xaon

iTrader: (12)

I'm in the process of getting my idle down to snuff tuning with speed density... right now i'm working on trying to keep the setup to maintain enough vacuum to keep the defroster vents closed off at idle.

My setup right now is a 408, 248/254 114+2lsa cam, AFR 225's, ~11.3:1 compression, LS6 intake.

With a 950rpm idle speed, my MAP sensor is showing 74-77kPA. The timing table cell it's looking to at 1000rpm@.24G/cyl is set at 32*, idle jumps around from about 14.5*-30* , AFR is commanded at 14.63 and wideband reports it right around that area.

What does everyone else's timing, and MAP sensor readings look like at idle?

Greg Fell

iTrader: (9)

Put your idle speed at 1100. The car will like it a lot more imo. I also feel its actually hard on the motor to have it lope too much. If you can imagine, the motor actually goes in reverse for a split second, then forward etc. It will slop the valvetrain around.

My MAP is ~ 65 at idle.

xaon

iTrader: (12)

my car doesn't have an aggressive idle to it, it's quite tame... running it up to 1100 gets rid of all lope. The idle speed is fine, I just have zilch for vacuum... I finally got around to measuring the vacuum, and i'm only building about 8.5 inHG at idle. Running up to 1100 only gave me another .5inHG... still not enough for the a/c system to work properly.

I'm stumped as to how to get more vacuum out of the setup, I'm starting to wonder if the air is moving way too fast in the intake and I need to step up to a FAST 90 setup... or if i'm just ultimately doomed and need to get a vacuum pump or a different cam. *sigh*

What kind of vacuum does everybody else get at idle?

Slow Z28

iTrader: (19)

Any other answers to this one? I was reading 80 at idle, and the thing just did not want to be tuned at all no matter what we did, the thing just would not act any different. could get it to idle, but step on the gas and it'd die out, but as soon as the throttle blade closed, then it would raise rpms

98Z28CobraKiller

iTrader: (17)

Is the RAF dialed in? Did you drill the TB or is the screw turned in? What are your IAC steps? You want this to be around 30-50 at temp. My vacuum at idle is about 5 psi and my AC works fine. I idle in the 65 KPA cells and at about 925 RPM with 31* timing. I had a problem with my AC only going thru the defroster also when I first put my car back together. As it turns out, the vacuum "T" broke somehow in the installation of the motor and it was not holding the vacuum. Kind of like a cracked Mc Donalds straw. Anyway, I removed it, siliconed it (cheap bastard) and put it back together VIOLA A/C!

Nihilanthic

More restriciton would mean more vacuum, all things being equal. A bigger intake would mean less vac.

You should get a vac pump for accessories IMHO.

xaon

iTrader: (12)

holy old thread batman.

FWIW. My A/C ended up eventually working more or less... it just cannot be turned on at the highest blower setting, you have to turn it on set at a lower fan setting and then move it up from there (at idle). I eventually swapped out the intake to a FAST 90 for grins, it made no change in the vacuum.

I've done alot more tuning on the car since may, and changed a bunch of different settings, it now idles smooth at 900rpm and everything works good.

Slow Z28

iTrader: (19)

i brought it up because of the high MAP reading. didn't want to start a new thread

It's what my problem is. I don't have a/c or a heater core to worry about. I literally can't even drive the car or give it gas

My 382 all bore, 11:1cr, 242/250/612/619 on a 114 with a Beck Sheetmetal intake is reading 80 on the MAP at idle. we played with timing, no matter what it was at 30 or 22 or X, it still read the same. we played with fueling, we raised idle to 1200rpm, etc...

the thing would just float at idle between 800-1200rpm and eventually settle down. to a 100rpm window.

then at the slightest hint of the tb opening, it'd lug down and soon as the TB was closed, the engine would THEN race up.

my disgust with it just eventually led me to remove the intake figuring it was just TOO much for the "small" engine

when i could get it to get up in rpm, there would be a blockage like it was hitting a rev limiter, BUT it was almost like a full second apart. like it would race and then hit a blockage and then come down, then race up

i don't think a vaccuum leak anywhere. it was all brand new lines, i didn't break the vaccuum tee that the map sensor had to be attached to

where could I have gone wrong(probably a long shot question considering i am not sending my log of scanning to you guys) a friend was using his HPTuners to help out.

TAQuickness

iTrader: (28)

use starter fluid and spray around the manifold and vacuum lines for leaks. you'd be surprised what a small leak can do.

also, use the bidi to adjust commanded fueling while you test idle transistions.