Diesels don’t like high RPM’s Here are my result with a warm engine. This really makes me want to do the 5th gear swap (swapping it for a gear 11% lower) at idle I sit at 905 rpm, can’t get below that. I put (CO ZX2) for reference.
So it looks like once I get above 2500 rpm I start to loose overall efficiency compared to a gasser?
Well, I am not part of a challenge, but I was extremely intrigued by these numbers from both the ZX2 and the diesel. I had been looking at these numbers since I got my scangauge and this is what pushed me into EOC. I can see why a diesel can do very well coasting in idle. This makes sense.
Here are my numbers at 200-210 WTF and 130 IATF. Plus or minus .1 liter for my 2001 Saturn SL SOHC. I also put CO ZX2's numbers in parenthesis. A rough estimate is that power output decreases 3% for every 1000 feet increase in altitude. I will assume fuel consumption should decrease also. I am at about 2600 feet. That would explain some of CO ZX2's lower numbers but there is a bit more going on than that. I am not sure that it makes sense to use that estiimate when discussing no load fuel use where the loads are mostly friction and pumping losses. However every vehicle I have driven across Colorado got better fuel miileage at higher altitudes.
My last trip across Colorado on I-70 was in a Ryder truck that got almost 8 mpg from Colorado Springs/Denver west bound. From Boise to SLC it got only 6 mpg. That fits quite nicely with theory.
With my Scangage set to fast update one can quite certainly watch the computer in the rich/lean cycles about stoichiometric. I believe this can be observed both steady state in the mpg numbers or in a test like this in the liters/hour numbers. As for observing this on the road climbing a hill in fifth gear at about half throttle my Saturn will sometimes cycle between 28 and 30 mpg. At first I just thought is was random variation and then I was able to repeat this several times.
Enough rambling. A clean 2000 GLTDI with 90k sold locally for 8500. I thought that was a good deal. I was way too late on that one. Sort of like all the local VX cars one sees for sale. They are all sold by the time I call.
I tried to put the different no load fuel consumptions in one place and make a graph. I thought it appeared that the gasoline engine fuel consumption was quite linear but the diesel was not as much so. If you double the RPM of the gasoline engines the fuel consumption doubles. The diesel is more complex. We all have a slight bend and 3000 rpm. It is much more pronounced with the TDI. With the ZX2 the bend probably does not excede experimental error.
It would be interesting to see the fuel consumption with each engine producing 15 hp at 2500 rpm.
I wonder if it has something to do with the turbo spooling up? Maybe once it running flat out on the TDI it smoothes out a bit? I really have no idea.
Power wise you can really feel the "pull" drop off about 3500rpm. I mean it still pulls but not as hard as it does from 1800-3000.
Off topic but what kind of RPMs are people running at 60 mph? I am about 2100. I am so close to installing a taller 5th gear, I have an option of either a 11% drop in RPM at 60 or a 13% drop. I am worried that with a 13% drop at idle I will be at 33 mph, since I drive at about 40 on the way to and from work.
There were different gearing for the Metro and xfi in 94 with the xfi having a higher mpg rating due to a taller 5th gear but my old Metro 5 door was turning redline at 135mph. My xB turns 3050 at 60mph and runs ok - I don't think it would be as driveable with taller gearing.
Nice write up. BeeUU what is your 5th now? I think my stock is .75 I can go to the .68 or .65. I have been told the gassers like the old TDI 5th gear becasue it is lower then the gasser 5th, but not to low. I can get either of those gears for $325 from a couple of places and there is a TDI guru about 90 miles from me that has swapped about 20 so far and charges about $80 to do it.