Vacuum question

[mikeextrafast]

How much vacuum is need for 4 wheel disc? I have a LS3 with a cam and it only pulls 7-8 inches at idol and I think it affect my braking . What would be the best fix for better brakes ?

[Apogee]

Everybody will give you a different answer, however for good vacuum assist brakes with a consistent pedal, we like to see at least 14" Hg at warm idle. Levels between 12"-14" Hg tend to provide marginal results with some pedal inconsistency and sub-12" Hg tends to be an uphill battle. Single digits are going to suck...most people can at least agree on that.

You have several options as I see it:

1. Convert to manual brakes. The bore size of your MC needs to be matched to your calipers, pedal ratio and pad compound, however we would generally run a more aggressive "GG" compound pad with manual brakes, something like the Hawk HP Plus, EBC Yellowstuff, etc. You have not provided any information about the actual brakes other than they're "discs", so the more information you can provide with respect to what you're running, the more focussed our responses can be to your specific application.

2. Convert to hydroboost. Assuming you have power steering, this is a solid option that divorces your brakes from your engine vacuum.

3. Add an auxilliary vacuum pump, vacuum canister/accumulator, and run it. I'm not a huge fan of the aux vacuum pumps myself as they tend to be loud, cycle frequently and have questionable reliability mounted in an engine compartment next to some headers.

Tobin
KORE3

[Hydratech®]

We have many local customers that stop by the shop here wondering if vacuum is their issue. I actually have some fun with this, in that I take a Robinaire air conditioning vacuum pump and suck and old air compressor tank down to 25" of vacuum. I then take a 3/8 vacuum rated 25' hose and connect it from the 30 gallon air compressor tank to the vehicle's brake booster. I then instruct the customer to roll forward and then rearward about 15-20' or so (while I roll forward and rearward with the compressor tank on wheels) to see what they think of their braking when hit with larger than stock vacuum levels.

Guess what? There has never ever been a single time where supplying an artificial amount of elevated vacuum has improved the braking to the customer's liking in this funky real world (here it is) test. There was that one time where the customer actually had me carefully put the old compressor tank in the trunk (and run the hose to the vacuum booster) so that he could drive it around the block (just imagine, LOL?). Skeptics...

We will then run the same test once one of our hydraulic brake assist systems are installed into their vehicle. The same look on their faces over and over again of surreal disbelief make me chuckle time and time again after all of these years - what, you didn't believe me? And that's just rolling out of the shop. The real surprise finally hits them when we get to the local industrial drive where they can really put the high speed braking into perspective. It has actually become so much fun for me that I have contemplated taking pictures of the looks on their faces after making a few hard stops - it's kind of like WTF? How is this really possible? I have had a few go into "Casper the white ghost mode" needing a few minutes to regain their composure afterwards. They go into thinking yeah, it better be improved from the hard earned cash that left my pocket, and then follow up always stating it has been the most skeptical expenditure, yet biggest bang for their buck ever installed onto their muscle car...

Try it at home to prove it out for yourself? Score a roll of vacuum rated 3/8 hose, hook it up to your wife's minivan, and supply dead stock high vacuum to your muscle car's vacuum booster (remotely from the other stock car pulling good vacuum). If your brakes still don't feel proper, then additional vacuum levels aren't going to help, right?

"Vacuum sucks" (pun intended)