Balance tube Fibremotive

[chris]

If I ever get the guts to install these Fibremotive heads, I was wondering about using a balance tube. Both heads have a plugged hole that I ASSume would be good for a balance tube but figured I'd ask people who are smarter than me! Could I use this port as a balance tube between both heads in the same fashion as the stock setup? Obviously the previous owner had them plugged but I thought it'd be a good idea to utilize them. What do you all think?

[Torskdoc423]

Don't see why not, then you can block off the carbs ports. The only down side I see is one hell of a vacuum leak if the hoses start leaking. It definately won't idle then.

[66vairguy]

I'm guessing those threaded ports will accept a threaded barbed hose fitting.

[cnicol]

In addition to L/R vacuum balance (not sure what that really does for us), it provides a more stable vacuum for PCV system, if that's part of your build.

[chris]

Thanks guys. If I end up using them, I want to maintain as much street manners as possible!

[sweet66monza]

Thinking back on my dad's fibremotive setup, I had no balance tube and also no pcv. One head fitting went to the vacuum advance and the other went to the dash vacuum gauge. The crankcase breather was vented into one of the air cleaner bases, but no vacuum connection.

Knowing what I now know, when (if) it goes back together, I will probably make a balance tube and a real pcv setup. That motor was a strong runner and a lot of fun

[chris]

Thinking back on my dad's fibremotive setup, I had no balance tube and also no pcv. One head fitting went to the vacuum advance and the other went to the dash vacuum gauge. The crankcase breather was vented into one of the air cleaner bases, but no vacuum connection.

Knowing what I now know, when (if) it goes back together, I will probably make a balance tube and a real pcv setup. That motor was a strong runner and a lot of fun

Good move. I’ll do it if you do it .

[turbodan70]

they are junk , do not use them !! plenium are way too big

[Richard]

If I recall, there was discussion about the size of the balance tube on this 380 HP engine. My search didn't reveal what I was looking for, but i recall the builder saying he had started with a smaller tube with less favorable results.


I've read several reports that had the same thing to say about large plenum sizes.

"While a larger plenum can help improve top-end performance, a plenum that's too large can negatively affect low-end torque and throttle response."

[vairchet]

Had a pair of FibreMotive manifolds long ago. No one wanted them unless welded on 140hp heads. Since I had no use for them, off into the scrap pile they went.

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[chris]

Richard, thanks for the info on using a larger balance tube. I'm under no illusion that low RPM manners will be outstanding, as that's just the way it works with larger plenums and lazier airflow at that engine speed.

However, I am willing to try it since my car isn't my daily driver and I can do these things, and I have a couple things planned to test my theories on the lower RPM abilities. TurboDan, care to elaborate on your statement?

[Phil Dally]

I have first hand experience with larger volumes of fuel-air mixture and high RPM's.

The first Landspeed event that we had the plenum in my racecar we gained 10+ MPH.

In the Landspeed world that is a huge increase in speed from 167 (0.40" over) cubes.

We did have to keep revving it on the line but that may've been the B7HS NGK plugs.

[Phil Dally]

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