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Old 04-05-2007, 02:13 PM   #1
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Default Possible causes of power deficiency above ~5000rpm

I would like to hear some general opinions on the tuning that ought to be done to my PCM after putting in the new transmission with 3.73 gears and a 2800 stall TC. Doug and I have been discussing this concept at length over the phone, but I thought I would double check to see if there are any factors we're missing.

Basically, the car feels like it runs out of juice in the top end of each gear. It might be a lack of engine flow above 5000rpm, but we're also examining the possibility that the power isn't getting to the ground effectively. Doug and I are examining the option of having the torque converter lock in 2nd gear to transmit torque at a 1:1 ratio, thinking that the high RPMs after a WOT shift and the 3.73 gears will make up for the lockup. Has anybody else tried this in a FWD 3800 application? What other transmission tuning options should we look at if it seems the car is falling on its face after ~5000rpm?

We are also looking at the option that the engine can't flow efficiently in the 5000-6000rpm range. My cam timing was retarded 6 degrees during the transmission swap, which should have shifted the power and torque curves to the right and made them peak higher. We are exploring possible restrictions in the intake and/or heads that are keeping the engine from being its strongest above 5000rpm.

Remember, I have no concrete numbers to back this up... just using the good ol' butt dyno at this point. Bob and I will be hitting the drag strip on the 13th, so we'll actually have some track numbers after that. But I would still appreciate some brainstorming as to why the car isn't pulling harder right up to the shift point. With the higher stall TC, gears, and cam timing change, this motor should deliver power until 6000rpm. It feels like it'* either not making the power, or not putting it to the ground.
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Old 04-05-2007, 02:24 PM   #2
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see, i was thinking about this with your car a while ago. It was before the tranny swap and all. When you told me you went 15.1 with a 2.3 60' time i was thinking ok so he is around the same time i went with a higher 60 which shows spinning. So i figured in my head that your trap would be high, so i asked you and you said soemthing like 91. I am trapping 93 with rockers and you have a cam so i would figure you would trap higher. It may be me but even before the trans swap, i think something was wrong up top on your car. But that is just looking at your traps and thruthfully i dont know much about your setup or anything, just thinking out loud. PS- Good luck at the track and hopefully you get nicely into the 14'* and lay down some solid 60' times with those gears and convertor. I want to see how that comes off the line how i can get an idea of that setup or one close to it
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Old 04-05-2007, 04:43 PM   #3
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are you sure that TC is not slipping at the end as much below. and to lock it whit lockup that going to be bad for the transmission because its not made to be lock up on full power
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Old 04-05-2007, 05:01 PM   #4
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Valve float?
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Old 04-05-2007, 05:56 PM   #5
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Float...hmmm our springs aren't meant to be spinning that fast now are they?

Fuel ??? ever checked to ensure you aren't running out?
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Old 04-05-2007, 06:13 PM   #6
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I have alway complained of the same thing too. Your motor is more modified than mine but I still thinks it applies to mine too.

On mine, it feels like the motor has put out all it has and it feels like the tranny is trying to exploit more but finally upshifts. Also happens at about 5000-5500, I wonder what would happen if you had the tranny to shift before 5250. Can youd do that?
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Old 04-05-2007, 06:23 PM   #7
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Well i have the 95 and with my pcm we shift at around 5800-5900. I have rockers so that helps up top alot but i truely dont feel a sudden loss in power up top. I know that the loss is there and i do feel some loss but it isnt anything crazy. I would say i have to agree with bill and i would check fuel pressure maybe it is running lean up there. Have you had a scan tool on it lately? Maybe getting some knock up there (due to low fuel pressure or something else) or something? Just some ideas.
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Old 04-05-2007, 06:45 PM   #8
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I don't know your whole mod list, so forgive me if I recommend something you already have...

Out of breath? (bigger TB, better intake, exhaust mods, intake and head porting {as you mentioned}...)
Out of fuel? (higher flow injectors)
Tranny slipping? (shift kit)
Knock Retard? (better fuel, check engine over for causes of false knock)
Tune? (PCM or, better yet, a Tuner)
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Old 04-05-2007, 06:47 PM   #9
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I'll go with valve float. I had it for two years, and my stock springs were 10lbs heavier than a Series 2. I was getting float about 5200-5300 rpm'*.

Funny thing about valve float.....it can send a little unburn fuel to the O2 sensor, tricking the PCM into leaning your mixture a little.
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Old 04-05-2007, 06:59 PM   #10
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Maybe for some reason your transmission isn't making enough pressure up top. Could it be due to those 3.73s making everything spin so much faster?
Not too many people have done 3.73s in the 60e.
The 3.69s in the 65e are a different story with their better pumps.
When I was doing all that high rpm shifting on a dieing tranny, it would feel like it hit a wall up top. I was able to remedy the problem with fresher fluid and by adjusting the vac modulator.

Another thing that is definitely holding you back up top are those stock intake runners.

Edit, I can't remember, do you have stock springs? Whats the mileage?
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