running rich and therefore drops the injected amount. Thus less fuel used. This also goes with the idea of choking the intake to reduce the amount air that can get into the engine for the similar effect. I’m also putting into this group the concept of lower Octane fuel = more economy, that one still puzzles me


Second smaller group is what I call the big bang theory group. I was always told to get the most efficiency you need to get the most from the least. This goes off the CAI theory of more dense air produces a bigger bang per unit fuel, yes the ecu will see more air burnt and resultantly increase the mixture, but the extra work done means you can back off the throttle thus keeping the same mixture ration control by the ECU but just achieve the same work on less fuel. I’m also combining this with the higher octane side too – as to me it relates directly to the calorific/energy out value of fuel. To my mind if your ecu in the car keeps the mixture the same/burnt rate/ timing self optimised as per an modern ecu, for every ml of fuel a (Hi oct) you would generate more energy, per bang than fuel b (lo oct) and as a result you’d require more fuel to provide the same energy needed to cruise at a given speed.

If for example we take a pretty common direct stratified inject petrol engine that doesn’t require the fuel mix to vaporise in between an old school carb and piston would have though the best thing is to have cold dense air to create the most complete bang from a tiny amount of a hi octane fuel?

I’ll grant you that I might be missing something please set me straight

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Old 08-20-2009, 05:00 AM   #2 (permalink)
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I'm not going to comment much because it's 5am and someone can do a better job, but I just want to mention that efficient engine performance does not equal low fuel consumption.

For example, running your engine at 1000 rpm isn't a particularly efficient speed for the engine, but it usually will result in lower fuel consumption than a higher RPM with all else constant.
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Old 08-20-2009, 05:07 AM   #3 (permalink)
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as far as I know, it depends

Around here every car has waaaay more engine (and bulk) than it needs for efficient cruising. So things that detune the engine (i.e. hot air intake) can be effective.

But on the other extreme, you can make a vehicle more efficient by making it lighter and put a small engine in it, with turbo for even less weight and displacement. So that they incorporate more performance type mods (big bang?) because they are tiny to begin with, and CAI would be a good candidate in that scenario. But this is not a common machine in my experience. I think my 250cc motorbike comes close, but even it is a compromise between being able to cruise efficiently and being able to accelerate (it is a bit large for most efficient cruising IMHO).
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Old 08-20-2009, 07:18 PM   #4 (permalink)
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Your time and ingenuity would be better spent working on proven winners like fine-tuning your driving, improving aerodynamics, reducing weight and getting the gearing right. Maybe LRR tires.

The factory engine designers have resources you cannot begin to duplicate. I haven't seen anybody make any substantial (<5%) increases by diddy-wopping with the engine. Most of these engines (within the bounds of what the vehicle is) are pretty well sorted out. They have been at this a long time.
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Old 08-20-2009, 07:54 PM   #5 (permalink)
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decent thoughts. As I believe the auto industry is backwards attacking the engine with hot air is thier win. the engine is not gonna last. The company that made it won..as long as somebody got something they wanted out of the temporary dud called fuel injection.

Quote:
If for example we take a pretty common direct stratified inject petrol engine that doesn’t require the fuel mix to vaporise in between an old school carb and piston would have though the best thing is to have cold dense air to create the most complete bang from a tiny amount of a hi octane fuel?
all fuel has to vaporize. injected or not. the carbs go all the way to helium lightweights and needs more discipline in more than one category of fuel delivery..except for energy used to make it work. A bad day is known with a carb engine..the fuel injected on a bad day is a fire engulfing the car. (bad day is gassy polluted air).

the big bang theory is a good one. the most power for the least consumption, its called efficient. If one cannot control thier own system, it needs tricks, and they will be backwards attack and associated with a nation of origin..don't even get me started.
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Old 08-20-2009, 08:03 PM   #6 (permalink)
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dcb -

Quote:
Originally Posted by dcb View Post
as far as I know, it depends

Around here every car has waaaay more engine (and bulk) than it needs for efficient cruising. So things that detune the engine (i.e. hot air intake) can be effective.

...
That's my take on it.

Question: Of the OBDII variables that are available, would the positive or negative effect of the HAI/CAI be visible?

For the MPGuino people, I think they could prove/disprove the HAI by observing the change in MPG.

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Old 08-20-2009, 11:37 PM   #7 (permalink)
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Quote:
Originally Posted by robchalmers View Post
Big Big theory


On the forum there seems to be two schools of though of how to improve economy.

