For the modder - fuel cut is merely a switch away.. since your fuel cut is partially controlled by the TPS, which is only a small pot anyway, you might be able to rig up another pot that shows the ECU 0 throttle whenever you want it to.
This probably won't work on speed/density (mass air flow) systems.
Anyway - the idea is that if you MUST leave it in gear, and leave the engine on, set it up so that you can manually cut the fuel, then open the throttle to 100% (least pumping losses for the engine). In this way, you can partially modulate the amount of engine braking that is actually being done.
This could be achieved using some type of switch and a rotary pot.
I tried the open throttle on the Clunker when doing my 13 mile downhill. I switched off the key, and then tried going downhill in gear with the throttle both closed and open. It changed the sound of the engine, but didn't reduce engine drag at all. I think the only way to make that work would be to also hold the intake valves open, and my engine's an "interference" engine, so I think I'd end up with bent valves anyway.
is that thing about engine oil amount true? only fill up to the lower limit and you get less oil pumping losses?
Not oil pumping losses... but it does create less work for the engine to do, if the crank is churning that oil... you can get away from doing this by installing a windage tray... not only do you get the benefits of NOT risking oil starvation, but you will actually gain a few HP at the flywheel from the windage tray shaving oil off the crank, reducing the rotating weight (and thus the power needed to spin it) of the crankshaft. It's kinda like adding a lighter flywheel... it doesn't give you more horsepower, it just lets you use more of what's already being created.
Quote:
Originally Posted by Clev
I tried the open throttle on the Clunker when doing my 13 mile downhill. I switched off the key, and then tried going downhill in gear with the throttle both closed and open. It changed the sound of the engine, but didn't reduce engine drag at all. I think the only way to make that work would be to also hold the intake valves open, and my engine's an "interference" engine, so I think I'd end up with bent valves anyway.
I think this has alot to do with the engine size and type, among other considerations. To accurately see how it affects coastdown times, you'd have to AABBAA test it, honestly. It's not by and large a huge difference, but in some cars, there is a difference.
My loose-engined Civic, for instance - I would be able to modulate 3-5 MPH difference at the end of a long coast on the same stretch of flat road, when coasting from the 45mph stop sign to the same curve (really tight curve, have to slow down to like 20 or so) Usually, by the time I hit that curve, I'd be around 30 MPH... but using the throttle with the engine off, I could keep it around 33-35 MPH over that same 1000ft stretch. Of course, engine RPM also has alot to do with it, and I would never take it out of 3rd gear while doing this.
I'd like to think that people might open their eyes at some point... instead, I find it more and more likely that I'll just close mine. -- Author kept secret.
Je ne veux pas d'une meilleure vie. Je veux être heureux avec celle que j'ai maintenant.
(I do not want a better life. I want to be happy with the one I have now.)
I think this has alot to do with the engine size and type, among other considerations. To accurately see how it affects coastdown times, you'd have to AABBAA test it, honestly. It's not by and large a huge difference, but in some cars, there is a difference.
My loose-engined Civic, for instance - I would be able to modulate 3-5 MPH difference at the end of a long coast on the same stretch of flat road, when coasting from the 45mph stop sign to the same curve (really tight curve, have to slow down to like 20 or so) Usually, by the time I hit that curve, I'd be around 30 MPH... but using the throttle with the engine off, I could keep it around 33-35 MPH over that same 1000ft stretch. Of course, engine RPM also has alot to do with it, and I would never take it out of 3rd gear while doing this.
Ah, okay. I think my expectations were too high, and maybe it does make a difference, but not as much difference as I expected.
Frictional losses are most definitely the biggest culprit for engine braking... Imagine it this way -
You've got a 300 lb person sitting on your chest, and you're flat on your back on a hardwood floor, with your mouth and nose covered by a slightly porous wet rag. You're laboring to breathe at this point...
Remove that rag, but leave the fat guy. Now you can breathe freely, but your chest has trouble rising to get an "easy" breath...
When you open the throttle, you're just taking the rag off your engine's face - get it?
I'd like to think that people might open their eyes at some point... instead, I find it more and more likely that I'll just close mine. -- Author kept secret.
Je ne veux pas d'une meilleure vie. Je veux être heureux avec celle que j'ai maintenant.
(I do not want a better life. I want to be happy with the one I have now.)
You've got a 300 lb person sitting on your chest, and you're flat on your back on a hardwood floor, with your mouth and nose covered by a slightly porous wet rag. You're laboring to breathe at this point...
I love DFCO mode. This mode helped me go down about 1 litre on 100km. ( 5 to ~4).
Verified by refueling, driven over 100km (105) with average consumption 4,12 l/100km. (my personal record).
Driven at highland ( hills and downhills) and flat road.
Pulse and dfco mode at flat roads i tried also. But i have not data yet.
Engine-off glide i don't use because i'm too much scary :-/
Big Red - '89 F-250 4WD Custom 90 day: 15.34 mpg (US)
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Quote:
I love DFCO mode.
So do I!
That said, I only use DFCO as a substitute for my service brakes. For Decelerating and controlling my speed on a downgrade. From my point of view, those are the only scenarios that warrant its use.
It's helped me get fairly decent fuel economy from my "pony". It saves brake pads and fuel.
YMMV
