secondary?s

[bradslt5]

took the wifes car out to the strip sunday for the first time .and going over the time slips saw that there was a 3mph diff in 1/8 mile speeds from 90.4 to 93.4. 60fts were2.005to 2.10 qtr times and speeds werefrom 12.31 to 12.51mph 113.86 to 116.78. i know there is a slow leak in the secondary system. my ? is could the secondaries start closing or be sticking part way open while going down the strip. i use my g-tech to download onto my computor and it shows on all runs i shifted within 150 rpms an all runs . does anyone have any experience or thoughts on this . i know i need to fix it but its going to be tough with twins on the way

[Kevin]

I'm confused, why do you think there is a problem with your car?

[bradslt5]

because of the mile an hour dif in the 1/8th and 1/4. my black car stays within 1/2 mile an hr not a 3mph dif. i can rule out the other variables because of the g-tech info that show shift rpms and time of gear change and even wheel spin .all of that info was very close on each run .

[Kevin]

could be heat soak, wind, difference in 60' times...don't mean there is a problem with the car

[bradslt5]

there was o wind with an hr between passes no heat soak . 60ft time were within a tenth. . you could be right but i was just asking if anyone ever has experienced this problem . usually when a car changes that much 3mile an hr in an 1/8 it would show up as a big change in launch, gear change time ,or rpm, but when everything is so consistant as it showed it makes one/me wonder if they are either closing ar not opening all the way .. the da for the day between 1200-1300 all day. so i put it out to find if anyone else who took their car to the strip had that big a change ?????????????????

[tomtom72]

I have never run my 90 down the 1/4......so I can't add anything from experience that I have, but consider that at WOT the engine vacuum is waaaay low...right?

The actuators require 8" hg to be fully opened and held fully opened, right?

If there is a leak at an actuator and/or both actuators leak, and/or a leak somewhere else in the 2* plumbing then would the actuators pull the 2* butterflys fully open and hold them open at WOT?

The reason for the pump,( if I'm not wrong...I wouldn't bet on that) .....the pump supplies the vacuum to the 2* system that is not generated by the motor at WOT, right? I thought that the FSM said that at WOT there may not be enough motor vacuum to hold the 2* butterflys fully open, right?

I don't know except that it could be logical to suspect a performance difference at WOT between a Z with a good 2* vacuum system and a Z with a 2* vacuum system that is leaking, specially at WOT operation, JMHO.


Tom

[XfireZ51]

Originally Posted by bradslt5

took the wifes car out to the strip sunday for the first time .and going over the time slips saw that there was a 3mph diff in 1/8 mile speeds from 90.4 to 93.4. 60fts were2.005to 2.10 qtr times and speeds werefrom 12.31 to 12.51mph 113.86 to 116.78. i know there is a slow leak in the secondary system. my ? is could the secondaries start closing or be sticking part way open while going down the strip. i use my g-tech to download onto my computor and it shows on all runs i shifted within 150 rpms an all runs . does anyone have any experience or thoughts on this . i know i need to fix it but its going to be tough with twins on the way

Is there a different claibration in the 2 cars?

[petefias]

Can't comment on a 3MPH variance between runs, but if the secondaries have big vacum leak a code will set. At least it did on my MY95. Once I fixed the leak (under the plenum) all was fine.

[rkreigh]

unless you have an exceptionally bad leak (it will code) a quarter mile run won't cause secondaries to close

the vacuum pump was there to supplement eng vacuum and normally once they are open, you are good to go unless you are doing an very long time at WOT

graham commented on this that one some cars, the pump would be faulty and the secondaries would open up and stay fine on eng vacuum alone

I don't worry about it anymore, mine are GONE!!

another good gm philosophy that should apply here, parts left out don't break

only disappointing part is that I didn't pick up much hp either, just a smidge of mid range torq.

the heads are the limitation now on my car

but 508 rwhp is still pretty thrilling for a lil ol 390

[bradslt5]

I think that is the plan to just get rid of them and be done with it . i hear some tie them open ? what do i have to leave connected vaccume wise to keep the computor happy? on the tune on the 2 different cars yes they are different the black car is fully ported where the red car is just injector housings and plenum. black car is 8 tenths faster . but the red one is very quiet and cushy for the wife .