Wicked93gs

Just as the title says, for my project I would like a smaller booster and I would like to avoid a hydroboost setup if possible. Anyone know what interchanges? The Miata booster specifically interests me if it works since its an inch smaller in diameter and 3/4" smaller in depth. I am fully aware that doing this will increase pedal effort to some degree. Any other smaller boosters around that fit? Maybe a 323?

lduley

iTrader: (1)

Why? this idea isn't advantageous in any way, especially in safety of yourself, or others

clokker

iTrader: (2)

Have you considered a fully manual, dual cylinder setup?
If space constraints are your issue, that might help and you can further adapt to restrictions with remote reservoirs.

Wicked93gs

I am not some idiot off the street that wants a smaller booster for no reason. On my project I have space constraints. A properly setup system wont cause any safety concerns. I have owned cars with manual brakes before of the same weight as an RX7, they work just fine. Of course, I also dont tailgate people...I always leave at least 50ft.

As for manual brakes. I have played with the idea, the only concern I would have is the fact the RX7 was never designed for a manual brake option...meaning that even if I reduce the master cylinder size enough for decent pedal pressure then I run into the possible problem of unworkable pedal travel. Do you have any feedback from people who have done manual brakes in a FC? What size master would I be looking at? 5/8? 3/4?. The resevoir itself doesnt cause my space constraints...its all the booster...a combination of diameter and depth causing interference issues with the intake manifold plenum on my swap.

clokker

iTrader: (2)

Calipers are agnostic with respect to "booster/no booster"...pressure is pressure as far as they are concerned.
I've not done this in a FC but did convert my old 240Z (to great effect, I must say).
This is backwards...increasing the cylinder size increases the pedal pressure (and decreases travel).
All the cylinder makers (Wilwood, Outlaw, etc.) have formulae on their sites to calculate the appropriate size for the piston area of your calipers. Add in a proportioning valve (or bias bar) to fine tune the front>rear bias and you'd be good.

ColinShark

You guys are on the same page, not backwards.

lduley

iTrader: (1)

I was more referring to the other idiots on the road that don't know how to brake even WITH proper brakes that pull out in front of you. I won't argue the 7 is a light car and manual brakes shouldn't be a problem, just don't want you kicking yourself in the **** if somebody pulls out in front of you and damn, wish I had power brakes

but, its a double edged sword, chance of it happening are slim and all the other blah blah, just voicein

Wicked93gs

This is very true, it is a double edged sword and power brakes are certainly easier on your right leg under heavy braking. I did answer my own question tonight though...I robbed Peter to pay Paul...I robbed my Miata's booster and tried bolting it up...its a direct bolt in except for the clevis where it attaches to the brake pedal, I pried the Miata's clevis further open, but it would have been easier to just swap to the RX7 clevis really



after I get this thing running I will test out brake feel and see if a smaller master cylinder is needed. I doubt it will be though, since the RX7 is only a few hundred pounds heavier than the Miata, though it most certainly has bigger brakes

It may be that I need a remote reservoir though, clearance sits at about 1/4" there. The motor mounts I have shouldn't allow very much side to side movement though...guess I will find out once its running.

clokker

iTrader: (2)

Well, I see your dilemma.

Did you make the intake plenum?
I'm no expert but seems like I typically see them taper as they approach the most distant intake runner...which would greatly increase space for the brake setup.

As for remote reservoirs, assuming you're comfortable with junkyards, Mitsubishi used remote reservoir master cylinders in many mid-90's models. They will bolt right on to a Mazda booster (although you probably will have to adjust the booster pushrod). I don't recall the range (if any) of cylinder diameters but it'd be worth checking out.

Wicked93gs

Yeah...plenum design is mine(welded before the engine mounts stole 3/8" more space than I calculated). I really didnt want any more taper than I have anyway though since its not really a plenum...its a boost containing airbox for the ITBs and I didnt want to choke that last ITB too much...even if it only makes an appreciable difference when not in boost.

Junkyard parts are fine...especially when they dont involve moving parts since you can refurbish them to a degree before installation. What models should I look for a remote resevoir from? Also...any chance of meeping the warning sensor? I find its nice to have a low fuid warning light, its helped me out in the past.

clokker

iTrader: (2)

Retaining the low fluid warning is simple.
Remember that all the manufacturers are sourcing parts from a relatively small vendor pool (Sumitomo, Nissan, etc.) and the switches are simple and generic. Be sure to get the pigtail when you pull the master and the wiring is dead easy, just two leads.

When I search the yard I'm focused on the parts, not the cars in general.
It's silly I know, but I rarely pay attention to the Y/M/M of the donors.
This makes me a bad internet info source and it's a failing I'd like to correct.

