vacuum for brakes & PCV
Thread Starter
Burning Brakes
Joined: Jun 2003
Posts: 1,022
Likes: 6
From: CT
vacuum for brakes & PCV
I have power brakes and my motor makes 11" hg at idle. The car doesn't stop very good from faster speeds and the pedal isn't firm enough. I bled the system and flushed the old fluid out with fresh fluid, master cylinder is only 2 years old(was bench bled), no leaks, good rotors and good life on the pads. I just installed a summit racing vac canister and the gauge on the canister reads 17" hg now and it goes up to 20-21" if I rev it up a bit. The brakes have improved slightly but still dont feel safe enough for aggressive driving.
I have only one vacuum line coming off the back 3/8" port on my demon carb with a T-fitting. One end of the T fitting goes to the PCV on the valve cover and the other end goes to the summit canister then to the brake booster.
Should I run the brakes vac on its own line and go to the intake instead of the carb?? my RPM intake has a 5/8" plug under the carb and I couldn't find any vac fittings for it. checked summit for 5/8" threaded 90 deg fitting with 3/8" line fitting and couldn't find one.
Do I need to keep the PCV or could I just a breather cap on valve cover?
Will running vac off the carb affect the way carb runs? After I installed the vac canister It feels like the motor runs a little rougher. I have to double check for leaks tomorrow.
I'm only running vac to the brakes, pcv, and vac advance. I had leaks in the headlight system so I just have them disconnected for now.
Thanks
I have only one vacuum line coming off the back 3/8" port on my demon carb with a T-fitting. One end of the T fitting goes to the PCV on the valve cover and the other end goes to the summit canister then to the brake booster.
Should I run the brakes vac on its own line and go to the intake instead of the carb?? my RPM intake has a 5/8" plug under the carb and I couldn't find any vac fittings for it. checked summit for 5/8" threaded 90 deg fitting with 3/8" line fitting and couldn't find one.
Do I need to keep the PCV or could I just a breather cap on valve cover?
Will running vac off the carb affect the way carb runs? After I installed the vac canister It feels like the motor runs a little rougher. I have to double check for leaks tomorrow.
I'm only running vac to the brakes, pcv, and vac advance. I had leaks in the headlight system so I just have them disconnected for now.
Thanks
Safety Car
Joined: Oct 2007
Posts: 3,729
Likes: 267
From: Austin Texas
Corvette of the Year Winner 2017
2016 C3 of Year Finalist
you need to isolate everything, brakes, PCV valve, a/c heater vacuum actuators,
then take a vacuum reading, that is very low unless you have a huge cam.
you said plugged the headlights because of leaks, hmmm....
the relays can also leak, and the vacuum tank. 69VETT
then take a vacuum reading, that is very low unless you have a huge cam.
you said plugged the headlights because of leaks, hmmm....
the relays can also leak, and the vacuum tank. 69VETT
Team Owner
Joined: Apr 1999
Posts: 21,953
Likes: 1,445
From: Reno Nevada
2024 C3 of the Year Finalist- Modified
You need to run the brakes off of a separate 3/8th line. When I used a PCV I had to tap an extra 3/8th brass nipple for my brakes.
I personally don't use a PCV anymore. I use a twin breather setup.
I personally don't use a PCV anymore. I use a twin breather setup.
Instructor
Joined: Mar 2009
Posts: 187
Likes: 1
From: WA
Are there advantages/disadvantages to using a twin breather setup? I would only like to eliminate my PCV to clean up the engine compartment.
Team Owner
Joined: Apr 1999
Posts: 21,953
Likes: 1,445
From: Reno Nevada
2024 C3 of the Year Finalist- Modified
Le Mans Master
Joined: Nov 2008
Posts: 5,691
Likes: 12
From: columbus oh
you may or may not run a pcv, it's up to you, personally i think you have a leak somewhere and you do not have to run the pcv and other vacuum slaves from seperate ports.....also the large port at the carb base is the same as a port in the intake manifold....you can run everything from one port with no problems........
Thread Starter
Burning Brakes
Joined: Jun 2003
Posts: 1,022
Likes: 6
From: CT
I measured vacuum with a gauge running to the small port on the carb base plate. It was the only vac line hooked up and all the other ports were plugged and the guage read 11-12" hg with idle at 900rpm. the cam has a slight rough idle to it with 110LSA.
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Thread Starter
Burning Brakes
Joined: Jun 2003
Posts: 1,022
Likes: 6
From: CT
The headlight system has a leak somewhere in it, one would pop up slow and the other headlight would take forever. Instead of tracking the problem I just pulled the vac line off the motor and haven't run headlight vac for the last few years lol. I usually dont drive it at night and if I do i reach under the front of the car and pop them up and down by hand.
So the only vac have coming from the motor is for brakes, pvc, and my vac advance. So the headlight system doesn't come into play for now.
I have a RPM intake and the stock intake and vac ports are gone. the vac port under the carb is plugged and sealed, I just picked up a fitting for it at napa and will try the brakes off manifold vac instead of the pcv
Last edited by L-82kid; Jun 17, 2009 at 05:23 PM.
Thread Starter
Burning Brakes
Joined: Jun 2003
Posts: 1,022
Likes: 6
From: CT
I reworked the vac setup. I have the brakes going to the intake and the pcv going to the carb. This made a huge difference. I recheck the vac from carb base plate the same way I did before and I have 14.5" Hg now instead of 11" hg. The car idles better and throttle response is more chrisp. Most important the brakes work 10x better now, with the new summit vac canister the brakes are getting 20" hg now. 
I'm keeping the pcv for now until I read more into it.
Thanks for the help guys
I'm keeping the pcv for now until I read more into it.
Thanks for the help guys
