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#1
02-28-2022, 09:33 AM
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Vacuum for power brakes
New 463 is in the Trans Am. Currently have the power brake hose connected to the vacuum port on the QF 950 carb, and the pcv hose connected to a hose barb that I installed in my 1" carb spacer. The power brakes work but are marginal. Would there be any advantage in moving the brake hose to the carb spacer port or do both of these ports see the same vacuum signal? I will probably add a vacuum pump in the future but hoping to make things work for now.
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69 Bird w/1970 400 block(409 cubes), #64 heads, hyd. roller, Q-jet by Jeff E., original interior, ps, pdb, th350, and 3.73 gears. Pump gas, street driven muscle. 3800 lbs. race weight. Best, 11.39 @118, my son's car. 79 T/A w/463, Scat crank, Eagle rods, Icon pistons, Lunati solid roller, 262/270, KRE 325 heads, Northwind intake, QF950 carb, full interior, ps, pdb, th350, and 3.73 gears. Pump gas, 3650 lbs. race weight. 10.68 @ 126 so far... no tuning yet. |
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#2
02-28-2022, 10:08 AM
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Based on the small details provided, I would say just try it ans see what happens. If the QF fitting has a large 3/8" barb and doesn't neck down to a tiny outlet in the carb base, it shouldn't make any difference. It's the same vacuum. You need a signal and adequate volume. My experience is you need plenty of volume and absolute minimum 12" HG of vacuum to have decent feel with a vacuum booster. If lower than that, you need to provide additional vacuum supply to the booster. Either a storage canister, vacuum pump or different system for boost. Good luck.
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#3
02-28-2022, 11:49 AM
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Put a Hydraboost on it and never look back
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68 Firebird. IA2 block, 505 cu in, E-head, Solid roller 3650 weight. Reid TH400 4:11 gear. 29" slick. Best so far 10.12@133 mph. 1.43 60 ft. 76 Trans am, TKX .81 o/d, 3.73 Moser rearend, 468 with KRE D-ports, Doug headers, 3" Exh. |
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#4
02-28-2022, 01:10 PM
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What booster do you have? The 11" single or the 9" 79-81 TA 4 WD dual?
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Skip Fix 1978 Trans Am original owner 10.99 @ 124 pump gas 455 E heads, NO Bird ever! 1981 Black SE Trans Am stockish 6X 400ci, turbo 301 on a stand 1965 GTO 4 barrel 3 speed project 2004 GTO Pulse Red stock motor computer tune 13.43@103.4 1964 Impala SS 409/470ci 600 HP stroker project 1979 Camaro IAII Edelbrock head 500" 695 HP 10.33@132 3595lbs |
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#5
02-28-2022, 01:37 PM
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I second that.
Quote:
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#6
02-28-2022, 01:51 PM
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My 78 TA with the 9" dual booster would work fine at 10" 9" not always.
__________________
Skip Fix 1978 Trans Am original owner 10.99 @ 124 pump gas 455 E heads, NO Bird ever! 1981 Black SE Trans Am stockish 6X 400ci, turbo 301 on a stand 1965 GTO 4 barrel 3 speed project 2004 GTO Pulse Red stock motor computer tune 13.43@103.4 1964 Impala SS 409/470ci 600 HP stroker project 1979 Camaro IAII Edelbrock head 500" 695 HP 10.33@132 3595lbs |
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#7
02-28-2022, 02:40 PM
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Skip, not sure how you measure the booster but I am pretty sure I have the 11" single. My brakes are the factory front disc/rear drum. I have 10" HG at idle.
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69 Bird w/1970 400 block(409 cubes), #64 heads, hyd. roller, Q-jet by Jeff E., original interior, ps, pdb, th350, and 3.73 gears. Pump gas, street driven muscle. 3800 lbs. race weight. Best, 11.39 @118, my son's car. 79 T/A w/463, Scat crank, Eagle rods, Icon pistons, Lunati solid roller, 262/270, KRE 325 heads, Northwind intake, QF950 carb, full interior, ps, pdb, th350, and 3.73 gears. Pump gas, 3650 lbs. race weight. 10.68 @ 126 so far... no tuning yet. |
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#8
02-28-2022, 03:20 PM
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the dual boosters are pretty good
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#9
02-28-2022, 04:04 PM
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Disc drum had the bigger 11" single.
