Power Brake Boosters

[MGBV8]

I started a new thread so we can do some brainstorming on power brake boosters.

I am not happy with the amount of boost I get from the OEM booster.  50% more would be nice.  

My biggest reason is my right knee.  I have been driving Ol' Red 30 years, now.  Because of my long legs, I have to hit the brakes with my right leg angled.  This is wearing on my knee.  I want to reduce the pedal effort to something a bit closer to my son's Accord Coupe.

Jim Stabe has just upgraded his ride with two new remote boosters.

http://forum.britishv8.org/read.php?7,64513,64528#msg-64528

So what will it take?  Two remote boosters, like Jim?  Or, maybe find a dual booster that will bolt to my master cylinder?

Does anyone know the ratio of the OEM booster?

[MGBV8]

Gonna spend some time investigating a 7" dual diaphragm booster.

I think stock is a 6" single.  The 7" passes the eyeball test.  As a friend once said, " That's do-able."  Great positive attitude.

How much more boost?  Don't know, yet.

[BlownMGB-V8]

How about a link to that booster Jim Staube used? I'd like to give it another look.

Jim

[mstemp]

Carl,

Here is my dual 7" Booster. Been using it for about 17 years and it's worked great. Finish is showing it age but other than that no complaints. Bolted straight to stock location on my 1980 B. Got it from a hot rod parts web based company in WA. Ford 7/8" master, maybe, don't recall and I am a poor accountant etc. Great pedal effort, more power than stock but it did not lose any feel. Bit tight with my FI but just cleared air intake as you can see.

[MGBV8]

And here I thought I had stumbled across a new, easy brake mod!

Did you have to extend your brake lines, Mike?  How much did it change the pedal effort?

[MGBV8]

Jim Stabe said he used two VH 44 remote boosters by PBR.  They are available in different specs.

From Jim:

Google images had a few spec sheets for different versions of the VH44 and also for the larger VH40. The specs included the output port size and the ones I got had a 3/8" 24 thread in them. I connected to my existing plumbing by using a 3/8 24 to -3 AN adaptor with a copper washer and then using 37 degree -3 AN tubing nuts and sleeves. Some of the versions used 5/16 output threads.

[MGBV8]

[MGBV8]

http://hydroboost.com.au/boostertypes.htm

http://hydroboost.com.au/techtalk.htm

[mstemp]

Carl,

Needed 3 short section of lines. Other than that it's stock lines but with addition of 10lb residual valves on rear and a rear bias valve. Car has Rover SD1 4 piston calipers though, so tough to give direct comparison to stock booster as it was all done at same time.

[MGBV8]

Thanks Mike!

I have been planing to add a 2 lb residual valve to the front.  So adding a 10 lb to the rear would take car of needing slightly longer brake lines.  Since, I think, the 7" dual booster is longer than the OEM booster.

There ya go, Graham.  Git'er built & let us know what ya think.  

[MGBV8]

Hmm, another angle.  Is it possible to get a same size as OEM booster with a higher boost ratio?

[Jim Stabe]

I'm far from an expert on boosters but I believe that dual diaphragm units have a greater pressure rise than single diaphragm units. Not sure what a stock MGB comes with but it might be worth a couple phone calls to the folks that make them.

[ex-tyke]

One issue that I'm reading about is that boosters require a minimum 17-20" vacuum to operate correctly. One typical 7" dia., universal booster advertised on ebay, specifically notes that "requires 18" vacuum".
Given that my cam gives me, at best, 13" vacuum at idle, I'm not convinced that a booster is available for my setup.
Guess I stick with manual brakes unless someone says otherwise!

[mgb260]

Graham, Muscle car guys use a vacuum reservoir(can) to compensate for low idle vacuum.

https://www.youtube.com/watch?v=v9G0TN4ZacM

[ex-tyke]

Analysing what you posted, Jim, it seems to me that addition of a reservoir only adds reserve volume to a system without addressing the fundamental issue of low vacuum. After all, isn't brake/booster performance increased when there is a larger pressure delta across the diaphragm.
 Doesn't it makes sense that if atmospheric is on one side of the diaphragm and 13"Hg vs 20"Hg  on t'other side, that pedal assist would be noticeably different.......or am I overthinking this!
Maybe that's why Carl's brake performance is questionable....not sufficient vacuum!

[mgb260]

Graham, this video explains it pretty good:

https://www.youtube.com/watch?v=0OMIzCvYefY

[Jim Stabe]

If you look at what you are doing when braking, you may find you have more than enough vacuum. At idle you may only have 13" but when you are traveling at 40, 50 60 mph you are more likely at 16" or better. Suddenly you need to stop, you lift off the gas and apply the brake. While you are driving along at speed your vacuum is likely 15"-17" but when you take your foot off the gas the vacuum jumps to 20" or more. and with a reservoir that has a one way check valve, the vacuum will be captured at the higher level. My car idles at 16" and cruises at 15" to 17" but when I let off the gas it is way over 20" and the booster works very well. You seldom need boosted brakes at idle.

[ex-tyke]

Gents - thanks for the enlightenment!

[MG four six eight]

Carl
A few newer GM cars use an electric vacuum pump. I know that the Chevy Cruze does for sure and it is there to add supplemental vacuum for the brake booster, due to the small engine displacement and the fact that it's turbocharged.
I seem to remember seeing them on newer Tahoes as well. Not sure what year though, but I'm thinking in the 2010 to 2013 range. 2015 and newer use a mechanical vacuum pump that is belt driven.

I would think that it may be possible to incorporate the electric vacuum pump in the system with a vacuum switch that turns the unit on if the vacuum drops to a certain level. The best part is that they are fairly small and could be mounted just about anywhere.
With higher vacuum applied to the booster, you may even find that the stock booster is adequate!
 
Bill

[MGBV8]

Thanks, Bill!

I have been aware of using a reserve vacuum can for a long time, as I have huge cam in my Camaro.  Never occurred to me that I would need one for my MGB.  I guess first order of business is to measure it.  The high comp. JN block does use a slightly larger cam.

I noticed that the remote boosters have different ratios, so thought maybe I could find a direct swap that had a higher ratio.  They don't always give that info, though.

[Jim Stabe]

I ran across this on the internet this morning. http://brakepower.com/help_abc_16_BAR_t.htm

[BlownMGB-V8]

The booster itself is a vacuum canister, and should hold enough for one or two boosted applications, maybe more depending on how hard you hit the pedal. An aux canister will add more uses between. You can base the size on the booster itself.

Jim

[MGBV8]

Yeah, a reserve canister is not going to help an engine with low vacuum to begin with.  I guess that means using an electric vacuum pump, like Bill suggested.

Here is a Brake Bias calculator to go with the one Jim S. posted.

http://www.tceperformanceproducts.com/bias-calculator/

[Jim Stabe]

This is the calculator I used to design my brake system. It is an Excel spreadsheet so I couldn't post mine on this site but you can download it - it is the attachment in the first post. I like this one because it takes center of gravity height into account as weight is transferred during a stop. It came out pretty much on the money for my car.
http://locostusa.com/forums/viewtopic.php?f=5&t=14424&p=153058

[88v8]

My TR6 with its big cam, made 7" at idle. And it does matter, because if you're tootling down the high street at pretty much idle, that's how much vacuum you have when some pedestrian walks out in front of you.
So I fitted an electric vac pump and a vacuum switch, gave me 19".

Worked well for the five years I ran the car.

Ivor