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Old 02-24-2014, 12:21 AM   #1 (permalink)
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Best P&G technique with low peak torque (turbo engine)?

Hello, I'm new to the forums and recently picked up pulse and glide based on reading several posts here. I've seen about a 7% mpg increase using engine on, neutral glides, and a 7-10 mph window on 45 mph surface roads. Where I think I can gain more mpgs is in the rate at which I accelerate. Peak torque arrives at 1750 rpms which is about 250 above the point which the engine will lug. My question is this--since my engine is turbocharged am I better off accelerating hard (to spool the turbo and hit peak torque) or to accelerate slowly and avoid activating the turbocharger? Any other advice on PNG with a turbo is welcome!

I will continue experimenting and report back, but thought some of the wizards here could point me in the right direction.

Additional information: using 93 octane (price difference is made up for by 6% increase measured at fill up), tires at 33 psi (VW recommended +3), car is unmodded and I just had an oil change 2k miles ago.

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Old 02-24-2014, 04:26 PM   #2 (permalink)
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You'll want to accelerate hard enough, but not so much that it kicks you into open loop where you'll hit fuel enrichment and ignition timing penalties. Do you have a SG or UG so you can monitor that?
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Old 02-24-2014, 10:44 PM   #3 (permalink)
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I think I know the feeling when it goes open loop. I was varying throttle today and beyond a certain threshold the acceleration really picked up. I'll have to test it out on my commute tomorrow. I don't have an SG or UG, but my car has a built in instantaneous reading (albeit one that refreshes at a slow rate). Would the SG/UG provide more benefits beyond that? I'm a bit ignorant of the benefits.
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Old 02-25-2014, 12:45 AM   #4 (permalink)
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the SG or UG will provide more benefits and you can also adjust the speed at which it displays readings from ultra slow to ultra fast, the consensus around here is its not about accelerating its about the second half or the coasting part of it, i have heard again and again ,, slam on it hard enough but be sure to stay out of open loop, you may need instrimuntation to accurately measure this, i used to accelerate slow thinking i was saving fuel but as soon as i tested the moderate to hard acceleration i noticed a gain in mpg, i am assuming if you accelerate to slow your MPG stay lower for longer decreasing efficiency, the goal is to get up to cruising speed as quickly as possible without reaching open loop,
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Old 02-25-2014, 08:52 AM   #5 (permalink)
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Quote:
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You'll want to accelerate hard enough, but not so much that it kicks you into open loop where you'll hit fuel enrichment and ignition timing penalties. Do you have a SG or UG so you can monitor that?
Enrichment seems to be a myth. Of my cars only the Skyline does enrichment at WOT. It's been posted time and time again, but I wonder how many cars actually do it?

Nowadays, I accelerate at WOT and shift at around peak torque. In low boost turbo cars, I believe shifting at peak torque is the way to go.

I don't think a SG/UG is of much use. You can set it to 'fast' refresh rate, but it's really no faster than my factory MPG display. The only plus side is you can calibrate SG/UG to your driving so it's slightly more accurate (potentially). Normal drivers find Fiat's OEM instrumentation to be optimistic, but (possibly because I glide a LOT) I've found it pesimistic on occasion. Unless you want the other OBD based features, I wouldn't bother with aftermarket instrumentation.

If you really want accuracy, MPGuino is the way to go.
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Old 02-25-2014, 10:27 AM   #6 (permalink)
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The SG isn't about using it for the MPG IMO. I never have my MPG reading up. I use it for other things like monitoring engine load, engine coolant temp, and for my Prius some hybrid stuff. Ask anyone here who has gotten 100% over the EPA rating for their car, instrumentation is critical to get there.