Here is the one on my 78 best picture I could find of the 9"
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Skip Fix 1978 Trans Am original owner 10.99 @ 124 pump gas 455 E heads, NO Bird ever! 1981 Black SE Trans Am stockish 6X 400ci, turbo 301 on a stand 1965 GTO 4 barrel 3 speed project 2004 GTO Pulse Red stock motor computer tune 13.43@103.4 1964 Impala SS 409/470ci 600 HP stroker project 1979 Camaro IAII Edelbrock head 500" 695 HP 10.33@132 3595lbs |
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#10
02-28-2022, 06:52 PM
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Thanks for the pic, I see one other benefit to the 9" is the extra clearance at the valve cover. I only have about 1/8" with the 11" booster.
__________________
69 Bird w/1970 400 block(409 cubes), #64 heads, hyd. roller, Q-jet by Jeff E., original interior, ps, pdb, th350, and 3.73 gears. Pump gas, street driven muscle. 3800 lbs. race weight. Best, 11.39 @118, my son's car. 79 T/A w/463, Scat crank, Eagle rods, Icon pistons, Lunati solid roller, 262/270, KRE 325 heads, Northwind intake, QF950 carb, full interior, ps, pdb, th350, and 3.73 gears. Pump gas, 3650 lbs. race weight. 10.68 @ 126 so far... no tuning yet. |
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#11
03-01-2022, 12:45 AM
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With 10" of vacuum, I don't know if I would go to all the work of changing to a dual vacuum booster. I would tend to recommend a hydroboost in your application. It is even smaller yet, giving more room around the valve cover. Also hydroboost is very powerful as far as a boost system. They produce incredible stopping pressures with light effort. One of the reasons they were a favorite on heavy cars.
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#12
03-01-2022, 09:11 AM
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the other thing you can consider if you don't want hydroboost is a vacuum pump
i have one from CVR and it's great, turns on/off itself as needed, two wires to hook up, hydro was just starting to come out and i didn't know about it at that time one of these days i plan on mounting the pump in the trunk i have no problems with that pump and the small diameter booster i am using i did have the one from SSBC (think comp cams also sold it) but their on/off switch/valve was a PITA, not sure if they still make that one, but i'm sure they have made modifications as it's been a decade or two since i used that one i think some GM cars in the past came with pumps in the trunk, some reason Caddies/Olds come to mind |
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#13
03-01-2022, 09:19 AM
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Thanks for all the suggestions; several options to consider that will get the job done without too much expense. Thankfully I am in no rush to get this done. And I want it to be right the first time.
__________________
69 Bird w/1970 400 block(409 cubes), #64 heads, hyd. roller, Q-jet by Jeff E., original interior, ps, pdb, th350, and 3.73 gears. Pump gas, street driven muscle. 3800 lbs. race weight. Best, 11.39 @118, my son's car. 79 T/A w/463, Scat crank, Eagle rods, Icon pistons, Lunati solid roller, 262/270, KRE 325 heads, Northwind intake, QF950 carb, full interior, ps, pdb, th350, and 3.73 gears. Pump gas, 3650 lbs. race weight. 10.68 @ 126 so far... no tuning yet. |
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#14
03-01-2022, 12:07 PM
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Hydroboost is great, but your Steering Gear Box and P/S Pump better be in top notch condition, and not overheat with also having to power the HB.
I couldn't get enough vacuum with a Dual Booster, and no room for a big ugly one. I used this, and it is way cheaper than Hydroboost. https://www.jegs.com/i/JEGS/555/63016/10002/-1 And also used this to hold some vacuum so the Vacuum Pump does not run constantly. https://www.jegs.com/i/JEGS/555/63011/10002/-1 Gave me 20" of vacuum and the brakes work well. |
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