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Discussion Starter · #1 · (Edited)
hi Everyone,

I have a question about Individual Throttle Bodies and Map sensors.

As many people have noted in this forum from time to time, ITBs and MAP don’t work well together, however while searching around this evening I noticed the following (quite old) thread

http://www.alfabb.com/bb/forums/engine-management/25478-success-megasquirt-n-edis-2-0l-alfa-gtv.html

I notice that Kito mentioned the following in the first post,

. Our experience with throttle bodies is that they sometimes have an erratic vacuum signal. We solved this by using the buffer to ensure proper vacuum signals to the MegaSquirt ECU.

Does anyone know what the 'Buffer' is, how it works, where to get one or how to build it?

Thanks in advance
Sam
 

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There's something defective with the link above (or at least it doesn't work for me)

That being said, I'd hazard that the buffer they speak of is a restriction built into the sensor connection nipple of the vacuum chamber.

Premis is all TB's go to a singular chamber of a few cu/in volume, then the nipple on that that the MAP sensor would go to has its orafice restricted down to something (usually) near the .03"~.06" range.

Net result is the chamber creates less pulsing due to all cylinders pulling into a volume instead of one just thumping the air in and out of a hose, and the orafice restriction further slows the back~and~forth motion of what pulsing air there is in the chamber, which in turn helps stabilize to sensor output

With such a configuration an ITB setup (while having inherantly low vacuum compared to STB) can produce a reasonably steady vacuum signal through a 1 bar sensor that doesn't fluctuate by more than roughly .5~.7 psi at idle.
Its not rock steady, but its way more betterer than what you'd get tapping one or more cylinders in an unrestricted fashion.
 

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This is what I used for a vacuum hub on my ITB setup. It has about a 3/8" x 4" long chamber that picks up the vacuum lines from each ITB, fuel pressure regulator, vacuum line to the power brake booster and one line that runs back to the map sensor in the ecu.
 

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Discussion Starter · #4 · (Edited)
Hi Murray & Darren

thanks for your help with this, your feedback has led me to do some further research and thinking, but I still have a couple more questions …

With the chamber, does it mean you can control the MS on Map alone, or do you still need the TPS?

Also, is there a particular rule of thumb when making the chamber or a particular size?
i.e. the bigger the better, or the size has a relationship to something ??

I'm thinking of using 18mm x 100mm (3/4” x 4”) Copper pipe with 4 nipples brazed on for the TB and another for the MAP.

Unless I’ve misunderstood something – I think I can use the chamber for a number of reasons.

1) To get a stable(ish) vacuum for the MAP
2) I ‘m thinking of using a stepper motor Idle valve to contol idel. The opening is approx. 3/4”” (18mm) so I can just mate it up to an open end if the 3/4" copper pipe and block off the other end.

Do you think this makes sense? Would it work?

Thanks advance

Sam
 

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Yes, your idea about the copper pipe will work. Dimensionally sound too.
In fact its what I used initially when I converted to ITB's.

Restricting the orafice that leads to the MAP sensor would still be in order though as anything you can do to reduce pulsing will give a better/more stable signal via the MAP sensor for the ECU to work with.

Dunno about the stepper motor bit as that is something my system isn't capable of operating, so never got into the nuances of it. (my idle is controlled the old fasioned way: mechanical stops and a preset mixture)

You're still going to need a TPS in there, but it'll be relegated more toward literally that (internal ECU mapping fidgeting the mixture due to position and WOT enrichment, idle position mixture change and mabe even fuel cut if throttle is closed above X rpm in some systems) while the actual bulk of mapping mixture would be based on RPM combined with MAP in many aftermarket systems.
 

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a small fuel filter works very well for this.
I did the cut out in line with the butterfly axle and bring the 2 sets together in a Y and that seemed to work OK I did not even add a buffer. But I did use a very thin hose which also will act like a buffer.
 

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I kinda copy-ed this but just took the 2 ports into a Y and the tube to my ecu is very tiny. but the hose feeding the Y is big so this is like a tiny plenum and balance out the cylinders and makes for a better idle

Bottom is mine. You can see the troff I milled in line with the axle.
And I tapped the one hole for the roll pin and put in a set screw, to keep it air tight. I had drilled the 2 holes for roll pins long ago to keep everything lined up lined up.
 

