Distributor Vac. Brake Line

KGS

KGS

Well-known member
Does anyone know the correct size of the Vacuum Brake line
that runs from the manifold to the distributor?
The closest I can come to it is 3/16 which NAPA has, but the ID
seems too small. Or does that matter. Ken
 
The one I have measures 3/16" (.187") od and 9/64" (.145") id. 3/16 brake tubing will work. It's only 1/64" smaller on the id. All the brake tubing I have is 1/8" id. You only need a vacuum signal for the distributor so 1/8" id is more than adequate.
 
3/16" is corect size. Accualy on vacume lines smaller is better.ken ct. I have the correct fittings if you need them.
 
Thanks for the replies. It looks like the suppy at NAPA
will do the job.
KenCT, Thanks but I have the fittings. I just need a longer
line to accomodate the vac. position on a blower manifold
I'm working on. Ken
 
If what you have is flare fittings ,they will not work correct fittings have a sharp taper to the inboard end and is squeezed onto the tubing when tightened up. More of a compression fitting w/o the ferrel. ken ct.
 
KGS said:
Thanks for the replies. It looks like the suppy at NAPA
will do the job.
KenCT, Thanks but I have the fittings. I just need a longer
line to accomodate the vac. position on a blower manifold
I'm working on. Ken
Click to expand...


I like that idea , a vacuum line on a blown engine to the distributor brake. Vac = no retard and boost would push the piston in applying some retard to the advance ....:eek::)
 
Hey Jim, Thanks for the post. Now, I'm easily confused so I have to ask.
Are you implying that it really is a good idea or no.
The blower is a 39M McCulloch and it does have the vac. port provided as
an original manifold to supply vacuum to the distributor (Helmet type). It
will be used on an otherwise stock '39 221" motor just as McCulloch did back
in the day. Ken
 
I'm actually running one of your Crabs also Jim and I have a McCulloch supercharger on my engine (I told you about it when I ordered the crab.)

It didn't run so hot when I put it on , so I backed the vacuum brake nut off a LOT and it runs way better.

I'm pulling the vacuum line off the front vacuum port on a stock 1936 aluminum intake. I tested it with thumb power revving the engine and there is vacuum all the time at that point, decreasing as the rpms rise, but never blowing my thumb off the port. always sucking.

Anything I'm doing wrong?

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Have you ever tried running the vac off the bottom of the carb. That's where we're using it on an Eaton blower. Unfortunately we don't have it running yet.
 
The manifold air pressure above the blower and below the blower are bound to be different even if the blower doesn't put out much pressure. The vacuum brake is designed to work on a more normal manifold pressure and I think the closest thing to that would be between the carb throttle plates and the blower inlet but I don't know how it would compare to an unblown engine's M.A.P. There is low pressure due to engine draw and compressor draw too. I don't know what the compressor inlet pressure variation would compare to unless a person compared MAP gauge readings between a blown engine and an unblown engine to check it out.

The other option would be to go with mechanical advance only. It won't be as good on the gas but it will work to keep the timing somewhere near a decent specification.
 
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Vacume from the rear port of a later 94 carb is much less than manifold vac. Look at the size of the hole in the left side ventury its about the size of a smaller paper clip. ken ct.
 
Ron and Rotorwrench make a good point. That's probably what Bubba was pointing out. I've got a vacuum plate that should work. KenCt. thanks for the info on the flared fittings. That is what I have. Ken
 
Flare fittings will not work in the vacume port holes in the intake or rear of carb.These are unique fittings on ford carbs and intake. ken ct.
 
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