Holding boost with vacuum brakes

[John Larkin]

I've posed this question to several people, so I'm throwing it out to the group. I am converting to vacuum brakes this weekend hopefully. What are techniques or tips to hold lotsa boost at the line? Interested in ideas ranging from the amount of brake drag you should set the shoes at to how hard you gotta push the pedal down (and will my seatback snap off or steering wheel bend in half ).

 

[REDS HOT AIR]

mine work great but one to prove it is GENO he leaves off footbrake (no trans brake) and goes in the 1.3 60 fts.

with vacuum brakes..he cant hold them but so tight or he might sqeeze the cigerette out his mouth..

 

[rastaz]

Originally posted by REDS HOT AIR
mine work great but one to prove it is GENO he leaves off footbrake (no trans brake) and goes in the 1.3 60 fts.

True, but when I saw his car run it would start pushing through the lights and he'd just have to let that green monster go with a big red bulb glowing.

If your bracket racing and concerned about Reaction times and not redlighting I wouldn't recommend trying high boost launches on vacuum brakes. But if your just out to have fun then it doesn't matter .

I tried vacuum brakes once but always ran out of vacuum and had all sorts of problems staging. I like launching at 8lbs and couldn't do it with the vacuum brakes. I know Dennis Hogan runs at least one extra vacuum resevoir on his stock block car to help combat this problem.

HTH

 

[azgn]

I can easy hold 10 lbs on my vacuum setup....the trick is getting the boost to stay there and not shoot to 20! I use the 2 step rev limiter in the MSD set at 3000......after you come out of the burnout box, shift to neutral and let some vacuum build before staging

the trans brake is way better and more consistent, however with it i leave at about 4000 rpm (15-20 lbs)

 

[GNVAIR]

NO problems with my vacuum brakes either. I can easily hold 10lbs on the line. The secret is to make sure your rear brakes are adjusted correctly AND not to power brake when doing a burn out. That only adds heat to the drums and linings decreasing the availble grip. If you have a problem holding boost or loosing the vacuum, then I would start looking at a bad check valve in the booster. I know most of the TTA and Sy/Ty guys never have problems either. Unlike the crappy Power disasters. Ugggh!

 

[nitrousmike175]

I'm changing mine also to vaccum this weekend or next week,if i have a problem with vacuum hold would i hook up an extra canister if i needed it.

THANKS, MIKE

 

[Phatman]

Vacuum Reserve Can

JEGS # 270-99590-1

Crane Cams 1-800-345-4545

 

[John Larkin]

What about one of those juice can vacuum canisters off a Ford, ala junkyard? I guess you'd need a direct connection from the vac can to the booster and a check valve from the engine to the vac can? Does that sound like the right configuration?

 

[dfisher]

vacum

what converters are you guys running. I have this same problem no holding boost, rolls through the lites 1 pound of boost is all I can hold. I installed a jumper valve and going to a red stripe to help this issue. At the track people are trying to rush me to the staging lights so I cant use the ebrake not enough time and then they come over to tell me there car hauls a** . with the ebrake 12.71 foot brake 13.60. does the vacum canister help? Not to much info out in that any info will be a big help.

 

[azgn]

you have to have a converter matched to your combo....mine is 3600 stall

 

[WSLN 6]

I loose all vacuum after my burnout, and the pedal goes hard as a rock. I have to start pumping my brakes on the way to the christmas tree just to get any vacuum back.
I installed a new brake booster with check valve, and the brakes are good all around.
Would an external vacuum resevoir help out?

 

[REDS HOT AIR]

Originally posted by WSLN 6
I loose all vacuum after my burnout, and the pedal goes hard as a rock. I have to start pumping my brakes on the way to the christmas tree just to get any vacuum back.
I installed a new brake booster with check valve, and the brakes are good all around.
Would an external vacuum resevoir help out?

if you pump the brakes you make it worse since you use all the stored vacuum up.

when you let off after the burnout you should get a fresh charge of vacuum.

after shutting the car down wait about an hour or so and pull the checkvalve out of the booster and see if it still has vacuum ..if not you have a leak.

if its right it should be able to sit for months before loosing its vacuum.

and yes a canister will help but not if you dont have a good check valve.

 

[Turbocars]

I think vac brakes are great.........for the steet.

I love getting next to a vac brake equiped car at the track although I don"t encounter many. Typically they have one shot at holding boost, no pumping, which means they have to be at the second bulb and locked up. I don't have to deal with that or worry about losing vaccume. I can quicklly pre-stage, 'bump' it up to the second bulb as I am building boost, and go. I get to concentrate on the tree instead of worrying about pushing through or a 'no boost' launch.

OK Nick, I'm ready!

Hank

 

[TurboDave]

Originally posted by Turbocars
I think vac brakes are great.........for the steet.

I love getting next to a vac brake equiped car at the track although I don"t encounter many. Typically they have one shot at holding boost, no pumping, which means they have to be at the second bulb and locked up. I don't have to deal with that or worry about losing vaccume. I can quicklly pre-stage, 'bump' it up to the second bulb as I am building boost, and go. I get to concentrate on the tree instead of worrying about pushing through or a 'no boost' launch.

OK Nick, I'm ready!

Hank

Sounds like you and I must stage exactly the same. I pull to the pre stage light build the boost to about 2-3# and feather the brake pedal to get it into the stage light and from there, since boost is already up, it's just a matter of a second or two at the most to get it up to my launch boost. BTW, this technique works great for folks like me who like to stage last or at least "with" the other guy. I don't even start building boost in the pre stage light until the other lane is pre staged.

 

[Turbocars]

I think we do Dave. There are a couple ways to play the 'game'. but with not having to worry about vaccume or holding boost, it is my (our) choice!

Hank