Hey all, I'm working on a 84 Monte Carlo for a customer and need some advice. So, it has a built engine- I believe its still a small block 350 engine, but its been modified- has patriot heads, sounds like it has a cam, and looks to be freshly built- but the guy i'm working on it for bought it this way and didn't get any paper work on what officially has been done to the engine or car in general but the trans and some other things were all fresh as well. Anyways, it seems like the engine has trouble building vacuum at idle- the brake pedal is hard as a rock at idle, but once you're moving the booster works fine and brakes as it should, so seems to build plenty of vacuum under RPM, just not at idle. It runs good too so I don't think its a carb adjustment or anything like that type issue where it just needs to be dialed in. I know the way you build an engine can affect it's ability to create vacuum but i'm not super savvy on that either. So I was wondering, is it practical to maybe add a vacuum pump of some kind so that it has consistent vacuum/brake boost? If so, anyone ever added one and have a good recommendation on a good one? Or another idea to correct this? Thanks!

 

I had the same issue and documented my solution in this video:


The bottom line is the brake booster needs at least 16in of vacuum to function properly. With any heavier than stock cam, the engine's ability to pull vacuum is reduced.
Before you spend time and money on a solution, be sure to measure manifold vacuum at idle and test the booster with check-valve for vacuum leaks.
The pump I used was made by Leed Brakes and the vacuum can was from Summit.

 

Thanks for the reply and sorry for my late reply haha it's been hectic lately. Do you have links to the parts you used? Seems like a pretty simple install, do you happen to know how long it took you to install it? Any other tips?

 

Vacuum pump:
Vacuum canister: https://www.summitracing.com/parts/s...cuum-canisters

The brass fittings can be found at any well stocked hardware store or purchased online at eBay.The install of the vacuum pump, canister, and lines took me about 3-4 hours. About 2 hours went just to the layout and fitment of all the components, and drill & tap the pump mounting bracket to use the bolts that held the gasoline vapor carbon canister. Once I figured out how and where I was going to mount the components, the actual work of bolting things together was quick and easy. Mind you, that doesn't include the preparation, i.e., wiring the power relay to the ignition-switched feed which I did a couple of weeks earlier, and figuring out what parts I needed for the vacuum distribution manifolds; one on the canister, one near the booster.

The most valuable tip I can give you is be patient and methodical. The more attention you devote to prep, the less likely you'll need to uninstall something because something was overlooked, then reinstall.

If your car still has the gasoline vapor recovery carbon canister and you do not need to delete it like I did to make space for the vacuum pump, then leave it alone. If you do have to delete it, make sure you thoroughly research how it works on that car so you can deal with it intelligently. The one thing you don't want to do is vent it to open atmosphere; not only will vapors flow out all over the garage floor, you may draw contaminates into your gas tank. You don't want to simply plug the line either. If the vent line from the tank is plugged, pressure will build up in the tank which could cause seals or gaskets to leak. Connecting the vent line directly to carb or manifold vacuum may create sufficient negative pressure in the tank to cause it to collapse like if you squeeze an empty soda can.