VCT 6 - improved breathing, loss of torque
I have a series III AU Fairmont Ghia, auto, with the VCT motor. About three weeks ago we added an SS air inlet, K&N filter, Genie manifold, flow thru cat, and a 2.5" ss cat-back system.
Right away it was a lot more torquey - more push below 3,000 rpm, extended top end on the freeway, and lots more fun to drive - even though it sounded like a Cessna. Over the next ten days it got better and better (the power, not the noise).
The idea was to let the factory computer adapt to the new hardware over a couple of weeks, dyno it, fit a Chiptorque chip, and then dyno it again to get a good appreciation of what difference the chip makes. So last week, the guys added an exhaust tip that hadnít arrived earlier, installed the chip, and noted a slight increase in torque and power on the dyno.
They also noted that where the existing factory moulded plastic ducting leaves the filter box, itís only 2" diameter. So they decided to help it to breathe a bit better. They found that if they disconnected the filter box and the 2" restriction, they could pick up an extra 8 rwhp. (but strangely, if they aimed the dyno blower into the pipe like Ďassistedí ventilation then it lost about 5rwhp). So we decided to fit 3" stainless from the filter box to the throttle body. The guys modded the filter box to remove the 2" restriction, so itís now a full 3" straight out, and I drove the car away without a dyno run Ďcause I had some work commitments that couldnít wait.
The car felt a bit ordinary at first. I thought it was maybe a change in the power curve, because there was no noticeable surge through the rev range like before. But now Iíve been driving it for a couple of days, (total about 6 hours of freeway and town driving) I know it is definitely down on torque. Itís flat and lifeless like it used to be before we started Ďimprovingí it.
Putting the Chiptorque chip aside for the moment, I would have thought that with the improvement in induction pressure and flow, there would be a noticeable increase in both power and torque. But maybe at low revs (2 - 3k where I want more torque) all that extra induction flow isnít needed. Would removing the 2" restriction on the induction side be responsible for lowering the torque? Or is this a rubbish idea?
Iíll drive it for another couple of weeks to let the computer re-train, and if it is still ordinary then weíll go back to the dyno with a) the existing set-up, b) with the original factory restricted air duct from filter box to throttle body, c) without the chip.
If anyone has any words of wisdom or understanding of what could be happening here, Iíd appreciate it. Where could the torque have gone? Where did the fun go? Will the car 'improve' over the next couple of weeks as the chip and the computer and the new engine hardware get to know each other?
Last edited by the black pig; 10-12-2003 at 18:18.