blownrunner

91Z stock... Have a well maintained car, new injectors, pumps, and filter and everything, verified the secondaries open up, no vacuum leaks, have Mark's chip, no codes.

How much of a power increase when the secondaries kick in? I can feel a difference, but not much. Can't turn the secondaries off when in power mode when I am flooring it, guess the computer is prohibiting it. Sometimes I can get the rear tires to slip in 2nd gear, sometimes I can't. I live in Florida with the humidity.

Thinking of getting Mark's chip to eliminate secondaries, maybe the valves are sooted up or something, would this effect it greatly? And also headers and exhaust, the stock system which by the way is garbage: there are tool marks at every bend, the resonator was hammered in a little to clear the seatbelt bolt, and it looks like the mufflers were painted by throwing a bucket of paint on it.

The way you guys talk it should pull more, it is nothing compared to my 2002 Viper although it has way more torque. Thanks everyone.

zrc3john

Zs usually are not torque monsters.....Your 2002 Viper should have way more torque than the Z.....I mean it's a ten cylinder motor and there rated at over 500 ft.lbs or am I reading it wrong?

ZR-71

The only thing I can say is when I sometimes forget to turn the power key on, I definitely notice a decrease in power accelerating.

FASTAZU

If you can't tell a difference with key on and key off between 3-6k RPMs something is wrong. If you want more power headers and exhaust are just the first step

Dominic Sorresso

Key Off is about 250hp

Key On is 375hp+

You should be able to notice that difference.

Your Viper has 2 more cylinders and 150cu.in. more. I can guarantee u that if u drove modded LT-5 w similar displacement, you would be impressed.

jss06c6

You should definitely feel them open up. I have essentially the same setup you do, other than full Stainless Works 3" exhaust, headers to tips. With Marc's chip and secondaries "not" working due to a faulty check valve, the car only made 239 rwhp. I got the check valve fixed (allows the secondary vacuum pump to keep the secondaries open at WOT when manifold vacuum is low), the car put down 344 rwhp on dyno.

I am doing my own tuning now and brought the curve down (RPM) where secondaries begin to open. This allows me to "feel" the power surge earlier in moderate acceleration driving. You can definitely feel them engage.

Is your secondary vacuum pump cycling when you turn the key to "on" without starting the car? It should not cycle. If it does, you should look at the check valve, which unfortunately is under the plenum in a stock setup, and replace it. Very cheap part, but can definitely affect wot performance.

blownrunner

No, it does not cycle. Recently changed the seal for the vent between the heads in front of the starter and replaced both check valves while I was in there. Thanks for the reply's everyone, it's probably just in my head. Need to do the exhaust for starters.

jss06c6

Just to "feel" the secondaries, I believe you can run your experiment in reverse. Turn the power switch to Valet mode, take the car out on a safe road. Get it in 4th gear and from 2000 rpm, smoothly, but rapidly hit WOT. At 4,000 rpm, switch Valet switch to full power. You should feel the secondaries open up. Best evaluation is on a dyno, not a butt meter, but going this way, valet switch off to on, you should feel it. When you put on headers, you should retune your VE tables to get most out of them. Marc will reflash your chip to add a bit more fuel and add anti backfire as well. Just ship the chip to him and tell him what fuel you will be running (octane). VE tables are more involved and can't be done without driving the car and capturing fuel trim data.

Vette Daddy

Remove the plumbing and never look back.

tpepmeie

The ECM contains an upper RPM limit, whereby the power key will not change state above 4000 rpm. For our safety, I'm sure. So, the experiment you describe won't work above 4000 rpm.

Marc had a method on his website to activate the port throttles manually for diagnostic purposes, and see with a flashlight whether they are opening. Not while driving, of course, but a worthwhile check anyway.

jss06c6

​​​​​​Yes, I've done this by shorting pin 17 (pink or pink w/black) on ECM to see the secondaries open. Problem is that this did not properly test WOT when manifold vacuum is very low on my car. The secondaries were not staying open at WOT with the check valve leaking in my vacuum pump circuit.
Won't contest the RPM limit in the stock tune (I'll look at mine to see how it's set). I have performed the test I described, possibly switching at 3000 RPM and definitely felt my secondaries open after i repaired the check valve. The "test" before I fixed it and on the dyno proved they were not opening at WOT, despite the ECM command to open being received.

I would expect the OP has secondaries that are working fine. Best test is indeed on a dyno, not simply driving.

Rkreigh

it's a great and ez to do mod. you can just wire them open and put the chip in and see if you like it. Not going to give you much power though as the throttle response and small increase in torq (very small like 5 ft lbs) in the mid range is all you will see. The factory system opens pretty quickly the the flapper once open only hurts a few cfm.

The real advantage is simplicity (and combatting alzheimers forgetting to "key" the car). You can also now open up the porting on the heads too. While the ZR-1 will not shove you in the back like the torq monster viper, it will sure keep up with it with a bit of TLC for the Z

blownrunner

Thanks everyone so much for the reply's, going to bypass the secondaries before I start goofing with the exhaust. On a plus side, it is cooler now in Florida with less humidity so it should be making a lot more power.