But probably won't.

Wicked93gs

Well, it seems I do have one area of interference. Its the brake line coming out the passenger side of the master cylinder. I cant seem to come up with any other solution due to space constraints other than to use a master cylinder with lines on the driver side...unfortunately I cant seem to find a Mazda master with no lines on the driver side. Any ideas on that?

clokker

iTrader: (2)

Is there room for a banjo fitting?

Wicked93gs

Nope...its touching the tube nut...room for nothing...its a shame I cant just re-drill the port on the other side, not even sure what type of drill bit/tool is used to make a inverted flare hole

clokker

iTrader: (2)

The ports on my favorite cylinder- the 1 1/16" Subaru- are both on the left side and would solve your clearance issue.
I've never tried it on a smaller booster though, so wouldn't know the efficacy.

Wicked93gs

How is pedal effort compared to stock with the factory booster with that cylinder? Also...does it share the Mazda bolt pattern?

clokker

iTrader: (2)

I've not used it with anything but the matching Subaru booster, so I don't know how your Miata booster would perform with it.
The mounting is the same, so it would bolt right up.

Wicked93gs

Let me ask you this then...are there smaller(say 7/8) Subaru cylinders I could use with the outlets on the left?

clokker

iTrader: (2)

There are any number of Japanese cars with master cylinders that have the same mounting flange as ours in a variety of sizes and port arrangements.
A meander through a junkyard should present several options.

Wicked93gs

Are all the pushrods compatible though? That is the question. I find myself working 6 days a week right now so a junyard walk(as much as I enjoy them) isnt in the cards. A google search turns up a Volvo 145(never heard of that model) that has a 7/8 bore with ports where I need them, but who knows whether the bolt hole spread is right, or whether the pushrod will work.

clokker

iTrader: (2)

The pushrod is the very reason I prefer to pull the booster and cylinder as an assembly.

All of my yarding was in search of larger boosters/MCs, but I'm sure there are suitable smaller units available.
The Volvo is probably not a good candidate; besides the almost certain flange mismatch, Euro cars use a different (bubble) flare, so your current lines/fittings would not work.

I'm kinda thinking that modifying your plenum might be a more viable option at this point.

BLUE TII

iTrader: (9)

Could you tilt the engine or move it over to the US Passenger side?

The original engine wasn't square in the engine bay, I don't see any reason the replacement has to be.

Wicked93gs

Cant move or tilt the engine...on the passenger side the turbo CHRA only has 1/4"..maybe 3/8" of clearance from the shock tower. I guess I can always use an adjustable pushrod(or make on...certainly wont be the most difficult thing I have fabbed for this project) when swapping to a different master cylinder. I dont even know why parts manufacturers would ever place the lines on the engine side...it makes no sense...more difficult to get to and they cause issues like this...simply avoided like classic american car manufacturers did by always placing them on the left.

clokker

iTrader: (2)

I'd not noticed American port placement before but to be fair, you are complaining about a situation you brought upon yourself.
In a more or less stock bay there are acres of room around the MC.

Seems like you're willing to downgrade braking performance to accommodate the intake plenum and that is a bad idea.
Ideally, you'd want a larger, dual diaphragm booster paired with a larger cylinder but the plenum is dictating the reverse.

One expensive option would be a set of floor mounted pedals or fabbing a linkage system to move the cylinder inside the cabin.

Can you provide a pic that shows the plenum>cylinder relationship in more detail?
How far is the end of the plenum from the firewall?

Wicked93gs

True...me complaining about the situation wont help anything. On the other hand, booster size does not affect braking performance...it only affects pedal effort, otherwise manual brakes would be just plain dangerous and that is simply not the case. Maybe a hydroboost setup is the way to go...easy to source from a junkyard as well, with Astrovans being a common donor. If I use the Miata booster with a 13/16(or whatever size that is closest) master I should retain stock braking effort with a slightly longer pedal travel. If I retain a 7/8 cylinder with the Miata booster I retain the stock pedal travel at slightly higher pedal effort...more effort doesnt mean it stops slower...it just takes more muscle on my part...braking isnt compromised. You might be able to argue a smaller cylinder will cause a longer throw and a longer throw takes marginally more time so in that case you could consider braking compromised. As for changing the plenum design...no reason to do that if a master cylinder swap will do the trick. I am stubbornly hanging onto the ITB and airbox design since I have so much time already invested in it. If I cant find a satisfactory cylinder then I may add some type of divot to clear the tube nut and line, but doing so will compromise airflow, so its a last resort.

The back corner of the plenum is maybe 1.5" off the firewall, I will get a picture later.