IAC/booster vacuum lines on a turbo m20?

[Kozworth]

I was wondering how you guys run your IAC when you have intercooler piping and a coupling up to the throttle body? Since the throttle plate is closed, all I could think of is somehow throwing the stock IAC into the piping to idle like normal, but half the pictures ive seen of boosted m20s do not even have an iac. Do you need it? If so, how do you keep it so it doesnt shoot out while there is positive pressure in the intercooler piping?

Also, I was wondering about the brake booster vacuum lines. These lines come into the stock intake bellows, (If the IAC Is deleted, would you just plug it?) if the iac remains, do you just somehow fit it into ic piping? Same question aswell, how do you keep it connected to widthstand boost pressure?

Thanks

[codrum]

If you need the IAC is debatable, I removed mine and haven't had issues but my car is not a daily driver. The m20s do have an idle adjustment screw on the TB that can be used to crack open the valve to let a little air in. One method is to use that in conjunction with tuning to find a sweet spot for cold and warm idle. In my experience cold idle with no IAC works ok with adjusting the TB screw, I have to hold the throttle plate open a little bit on first start but it hasn't bothered me. Once the car warms up it idles high, around 1000-1100 RPM but it is fairly consistent - it's something I've become accustomed to.

When I was first researching this there was a Glen's Garage board that would handle the 3-wire PWM IAC like we have. I was also able to dig up this article on diyautotune but I'm not really sure where the community is at otherwise.

As far as keeping vac lines and the like in place I've not had issue with tightening them down with screw style host clamps. I put a rubber plug on the IAC hole with a clamp and it has yet to pop off running 15psi. Hopefully others can speak to this under higher pressures.

[Kozworth]

I remember someone posting they had to jb weld/loctite on the fitment of the IAC.

I sorta figured the only way they idle'd was to adjust the throttleplate open a crack and have it idle at about 1k like you stated. The only issue is this car is going to be a daily driver in NJ, where we get a variety of cold to warm temps. I wasnt looking to use stock intake bellows since its supposibly good for 8psi then you have to do the ziptie/ductape special. I am probably running more towards 2.5'' piping to a 2.5->3 inch coupler, because as I remember the stock tb is a 3 inch one.

[travish325]

I jb welded mine in. 20psi and they never popped out, And you can run the stock iac just fine.

What engine management will you be running? with ms you dont even need an iac

[einstein57]

GE silicone intake boots. Factory boots tend to rupture around 8 psi.

[travish325]

+1^


or cx racing makes a nice aluminum elbow, it works pretty good

[Kozworth]

im looking into a PNP MS as my mgmt. I know you can control idle on it but wasnt totally sure if it was enough to completely delete the iac, since the butterfly in the tb would still be closed.

I was considering the silicone boot aswell, but I am running 2.5 inch piping, and if I remember correctly the TB is 3 inch. So then I would have to run a 2.5/3 inch coupler, then the silicone boot, and this seems like a no go. Only option in doing this would to be a 3 inch "pipe splice" or just like a short section of pipe between the 2.5/3 inch coupler and the silicone boot but that just seems sketchy.

[travish325]

t/b should be 2.75in

[einstein57]

If you have quality intercooler plumbing like cxracing or better you can stretch it. An exhaust tubing stretcher worked perfectly on cx racing aluminum. Other cheaper tubes will split.

I think we stretched this one



This was definitely stretched.

[Kozworth]

Looks like I will probably run that setup. So you just basically stretch out the end of the ic piping to fit the 2.75'' GE boot? I assume you can use some sort of a tapered "cone" if you will and bash it to in essence "bore" it out? If you cant tell I am just trying to make it work out the college kid way lol.

While I'm in here, what was the cons of running the PVC on a turbo car? I read a lot of people run catch cans. How do you delete the breather tube? Is this necessary

[einstein57]

Go to your local muffler shop and ask them to stretch it for you. Can't be more then $5-10. The valve cover breather can not be pressurized. It needs to be either under vacuum or vented to atmosphere. Most people just run a piece of hose straight down to the ground. The proper way would be to have it plumbed back in after the air filter but before the turbo. A catch can would work in that situation as well so your intercooler does not gradually fill with oil. Gets pretty nasty after a year or two.


This is how i do throttle bodies but you can just buy a rubber nipple from your local auto parts store.