I am running a 292h cam in my 410. I drove it for the first time today and my power brakes seem very weak, like having manual brake's. Does anyone know if I need a vacuum canister or does it sound more like a bad booster? If I get a vacuum tester what should the vacuum read coming out of the carb?

 

Josh, run the engine at 1500 RPM or so and then step on the brake pedal, at that rpm there will be enough vacuum for the booster to operate normally. If you still have hard pedal it is likely a booster problem. To check run engine fast again and then shut it off and depress the brake pedal, there should be 1 or 2 power assisted pedal applications, if you hear a hissing sound when you shut off the engine or while stepping on the pedal, the booster is leaking(or maybe the check valve).

The vacuum at idle should be at least 12 in. hg. for adequate power brakes.

 

Some 80's model Chevy Cavaliers had a vacuum pump on them if you end up needing one.

 

As you've found out, that cam won't generate very much vacuum when wou need it. If you want to keep your power brakes, you'll need to install a vacuum pump, or install a vacuum storage canister.

 

The pedal is hard when trying to stop but when sitting still giving it gas it seems fine. I thought I had read somewhere before that the 292H had a problem building vacuum. I swiped a vacuum canister off of a 74 truck before we hauled it to the junk yard. I will borrow a vacuum gauge and check the vacuum before I go to far. Thanks Torque1st, if the one I have don't work I will keep that in mind.

 

Putt you said that the vacuum should be at least 12 at idle. I was told today that is couldn't be lower then 18, 20 would be ideal. I guess everyone has there own ideas. I dought I will have anything even close to that, but hears hoping.

 

[QUOTE=pbear6969]Putt you said that the vacuum should be at least 12 at idle. I was told today that is couldn't be lower then 18, 20 would be ideal. I guess everyone has there own ideas. QUOTE]

I think he meant you need at least 12" of vacuum to run a brake booster. The 18 to 20" of vacuum refers to an engine with a factory cam.

I'm just curious, what's your compression ratio, are you running headers, and what's the stall speed of your converter?

 

I think he meant you need at least 12" of vacuum to run a brake booster. The 18 to 20" of vacuum refers to an engine with a factory cam.

I'm just curious, what's your compression ratio, are you running headers, and what's the stall speed of your converter?[/QUOTE]

Thanks for clearing that up! I just talked to a friend and he has a vacuum gauge I can borrow, so maybe I can check it tomorrow and see what I got. Will post it after I check it. As far as the compression ratio, it is (if I figured right) around 10.75 to 1 with a dynamic of 8.57 . Those are guess-ti-mates. lol Yes I am running a set of Headman 89100 headers and the stall is 3000 rpm. That is the stall that Comp recommended I use.

 

My next 390 will sound like that. :-)

It should be a killer combo when it's all dialed in. Good luck and keep us posted!

 

Did you download the video's and listen to it?

Checked vacuum today and it only has about 5" going to the booster. I don't have it all dialed in yet so maybe when I get the timing set right and the carb adjusted I can get more. I put a vacuum gauge on my booster today and tried to pump up some vacuum and it wouldn't hold any!! Does this mean a bad booster or does it take more then a handheld vacuum pump to build pressure? I ran it for a minute and then my dad pulled the valve out of hte booster and nothing. No noise at all. Might have several problems, just need to keep at it I guess.

 

Your vacuum booster is leaking!! And yes I meant you need at least 12 in of vacuum to operate a vacuum brake booster, and even that is marginal and may require a vacuum reservoir.

You should be able to get more than 5" of vacuum however, so more tuning is needed.... but you knew that!! Try plugging the brake booster line and then see what your idle vacuum is(might require some mild tuning to compensate for the leaky booster).

 

The booster problem sounds correct. When I hit the brakes while idleing the truck died. Yeah tuning is definatly needed. Hopefully this weekend. New booster should be here today.

 

[QUOTE=pbear6969]Did you download the video's and listen to it?QUOTE]

Yeah, I did. it sounds good. What are you using for rocker arms and shafts, factory parts or aftermarket?

 

[QUOTE=390fe]
I am using new stock shafts bought from Napa for $26 each. The rockers are Comp Cams Aluminum Roller Rockers, 1.76 ratio. I think the part number for the rockers is 1046-16.

 

Got the booster put on today and got some ignition problems fixed/tuned. Still not done adjusting but it's better then last time. The new brake booster and tuning gave me much better brakes. Still kind of soft, but after soome further tuning I think it will work fine. Didn't have time to check the vacuum from the carb again, but I will after more tuning and post it. Thanks for the help everyone!!!!!!