What's better on hills: DWL or Pulse up, Glide down?

[monroe74]

"It is possible to calculate power without a dyno (a few ways actually)"

If you can point me towards info on that subject, that would be great.

[Duffman]

Method #1, use of accelerometers combined with a known mass of the car. There are a few off the shelf products such as: http://www.gtechpro.com , I think there is another company making a similar product as well. I'm not really sure its total capability as far as plotting a HP curve but these are getting more sophisticated every year.

#2
http://www.amazon.com/Performance-Ig...0723303&sr=1-1
This book has a step by step procedure to do it with a stopwatch. I highly recommend this book to anyone who frequents this site as there is a ton of good information in this book!

I had #2 in mind when I said it might not be the most accurate.

[monroe74]

Very helpful links, thank you.

Next I have to move to a flat place. Nothing but hills around here, and they seem to make this kind of analysis more complicated.

[JohnnyGrey]

Neither throttle angle nor RPM form a linear relationship with fuel usage. You can't rely on a SG either because it doesn't account for varying volumetric effeciency differences on non-MAF engines, like the one I have.

Your engine actually pulls in less air per stroke at redline than at torque peak. Any formula that computes air consumed by MAP and RPM cannot account for this. If fuel consumption vs RPM were linear at WOT, you'd have a perfectly flat torque curve.

Also throttle angle is not a linear measure for fuel consumption. At low RPMs, it doesn't take much throttle to really raise manifold pressure. There isn't much difference between 40% and 100% throttle at 1500 RPM. This is because at speeds this low, it doesn't take much air to pass the throttle plate and fill the cylinders to a great degree. At 5000 RPM, the engine demands a lot of air, so it takes a significant amount of throttle to hit 5000RPM even in neutral.

[Duffman]

YES YES YES.
It is amazing when talking to laypeople (I’m not calling anyone here that) about making HP they think its as simple as just dumping more and more fuel in. Power is actually airflow limited not fuel as it will only take so much fuel.

The throttle butterfly valve rotates from 0 degrees (closed) to 90 degrees (fully open). At lower RPMs where the throttle body is relatively large compared to airflow required the difference between 80 degrees and WOT might be negligible airflow but your seat of the pants meter feels more power because the engine is making more power from chemical means (fuel) instead of mechanical (airflow). This is why I am hammering away on A/F ratio because there may be no appreciable air increase in the last 10 degrees and this means no pumping losses saved either.

I am surprised that nobody on here talks about reprogramming the ECU or fooling it by altering the readings that the sensors are feeding it. I would think this would be an easy way for a few more MPG.

[JohnnyGrey]

I am surprised that nobody on here talks about reprogramming the ECU or fooling it by altering the readings that the sensors are feeding it. I would think this would be an easy way for a few more MPG.

I have talked about altering the O2 signal quite a few times. In addition, I've actually done it on my daily driver. However, you cannot reprogram the closed loop behavior of engines equipped with a narrow band O2 sensor (don't get me started on EFIE!), only the open loop. Racers operate in open loop, hypermilers operate in closed loop. There are very few parameters available in most ECUs to squeeze out a few more mpgs. Some of these are idle speed, cold engine enrichment values, fuel cutoff thresholds and decel leaning. To lean out across the board, you need a wideband with a variable narrowband emulator.

[Duffman]

Originally Posted by JohnnyGrey

I have talked about altering the O2 signal quite a few times.

What did you do to it?

[DifferentPointofView]

I just tried to imagine the most un-Honda vehicle I could: Chevy Suburban.

My Jeep makes all of it's torque at 3k and under, peaks at 3k and drops like a rock over 3200k. Redline at 5k.

I still don't see how flooring it up hill and coasting down saves the same amount of gas than coasting uphill and flooring down.

If I were on a bike, I would use less of my energy coasting up and using no energy, and then using gravity to help me use less energy going down. I still get back up to the speed required, and I can still engine brake once up to the right speed, saving even more energy.

But if I pedaled as hard as I could up the hill, and then coasted down, I'd use more energy, because not only did I push myself to the max, but I had to fight gravity as well, and coasting downhill did not net me the return of pushing myself up the hill.

[brucey]

I did a return trip of 240 miles and returned slightly worse economy going through WV. I kept the car in gear the entire time, stayed roughly the same speed. I got 31.9 mpg. The first part, I got 34. The only difference was there was LESS traffic on the return trip than before. Maybe a few degrees in temperature, too. There are huge grades here in WV that you can really coast on, with engine braking not so much coasting. In neutral I can easily coast at least a full 10 miles of the trip. And in several locations I will get going 80 mph in neutral before I put it in gear just to slow back down some.

[monroe74]

johnny: "Neither throttle angle nor RPM form a linear relationship with fuel usage."

I didn't mean to suggest that it was perfectly linear, but isn't it generally linear?

"If fuel consumption vs RPM were linear at WOT, you'd have a perfectly flat torque curve."

My casual observation, as I accelerate with WOT, while watching injector duty cycle (displayed on my dwell meter), is that RPM and duty cycle seem pretty linear. The numbers even coincide in a nice simple way, i.e., a duty cycle of 10% corresponds roughly to 1000 RPM. And a duty cycle of 30% corresponds roughly to 3000 RPM. Regardless of gear/vehicle speed, assuming that I'm using WOT.

Maybe this just means that my engine, at least in that range, has a fairly flat torque curve?

I also wonder if an engine with a wideband sensor would have more of tendency to behave this way (i.e., be more linear than one would expect).