Brake Performance Question
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Mountain Pass
Joined: Nov 2016
Posts: 148
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It takes a pretty big cam to only have 15" of vac at idle. I have a edelbrock performer cam in my 400 and it pulls 22" of vac at 800 RPM not in gear. I would say this is a RV type cam.
I think you may have something wrong with either a vacuum leak or a bad cam (flat cam lobe or two). A cam that would only pull 15" vac on a 460 and wouldn't idle at less than 1000 would be big and would idle really rough/choppy.
What is your initial timing set at?
Now with all that.... it still may be your brake system that is having a problem. Here are some questions to test your brake booster for leaks? How long after you turn your engine off does the booster hold vacuum and after the engine is turned off is the brake peddle still easy to push down once and then get harder after that? If you disconnect your booster and plug the vacuum line does your engine vacuum go up? Does your engine vacuum change when you press the brake peddle when in idle?
I think you may have something wrong with either a vacuum leak or a bad cam (flat cam lobe or two). A cam that would only pull 15" vac on a 460 and wouldn't idle at less than 1000 would be big and would idle really rough/choppy.
What is your initial timing set at?
Now with all that.... it still may be your brake system that is having a problem. Here are some questions to test your brake booster for leaks? How long after you turn your engine off does the booster hold vacuum and after the engine is turned off is the brake peddle still easy to push down once and then get harder after that? If you disconnect your booster and plug the vacuum line does your engine vacuum go up? Does your engine vacuum change when you press the brake peddle when in idle?
initial timing is at about 20-22 degrees with mechanical advance limited to 16 for total of 38. No vacuum advance on the Pertronix distributor that’s on the truck. If I back initial timing off the idle quality degrades along with vacuum.
it will idle at 750 in gear but it’s choppy. It will idle at that speed in park if I adjust the throttle body butterfly’s but then it will stall in gear. From what I’ve read this also seems normal the way the Atomic EFI is setup.
hopefully I’m missing something and not a trashed cam. I’ve checked for intake leaks with no luck. Vacuum only serves the C6 and brakes. Everything else is capped at the tree and I don’t find any where it could be leaking.
Lead Driver
Joined: Oct 2018
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22 is a lot of initial. normally that much will kick the starter , if it's not it makes me wonder if you don't have something going on in your ignition. possibly your dampener has slipped even.
15 inches isn't that bad if you have a cam of any sorts. I have street cars that won't make more than 12 on a good day.
It's not going to help your brakes any but if you don't have the provision for vacuum advance on yout distributor dump the POS and get one that does. you'll get better fuel economy and run lower EGT's.
15 inches isn't that bad if you have a cam of any sorts. I have street cars that won't make more than 12 on a good day.
It's not going to help your brakes any but if you don't have the provision for vacuum advance on yout distributor dump the POS and get one that does. you'll get better fuel economy and run lower EGT's.
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