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Discussion Starter · #8 ·
HI Slyalfa

Sorry for the late response, I just noticed your post

Unfortunately I still haven’t got around to this part of the build yet as I've struck a problem that’s holding me up.

I’m currently trying to get an EDIS ignition setup working, (can’t get the tacho signal to work)

I plan to get the ignition up and running completely off the Megasquirt before I rip the carbs out and replace them with the fuel injection at whihch time the MS will then control the lot - your advice should come in handy then.

Sam
 

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Just building this MAP chamber myself. I used a 12" length of aluminum pipe. ID is 0.75". I have drilled and tapped 4 ports so far. I put them directly below the ITB ports. I could almost mount them solidly, but I just eye-balled the position. The hoses have a slight bend. These are fuel hoses in #1 and #4 just to position it. I will use better hose later.

1st question is, is this chamber too big? I like it, but I'm not married to it's actual size. I could cut it in half and drill holes closer together. What's nice is I should be able to mount it using the Spica fuel line clamp studs. Is would be a nicely mounted and hidden setup.

2nd question. If I did not mount it, could I let it hang by the hoses? I'm guessing that is a bad idea but looks plausible.

3rd question. I'm still wondering how to plug up each end of the pipe. I have an aluminum rod that slides in. It appears in the picture just below the pile in the last the last one. I was thinking of taking two slices of this rod and welding them into the end of the pipe. But is welding really necessary? Could I just glue or epoxy them in? Would the glue crack and then leak? Would a big rubber cap on each end be enough to hold the vacuum?

This is a Twin Spark manifold with Spica throttle bodies for anyone that doesn't recognize it, btw.

Thanks,
 

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Discussion Starter · #10 ·
My vacuum chamber is just a piece of copper plumbing pipe 3/4 inch diameter and about 9 or 10 inches long.
I silver soldered 6 barbs onto it.
4 for each throttle body, another for the fuel pressure vacuum and another for the Map sensor.
With the maps sensor, I shoved a 0.8 (or was it 0.6?) Mig welding tip in to it smooth out the signal.
I initially started with MSII v2.86 of the code running on SD which worked quite well all things considered, but the Fuel table resolution was too small to tune it properly. i.e. idling at 70kpa only left a couple of rows to tune it in.
I migrated over to MS extra, but I’m having some issues and I’m asking a friend for his map to see where I’m going wrong.
As a backup, I’ve been thinking of going back to 2.86 and hooking up a SyncMap, but that’s a last resort.


As far as your questions

1st question is, is this chamber too big? I like it, but I'm not married to it's actual size. I could cut it in half and drill holes closer together. What's nice is I should be able to mount it using the Spica fuel line clamp studs. Is would be a nicely mounted and hidden setup.
I don’t thinks it’s too big, up to you if you want to make it smaller, but I think 10 inches or so isn’t too bad.

2nd question. If I did not mount it, could I let it hang by the hoses? I'm guessing that is a bad idea but looks plausible.
Dunno, I guess the hoses would eventually give way? Besides it would be flapping and banging around on things wouldn’t it?

3rd question. I'm still wondering how to plug up each end of the pipe. I have an aluminum rod that slides in. It appears in the picture just below the pile in the last the last one. I was thinking of taking two slices of this rod and welding them into the end of the pipe. But is welding really necessary? Could I just glue or epoxy them in? Would the glue crack and then leak? Would a big rubber cap on each end be enough to hold the vacuum?
It’s up to you; I think all of the above would work, as long as its airtight. If welding is a problem then I would just use JB weld or something similar.
JB takes reasonable heat before it softens, otherwise make sure you use epoxy glue that handles under hood heat
I have my IAC valve on one end. The opening goes straight into the IAC so that solved that and the other was just a copper pipe end-stop from the hardware store that I brazed on.
 

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I don't think size matters here. :smartass: Figure how many ports you need and add one for a spare.
 

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Thanks for the responses. I'll keep the size as is and proceed. This should be easily removable, so adding an extra one would be simple. I am using a bunch of spare Spica nipples. I drill and tap the aluminum tube and screw them in. It is very easy.

