Suggestions for making an ITB vacuum manifold and idle system?

So this is what I have:

These M3 throttle bodies don't have the classic individual needle valve....what they have instead is individual vacuum ports which in the BMW application connected to a common manifold for each bank of cylinders that then fed together to connect to an electric stepper motor controlled IAC valve. Since the port spacing has changed(as well as dropping from 8 down to 6 throttle bodies) I obviously can no longer use the BMW manifolds, so I am thinking of tapping each of the vacuum ports and running a vacuum line from each one to this:

This used to be a catch-can(I found it in some dusty box in my garage). I chose this because unlike a standard vacuum block this has enough volume to hopefully dampen the erratic vacuum pulse each cylinder will give off. The goal here to end up with a clean vacuum signal for the Megasquirt ECU and for the FPR(my brakes are manual, so I don't need vacuum for that).

This seems like a fairly solid plan to me, but I am open to any ideas to improve it. ITBs tend to be notorious for poor vacuum signals. As far as the idle control....I just plan to use a manual air control valve(I really have no desire to have a stepper motor IAC valve, since the only time those are actually useful is when the weather is cold, I already have several stepper motors Megasquirt will be controlling, I would like to simplify things as much as possible)

Pretty solid plan overall. As for the vacuum signal for tuning, there's a couple strategies you can use if you get an inconsistent signal - either use the MAP sampling strategies or alpha-N, depending on how much vacuum  the motor pulls at idle.

Use MSExtra firmware and go with ITB mode to blend Alpha-N and MAP modes for better tuning across the range.  It uses MAP at low throttle openings and lower speeds and Alpha-N for larger opening and higher speeds.

That said, you've got a great start there for MAP signal.  On my car, I had to put a restrictor in the MAP line to the ECU to get a quiet enough signal.  The trick was getting the right size to not go overboard and lose the actual data you want to capture and react to, so that takes some experimentation.

In reply to Stefan :

I have read that putting a carb jet inline with the hoses from each throttle body will also damp the signal to clean it up...ever hear of that particular trick? I would try a check valve....but cant imagine they would last long constantly fluttering open and shut

In reply to Wicked93gs :

I would think that putting restrictors between TBs and your tank would limit the ability to move enough air for idle control, and maybe make it slow to react since it would have to move enough air through those restrictions to drain/fill the tank to match it to manifold pressure. OTOH, the latter might just be effective smoothing...

Check valve doesn't make any sense to me... You don't want the tank to hold pressure or vacuum relative to the manifold, as that would be hiding info from the MS. Or maybe I'm misunderstanding the proposition.

Do you really need an IAC?

Unless you're running something with a radical cam, you can get by without it.  People with VWs infected by the Bosch idle motor device would remove it, cap the ports, and find that the idle was perfectly acceptable hot and cold.

Worst case. you might need to do your idle speed control with ignition timing instead of airflow.  I know for certain that Megasquirt can do this.

In reply to Knurled. :

I got the impression he wanted to have a valve for idle control, but was going to operate it manually. Last sentence of first post.

Yep, even with the bumpy cam and low compression ratio in my ITB project, it only ever needed a bit of help with idle when it was really cold and then it was just a matter of side-stepping the throttle a bit until I got down the street a little ways.

I did have the Bosch heat sensitive IAC, but I never fully connected it before I switched back to a single TB (prep for added turbo noises, because I lack skills and time to build a proper plenum for the ITBs).

A buddy built a similar car/motor as mine only with an MS2 w/extra code (instead of the MS1nExtra on mine) and ITB mode solved a lot of the annoying little issues I had with mine.  Hopefully once he's done playing with his Lambo he'll get back to that project (he's the one with the Jalpa project here, it's pretty awesome and it also is running ITBs on MegaSquirt).

So yeah, IAC might be nice to add down the road, if you make it truly a DD and need to drive it on really cold days, etc, but for most days it isn't a critical thing compared to getting it up and driving which is where quite a bit of work is involved and reducing the number of variables makes that much, much easier.

I had to go with Alpha-N on my 4AGE 20V (ITB's).  Otherwise, the vacuum signal was:  Idle=vacuum.  Touch pedal and no vacuum.  Kinda hard to tune that way.

I wonder if a IAC from a Caddy 4.5/4.9 would be good.

It is a stepper motor in standard GM practice, but it physically opens the throttle.  It also serves as an idle switch.  Kind of a neat setup, you might be able to use the idle switch portion to engage/disengage idle control with one of the general inputs and 2d maps, since you wouldn't really be able to use the TPS for that purpose.

Now that the coffee is kicking in, this might be the best option anyway, since if you do an alpha-N tune, the variable air bypassing the throttle plates with an air type IAC would make your idle extremely difficult to tune for fuel, if not impossible.  Physically moving the throttle plate instead would neatly sidestep that issue.

