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Power suck right before secondaries open?

CLASSVT

Veteran CEG'er
Joined
May 2, 2003
Messages
736
Location
Fort Wayne, In
I got my 3L Hybrid dyno tuned last summer, and got fairly good results from it. I'll try to post my dyno graph later, but the tech spent hours and hours and hours trying to get rid of the dip in power right before the secondaries open. No matter what, he couldn't eliminate it.

I can definitely feel this when I'm driving. Any time I'm not WOT from first gear on through, it's very apparent. It's less apparent when WOT first on. Anyone have experience with tuning this power suck out of these cars? Again, I'll try to post my dyno graph later if I don't fail miserably.
 
Mod's please delete this duplicate post. I was getting an "empty response" error and thought the post had failed.
 
Not 100% sure, but I think you have to move the secondaries rpm point. This topic has been kicked around a bunch, it will be intersting to see what the old timers have to say,
 
We actually did move them. We moved them higher up in the RPM range a bit. I think it offers a smoother and better driving experience when you're just driving leisurely. I'm happy with that aspect, and I'm happy with the extra low-end torque I got from the tune, but it would be great to be able to tune out that dead spot.
 
You may need to move the short runner opening point lower in RPM. Depending on what you've done with the intake manifold, the long runners may be becoming inefficient and causing torque to drop before the IMRC opens the short runners.

Back in the day, when we were diddling with the V6 Taurus SHO intakes, doing something like extrude honing the intake runners made the long runners more efficient so we moved the crossover to the short runners to a higher RPM.

I suppose it's possible that in your case, an intake configuration (runner and plenum volume) that was optimum for 2.5L might become less optimum at a lower RPM feeding 3L of displacement, so you might need an earlier crossover to the short runners.

There was a story going around when the Taurus SHO was introduced that the tuners deliberately delayed the short runner opening so torque would drop, and then come back with a bang as RPM's climbed, as this reminded old farts like me of the back barrels opening in a 4-barrel carb. Back when I was at Ford, my tuning contacts at AED confirmed that the runner opening was deliberately delayed.

A lot of tuning is science and very predictable, but sometimes it's trying a whole bunch of stuff and seeing what works best.

EDIT: It would help to see a torque curve from the dyno work you had done.
 
Yeah, I was using goofy terms. Looking at the curves above, I would open up the secondaries at about 3k and see how you like it.
 
Well, I seem to remember that being about where they were stock, but the graph doesn't really support that does it? I remember feeling like they opened up too soon when driving around at leisure.
 
Well, that's the problem with tuning. You almost need two different tunes, depending upon the driving mood. When going WOT, switch to the secondaries at a lower RPM (3000?). When at half throttle or less, use 3700 RPM for the switch point.

I work with programming control systems for compression equipment, so I see these kind of problems in our process designs. Replace the car computer with an Allen Bradley CLX processor, and I can program the sh*t out of it...
 
I hear ya. Of course I only have the one tune. So to do anything about this I would have to head back onto the dyno, or is there a way to program just that one variable with the SCT tuner?

EDIT: Actually, that would be a PITA to load a tune each time I took it for a drive. I pretty much drive WOT a few times every time I drive it. The rest of the time it's traffic or leisurely driving. Still curious if anyone has been able to tweak their tune to avoid this dip in power though.
 
We actually disabled the secondaries for a run on the dyno to see how it responded, and it was not impressive.

They're mechanically held closed, did you tie them open?

What intake are you using and has it been modified in any way?
 
I'm not an expert on this, but I'm fairly certain the tech was able to program a run with the secondaries open the entire time. My intake is the Nautilus CAI with the filter inside the fender. I have that in my signature, but it seems that is all gone?
 
I don't have a print out from that pull, and it was pretty long ago. Perhaps it was the torque, can't be sure. But I remember we were both satisfied that the numbers were definitely worse than with the secondaries operational, and moved on.
 
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