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Old 10-14-2011, 10:55 AM   #11 (permalink)
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Because I keep my 5-speed diesel Beetle in low rpm's it is only feasible to glide on the down hill sections and slight declines. My diesel has enough torque to drive in 5th hear at 30 mph @ 1000 rpm's,it has the ability to pick up speed smoothly at that rpm/speed.
If at faster speeds and on a decline I can put it neutral my rpm's drop to a idle and I coast/glide gaining speed or slightly losing speed,usually the former.
at 60 mph my rpm is just under 2000 rpm this is where my car needs help aka a taller fifth gear or another final drive.
it seems pointless to glide when my rpm's are in the low range. (almost always) I about never drive my Beetle over 2000 rpm..

On a side note I do coast on declines even if my rpm's are low to begin with,coasting makes them even lower. So I coast, hmm I'm a coaster, just coasting thru life taken it easy..in the slow lane, Wow sounds boring but to the contrary I find it interesting enough!

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Last edited by ecomodded; 10-15-2011 at 11:29 AM.. Reason: to add a side note !
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Old 10-15-2011, 12:21 PM   #12 (permalink)
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Quote:
Originally Posted by Diesel_Dave View Post
How did you manage to get a DPF on a '85 vehicle?
Oddly enough, some of those came with DPFs, but they were all recalled and removed because they plug with no way of cleaning them out. If his car is still equipped, it would be hurting the fuel mileage in all conditions; removing it would enable further mileage gains with P&G.
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Old 10-17-2011, 05:53 AM   #13 (permalink)
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I just finished a trip and a tank using some advice from this thread. Specifically, I throttled harder during the pulse phase. The vehicle is a, currently not very aerodynamic, diesel pick-up truck with manual transmission. The engine puts out some serious torque in a 1000 rpm band so the truck accelerates quickly even in steep inclinations when flooring it. Therefore I used p&g consistently even in inclinations despite the gliding phase suffering. Previously I used to keep a steady speed uphills.
Anyway, the net result was a very good improvement. I got 6.5 liter/10 km one way and 6.0 the other way. Previous figures for this run was about 7.4 when driving with a gasoline style p&g. For comparison, running on cruise control yields 8.7.

Now the question:
Since this vehicle is "a brick" and does not glide well, there are a pretty large number of acceleration phases for a given distance. The engine and turbo is larger than your average car so the turbo lag is significant. It takes a couple of seconds until the torque wave kicks in, especially in highest gear. This means I am flooring it without getting much in return a lot of the time.
Is this really the best way of applying power?

The built in fuel meter only averages consumption over longer time so I can't study this in real time. Anyone with knowledge on modern diesels that can say something about the typical engine mapping and efficiency before the turbo starts producing?
Should I gear down to reduce lag and have shorter pulses? (more rpm and transmission losses and more wear on tyres etc.)
Should I apply power more progressively and not floor it at once?
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Old 10-17-2011, 08:09 AM   #14 (permalink)
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HAHA, very good results!
Probably you should try one gear down (4th instead of 5th?) so that engine is in right rpms from the beginning of the pulse. I just got my diesel so I am not expert at all, but Vekke writed that and he is getting really good hypermiling numbers.

Quote:
Vekke, 10-10-2011, 05:16 PM
On diesel you have to make the Push with full throttle (97%). RPMs should start the push at torgue peak or rigth before it. On a 1.9 TDI that is about 1800rpm. Use the shortest gear that meets the RPM reguirement. Usually 4:th gear.
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Old 10-17-2011, 09:25 AM   #15 (permalink)
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The engine is in the right rpm range for full torque but there is still turbo lag. The turbo needs a good flow of exhausts to spin up. Once it does, there is plenty of power even in the highest gear. The question is what is going on with the efficiency during the lag-phase...

I'm the scientific type of guy so I'm looking for actual numbers and figures from real measurements. I'd love to do my own experiments but my lack of real-time instrumentation makes it difficult in this case.
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Old 10-17-2011, 10:17 AM   #16 (permalink)
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HAHA, upload the details of your truck so we have more information.

When driving my diesel truck I don't floor it when I pulse, I just use a fairly smooth acceleration (so there's little turbo lag). That being said, my truck has a VG turbo so there's less turbo lag anyway.
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Old 10-17-2011, 12:32 PM   #17 (permalink)
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Trying to increase post count so I can use links and pictures...
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Old 10-17-2011, 12:33 PM   #18 (permalink)
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The vehicle is the Mitsubishi L200, named the "Triton" in some locations on our insignificant little planet.
The engine is a 2.5 l, VG turbo, 400 Nm at 2000 - 2800 rpm. Vehicle weight is about 2000 kg. (now you get a chance to practice some metric units...)

I found some power curves on a site belonging to an aftermarket chip trimmer. The green curves are for the stock engine. The second graph is a bit unusual but it illustrates the turbo lag as the time it takes from throttle until torque. If one is to believe the graph, the lag is 2.27 seconds until 90% torque although it doesn't say from where in the rpm-range. This approximately correlates to the driving experience at a speed matching 2000 rpm. (smooth clutch engagement and then almost full throttle)


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Old 10-17-2011, 12:34 PM   #19 (permalink)
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This graph didn't make it in the previous post ...

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Old 10-18-2011, 12:08 PM   #20 (permalink)
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Chip tuning helps for sure to the turbo lag.

- What gear did you use? You should use the smallest gear which starts from 2000 rpm.
- What speed did you use the P&G

If the push and glide times are the same push 7 seconds and glide 7 seconds I dont bother to do P&G:ing. IMO there is no gains to be made in those circumstaces. That speed when this happens depends on your Cd and trucks weight and power(torgue) to ratio and few other factors.

For turbo lag you can also remove the intercooler. Specially in the nordic winter unless you dont tow something very heavy with your truck often.

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