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There is two sides to this debate, however I'm trying to collect some data to make an informed decision so any help would be appreciated.

Due to the space restrictions in a non-US MX5, combined with ITB's leads to a compromise in trumpet length. Therefore the suggestion has been to remove the booster, hence freeing up space. At the moment I have an alternative, which is turn the trumpets 90 deg and bring them towards the bonnet and cut a hole in the bonnet. Competition Systems needs to advise the impact on the 90 deg bend, but it is the current plan.

Stock info:
NA6/8 at 44 lb/ft pedal pressure = 754/796 PSI brake line pressure. Booster is 4.74:1
NB at 44 lb/ft pedal pressure = 1038 PSI brake line pressure. Booster is 9.7:1
NB8B at 44 lb/ft pedal pressure = 638 PSI brake line pressure. Booster is 6.4:1

Now my set up is with NB8B brakes BUT the NA6 booster/master cylinder. In my mind this means that I will have more travel than a stock NB8B and they will be less 'touchy'. However when compared to a NB they will 'feel' like they need to be pushed to the floor due to the different booster ratio.

Again with my logic, less pedal travel will make brake modulation a little harder whereas more pedal travel (more effort) allows for greater modulation. For the track the ability to modulate is probably more important than having a short travel.

Therefore the solution to removing the booster would be to replicate the 754/796 line pressure at 44 lb/ft pedal pressure.

Data to be collected:
1. Brake line pressure at 44 lb/ft. Force gauge needed to check!
2. Actual vacuum being supplied to booster. The booster should be receiving 66.7 Kpa of vacuum.

Now when looking at some unboosted cars it is more than likely the booster has been deleted for 'show' or a complete custom boosterless brake system has been designed. Just deleting a booster from an assembly that has been holistically designed does not sound right. The master cylinder size can be changed, the pivot point can be changed or even a pedal box installed and more aggressive brake pads however is this 'improving' the brakes?

At the Jap Nats I'm going to take a walk and see how many cars run boosters and if possible talk to the drivers for their thoughts.

Let the debate continue, if at all...

You have summed it up pretty well.

Basically, a simple delete without changing pivot and/or rod arm length will result in spongy, dead brakes. Don't do it.

If you simply move the pivot and arm length to replicate the foot-to-line pressure ratio, you will end up with a pedal that is 10 miles long. Great for progressive braking but I suspect it will be too long to be effective.

Generally, and for this reason, a booster delete necessitates you going BIGGER in the master cylinder so that the same pedal travel with a shorter rod/arm length pushes the same amount of fluid as the smaller (boosted) master cylinder with the longer arm.

In this way, I have seen the Wilwood 1 inch unit used in this application on an MX5. In my (unboosted) car, we are running dual masters but smaller - 0.7" for the rears and 0.75" for the fronts (4 pot AP). This setup works great.

Dual masters is definitely the way to go if there is a workable solution.


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There's a guy in the states who's build I've read through on an astina (pretty much identical setup as an na8) who's deleted booster, 1" master, 6 pot brakes at front, 2 pot rears I believe. No modification to pedal etc. Says less pressure required than factory setup due to multiple smaller pistons vs 4 larger ones. Not sure of the exact scientific reasons but that's just some info I've gleaned.

sailaholic wrote:Dual masters is definitely the way to go if there is a workable solution.

It can be done on an NA, my car is proof. The install is a serious PITA though. I didn't do mine, but I have had the whole system out of the car, rebuilt it and reinstalled it so I know how it works. Mine are mounted on a Tilton carrier inside the cockpit and pedal assembly modified to fit. Installation and maintenance is not easy though.

Mine was done using Tilton 74 series masters though, and the fit is TIGHT. If I was to try this myself with another car, I'd try something more compact (like the Tilton 75 series).

Do you have any pictures you're willing to share Zossy?

I'll try to remember to take some when I get home. It's hard to see up under the dash where they're mounted but I'll do my best.

That would be cool. Thanks

I'll second plohl's request.

So essentially zossy1 your solution was a complete new brake system designed to run without a booster.

Magpie wrote:I'll second plohl's request.

So essentially zossy1 your solution was a complete new brake system designed to run without a booster.

No, not really.

My car has stock MX5 rear brakes, AP fronts, with MX5 lines back to the OEM master Cyl/booster location. At that point, the fronts are T-joined into one line, and new hard lines plumbed in from the rear (single line) and the front (two into one line), with these two hard lines (one front, one rear) running through the booster hole in the firewall and into the cockpit. There, they join on to two master cylinders (a 0.7" for the rear and a 0.75" for the front) that are mounted on a Tilton pedal assembly like this, only modified to fit where the factory brake pedal used to be and clutch side removed:

http://tiltonracing.com/product/600-ser ... -assembly/

This also allows the use of in-cockpit bias via a balance bar.

As promised:

Don't they delete the booster when doing showcars? They mount them inside the car under the dash (I think).

Show cars, at least to me are just that, for show hence art over function. However you can purchase remote boosters.

For example http://www.hemiperformance.com.au/store2/p_2507_PBR-VH44J-Remote-Brake-Booster-Suit-Disc-Brakes

Maybe some show cars have a remote booster hidden somewhere, interested to hear any feedback on this. My question more relates to dríven cars (track/road).

Zossy1 thanks. Any reason you did not do a full pedal box?

As I said before, I didn't build it - this is how I bought the car. However, if I had built it, I wouldn't have gone to the trouble of doing a full pedal box as there really is no need to mess with the clutch assembly.

However, I would have used more compact master cylinders, and probably flexible braided lines (rather than hard lines) through the firewall.

Why not just relocate the booster?

More room for trumpets etc, and you still get to have decent brakes.