Vacuum Requirements

[mashud46]

Does anyone know how much vacuum the stock brake booster and HVAC requires? Doing an engine swap and debating on mild or wild cam due to vacuum impacts... Open to installing an electric vacuum pump if need be, just curious how much vacuum is needed to satisfy the brake booster, HVAC controls and cruise control. All emissions have been deleted

 

[565bbchevy]

I believe 16-18 inches is required for the booster to function properly, I would use a vacuum canister first, so you have the extra reserve and then install a vacuum pump from there if required,
On my Monte I run a pulley driven vacuum pump that requires no vacuum source and self regulates itself at 28 in,
I got the pump from a Ford diesel truck and my stopping power is very good with my Wilwood brakes.

 

[oldsofb]

It's not just the amount needed to make it work, but you need enough to get quick recovery time. 17-22 in. Hg is a typical stock engine vacuum reading at idle.

10 in. Hg might be enough to get good function from the booster, but it may take a while to recover if you needed to brake repeatedly.


Hutch

 

[78Delta88]

I think the number is about 8 minimum, but as stated you need a can. If you think back to the big body cars, Cadillac 472 with AC, Lincoln 460, Ford's with 400 and 429 had the can under the hood that looked like a tomato Juice can. The can supplied loss of vacuum for bigger booster, bigger brakes. A typical stock 305/350 will have the small round one, two lines and one has a one way check valve.

On a stock engine running 18 to 22 refills the can while at idle at the stop light. When at cruise and you are around 10 to 12 still enough to run the booster.

If you find you need extra vacuum very very easy to make a can I.e.: (vacuum reservoir).

 

[mashud46]

I figured about as much. Knew you guys would be on top of it. I'm going to run an electric pump and go with a hot cam. What's the best way to run the vacuum lines? Pump to a canister, then leave the canister to booster, cruise, and hvac? Can I tie the pump and engine vacuum together going into the canister so I still have vacuum if the pump were to fail?

 

[64nailhead]

IMO a better program is to run a hydro boost for the brakes and a vacuum canister for everything else (HVAC).

 

[bracketchev1221]

My 78 wasn’t as sensitive to vacuum as my 70 is. I ran a Crane 250/260 @.050 .533/.555 106 lsa solid lifter cam in my 11:1 355 and the car did fine with nothing. I got stuck in traffic in New York with it and never thought twice about vacuum. My 70 has a small solid roller in it and gets 2 pumps of the brake and it’s done . I’m going with a Leeds vacuum pump in the 70.

 

[78Delta88]

Depending on your pump, 3/8 line pump to can. 3/8 line with check valve from can to booster. 1/4 line with check valve to a Multiport manifold. Like how Ford did on the LTD Police Cars. All the smaller lines for AC, Vac Modulator on trans, or other items.

 

[78Delta88]

On the hydro boost.. Few years back helped restore a late 70s Lincoln Mark V with a Ford 400M. It came with hydro boost, about same time we took a unit from a wrecked Astro Van and put it on a mid 80s S10 with fairly radical cam. Only issue I have with hydro boost is it always seems to leak and make under hood greasy nasty.

 

[MrSony]

I've got a 310 duration cam. I'm around 10", it's fine enough. Cam is too big for my application though.