Firstly what I’m calling hot camp. The concept as I grasp it is that warmer air is less dense so the is less 02 hitting the lambda sensor in the exhaust – ECU thinks the car is running rich and therefore drops the injected amount. Thus less fuel used. This also goes with the idea of choking the intake to reduce the amount air that can get into the engine for the similar effect. I’m also putting into this group the concept of lower Octane fuel = more economy, that one still puzzles me


Second smaller group is what I call the big bang theory group. I was always told to get the most efficiency you need to get the most from the least. This goes off the CAI theory of more dense air produces a bigger bang per unit fuel, yes the ecu will see more air burnt and resultantly increase the mixture, but the extra work done means you can back off the throttle thus keeping the same mixture ration control by the ECU but just achieve the same work on less fuel. I’m also combining this with the higher octane side too – as to me it relates directly to the calorific/energy out value of fuel. To my mind if your ecu in the car keeps the mixture the same/burnt rate/ timing self optimised as per an modern ecu, for every ml of fuel a (Hi oct) you would generate more energy, per bang than fuel b (lo oct) and as a result you’d require more fuel to provide the same energy needed to cruise at a given speed.

If for example we take a pretty common direct stratified inject petrol engine that doesn’t require the fuel mix to vaporise in between an old school carb and piston would have though the best thing is to have cold dense air to create the most complete bang from a tiny amount of a hi octane fuel?

I’ll grant you that I might be missing something please set me straight
I'm kinda in the middle as far as the big bang people and the hot camp.

I think the hot air people are seeing more improvements from fuel vaporizing when ambient temperatures are low. The fuel is having a hard time going from fuel droplet to fuel vapor. Plus with today's fuels, they the "oil companies" have been told to reduce VOC from big brother. So the fuel has some issues when it comes to vaporizing. You can see this when you accidentally spill some fuel on the ground and watch it evaporate. It takes for ever compared to fuel 30 + years ago. On stock ecu's they will also notice as you said a warmer reading from the IAT sensor and will reduce the injectors pulse width.

I agree with the big bang people also. This comes down to improving BSFC. Making the engine utilize every amount of BTU's it can from the fuel. There is some room to improve from a stock engine. But from a emission standpoint it might not be good.

This is where I'm at now. I have gone from a 14.7 A/F ratio to a 15.5 A/F ratio to now a 17.1 A/F ratio. I haven't fuel-logged my 17.1 A/F ratio yet but as far as MPG it will be a success.( still working on timing values)

This is a advantage I have over a lot of people on this forum. I can actually see in real time where my injector pulse width is coming from on my fuel maps and ignition maps. My efi system high lights the cell that your running in.

What I have found that's interesting is that when you just start taking away fuel you will lose power and you will notice that it will go to the next higher load cell. Plus you can see it on the tps log. The way I over come this and get back to the same injector pulse width and fuel cell is to increase timing at that cell by a few degrees.

At these lean A/F ratios the car needs more timing because a leaner A/F has a slower burn rate then a richer one. At least at this A/F level. Now when the car is at full load this will not apply because the fuel is being used as a thermal cooling control for combustion. The extra fuel is just going out the exhaust but if its not their you will run into a knock situation.
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Old 08-25-2009, 08:04 PM   #8 (permalink)
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It's very much on a case-by-case basis...

I run a hotter intake air temp for quicker warm-up, TC engagement, and whatever else it does. My studies have shown that air temps less than 100-110F decrease FE after warmup. Why? Not sure. It only has worked on the Integra and not the '99 TL or '06 TSX.

Now for the premium fuel argument. Again case-by-case. 3A-3B-3A tests (needed to run through 3 tanks of each to normalize the fuel content and vehicle's fuzzy logic) showed no appreciable gain in the "premium recommended" TSX. It has provided better in FE in rentals, such as the Volvo S40, 5AT non-turbo.

Back to Teggy, the timing is physically advanced to its limit; although somewhat regulated by electronic timing control, the overall index has advanced and (likely provides) more power (as detected by the "butt-dyno") and a tested improvement in FE. Check my 100+ fuel entries for some data.

So, to combat the effects of a hotter intake and advanced timing on detonation, I run premium, 91 Octane fuel. An extra $2.00 per tank for an extra 3+ MPG and engine protection seems reasonable. When it gets bitterly cold, I can back-off that octane rating since hot air is harder to retain.

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Old 08-25-2009, 11:52 PM   #9 (permalink)
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Old 08-26-2009, 09:26 AM   #10 (permalink)
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I think this discussion is really about Big Band vs Small Bang. WAI reduces the power of your motor which is just like putting a smaller motor in. Increases in FE come because this forces you to drive slower! At a steady highway speed it takes just as much HP to move your car regardless of the size or state of tune of your motor. Under those conditions your FE is determined solely by the effeciency of your motor. WAI gives you the power of a smaller motor without reducing the inherent losses of the larger one you still have, therefore it is less efficient. I remember years ago reading a mileage expert saying that the way to get better FE is to drive like you have an egg between your right foot and the pedal. I think that if you did an A-B-A test between WAI and CAI in which you controlled the acceleration to match it between tests you would find no advantage to WAI.
That my 2 cents
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