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Discussion Starter #21
I know you're looking for corroboration, but let me just reiterate in the meantime: From what I recall reading, the 4L60 is very strong IN OVERDRIVE when the torque goes from input to output, but not when the wheels run the engine as in compression braking. I doubt (from what little I know) that DFCO coasting will break anything. If anyone else knows about this and can address this concern, please join in.
 
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Discussion Starter #22
I cross-posted in the drivetrain section.. Maybe Shane or Joel will comment..
 
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Discussion Starter #23
I would be more worried about engine wear. If DFCO could improve more gas mileage without too many side effects I'm sure GM would set it up more aggressively.

I simply adjusted DFCO in my tune for the gearing and engine vacuum of my car.
 
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Discussion Starter #24
When I talked to Jessie at Wait4MePerformance, he indicated that agressive DFCO is hard on pistons and rings due to the decel sucks the oil off the cyl walls due to the strong vacuum.

He said with supercharged cars on the dyno if they don't kick into Neutral when the car comes out of power due to the lack of fuel and air, will crack the pistons in the area between the ring land and the piston face.

He said if you ever tear down an engine that had agressive DFCO on it you will see high piston wear.
 
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Discussion Starter #25
So I wonder how aggressive is too agressive. It does sound cool, but I'd rather replace brakes than pistons.. :D
 
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Discussion Starter #26
My settings are about as agressive as I can figure out. still have a little "bump" when fuel turns back on around 44 mph. I don't like it, but haven't messed with fixing it either lately.
 
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Discussion Starter #27
Well Joel responded to the cross post. Sounds like it shouldn't be too bad on the transmission as long as your not manually going from 4th to 3rd to slow down.

Thats reassuring, but theres still this whole piston / cylinder wall thing..
 
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Discussion Starter #29
Readin' two threads at the same time is hard; next time, somebody just PM me with the link and I'll come respond over here. Yeah, I wouldn't worry too much about the 4-3 downshift. Just how low a mph are you running DFCO to?

Before I even started messing with 4L60Es, my dad said something very wise regarding manual downshifting: "It is cheaper (and easier) to replace the brakes than it is the transmission." Perhaps it is best not to get too carried away with DFCO on automatic-equipped cars.
 
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Discussion Starter #30
I have it set to go to 600 rpm or so, so that turns on fuel again around 44 mph typically.
 
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Discussion Starter #31
Originally posted by sherlock9c1:

Before I even started messing with 4L60Es, my dad said something very wise regarding manual downshifting: "It is cheaper (and easier) to replace the brakes than it is the transmission." Perhaps it is best not to get too carried away with DFCO on automatic-equipped cars.
I mentioned something similar, rather replace brakes then pistons.. (Or trans)..

I'm not going to go very radical, just love the way it sounds with my exhaust..
 
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Discussion Starter #32
I'll tell you the one thing I love about DFCO, is right before a hill, putting it in 2 (with some throttle of course), then riding the DFCO down the hill while blasting the stereo and cranking the AC and knowing it's all being paid for by gravity.... :D
 
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Discussion Starter #33
RamAirRocket

I'm bringing it back.

Have you nailed down, exactly how DFCO enables yet?

I have one car that is eluding me on the DFCO... large stall, descent sized cam....
 
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Discussion Starter #34
Well, this is what I know at the moment.

The higher rpm stall converters can hurt the ability to run DFCO unless the converter is locked on decel. But in unlocked mode when DFCO is on, it will drop down rpm waaay to low and could easily stall the engine if allowed to go that low (that is bad, avoid!)

Recently I had to swap to a 3.08 rear end from my 3.42's and in all my efforts, I could not get DFCO to stay engaged below 49-50 mph. So I enabled the option to keep TCC locked at Low TPS. That made a world of difference. I can go all the way down to 38-39 mph now with DFCO on and TCC remaining locked, and it has a pretty smooth transition to enable fueling again.

But when I tried it on my car with 3.42's it was a real pain, it was pretty rough at cruise in the 40-50 mph range and giving light throttle with TCC locked, then let up on throttle and it would clunk and was fairly violent on the car. That rear end is sorta worn, so that might have agrivatted it, and possibly pushing the lockup engage point may have helped, but I wasn't too thrilled with the roughness and abandoned testing for concern of the TCC being damaged (yes, it was that bad)....
 
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Discussion Starter #35
Yeah, make sure both "TCC Release" switches are unchecked.
 
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Discussion Starter #37
MikeOD

Good job on the stiky. This thread is the best post I could find on DFCO on all of the internet and fourms :)

RamAirRocket

3.73s, 4500true stall, big cam big heads light idle vacuum...... That is the combo for a car with really difficult DFCO enable.....

I have got DCFO with this combo but have to cross 25"hg of real vacuum to make it engauge. At just 24"hg, AKA 1hg difference, it shut off and belnds back to normal. :-(

Any comments?

[ 06-25-2007, 01:48 PM: Message edited by: ProTools4 ]
 
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Discussion Starter #38
Can you post a datalog of the car running where DFCO does and does not engage?

I can see what I can come up with for something that might work.

If you can't post it, just email it to me.
 

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Well, things are going on slowly to get DFCO as agressive as I can. I don't know how much interest there is here, but I know I have search the net over to find very little meat on DFCO.

DFCO Enable RPM: 1300 RPM
DFCO Disable RPM: 600 RPM
DFCO Enable MAP: 20 KPa
DFCO Disable MAP: 36 KPa
DFCO Disable RPM Decrease: 3750 rpm
DFCO Enable Coolant Temp: 20 Degrees C
DFCO Enable MPH: 18 mph
DFCO Enable Delay: 0
DFCO Spark Retard: 23 degrees
DFCO Exit Spark Blending % TPS vs RPM: **
DFCO Enable % TPS vs RPM: All 0
Throttle Follower IAC Offset vs MPH: All 1

What I have learned is that the key to getting DFCO to kick in, it having the MAP pressure CROSS the DFCO Enable MAP. If you can't get the vacuum to cross it, it won't turn on. I wish it was as simple as make it railed high or low and keep it on all the time, but it won't work at all then.

** I haven't messed with Exit Blending yet, but my initial start is to run it all to 0 and then see how it reacts.

Having DFCO Disable rpm as low as you can tolerate keeps it turn on for as long as possible. I try to get it to nearly idle. As you approach idle, MAP goes up (towards 100) and will cut off when it hits the MAP Disable threshold. But, setting this high will also cause DFCO to not turn on. It almost seems that the vacuum before you attempt to enable it must between the Enable and Disable MAP to even have a chance to turn on.

I'll post more notes as I get time...
Are these still the best numbers you’ve come up with to get a good engine breaking feel out of your car ?
I just applied all your suggested numbers to my 96 Impala WX3.
gonna try them out tomorrow since this was one area my current mentor doesn’t have actual numbers to use in my JET DST programmer, he uses TunerCAT.
Thank You for the information and settings to use.
 

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Hey SoCal,
How did you end up liking these settings? I compared them to what I've come up with and there are similarities and differences. But I also have a 2.56 geared wagon so that could explain some of the difference. I've also made trans shift changes such as keeping the converter locked up and tweaking shift points.
I'm set pretty aggressively and do get some slight surging now and then. It is almost not noticeable. I may need to make further changes once I get the exhaust done. Once I'm able to hear the engine the slight surge may be much more noticeable.
 
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