47-55.1 power brake vacuum - The 1947 - Present Chevrolet & GMC Truck Message Board Network

nvrdone · 07-31-2021, 05:43 PM

ok, im working on my power brake up grade. wondering which port has the highest vacuum to hook the booster to - at the carb base or at the intake manifold runners?
engine is a basic 327 / 350 hp.
thanks for the help.

1project2many · 07-31-2021, 07:46 PM

The vacuum will be the same at either port. GM has used both locations over the years.

SFFD103 · 07-31-2021, 09:20 PM

Do you already have a new power booster purchased? Frame mount?

MiraclePieCo · 07-31-2021, 09:42 PM

Quote:

Originally Posted by 1project2many

The vacuum will be the same at either port. GM has used both locations over the years.

That ^^^

nvrdone · 07-31-2021, 10:22 PM

Ive got the frame mount booster & m/c installed. seems to work ok. Just wondering if I got the vacuum line hooked up to the proper port. there were no instructions with the kit

**mr48chev** · 08-02-2021, 12:07 PM

If the carb has a port on the back center to take the vacuum off for the booster that is where I would hook it up but some don't and off the 6/8 runner works equally well as far as vacuum to the booster goes.

dsraven · 08-03-2021, 12:07 AM

you can also plumb in a vacuum reservoir with appropriate check valves so you have that added safety for the power brakes. remember back in the 70's where some manufacturers had those "tomato cans" plumbed in under the hood? well, something like that but with the appropriate sized inlet/outlet. look for a donor car with a/c or even a donor car with a/c and vac operated heater valves (like an astro van with rear where they used a plastic sphere vacuum storage cannister)
like said above by others, plumb into the base of the carb if available because it is less "pulsed" than a port runner would be. it will see all the cylinder pulses instead of just a couple like a port runner would see. some manifolds have a split plenum as well that affects the carb base vacuum.
either way, use a good quality vac hose and clamps along with a tested check valve at the booster and possibly an inline filter you can find under the hood of a newer donor. steel/hard line will give better results on a long run than rubber line will but use some rubber in the area near the engine to allow for engine movement. hard line also looks cooler and more professional in my opinion. thats just my opinion though and it is YOUR truck.

07-31-2021, 05:43 PM	#1
nvrdone Registered User Join Date: Dec 2011 Location: Moxee WA Posts: 1,482	power brake vacuum ok, im working on my power brake up grade. wondering which port has the highest vacuum to hook the booster to - at the carb base or at the intake manifold runners? engine is a basic 327 / 350 hp. thanks for the help. __________________ 49 chevy 3100 3 window. 327 / m21 4 spd, 12 bolt w/ 3:55's Bought in 1973 for $235.00. Had it longer than my wife & Kids!!

07-31-2021, 07:46 PM	#2
1project2many Registered User Join Date: Mar 2012 Location: Lakes Region NH Posts: 3,200	Re: power brake vacuum The vacuum will be the same at either port. GM has used both locations over the years.

07-31-2021, 09:20 PM	#3
SFFD103 Registered User Join Date: Nov 2017 Location: Bay Area, CA Posts: 29	Re: power brake vacuum Do you already have a new power booster purchased? Frame mount?

07-31-2021, 10:22 PM	#5
nvrdone Registered User Join Date: Dec 2011 Location: Moxee WA Posts: 1,482	Re: power brake vacuum Ive got the frame mount booster & m/c installed. seems to work ok. Just wondering if I got the vacuum line hooked up to the proper port. there were no instructions with the kit __________________ 49 chevy 3100 3 window. 327 / m21 4 spd, 12 bolt w/ 3:55's Bought in 1973 for $235.00. Had it longer than my wife & Kids!!

08-02-2021, 12:07 PM	#6
mr48chev Registered User Join Date: Jul 2007 Location: Toppenish, WA Posts: 15,705	Re: power brake vacuum If the carb has a port on the back center to take the vacuum off for the booster that is where I would hook it up but some don't and off the 6/8 runner works equally well as far as vacuum to the booster goes. __________________ Founding member of the too many projects, too little time and money club. My ongoing truck projects: 48 Chev 3100 that will run a 292 Six. 71 GMC 2500 that is getting a Cad 500 transplant. 77 C 30 dualie, 454, 4 speed with a 10 foot flatbed and hoist. It does the heavy work and hauls the projects around.

08-03-2021, 12:07 AM	#7
dsraven Registered User Join Date: Nov 2010 Location: calgary alberta Posts: 8,323	Re: power brake vacuum you can also plumb in a vacuum reservoir with appropriate check valves so you have that added safety for the power brakes. remember back in the 70's where some manufacturers had those "tomato cans" plumbed in under the hood? well, something like that but with the appropriate sized inlet/outlet. look for a donor car with a/c or even a donor car with a/c and vac operated heater valves (like an astro van with rear where they used a plastic sphere vacuum storage cannister) like said above by others, plumb into the base of the carb if available because it is less "pulsed" than a port runner would be. it will see all the cylinder pulses instead of just a couple like a port runner would see. some manifolds have a split plenum as well that affects the carb base vacuum. either way, use a good quality vac hose and clamps along with a tested check valve at the booster and possibly an inline filter you can find under the hood of a newer donor. steel/hard line will give better results on a long run than rubber line will but use some rubber in the area near the engine to allow for engine movement. hard line also looks cooler and more professional in my opinion. thats just my opinion though and it is YOUR truck.



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