Incidentally, the idle ports are on the top and go to the existing Spica block. I have kept the idle separate from the MAP ports. The Spica idle block has an internal volume of about 2cc max. Also, I can't get my mind around the concept of idle air flowing through an area that is supposed to be a measurable vacuum. It may work, but I just can't understand it.

The Spica block will flow idle air and the oil vapor separator idle port as is does with the original setup. This vacuum log will be connected to the MAP and the fuel pressure regulator. Brake vacuum is already plumbed on the side as the Spica intended. The idea here is to look stock. The Spica air box will mount on this setup as well, so the idle hose crosses over the top as it does stock. Putting the MAP vacuum chamber with fuel pressure regulator ports under and out of view is desirable in my case.

Thanks,
 

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Another question - I heard a couple years back, and I don't remember where, someone said to keep the hose to the MAP to less than 18" (~45cm). Anyone know if that is true and why? Anyone have a longer hose and see problems/no problems?

Anyone want to try replacing their short hose with a long one (20") and report back if anything changed?
 

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Another question - I heard a couple years back, and I don't remember where, someone said to keep the hose to the MAP to less than 18" (~45cm). Anyone know if that is true and why? Anyone have a longer hose and see problems/no problems?

Anyone want to try replacing their short hose with a long one (20") and report back if anything changed?
My MAP line is close to 6' if not over (from engine to behind passenger seat).
 

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Thanks Murray. That's good to know. No problems I assume?

For anyone using Spica throttle bodies and needing to place the vacuum chamber somewhere out of the way, I have completed the mounting. Take a look at the pictures. The hole for the Spica hard line clamps is M6x1.00mm. I got a 2" bolt and a nut. Using 1" pipe clamps I slid the bolt through the pipe clamps, threaded the nut on and screwed it into the Spica clamp hole. All tightened up is it snug. The silicone hose is short to the ports and has just a slight curve to it. It worked out very nicely.
 

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One last questions on those that used a mig tip as your orifice restrictor. Did you just shove it up the hose? Or did you use it as a nipple?

I visited my local tool shop and found them (in packs of 10 !!). They have threads on one end to attach to the welding machine, I guess. I could certainly tap my aluminum tube with the correct thread and screw this in as a nipple.
 

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One last questions on those that used a mig tip as your orifice restrictor. Did you just shove it up the hose? Or did you use it as a nipple?

I visited my local tool shop and found them (in packs of 10 !!). They have threads on one end to attach to the welding machine, I guess. I could certainly tap my aluminum tube with the correct thread and screw this in as a nipple.
I used them as my nipples on my vacuum manifold.
 

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Hello all. Bringing up this old post because I am still wondering something. I posed this question on post 12 of this thread and I still want to get people's thoughts on it.

I'm using Spica Throttle Bodies on my EFI engine. From pictures, both Murray and slyalfa are using them too. You guys don't seem to be using the idle ports or at least the Spica idle block in your setup. My question is about the Spica idle block suppling adequate vacuum to use on both the MAP signal and fuel pressure regualator vaccum.

I'm including a picture of the Spica idle block. It has 4 idle ports from the intake tracts feeding it. It has a volumn of about 2cc. It also has a pretty big hose going to the air box to supply fresh clean air to feed the idle ports. It also has room for more ports.

So. If air is passing from the intake to the idle ports through this block, is that a real vacuum as would be needed for the MAP signal and/or the fuel pressure regulator? My thinking is that this is not a true vacuum situation, but an air flow situation which would not provide the vacuum expected for MAP and fuel pressure regualator. Put asside the MAP oriface restriction needed for a minute.

Can anyone help me think through this process or tell me that I'm thinking correctly?
 

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I used TWIM throttle bodies not the Spica throttle bodies.

My vacuum is directly off each of the throttle bodies to a manifold that has a line to the ECU. See the black vacuum lines from the throttle bodies to the block of aluminum.

The chamber in the block of aluminum (that the black lines go to) is small, maybe 3/8" bore. There is also a vacuum line going to the fuel pressure regulator and the brake booster (with a check valve).

I would say the way you were talking about hooking the vacuum line to was not going to get you a vacuum reading the ECU can go off of.
 

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