The Stovebolt Site Forums The Shop Area Engine Shop How much vacuum from a 235?

I am over-analyzing the installation of a dual master cylinder with or without a power booster.

I am trying to locate a vacuum tool/guage to borrow but does anyone know how much vacuum a stock 235 with single carb will produce? Since I will convert to electric wipers I would use the port on the side of the manifold under the carb for the brake booster hose.

CPP says I need a minimum of 17 inches of vacuum for the booster. Will the 235 produce enough?

Thanks!

The amount of vacuum created is a result of the condition of the engine. An average 235 will idle between 15-20 lbs. A vacuum gauge can be the most valuable diagnostic tool in your box and they're not expensive. I suggest buy one instead of borrowing. Here's a link that explains readings:

http://www.centuryperformance.com/vacuum.asp

Curt B.

Would it help to use the double action style fuel pump to provide additional vacuum and run parallel lines to the booster?

Do you have any guess how much vacuum the fuel pump would add?

46SortaStock,

Your brake booster will not actually consume vacuum in the same sense a wiper motor would.

If the engine can develop 17 inches of vacuum, and it easily should, that vacuum will merely sit on your brake diaphragm and wait to do its thing...it isn't being 'used' per se!

I don't know how to express the theory, but in this case, it isn't thought of as a consumable , but more as a potential .

Stuart

A good running stock cam 235 will have plenty of vacuum for power brakes. You cannot use nor need a fuel pump booster for it. The power brake unit has a reservoir built into it with a check valve at the entrance. When you use your brakes you are decelerating & vacuum is at it's highest. You want 3/8 hose going to the booster. There is a filter you can put in the hose that protects the booster. It came on all g.m.,s starting around the mid 70,s.

Good information from Wrenchbender, Ret.

I'm curious about the difference in feel between the original non-power single reservoir MC and and a dual reservoir power unit. After driving a 1957 Chevy station wagon with a single reservoir and no power for years I hopped into a K-5 Blazer with power disks in front for a quick trip. Had the same experience as driving a German Leo 1 after years in US M-60A1s. The Leo also has disk brakes and I stood them both on their noses. Very embarrassing.

After driving a lot of different cars now I may not have a problem with the difference any more, but . . .

Also, is it possible to have a brake hydraulic system that will overpower the mechanical parts? Basically, is there much chance of locking up a wheel, or wheels, without trying to make a panic stop?

I have a 9 inch booster that I pulled out of a friend's 1983 Cutlass before it went to the junkyard. It has the hose and filter with it. I plan to replace the MC.

Thanks for the advice so far....and keep the comments coming.

I've built 50's and 60's trucks with both power and manual brakes. If you are upgrading to front discs, I've noted that adding a power booster, even with a properly designed system (no ABS) can become very twitchy under heavy braking.

My current 54-3100 with manual corvette master, front discs, adjustable proportioning valve is much more predictable...has better feedback and is less likely to lock up under heavy braking.
I found the power assists were so sensative that under heavy braking, your own body weight moving forward, can compound the pressure on the brake pedal. If you choose to run 4 wheel drums I might be more inclined to opt for power assist.
However, I would drill out the 1/8 NPT fitting on the intake to 3/8 NPT to obtain enough volume of vacuum.

On the 9" booster I would dispose of the stock proportioning valve setup and go with an adjustable valve...fewer plumbing and bleeding problems. Being able to control rear bias will be to your advantage.

There is a lot of good brake info at the following sites:

http://www.ecihotrodbrakes.com
http://www.mpbrakes.com
http://classicperform.com

Hope this helps.

Dave

Fla54Chev3100,

Thank you for your input. As I said in my opener I am over-analyzing. I've been to those suggested sites and several more and I have ended up in the over-whelmed phase. I have also read complaints on other threads about touchy or twitchy brakes but I don't remember if it was from you.

My gut feel from the beginning was to keep it simple and no boost. In a panic situation in a modern car you can quickly re-start the engine if it died. Bolts have floor starters and that's the foot on the brake

My 46 has a pedal bracket that mounts to the bellhousing and trans (T-5 in my case) that places the MC right next to the trans. So if I use a booster it will have to be frame mounted with linkage fabricated from the stock MC location.

Research said I needed at least 1,000 PSI to operate the disc brakes. I would have to use a MC with a really small bore. I am considering fabricating a 90 degree mount (similar to ECI underdash style for example) and use that triangle pivot to change my pedal ratio from 5:1 to something more like 7:1 to increase the psi output without a booster.

Clear as mud?

I'm withya!!! In my quest to keep everything "as simple as possible"...eliminate potential problems yet optimize performance, I've discovered that you don't always have to follow the crowd to get it done. I've seen several booster setups that just didn't line up correctly, that caused major interference problems with transmissions, cross members and in the end, didn't deliver the performance that a much simpler system would offer.

It's obvious you've been doing your homework...adjusting pedal ratios and paying attention to system requirements, can go a long way to getting the system correct. Relying on some vendor, who is out to make a "one-size-fits-all" package, can lighten your wallet and leave you with mediocre performance. Sometimes the "easiest way" isn't the best way!!!

Dave