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Old 11-08-2011, 04:53 PM   #11 (permalink)
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You can have very low manifold vacuum even at low percentages of throttle position. This happens when you are using a higher gear and less throttle to accelerate. If you have the ability to read manifold vacuum this will be about 1 to 2 inches of vacuum reading. If you are in the correct range of gearing you will accelerate efficiently.

Conversely, if you are reading MAP then it will be above 80-90% when you are in higher gears and accelerating at the best RPM range. If you go to the next gear higher and do not achieve the desired rate of acceleration then the lower gear is the best choice. This is because you can take much longer to reach the desired speed if you choose too high a gear. Fortunately I found the best rate of acceleration to be right at what traffic normally accelerates from a stop. This way you are neither pushing the car in front or impeding the car behind you, which in either case can cause the drivers around you to do stupid things that increase your danger of an incident.

You can alter your rate of acceleration by using higher or lower gears, but as long as you maintain a consistent load at 80-90% you will get to speed with the least fuel. You can go too far in either direction to high a gear and you do not accelerate rapidly enough and spend to much time using to much fuel. To low a gear and your RPMs go beyond your best BSFC range.

Think of climbing a grade. As the grade increases you are forced to decide to downshift or loose speed. When the gear you are in can no longer maintain your desired speed then you go to a lower gear while maintaining the same load and BSFC. Some engines might do well at 1500 RPM while others will need to be at 2500 RPM. Looking at your specific BSFC chart will show you the best range of RPM to maintain highest efficiency. Just keep the load at the 80-90% point. It may be only 30-40% of the available range of your throttle position, but if you are at the correct MAP or vacuum, then you are getting the most for your energy use.

While it may seem to be you are using to much fuel at that instant when you are at best BSFC, you must understand that best BSFC is never lowest fuel consumption overall. It is the most power you can create for the least amount of fuel. Increasing the velocity of you vehicle is storing energy in the faster mass of the vehicle itself. Then you spend that energy coasting with no fuel consumed (engine off) or very little fuel consumed (engine idling). While engine off is the best, if your car is an automatic and you must keep the engine idling to operate the oil pump in the transmission you can still coast with very high MPG.

Lets say my Maxima is coming off the Interstate at 65 MPH. I shift into neutral with the engine idling. If my engine uses .3 GPH idling, and I could coast for an hour like that, then I would get about 200 MPG coasting for that time period. It would be infinite if I turned the engine off but it would also destroy my transmission, so I let it idle.


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Old 11-08-2011, 04:58 PM   #12 (permalink)
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I have seen engine load % reported by some obd2 diagnostic tools, as some ecm's actually report this themselves. I don't know if this is necessarily the case for your vehicle or mine, or if the number represented by UG is reading from this or calculating its own. In my case, I'm noticing that I rarely show it over 25-30% during acceleration so far, which seems fairly accurate... 25-30% of 500 HP is 125-150 HP or 250-300 ft-lbs if based of my torque number. It's a heavy truck, it takes a lot or power to ramp up to speed even when gentle with it. Even still, this seems a little crazy, because even at stock power the way I accelerate for economy, I'd expect the actual HP/tq numbers for acceleration to be much lower, probably even half of above.

This brings me to other gauges that I believe to be derived from other sensors, such as the HP/Torque gauges (I think that's an EM-only feature, some of you may not have it). The setup asked me for my peak torque and RPM numbers, which is roughly 1000 @ 1800 RPM... at the wheel. As such, UG tells me that I'm idling at 505.6 ft-lbs, which is absurd. It also tells me I'm idling at 75+ HP, which is equally as absurd. It knows my boost is at 0 (approx) at idle, and I know the engine doesn't produce that power except under 100% load with 35+ psi boost...

I don't know why the UG would need to know the peak torque value for setup. And the toque value would be at the flywheel, not at the wheels. Where did you get the 1000 lb-ft @1800 rpm number. Stock peak torque is somewhere in the 600 lb-ft range I believe.

As an aside, I don't think you really need 500hp if you're going for FE. By my calculations, 500 hp will accelerate that 7900 lb truck of yours from 0-60 mph in 3.46 sec.
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Old 11-08-2011, 06:18 PM   #13 (permalink)
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The numbers are approximated based off of dyno results of a friend's truck, one which is not setup quite as well as mine. He pulled about 480 HP / 960 ft-lbs on a recent dyno day. I have better air/exhaust setup than him and run a higher output program, thus I'm nudging his numbers up just slightly for my estimate. I was hoping to hit a dyno this past weekend, but that didn't happen.

I can't shift fast enough for a 0-60 like that, and don't have access to 500 HP throughout the RPM range, obviously. My buddy's truck is quicker than mine, since he has an auto, his shifts are quicker and his turbo stays spooled more between shifts. I'd need about 200 HP more than I have today in order to make up for gearbox lag... more for the extra torque than the horsepower, though.

The high power isn't there for FE, obviously. It's only there to have fun. It's rarely enabled, otherwise I'd get myself into trouble.

The UG is just one of the tools in my box now to help push my FE higher, and to gain a better appreciation for what changes make to the big picture. I never expected the HP/Torque numbers it shows to be reasonable, I just thought it was interesting that it thought I was making 505.6 ft-lbs at 0.38% engine load at idle.

Hopefully after a few weeks/months using UG I'll be in a better place with it all.
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Old 11-08-2011, 07:18 PM   #14 (permalink)
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Originally Posted by redpoint5 View Post
What is engine load %. What does it measure?
From the UG manual :
Estimated percent of engine load.
Where engine load is calculated as

% Load = (Current Air flow)/(Peak Air Flow)
% Load = (Current Engine Torque)/(Peak Engine Torque)
The method used is vehicle dependent.

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