I am having some problems with my truck running just right I just got a motor off a friend for my 59 apache its a small block 355 4bolt and it has a comp cam with 525 lift turbo 400 w 1800 stall and a brake booster... it sounds great but i feel like its robbing all of my vacuum I have it running great but when i put it into drive while pushing my brake pedal in it wants to cut off but when I put it in drive then let off the brake quickly it will continue to run I have a holley 600 Im not running a pcv valve so i hooked my brake booster to the big port on the carb and my trans vacuum is hooked to my intake if you have any questions please ask
I thought the trans should be connected to ported vac at the base of the carb. I could be wrong on that, but I know mine comes from the carb base instead of the intake.
See and his trans was hooked to the port on the intake where my is hooked up and he had the same motor stall and trans
It sounds like you have a bad booster to me. Does it hiss when you are on the brake? It shouldn't. My trans is manifold vac no problems.
I'm changing out the booster on my wife' ot rig right now because of almost the same thing. When you push the pedal the engine speed changes and it runs rough until you let off the pedal. I've run the trans vacuum pickup to the fitting in the provided hole in the #8 cylinder leg of the manifold for years with no problem and run the booster to the vacuum fitting on the carb with no problems. Check to see if you can hear the vacuum leak when you push the brake pedal with the engine running. After reading down the page the cam may be causing a low vacuum condition but the booster shouldn't cause the engine to run rough if it is good, you just wouldn't get an effective boost on the brakes.
I checked on youtube a method using canned propane to find leaks on an running engine, it is kind of cool (can't find it right now) but engine will **** gas thru the leak and rpms will increase. This is one using carb cleaner, neat too but I don't like it because it may strip paint off my engine.. http://www.youtube.com/watch?v=9CPqbaSgcok
Clamp off the booster hose with vise grips and see how it behaves. Maybe a bad check valve in the booster? Bob
I was thinking the same as bobss396. If you disconnect the brake booster and plug the port on the carb, how does it react then.
what bobss396 said--had the same issue recently on a new build with new pts--step on brake, engine would act like vac leak, plugged the line and problem went away--new booster was bad
The cam " advertised " duration or better yet the duration @ .050" will be needed to help with this situation. I can tell you with no uncertainty, you dont have enough converter. You must also be in a somewhat of a safety issue here with what must be very low manifold vacuum and power brakes, you need to address this before you or someone gets hurt. It doesn't matter where you pull the vacuum from, if there isn't any to be had. You might also and probably do have issues with your carb's power valve and also the distributor va*** advance if your running one. Yes, it probably idles like a top fueler, doesn't mean it running good though. I'm not trying to ruin your day friend, just help. Sadly guys overcam thier vehicles to sound cool, and then try and bandaid a bunch of driveability problems. Heres somethings to consider, changing the cam of course is one, but you can keep the cam and consider just a set of variable duration lifters. This will help with the low va*** signal. A vacuum storage canister is a excellent idea to have also. A high dollar cure is a electric vacuum pump. Your probably going to find your carb a little on the small side, once you get things dialed in. I dont know enough about the rest of your combo to say for sure. You could also switch to a manual brake master cylinder, but be sure to have the correct pedal ratio if you do. Hopefully we have all given you some things to consider and others to address as soon as possible, best of luck, TR
Also, I'd hook up the booster to the big port on the back of the intake manifold. Then I would give the ****** module its own line from the base of the carb. If you have to "T" the fitting from the intake/brake booster you can, but be sure that line and fitting is big enough to supply enough signal to the booster. Just like the factory does it. If you have a 3/8" fitting on back of the base of the carb, that is generally for the PCV valve. TR
Since PVC valves use vacuum, do they effect the available vacuum needed to achieve max vacuum for the brakes? .
No the PCV valve is made internally to actually flow less air at idle than it does under load when it is needed more. If you have your foot on the brake you probably don't have your foot on the gas pedal so the vacuum is high as it can be for your engine combination.
The vacuum plumbing sounds correct, although you might want to add a PCV valve. The brake booster and transmission vacuum hose can be connected to the intake with a T fitting, then you'd connect the PCV to the carb. It's a good idea to make the brake booster fitting pretty substantial, more than just a hose slipped over a metal tube. But yeah, ***uming this http://www.summitracing.com/parts/CCA-12-214-4/ is the .525" lift Comp cam, you want a heck of a lot more stall speed, like 3500 or so
That sounds like the comp magnum cam. If I remember correctly that puts duration around 240. 1800 stall is pretty tight for that cam.
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