Vacuum Brake Boost vs. Electronic Brake Boost?

[BaseSquatch]

On the 2021 Bronco tech specs sheet, I noticed the following:

The 2.3L gets vacuum brake boost, while the 2.7L gets electronic brake boost. What is the difference between the two systems? I haven’t been able to find much information online.

I’ve also noticed a few other differences between the two engines (besides the actual engine assembly).

For example, according to the 2021 Bronco Owners Manual, only the 2.3L gets a Turbo Boost Guage:

And while both engines get Trail Control and Trail Turn Assist, only the 2.7L gets Trail One Pedal Drive:

I wonder if that has anything to do with the different brake systems between the two engines?

Thanks ahead of time for the help!

 

[OX1]

It's been used since at least the 80's on Fords. The Lincoln MK VII's had it with integral ABS. All it does is typically use an electric motor to create pressure for hydro-boost brakes. Instead of vac doing the "boosting", it uses hydraulic pressure.

They do it mostly as it is a much smaller package that can put out as much (or more) "assist" as a 12" dia dual diaphram vac brake booster (that came on say a 90's, F350). Very popular swap on classic bronco's as there is little space between even a 302 V-8 valve cover and where the MC is mounted on firewall. I put it on my 70 bronco.............

I have a simpler, single point version, on one of my trailers that I converted to 78/79 Bronco disk brakes. Works awesome, much better than even my brand new 14K, 26' alum car trailer drums. It uses the brake controller to progressively actuate hydraulics (brakes), just like the new bronco will.

 

[HBTFD]

Most vehicles historically use vacuum, in the 60s it was advertised as “power brakes”.

 

[Drex]

Normally aspirated engines create vacuum when not at full open throttle, maximum vacuum with it closed, like under a braking situation. Aside from some tuned intakes, the minimum vacuum is normal air pressure is zero gage (14.7lb per square inch or whatever local air pressure might be as that is the normal force pushing in at all times). It is used to increase the brake line pressure, enhancing the pressure applied to the calipers. Turbo cars push air into the engine and reduce vacuum at the same throttle positions. They can go negative vacuum because they are artificially cramming air into the intake using energy from the exhaust. Negative vacuum is called boost. The pressure above ambient outside air pressure. The key is that even at low load and RPM the intake vacuum can be low (getting closer to zero gage) as the turbos are always pushing some air in (a throttle is never 100% closed, needs some air to not stall when at idle). Can create situations where there is varying or not enough vacuum to help power the braking system. The electronic kind uses a pump to create vacuum to drive the brakes no matter what the engine intake vacuum. My supposition in this case is that the turbos on the 2.7 are negating enough vacuum for the brakes to be mushy in some instances, while the 2.3 is less affected because the turbo is not moving enough air to interfere with the braking system. Essentially, it 'spools up' well above idle speed and doesn't see up the vacuum when the throttle is closed.

 

[King Luis]

Normally aspirated engines create vacuum when not at full open throttle, maximum vacuum with it closed, like under a braking situation. Aside from some tuned intakes, the minimum vacuum is normal air pressure is zero gage (14.7lb per square inch or whatever local air pressure might be as that is the normal force pushing in at all times). It is used to increase the brake line pressure, enhancing the pressure applied to the calipers. Turbo cars push air into the engine and reduce vacuum at the same throttle positions. They can go negative vacuum because they are artificially cramming air into the intake using energy from the exhaust. Negative vacuum is called boost. The pressure above ambient outside air pressure. The key is that even at low load and RPM the intake vacuum can be low (getting closer to zero gage) as the turbos are always pushing some air in (a throttle is never 100% closed, needs some air to not stall when at idle). Can create situations where there is varying or not enough vacuum to help power the braking system. The electronic kind uses a pump to create vacuum to drive the brakes no matter what the engine intake vacuum. My supposition in this case is that the turbos on the 2.7 are negating enough vacuum for the brakes to be mushy in some instances, while the 2.3 is less affected because the turbo is not moving enough air to interfere with the braking system. Essentially, it 'spools up' well above idle speed and doesn't see up the vacuum when the throttle is closed.

i still don't get it. because the 2.7 has twin turbos it needs the electronic brake booster vs the single turbo of the 2.3? something isn't really adding up. is there an ELI5 version?

 

[Designkid]

If I was a betting man I would say it has to do with crawl control/1 pedal driving. From my experience with Toyotas, the ones that get crawl control have electronic brake boosters/abs unit. Each individual brake are electronically controlled with the feature (you can hear it working which is unsettling if you've ever been in one) hence the need for an electric brake booster. As 1 pedal drive works the brakes without you pressing the pedal leads me to believe that is why only the 2.7 gets it.

 

[colintrax]

Edit: I was wrong.

 

[OX1]

My 2.7 Fusion has vac brakes that are pretty darn good, so it has nothing to do with the engine itself.

 

[BaseSquatch]

It's been used since at least the 80's on Fords. The Lincoln MK VII's had it with integral ABS. All it does is typically use an electric motor to create pressure for hydro-boost brakes. Instead of vac doing the "boosting", it uses hydraulic pressure.

They do it mostly as it is a much smaller package that can put out as much (or more) "assist" as a 12" dia dual diaphram vac brake booster (that came on say a 90's, F350). Very popular swap on classic bronco's as there is little space between even a 302 V-8 valve cover and where the MC is mounted on firewall. I put it on my 70 bronco.............

