ruger311

Ok, this is a pretty big issue,

on my 89 GT Vert with the 347 running the COMP XE282HR cam and the 5 lug conversion, i have the 10th anniversary cobra calipers with proslot 13" rotors,MM SS brake lines, etc..and i left drums in the rear, i upgraded the MC to the 93 Cobra with the 1" bore, from my stock MC, i did not swap the Brake Booster to the SN95,,,, ok here is the deal

currently with the cam choice i am only pulling 9-10.5 or so inches of vacuum, as we all know this is not enough to push those brakes, i cant even lock up the rears at 10-15mph, i bought the COMP vacuum canister thinking this would make a difference and it did for about 2 seconds but still cannot lock the brakes up at all, this would suck to be on the track at 125+ and not be able to stop,,,

here is my options,,, im not sure if going with the SN95 brake booster will help out with the brakes b/c i only have the ~10" of vacuum,, is 10" enough to power the SN95 BB?????

if it is not has anyone had any experience with the Electric Vacuum Pumps that claim to have a constant 20-22" of vacuum??? do they work, how loud are they, do they just come on with it senses sub 20" vacuum pressure???? my car is pretty damn loud and i dont think i would hear it over the exhaust or engine,

another option is the Hydroboost hydraulic brake booster, these run off of the power steering pump, my only worry on these are that more hydraulic hoses to buy and pistons wear out over time, also if i have any kind of leak in the system i have no brakes, and if for some reason my engine dies then i have no power, with the electric i would have vacuum all the time as long as battery was connected,,,

if anyone has any information on this topic i would really appreciate it, kinda sucks not to be able to run the **** outta the car and worry about it stopping,,, of course there is always the E-Brake,,,

samseed101

I haven't had any experience with electric pumps personally, but I have seen then many times. The ones I have seen only kick in when the vacuum drops below a certain level, and although you can hear them, they were'nt extremely loud or annoying or anything. But in your case, it seems like it would be running most of the time, if not constantly.

Even with an aggressive cam, I'm suprised that you can't get a few more inches of vacuum there. Did you get the car fully tuned after installing the cam or did they just mess with fuel pressure and timing? I won't insult your intelligence by asking you to check for vacuum leaks.

w8less

with my sn car i had a vacuum canister on it and was able to lock up the brakes maybe u just need the brake booster

my cam was 560/576 300/310 110

samseed101

although thinking about it... if it's a really badass aggressive camshaft, tehn I could see you having problems with power brakes... But I still would have guessd that you would have had 12" at idle. 10 is way down there, lol.

If everything is as good as it is going to get, then you may have to make some changes to keep the power brakes (as you already figured out.) An electric pump and a good canister will help out, but I'm not sure if you'd like it, if you are trying to limit noise as much as possible.

ruger311

sam

thanks for the response,,, i was surprised that the canister did not help that much which leads me to believe that the bigger SN95 BB would not help <----- just guessing here,,, all i did from my previous 347 stock block build was swapped everything into a Dart Iron Eagle block, we broke it in on the dyno and had it fully tuned using SCT chip and of course computer software, its running solid except for the ign cut out round 5300-5500 rpm,,, yes i have checked for vacuum leaks, to make sure of that i went straight from my RPMII to the BB first, and then put in the canister between the BB and intake,,,

ruger311

i dont really care about the noise b/c w/ 3" exhaust and dumps it wont be louder than that for sure,,, im just wondering if it is something that i did and not just the low vacuum,,, i know on some solar cars that we built in college we had ele pumps and they were a lil loud but those cars also didnt have engines to deaden the noise,, i will only be using the brakes like you would on the street, as this is a street/strip car,,, just dont want to spend $75 for a SN95 BB if it isnt going to help and $75 is a good chunk of money towards a $279 ele pump,,,,i just want to know that i can stop for sure

ruger311

what i want to really know is if the ele pump will allow me to lock em up,, and if it has 22" continuous vacuum is that all the time or what????

when i installed the 93 cobra MC i turned the plunger on the BB out about 1 1/4" turns like they say to do and thats all i have changed,,, even when i had the stock MC when i had the stock block 347 it stopped a lil better than now

samseed101

I tend to like my brake booster. I found that I can usually get 2 - 3 good solid depressions of the brake using nothing but the resovior... meaning that with the engine completely shut off, I can fully depress the brakes and stop the car 2 - 3 times before the resovoir is depleted.

Even with the canister in place it didn't allow you to fully lock up the brakes? You should at least be able to get 1 or 2 uses out of it. Is the check valve working properly?

I know your vacuum level sucks (no pun intended) but I don't see any reason why you can't at least get one full,quickdepression of the brakes, especially with the canister.

Unfortunately, you may be stuck going with an electric pump. They work great, but I imagine it would be running a lot in your situation in city driving. Probably not so much of a problem when vacuum demands are low though.

samseed101

If you get the electric pump, if it's installed correctly, and if your BB isn't malfunctioning then it will definitely allow you to lock them up.

To answer the second part of your question (is it 22" continuous).. that depends. Most of the time, they are internally regulated to turn on when vacuum drops below a certain level...say 15" of vacuum, and to shut off once it reaches a certain level, say 22" of vacuum. So in theory, it will hold at least 22" and if it falls below that level, it will turn itself on.

However, if your BB is malfunctioning or you have a bad check valve, etc... then it would never be able to reach the desired level and may be constantly on while stuk at a lower level.

w8less

i wonder why it didn't help? like i said i could look it up maybe twice and then could notice a difference in brake pressure