Paging Zippy / TCC locked = increased MAP??

[TurbochargedBerserker]

Ok, I've been playing with my tranny settings looking for the uber economy tune.

 

I have it shifting early and then locking up the TCC to keep it below 1500 rpm most of the time with an occasional peak to 2k. Basically, I'm using the triple disc TCC to simulate overdrive in 2,3, and 4.

 

1. I get some lugging when locking the TCC and have been fixing this as makes sense if you think about lugging from a manual tranny pov (e.g. I move the apply points up a few mph until the lugging goes away). The result is less lugging but higher shift points and higher rpms at steady state speeds. I'm okay with that if it increases the smoothness, but the real question is I've seen some dips to 12 afr at times when the tcc locks and rpms drop below ~1k. I noticed that locking up the tcc causes my MAP to jump (enough to hit 105kpa and be into my go-fast AFRs). Also with the TCC locked, my MAP values are higher than in an unlocked state -- whereas unlocked is in the 50-75kpa range, locked is in the 80-100kpa range. I know the engine is under more load, but the increase in kpa seems disproportionate.

 

Are these increases in MAP as expected? If so, can someone explain

 

2. When the tcc locks up it hits hard... Almost like a 2 washer shift kit. Is this a symptom of locking it up too soon (as the lugging is I assume)?

 

3. Would I be better off increasing the time in each gear, locking the TCC 3-5mph after the shift and letting it wind out a little with the TCC locked? (Instead of mimicing a shift mid way through the gear)

[zippy]

1. The condition you're experiencing with the converter locked in at low rpm is basicly just building boost because of how low the rpm his. It doesn't take high cfm levels to make boost down that low and your turbo will begin to produce boost quickly under that low of rpm because of the high load. Your cfm level required to achieve boost at that low of rpm isn't much and with your setup having the 6.7L you are easily pushing enough exhaust gas to spool the turbo.

 

2. The tcc locking up hard at the low rpm that you're working with at the moment is likely from two issue's. One is the triple disc clutch which locks like you'd find in a manual trans car with a healthy clutch. It's just well built. I've often ran into issue's with the triple disc converters slipping the belt when the converter locks in. The other reason is from the low rpm. At low rpm you are experiencing your highest amount of torque converter slippage and at the low throttle you're also at a point where you will get the most bog from the engine. This is the same kind of effect you get driving a vehicle with a strong clutch and releasing it too quickly without giving it enough throttle. It makes the engagement feel real harsh.

 

3. Yes, that is what I'd do. I would not use the tcc in second except under wide open (80% throttle or more) in your case. I would make sure the tcc is switched to not locked during the shift and program it to be locking about 3 mph past the shift and only in 3rd and 4th. Under the light throttle % numbers you'll also want to make sure the tcc unlocking and downshifting are done at fairly low throttle % differences. This will keep you from getting the rpm low enough and load high enough to get into boost.

[TurbochargedBerserker]

Thanks man -- and thanks for explaining it in manual tranny terms so I can understand ;)

[zippy]

i hope it helped. it took me a bit to figure out an easy way to explain it. not saying you wouldn't understand it a different way, but getting thoughts to the keyboard can be difficult.

[TurbochargedBerserker]

You know me, man. Auto trannies are still voodoo Too much fluid and stuff where I expect shiny metal hehe. I appreciate all the manual tranny analogies you can come up with.