I have a simpler, single point version, on one of my trailers that I converted to 78/79 Bronco disk brakes. Works awesome, much better than even my brand new 14K, 26' alum car trailer drums. It uses the brake controller to progressively actuate hydraulics (brakes), just like the new bronco will.

Great visuals, thank you!

 

[BaseSquatch]

Normally aspirated engines create vacuum when not at full open throttle, maximum vacuum with it closed, like under a braking situation. Aside from some tuned intakes, the minimum vacuum is normal air pressure is zero gage (14.7lb per square inch or whatever local air pressure might be as that is the normal force pushing in at all times). It is used to increase the brake line pressure, enhancing the pressure applied to the calipers. Turbo cars push air into the engine and reduce vacuum at the same throttle positions. They can go negative vacuum because they are artificially cramming air into the intake using energy from the exhaust. Negative vacuum is called boost. The pressure above ambient outside air pressure. The key is that even at low load and RPM the intake vacuum can be low (getting closer to zero gage) as the turbos are always pushing some air in (a throttle is never 100% closed, needs some air to not stall when at idle). Can create situations where there is varying or not enough vacuum to help power the braking system. The electronic kind uses a pump to create vacuum to drive the brakes no matter what the engine intake vacuum. My supposition in this case is that the turbos on the 2.7 are negating enough vacuum for the brakes to be mushy in some instances, while the 2.3 is less affected because the turbo is not moving enough air to interfere with the braking system. Essentially, it 'spools up' well above idle speed and doesn't see up the vacuum when the throttle is closed.

This makes a lot of sense. Thank you.

 

[Rick Astley]

For those wondering if there are modifications available to a vacuum boosted system, there are!

As we all know, an engine is essentially an air pump and utilizing that for downstream benefits has been reliable for nearly a century.

Highly recommend Booster Dewey if you're looking to modify your Bronco boosters for better performance.

http://boosterdeweyexchange.com/

If you've never driven a car with vacuum actuated windshield wipers or windows, then you don't know the joy of rev-matching your engine to an accessory. It's quite a bit of fun to get the timing right, as long as you've dialed in at least 17 inches of mercury you're golden!

Flathead engines were, of course, more tricky to pull mercury.

 

[colintrax]

The 2.3eco boost is not related to the old n/a 2.3. It is a development of Ford’s 2.0l EB engine. So, there is no n/a version of the current 2.3 used in the Bronco/Ranger/etc…

I thought the 2.3 was a derivative of the old Mazda engine, but I just looked it up and you're correct. The old 2.0 was based off the Mazda engine, but when the 2.3 was brought to market, an entirely new 2.0 was as well. Ill delete my comment above to keep misinformation from floating around. Thanks!

 

[Tricky Dick]

It's been used since at least the 80's on Fords. The Lincoln MK VII's had it with integral ABS. All it does is typically use an electric motor to create pressure for hydro-boost brakes. Instead of vac doing the "boosting", it uses hydraulic pressure.

They do it mostly as it is a much smaller package that can put out as much (or more) "assist" as a 12" dia dual diaphram vac brake booster (that came on say a 90's, F350). Very popular swap on classic bronco's as there is little space between even a 302 V-8 valve cover and where the MC is mounted on firewall. I put it on my 70 bronco.............

I think you may be conflating hydroboost brakes (pictured) with electric.

 

[Tricky Dick]

I thought the 2.3 was a derivative of the old Mazda engine, but I just looked it up and you're correct. The old 2.0 was based off the Mazda engine, but when the 2.3 was brought to market, an entirely new 2.0 was as well. Ill delete my comment above to keep misinformation from floating around. Thanks!

The 2.0L and 2.3L EBs are still Mazda based, unrelated to prior 2.0Ls like the Zetec and 2.3Ls like the Lima.

 

[Raptor911]

Good info BUT the GEN2 Raptor has vacuum brake boost while the GEN3 Raptor uses electronic brake boost. And the GEN2 and GEN3 Raptor has the exact same engine.

Normally aspirated engines create vacuum when not at full open throttle, maximum vacuum with it closed, like under a braking situation. Aside from some tuned intakes, the minimum vacuum is normal air pressure is zero gage (14.7lb per square inch or whatever local air pressure might be as that is the normal force pushing in at all times). It is used to increase the brake line pressure, enhancing the pressure applied to the calipers. Turbo cars push air into the engine and reduce vacuum at the same throttle positions. They can go negative vacuum because they are artificially cramming air into the intake using energy from the exhaust. Negative vacuum is called boost. The pressure above ambient outside air pressure. The key is that even at low load and RPM the intake vacuum can be low (getting closer to zero gage) as the turbos are always pushing some air in (a throttle is never 100% closed, needs some air to not stall when at idle). Can create situations where there is varying or not enough vacuum to help power the braking system. The electronic kind uses a pump to create vacuum to drive the brakes no matter what the engine intake vacuum. My supposition in this case is that the turbos on the 2.7 are negating enough vacuum for the brakes to be mushy in some instances, while the 2.3 is less affected because the turbo is not moving enough air to interfere with the braking system. Essentially, it 'spools up' well above idle speed and doesn't see up the vacuum when the throttle is closed.