Bestow unto me: Your knowledge on the most basic of vacuum setups
 

I have a car i'm working on that i literally only have two things that need vacuum.

1) MAP sensor.
2) Brake booster.


What i have:

1) Vacuum rails on each cylinder bank.

What i don't have:

1) Intake manifold.


What's the cheapest, yet elegant way to do this while keeping the brake booster and the MAP happy? I'm a little worried about volume, don't want the MAP freaking out when i'm on the brakes, and i HAVE to tie both of the rails together somehow before the MAP sensor is in the system.

Elegant and correct takes precedent over "cheapest."

What i'm initially thinking:

Tie rails together, run to distribution block. Run MAP off of block. Run another line to an aftermarket reservoir with check valve, which then runs to brake booster. Is this overkill and needlessly complicated?

pics? I'm assuming its ITB, if so, I think the throttlebodies will have a vacuum nipple you can use on each one.

How many cylinder banks you got?

They do, but they're plugged, and will remain that way, since i have nice big vacuum rails fabbed up to use. Plus i don't really want to either:

1) Run a rats nest of vacuum lines to a block from each cylinder
2) Run a map off of one cylinder. Impossible to tune.


Two. :)

https://www.miataturbo.net/attachmen...ine=1351521407


Here's a better picture that you should be able to see the rails in. (Bottom brass nipples)

https://www.miataturbo.net/attachmen...ine=1351521407
IMGP4387 by concealer404, on Flickr

The brake booster has its own check valve, no? What does adding a second one do?

--Ian

My experience with ITBs leads me to believe that the MAP sensor is borderline useless.
Assuming your ECU has a baro in it and doesnt need the MAP for taking a pre-cranking baro reading like some do.

I BELIEVE (if i believe what the internet tells me) that the check valve was in-line, not in the booster itself. None of the factory lines exist anymore in any way, so i have to build everything from scratch.

I will double check that the boost has a check, though.

I think the ticket here is to tie the two vacuum rails together before the MAP, then go from MAP to one of these: Steel Black Finish Vacuum System Reservoir Tank Universal Fit Hot Rat Rod | eBay

And then to booster.

The plan is to tune in "blended" mode.

The one I was thinking of is in the factory line, yes. It's in the ~ 6 inch long rubber hose that connects the factory booster to the hard line that crosses over the firewall. It's inside the line, not visible.

--Ian

At this point, i should clarify that i'm not working on a Miata in this case. :)

But i would guess that the Escort had the same sort of thing going on. There were no outwardly-visible signs of a check valve.

KL in an escort? https://www.miataturbo.net/attachmen...ine=1351561106

Yep in a 93 GT. SCCA Solo SMF assault.

Run a vac pump for the brake booster? Hell if its not a street driven car, see if its reasonable to just make a vac reservoir and charge it between runs for the brake booster, that will be lighter.

The true correct way to run map sensors on itbs is to put a map on each cylinder and use an ecu that supports that many map sensors, or make a circuit to blend all the map signals together (just connecting all the cylinders in a vac manifold and running a map off there doesnt work right). Alternatively you could just tune the thing straight alpha-n including timing and just use the map for baro correction. As much as I hate alpha-n, if I was tuning a naturally aspirated auto-x car it comes with a lot of benefits like instantly responding to throttle changes with minimal transient corrections.

Let's keep this as simple as possible. That sounds dumb. Both of them. The first one because it's more complicated and heavier. The second one because it's a pain in the ass and MIGHT save an ounce of vacuum line.

Either way, the car is plated, registered, and insured, and will stay that way since i'm not going to trailer it to local events.

I said "Blended Mode" earlier. It where you use both MAP and Alpha-N. This thread isn't about how i should tune my car, it's about the simplest and easiest way to run what little vacuum system i need.

So you basically just want my first sentence of my 2nd paragraph.

No, not really.

I know how the car is being tuned. That's not open for discussion, and wasn't a topic in this thread.


Just so we're clear, i'm more concerned with brakes, which is why i specifically posted a reservoir with a built in check valve earlier.

You are no doing anything crazy here. Run the vacuum reservoir with a check valve, plumb it to both rails. They work and have been around for ever. Problem solved.

I didn't think so, but i just wanted to make sure before i set myself up for failure again. :rofl: This entire build has been one step forward, three steps back for the last 2 years, and i'm pretty burnt out on it.

I appreciate the reinforcement. :)

You have nothing to worry about. Sourcing vacuum for your brake booster and MAP signal from the same junction won't cause any problems.

Here's my common rail IRTB vacuum setup, and what you could do with yours.

FWIW, unless you have insane amounts of lift and duration, running a purely MAP setup will be absolutely fine - I do. Even with crazy cams, it should still run fine.

Here's a nifty small vacuum distribution block from BEGI:
Signal Source Fitting - Two Vacuum Sources BEGi

https://www.miataturbo.net/attachmen...4&d=1351872434

Neat thank you! :)