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Old 04-19-2013, 01:14 PM
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Vacuum/boost gauge on roots

Is there a vacuum circuit you can make with a one way valve and Tee, to get accurate vacuum readings along with boost? I want to get rid of the separate gauges.

I did a search, did not find much. If you could mix the manifold signal from the carb base, and the boost port from the blower housing, it could work.

The impeller turning scatters the vacuum signal.

How do you roots blown guys run a single vac/boost gauge?
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Old 04-19-2013, 01:41 PM
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Single vac/boost guage is tapped into the intake. There is vacuum until the engine is under load and then it creates boost. Good thing to have a vac guage above the blower too, just under the carbs for tuning.
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Old 04-19-2013, 01:57 PM
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So, drill into the baseplate and tap a port. Why is the blower housing port not the same as the baseplate runner?

Will the baseplate signal reads both boost and vacuum without impeller interference?
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Old 04-19-2013, 02:24 PM
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You can get rid of the manifold vacuum gauge fluctuation by dampening/restricting the hose with a restrictor orrifice.
Most dedicated manifold vacuum gauges already have this. If yours is not damped you will have to experiment with the orrifce size.

You do not try to mix the above blower and below blower vacuum signals. Give you head a shake.
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Old 04-19-2013, 02:30 PM
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I have a vacuum port in the carb adapter on top of the blower. I hook a vacuum guage to this for tuning. I have the intake (below the blower) tapped (2 of them). This is where the boost/vacuum guage is hooked. Also have the carbs referenced here, hooked to MSD 6BTM, and water/meth control - all in the intake.

I am not sure what you are refering to for "baseplate", "blower housing port" and "baseplate runner" so we are talking about the same thing.
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Old 04-19-2013, 03:10 PM
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The baseplate in this context is referring to the intake or what the blower housing bolts too. That earns the head shake, you wanted to give me.

I was asking if anybody had a vacuum circuit. Try? I was asking if.

My question was how do I run a single gauge that displays vacuum and boost accurately. Do I need to explain that further?

Lets start here...

Are you aware of interference in the vacuum signal caused by the impellers?
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Old 04-19-2013, 03:23 PM
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[QUOTE=F-BIRD'88;1668280]You can get rid of the manifold vacuum gauge fluctuation by dampening/restricting the hose with a restrictor orrifice.
Most dedicated manifold vacuum gauges already have this. If yours is not damped you will have to experiment with the orrifce size.
QUOTE]

The problem is that one gauge in the cabin reads 12" vac cruising around. The cabin other reads correctly at 19-20. That one comes from the carb base.

It is not fluctuating up and down per say . Is this advice still for that?





In the rear you can see the boost signal port in side of the housing.
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Old 04-19-2013, 03:47 PM
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Ahhh, pictures sure help. I thought you had a 6-71 or 8-71. To run one boost/vacuum guage, I would plum it below the rotors - in the intake plenum. You will probably read more boost under the carb as the rotors are pulling air in at that point.
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Old 04-20-2013, 03:47 PM
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Willys I think you mean vacuum under the carb.

As for pulsing....you can be assured your "pulse rate" will take a jump as boost goes over 5 psi. haha You may have a "heart attack" if it goes over 8psi and motor starts detonating.

Just plug a vac/boost gage in the manifold under the blower. I don't worry too much about carb vacuum as the PV is boost referenced anyway. You will always have vac under the carb. If you have the small air cleaners in the scoop like many of us use the boost may not be as high as it could be and the carb vac can go up due to the restriction. I keep mine really clean and very very lightly oiled so I don't see the problem just cruising.
If I was to race the car I would take them out.

I also take the vac advance out of the manifold. However be aware that excess boost can pop the vac adv diaghram. I've done it twice. It would be nice to have a 2 way check valve in this line but the only one I've run across is too big and ugly. I have one for the vac modulator on the trans but took it off as I found I didn't need it.
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Old 04-20-2013, 06:24 PM
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Bentwings: Oops yes, thanks for catching that.
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Old 04-29-2013, 05:45 PM
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Nobody knows how to make a vacuum / boost, all in one, gauge function in my situation?

The reason Im asking is because there will be pillar pods, like on my acura, available for my truck soon. The 2 gauge pod is what im thinking, but I will need to consolidate my vacuum and boost gauge into one.

This is how I want my trucks gauges to be.



This is how they are now.

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