Well, to be specific I am running MS3 with the MS3x expansion card. The engine is a 3.7L Ford Cyclone engine with Ti-VCT(meaning 4 cam phasers to control, which I believe are all stepper motors?) I also have the crankshaft position sensor(VR sensor) and 4 camshaft position sensors(all VR sensors) in addition to all the standard inputs such as MAT, CLT, MAP and outputs for 6 individual coil packs(and injectors of course)...so its going to be a real mess trying to control the engine...much more to worry about than with most of the Megasquirt installations I have done so far. To be honest I never actually bothered with IAC anyway...as Stefan said, the only time it really makes a difference is on cold days...and that can be handled simply manually modulating the pedal for the first few minutes, which I don't mind doing. In the past I just adjusted the throttle stop and that was that...but I can't use that method with 6 throttle bodies...hence just an airflow speed control valve to intentionally cause a controlled vacuum leak instead. Obviously when BMW used these throttle bodies on the BMW they were able to get a good MAP signal from the manifold off of just one bank of cylinders....as evidenced by the MAP sensor installed on one of the BMW vacuum manifolds I have...and I have heard of people being able to tune ITBs with Megasquirt based purely off of speed density which also implies a clean useable vacuum signal....even if that signal is only in the range of 50-100KPA, you just use the reduced range to increase resolution via the VE map.

I am one of the guys who ran ITBs with speed density.  Also had a fairly radical "cam".

I was playing around with one of my old datalogs and was looking at scatter plots, something I never played with.

I tried for a year or two to run SD on ITB's, despite everyone saying you can't.  I was stubborn.

Light cruise on the highway - 94kPa.  WOT - 96kPa.  Hard to tune.

When I finally went Alpha-N, the car had never run better.  It was hands-down the best way to tune it.

This year I've also finally disconnected the MAP sensor entirely and will use it for constant baro correction.

In reply to SkinnyG :

Out of curiosity, how long were the runners between the throttle plate and the valves?

I bet runner volume between the valve and the throttle plate has a lot to do with it too.  Of course the smaller that volume, the more benefits you gain with respect to throttle response...

SkinnyG is also talking about a 4AGE20v.  It's short.  Real short.  Maybe 3" from the plate to the first of the 3 valves?

Also note that Toyota did not use a MAP on that motor.  They did on the blacktop version, but I don't know how it is used in mapping.  There are may ways to use it, including for idle/low throttle position, then go Alpha-N on it after the motor is breathing, for instance.

Here is the tank...went ahead and tapped it for the 1/8 NPT fittings...but since I only had straight, still waiting on the 90s to really plumb it. I staggered the holes because I wanted to distribute the vacuum pulses a little more evenly than a straight line...and since I plan on using plug wire separators to organize the nylon lines coming in it will look better than them all being in-line.

P.S. I have no idea who would powdercoat aluminum but thats how this catch can came out of the box...powdercoated blue...going to strip all that ugliness away later with a wire wheel.

Dr. Hess said:

Also note that Toyota did not use a MAP on that motor.  They did on the blacktop version, but I don't know how it is used in mapping.  There are may ways to use it, including for idle/low throttle position, then go Alpha-N on it after the motor is breathing, for instance.

That's the ITB mode or Blended Mode that blends SD and Alpha-N together.  It seems to solve many of the drivability issues with ITBs.

Alpha N and itb mode only for itbs. Lots of people seem to want to run on speed density and its only harder to tune or impossible depeding on throttle size. 

Paul_VR6 said:

Alpha N and itb mode only for itbs. Lots of people seem to want to run on speed density and its only harder to tune or impossible depeding on throttle size. 

Running SD on ITB equipped cars is likely mostly about inexperience and that most of the online documentation is based around SD since MegaSquirt was mostly used to replace older fuel injection solutions that used a single TB or TBI.

Dr. Hess said:

SkinnyG is also talking about a 4AGE20v.  It's short.  Real short.  Maybe 3" from the plate to the first of the 3 valves?

I have a 16V blue top.  The throttle is pretty far away from the valve, as that is what I did back when I did this. 10+ years ago?

As for being unable to tune ITB's with SD being an issue of inexperience, I'm all ears.  But nobody (and I mean zero people) have offered "the fix" on any forum I've been on yet. The car has a totally stable idle map signal at 42kPa. Stock cam, even.

In reply to SkinnyG :

Hard to see exactly what is going on there...where do you have the vacuum lines attaching? Just to a single runner?

Skinny there is no fix. 42kpa idle but probably 99kpa at 5% throttle at 2500rpm. Makes things tricky. 

In reply to SkinnyG :

The fix is to go ITB mode on MS2 and above with the Extra code or pure Alpha-N.

Having a stable idle vacuum signal is not impossible to do on ITB installs.  It's what happens when that throttle is cracked where the problem lies.

First, addressing the topic at hand, I am not running any Idle Air circuitry.  I do have a bin at about 600rpm that bumps the timing quite a bit so it will idle somewhat when cold.  I've driven it for over 10 years without any idle control, and it's fine enough that I never bothered.  But it's not a winter car or a wet weather car (it's a Locost Super 7).

All the runners T together and fed the MAP. I did not run them into a can or a fuel filter or anything because I always had a very good MAP signal.

I've never run ITB mode which I'm going to assume is a combination between SD and Alpha-N.  I've found SD difficult to tune, but AN is awesome.  For my car, I have not felt any need to try and run blended tables or some sort of mix.  Alpha-N was so amazingly better, I am running Alpha-N.  I have had people on other forums tell me that you totally CAN run just Speed-Density on ITBs, and they poo-poo me for running Alpha-N. Alpha-N worked. Speed Density didn't. Blended tables should work fine, but not worth it for me.

Was running MS2, but switched to MS1 Extra so I could use the MS2 and IAC on my '77 Silverado (but it kicked my ass instead).

Back on topic - since I am no longer using a MAP sensor, I've debated using the now unused ports for some sort of Idle Air Controller, I have haven't worked out the details of exactly how I want to do that.