Vacuum question

[mobileaudio25]

the vacuum on my Malibu is only at 7" I did the blazer brake upgrade with slotted and drilled rotors and I can only tell a little bit of a difference from my stock setup. I have a vacuum canister and am thinking i need an electronic vacuum pump?

I'm running a muther thumper cam but does 7" at idle seem too low regardless of cam size?

Vacuum checked at carb under the throttle blades at a full vacuum port

 

[oldsmobile joe]

i think 7" of vacuum is too low for a vacuum powered brakes. how you resolve it is up to you. electric vacuum pump is one way, or you may want to look into a hydra boost style system. unfortunately I've never owned one. only worked on them a long time ago.

 

[Texas82GP]

Check out the belt driven vacuum pump 565bbchevy has. It is off of a diesel pickup. He said it was inexpensive and has been reliable. With 7" of vacuum, you don't have any brakes. Without cam specs I can't say if that is too low but it sounds pretty low. You want to set timing and idle mixture to achieve maximum possible vacuum. Post #5 in this recent thread....
https://gbodyforum.com/threads/vacuum-source-for-vacuum-brake-booster-conversion.61721/#post-528057

 

[JAMCAR223]

I assume ( and you know what they say about that ) that you did the Blazer swap ( not knocking this swap, I have it myself ) to compensate for the poor braking performance. You probably had low vacuum before the swap?? I think Jared has the best advice ( again assuming you have a carb'd car ) to tune the car to achieve the highest vacuum reading on your gauge. Adjust the timing, carb, and check for vacuum leaks.You probably don't need a vacuum pump.

 

[mobileaudio25]

i think 7" of vacuum is too low for a vacuum powered brakes. how you resolve it is up to you. electric vacuum pump is one way, or you may want to look into a hydra boost style system. unfortunately I've never owned one. only worked on them a long time ago.

Yeah I've looked into those. Very hard to find in a junkyard and a lot of money to buy the setup new.

 

[mobileaudio25]

Check out the belt driven vacuum pump 565bbchevy has. It is off of a diesel pickup. He said it was inexpensive and has been reliable. With 7" of vacuum, you don't have any brakes. Without cam specs I can't say if that is too low but it sounds pretty low. You want to set timing and idle mixture to achieve maximum possible vacuum. Post #5 in this recent thread....
https://gbodyforum.com/threads/vacuum-source-for-vacuum-brake-booster-conversion.61721/#post-528057

That is a pretty cool setup. I just had to deal will a lot of belt and pulley issues I don't really want to start messing with that again. My timing is 37 overall and 16 initial. Had my car on the dyno to get the fuel/air ratio correct so I would assume it is close to full vacuum .

 

[mobileaudio25]

I assume ( and you know what they say about that ) that you did the Blazer swap ( not knocking this swap, I have it myself ) to compensate for the poor braking performance. You probably had low vacuum before the swap?? I think Jared has the best advice ( again assuming you have a carb'd car ) to tune the car to achieve the highest vacuum reading on your gauge. Adjust the timing, carb, and check for vacuum leaks.You probably don't need a vacuum pump.

The muther thumper cam I'm running is designed to sound more Lopez or like a bigger cam. One of the side effects is the low vacuum. I definitely had low vacuum before the swap and knew I wouldn't have my brakes running correctly until I did something with the vacuum issue

 

[Texas82GP]

That is a pretty cool setup. I just had to deal will a lot of belt and pulley issues I don't really want to start messing with that again. My timing is 37 overall and 16 initial. Had my car on the dyno to get the fuel/air ratio correct so I would assume it is close to full vacuum .

Ok, so based on that, the low vacuum is from the cam. 7" is way low for a vacuum brake booster. It needs to see 18"-20". Reach out to Scott (Injectedcutty). I think he has an electric vacuum pump that only runs when the vacuum reservoir falls below a certain level of vacuum, like 18" (I don't remember for sure) and he has it wired into the brake light switch so it will only run when he's on the brakes. Maybe a setup like that would work for you. At 7" of vacuum you should just have a hard pedal and I'm guessing you can't lock the wheels with the brakes. If that's the case, be careful driving it. It won't stop like it should in a jam.

 

[mobileaudio25]

Ok, so based on that, the low vacuum is from the cam. 7" is way low for a vacuum brake booster. It needs to see 18"-20". Reach out to Scott (Injectedcutty). I think he has an electric vacuum pump that only runs when the vacuum reservoir falls below a certain level of vacuum, like 18" (I don't remember for sure) and he has it wired into the brake light switch so it will only run when he's on the brakes. Maybe a setup like that would work for you. At 7" of vacuum you should just have a hard pedal and I'm guessing you can't lock the wheels with the brakes. If that's the case, be careful driving it. It won't stop like it should in a jam.

Yeah it definitely does not stop like it should. However I wouldn't say it's very dangerous as I always keep my distance from cars around me... I stay back from behind cars to help the motor stay cool in traffic. I did have to add a vacuum canister and without that it was pretty dangerous to drive. I know my brakes are no where near their peak performance. That's how I was planning on running my vacuum pump I just can't wait to see how this thing really stops in the spring

 

[565bbchevy]

Do you have a gauge on your vacuum canister so you can read the stored vacuum?
And also make sure your check valve at the canister and at the master cylinder are both holding vacuum.