Enrichment and ignition retarding isn't a myth, especially on turbocharged engines. Just ask anyone who has done their own tuning. It is true that most cars these days stay in closed loop quite a bit (especially naturally aspirated engines), but it does happen, especially if you're accelerating around peak torque.
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Old 02-26-2014, 06:56 AM   #7 (permalink)
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Quote:
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The SG isn't about using it for the MPG IMO. I never have my MPG reading up. I use it for other things like monitoring engine load, engine coolant temp, and for my Prius some hybrid stuff. Ask anyone here who has gotten 100% over the EPA rating for their car, instrumentation is critical to get there.

Enrichment and ignition retarding isn't a myth, especially on turbocharged engines. Just ask anyone who has done their own tuning. It is true that most cars these days stay in closed loop quite a bit (especially naturally aspirated engines), but it does happen, especially if you're accelerating around peak torque.
I don't discount the need for instrumentation, I just feel that there's nothing at all wrong with the factory MPG display in most cases.

My turbo charged Fiat 500 stays in closed loop at WOT all the way to the rev limiter (as verified by SG). Most small Euro turbos are tuned for ecomony so I wouldn't be surprised if many of them do this. The Jeep and Merc also stay in closed loop at WOT, they may switch to open loop at well past sensible revs, neither would normally be revved anywhere near that point.

Given this I now simply accelerate at WOT which is a lot easier than aiming for 80% load or 14 inches on the vac gauge. The 80% load - stay out of enrichment idea seems gospel around here but in my experience it's not a blanket solution.

Now my R32 Turbo Skyline does enrichment, I can tell by the flames out the back But that's a 80's tech performance car, not really typical EM fodder.
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Old 03-09-2014, 11:22 PM   #8 (permalink)
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First, thanks for all of the inputs everyone! I wanted to provide an update: I had an 93 octane specific ECU tune installed on my car a couple of weeks back. In addition to increasing boost pressure at high rpms it advances engine timing. I averaged 34 mpg on the highway driving with load. On my daily commute my PnG efforts did not show much improvement still 32 mpg in the morning and 35-36 in the evening. I did a control test over the past week using conservative driving practices without PnG. Shifting at 2k rpms, accelerating slowly, coasting down the backsides of bridges, and avoiding cruise control like the devil I saw 31.5 avg for my morning commute and 36.2 for my evening commute. This tells me there's a clear flaw somewhere in my PnG technique. What's more it tells me that I should be able to break the 40 mpg mark with proper technique on my evening commute.

Over the next week I'm going to try 50% throttle pulsing to 2k rpms and I'll report back with my results. Any other suggestions or comments are welcome!
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Old 03-10-2014, 05:07 AM   #9 (permalink)
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Quote:
Originally Posted by oldtamiyaphile View Post
My turbo charged Fiat 500 stays in closed loop at WOT all the way to the rev limiter (as verified by SG). Most small Euro turbos are tuned for ecomony so I wouldn't be surprised if many of them do this. The Jeep and Merc also stay in closed loop at WOT, they may switch to open loop at well past sensible revs, neither would normally be revved anywhere near that point.

Given this I now simply accelerate at WOT which is a lot easier than aiming for 80% load or 14 inches on the vac gauge. The 80% load - stay out of enrichment idea seems gospel around here but in my experience it's not a blanket solution.
Newer cars are indeed closed loop through the whole rev range, except this closed loop is using a wideband O2 sensor. Because they have wideband sensors, almost all new cars are capable of running rich in closed loop and do so at WOT. Because of the 7 year (I think 7?) emissions equipment warranty requirements, modern cars actually can run very very rich (to cool the cat off with excess fuel), which is very bad for mpg. For example in the FRS/BRZ community people have seen noticable fuel economy improvements by optimizing the tune for power, which leans the engine out a bit at WOT. The fuel saved at high throttle positions can be significant.
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Old 03-21-2014, 03:42 PM   #10 (permalink)
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On my wrx sti

p&g works well if i 80% load with boost (avoid enrichment), then glide.

This works best for my turbo car because i only need to pulse for a short amount of time, thus allowing my glides to last waaaaaaay longer

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