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Ideas for vacuum log on triple manifold


madkaw

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Getting ready to mount my Mikuni triples with the shorty manifold. My manifold is tapped on each runner and I want to take advantage of that and create a log for a vacuum signal. I would like to make something that would double as a booster signal and an MAP signal. I have read that it needs to be removable in order to properly sync triple carbs. I'm not even sure where to start on this project and I am not having much luck searching this. Anyone done this and can I steal some ideas.

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Might be neat to get tricky and install a small shutoff on each runner outlet so you can disable some or all.

From that valve to a T with a small vacuum gauge on each runner.

And a small check valve so each runner is sucking independently and not bothering the others.

Then T-into a larger tube and go to one of those Vacuum chambers and onto the booster or wherever else.

Entirely overkill but might be fun.

 

I use one of those big vacuum reservoirs on my Triple DCOE setup but it only picks off the #6 runner and seems to work fine.

 

post-1894-034335700 1308513883_thumb.jpg

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i know a guy who has itbs on his l28. his vacuum log is cool, it goes to a vacuum canister for his brake booster as well as a map sensor connection for megasquirt. ill take a pic of it if we have a meeting on thursday.

marcus

Edited by akeboshi
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How about using a -6 fuel rail extrusion like this from Ross Machine. Thread fittings into the rail for each runner along it's length then thread one end for TPS and the other for the brake booster. I have a spare length of the stuff for sale if you decide to go this route.

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Thanks for the tip Rossman, but not sure how to connect that to each individual runner. I just read your build thread and I know this is log is a simple project for you, but I'm not quite as savvy when it comes to this machine stuff.

By the way, love your build and would like to go your same route some day, but for now -baby steps!

Also love the avatar. I was showing my 14 year old son you tube videos of Ultraman the other day and he was cracking up.

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Something similar to this but using the fuel rail instead of the fancy machined block they are using. Each fitting on the vacuum log has a line going to a fitting on each manifold port.

 

This is exactly what did - basically drill and tap the rail at points that line up with the ports on your manifold and fit vacuum line sized hose barb fittings to each. Here's a pic - it's the silver rail that's attached to the valve cover (note that I picked up the brake booster signal from a separate rail that is integrated into the plenum, but you could take it from the end if this rail if you like):

 

12inj-7.jpg

Edited by TimZ
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Tim that looks fantastic, do you have any more photos to share?

 

The silver log rail which bolts onto the valve cover has a sensor on the far left at the end, is that an Intake Air Temperature Sensor?

 

So what do you do when you need to caliberate the ITBS? Is it a case of plugging up the take offs on the intake manifold?

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Tim that looks fantastic, do you have any more photos to share?

 

The silver log rail which bolts onto the valve cover has a sensor on the far left at the end, is that an Intake Air Temperature Sensor?

 

So what do you do when you need to caliberate the ITBS? Is it a case of plugging up the take offs on the intake manifold?

 

The sensor is my MAP sensor - I'm using an exhaust backpressure (EBP) sensor from a duramax diesel - the pressure range is ~18in of vacuum to ~38psi boost, so it gives a much better fit to my engine and acts like a 4 bar, but with resolution more like a 3 bar.

 

The feed lines are small enough that they don't appreciably effect the readings when I balance the ITBs. This was another reason to run things like the brake booster from a different source. BTW, don't expect much vacuum at idle if you are running ITBs with any kind of aggressive cam- I see ~5in of vacuum at idle :blink: . I ended up running an electric vacuum pump from a VW diesel for the brake booster and accessories.

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ITB's are NOT like Carburettors!

 

At 'idle' they are CLOSED. "Idle Synch" is done through the vacuum log and a bypass line, or individual throttle plate bypasses (depending on who makes the ITB.) Ask anybody who has tried to synch an idle setup on ITB's how easy it is to get an idle speed below 1000 (or even 1200) using the 'idle stop screws'! It's best set closed if at all possible. Generally the injectors go downstream of the throttle plates anyway. In cases where they dont, then you can crack them incrementally, or in most pro setups they drill a very VERY small hole in the throttle plate.

 

Off-Idle synch is more important to see that they all reach WOT at the same time, and that is linkage length.

 

In between there is very little to do, if they all close at the same time, and all go WOT at the same time, they are for all intents 'balanced'...

 

The flow in that situation should not vary measurably between barrels in a body, or body to body. If it does it's mechanical wear in the cylinder causing it and must be remedied.

Edited by Tony D
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  • 5 months later...

I just shipped my Mikuni Manifold off and was reminded that I had barbs with a FULL 1/4" inside diameter hole in them (and used 5/15" fuel line), which fit on the stock Mikuni 1/8 NPT tapped holes in the manifold. It went to a -6 runner, but it will now be a -8 to better modulate pulsation for installation of the MAP sensor.

Edited by Tony D
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So are we saying here that the bigger the better-within reason. Looks like the mikuni manifold is as you say tapped for 1/8 pipe all the way across and one 1/4 pipe. I looked at pipe sizes and there isn't much difference as far as ID with these two sizes. The LOG I am using(basically a fuel rail) is set up for 1/4 pipe on the ends-or basically 1/2" ID.

 

Also-any general rules as far as keeping the vacuum log as short or as long as possible???. Looks like about 20" log would work for me , but someone had commented to keep the vacuum ports on the log close together.

 

One last thing-to make things easier to mount the log, I would be mounting the log a good 6 to 8 inches from the manifold, so the individual hoses will be longer then most set-ups I've seen---any problems with this???

Edited by madkaw
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Megajolt being in my future plan, I'm looking at what could be done also for MAP sensor.

Have you check out the following link? A member of the board tried different solutions, quite interesting reading.

 

plenum and vaccum hose design for individual runners

 

Sorry for the tangent, but I have Megajolt and will be finishing the install soon. Since the Cannon manifold has a built-in balance tube, I should be able to get away with using one of the already tapped ports to run a line to a vacuum canister and then to the MAP sensor. If your manifold has a balance tube already, it shouldn't be necessary to add a vacuum log.

 

For those without a balance tube, the solutions in this thread are solid. Just tap all runners and tie them into a log. If the log gives a poor signal, then implement a vacuum chamber.

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No problem on the 'tangent'; trying to find any info on this issue is a challenge.

The biggest issue for right now is placement of the log. Not a lot of room when your using the shorty Mikuni manifold. I would love to set it right on top of the manifold, but it would be a bit of a challenge for the fact that the hose lenghts would have to be micro short to keep the log away fron the throttle linkages. Not sure if i like TimZ 's idea of strapping to the side of the valve cover. I am thinking of securing the log to the CAI backing plate, but that would require longer vacuum lines(maybe too long), don't know if that would be a problem.

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No problem on the 'tangent'; trying to find any info on this issue is a challenge.

The biggest issue for right now is placement of the log. Not a lot of room when your using the shorty Mikuni manifold. I would love to set it right on top of the manifold, but it would be a bit of a challenge for the fact that the hose lenghts would have to be micro short to keep the log away fron the throttle linkages. Not sure if i like TimZ 's idea of strapping to the side of the valve cover. I am thinking of securing the log to the CAI backing plate, but that would require longer vacuum lines(maybe too long), don't know if that would be a problem.

 

It's not a problem, especially if the lines are small. Place the log where you see fit, as long as it's in the proximity of the intake, you'll be fine.

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