The reason I think the LML is faster than the 6.7L - Ford Powerstroke Diesel Forum
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post #1 of 6 Old 02-04-2011, 02:28 PM Thread Starter
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The reason I think the LML is faster than the 6.7L

From the first day I had my 6.7 I noticed that when I revved the engine in neutral the RPMs continued to clime after I lift off the throttle. The RPMs continue 500-1000 higher after I lift. Not only that but the time it takes for deceleration is longer than most engines I've been around. I believe this is a big contributor to the shifting problems in the transmission.
I'm not sure if this has to do with emissions equipment or the turbo design. I do believe it's the way fuel mapping is programed. Possibly to prevent turbo bark/chatter. If the engine slows to fast and the turbo is still spinning like a mad man the result would be a shock wave(turbo chatter) right? Ok so let's look at the turbo design... The turbo was built to be the most efficient turbo ever so they made the turbine wheels small and added a second one on the back. This adds mass to the turbo shaft. Since the turbine wheels are smaller they have less drag in the air. The only thing slowing them down is air pressure and air drag. Compounding this is the fact they are on a common shaft with only one exhaust turbine to assist in deceleration. The 6.4 has larger air drag profile and two turbines in the exhaust on separate shafts for drag to decelerate. I believe Ford compensated for this possible problem by creating a sort of post injection fuel map to slowly bring the RPMs down to prevent turbo chatter and other normal diesel noises. They went so far as making the oil pan composite to reduce noise so it could be possible.
All this makes great sense at lower RPMs. It's when you're in that 2500-3000 range it becomes less efficient. Which is great for normal driving! That's why I like my truck so much.
I would like to see faster shifts in the upper RPM range. In order to get that and not break things I think the engine needs to slow down faster.
So how do we get the best of both worlds?
I really want my cake so I can eat it too.
Sorry if I rambled... Just had a Redbull and a coffee. Haha

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post #2 of 6 Old 02-04-2011, 02:30 PM Thread Starter
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By the way correct me if I'm wrong... Just a theory I came up with on my way home from work.

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post #3 of 6 Old 02-04-2011, 06:31 PM
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I think Red Bull and coffee are excellent!!! Throw in a danish loaded with icing and your set!!!

Driving: 2011 Pale Adobe...F-350 CC 6.7 FX4 3:55-Locking Rear End-Dual Alternators-premium Lariat, moon rf, added wheel flares, 2-tone black base

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post #4 of 6 Old 02-04-2011, 07:42 PM Thread Starter
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Had one at 6:30 this morning after my first Redbull with my first coffee. Haha!!!!!

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post #5 of 6 Old 02-05-2011, 07:13 AM
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Interesting that you bring this up. I've been noticing this a lot lately. If I press the accelerator more than half way down from a dead stop in drive and then immediately let off, it continues accelerating a good 1-2 seconds after I've completely let off. Same thing in neutral. Seems a little unsafe to me, especially when your slowly nudging up in traffic.

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post #6 of 6 Old 02-05-2011, 05:05 PM Thread Starter
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I'm not worried about safety really but I have noticed that in traffic too. Usually I'm never that close to the car in front of me. I try not to use the brakes or the throttle in traffic to achieve better milage.

Does anyone else have any thoughts about this? Again I don't think it's a problem as trucks typically aren't racing. But I do have a kart/road racing background and am always trying to get the most fun out of my vehicles.

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