LocostUSA.com

Hi y'all

First time post... Long time troll.

I've trolled quite a bit and haven't been able to find a post about brake systems on "1.8L NB1 Miata" builds. It appears that there's a lot of people who have used a Miata as a base for their build, but I can't find a mention about how they've handled their brakes.

I picked up a Champion frame with a 00 Miata 6-Speed as a base for the build. I'd like to continue with this build on the same premise but my current snag is with the Master Brake Cylinder. I'm looking to delete the Booster from the system but leaves me with a potential 2.5:1 ratio for M/C to disc. That to say the least is not a desirable setup. I'd rather have a brake ratio closer to 6:1 but hoping to learn from previous experiences from the other Miata Locost owners.

My question is: What Non-Boosted Master Brake Cylinder are you using on your Miata brake system? Again, my current setup is 2000 Miata Disc/Calipers/Pedals system, and trying to see if there's a MC that I can get Off-the-shelf (I read somewhere that RX-7 MC married to Miata brake system may achieve desired results).

Thank You in advance!

When sourcing master cylinders, you should look for M/C that gets you in the bore area range 7 thru 10 to 1 ratio when comparing front or rear caliper diameters to the M/C bore area. Note a smaller diameter master cylinder applies more pressure on the brake pads, but will increased the pedal travel. Always put a light return spring on the brake pedal levers. This will make sure that the fluid return ports are un-covered when you lift your foot. When changing to manual Vs power brakes you will need to change the brake pedal lever ratio. Manual system typically have a ratio between 5 to1 and 6 to 1. When re-locating the push rod hole in the brake pedal lever try to keep the rod within 7* input angle, to reduce side loading of the piston in the MC. There are tons of MC's out there 5/8 to 1", range to choose from, plus by changing the pedal ratio you can easily dial in a brake system that you are comfortable with. Some people want a hard short travel while others want lite pedal longer travel. Your designing the system so you get to choose. If you are looking at any track use, you should probably consider a dual MC system. Davew

The booster provides no ratio. It applies around 100 lbs of force from engine vacuum to the master piston.

Your front calipers have 2 inch bores and the master is .875" so I'm not sure how you got that ratio.
I'd drill the pedal an inch closer to the pivot, leave the old hole, fit the master at the right height for the new hole, but leave room to move the master down to align with the original hole if needed after testing.

_________________
Miata UBJ: ES-2074R('70s maz pickup)
Ford IFS viewtopic.php?f=5&t=13225&p=134742
Simple Spring select viewtopic.php?f=5&t=11815
LxWxHt
360LA 442E: 134.5x46x15
Lotus7:115x39x7.25
Tiger Avon:114x40x13.3-12.6
Champion/Book:114x42x11
Gibbs/Haynes:122x42x14
VoDou:113x44x14
McSorley 442:122x46x14
Collins 241:127x46x12

I'm truly only trying to be a student at this moment, so please don't let my next statement appear to be a challenge. I'm simply seeking to understand what it is that everyone is referring to when they're talking about brake ratios.



If the caliper bore size is 2" and the M/C bore size is 0.875" then shouldn't I see that as a ratio of

Ratio 2.0:0.875

Which in turn converts to

2.0:0.875 approx 2.28:1.0

Which translates to a compression ratio of approximately 2.3:1?

So I should seek out a M/C that has a smaller bore size to achieve greater compression ratio?



So when everyone is talking about ratios in respect to the brake system, they're talking about the location of the M/C piston in respect to the location of the brake pedal lever?
So if I were to keep the Miata M/C then I should focus on positioning the M/C piston higher which should give me a shorter lever throw and greater compression leverage on the piston bore?!?!

So if my caliper bore is 2" in diameter and if I were to choose a M/C that has a 5/8"=0.675". This would give me a ratio of
2:0.675 which approximates to 2.96:1.0

Which leaves me with adjusting the M/C bore location to achieve the desired ratio of 7:0?



In preference, I'd like to keep everything as a Miata just to make life easier when it comes to part replacement/maintenance and mating the parts are a little easier. So M/C position relocation sounds promising to me.

I'd rather have this Locost as a daily driver as track days seem to take a bit too much time for me at this moment. Plus I recall last time I said "I'm just going to the track this once" I found myself in a second season on a now-modded vehicle thinking about how I can shave enough time to be able to attract a sponsor as my track-days were much more expensive than what I had originally intended (that was $0.00 of future money as it was supposed to be a one-time thing ). I tend to have a bit of a addictive personality when I find a hobby I enjoy.

" M/C that gets you in the bore area range 7 thru 10 to 1 ratio "
Grabber, see math below.
You have to compare the area of the bores, {Pi R sq'd} of the MC to caliper.

Here is a copy of my work sheet
Hi-ace braking caliper with stock GTS master cylinder
Front DX Caliper area = 3.042 Sq inch for 50mm* Dia. caliper.
Master Cylinder area = .518 Sq inch for .8125” Dia. Bore.
85 lbs @ 5 to 1 ratio = 425 lbs This pressure applied to your brake pedal
425 lbs > .518 sq/in = 820 psi line pressure*
3.042 sq inch x 820 psi = 2495 Force on disc

My stock Corolla brake lever ratio with power brakes was 3.5 to 1. I just moved the push rod hole up to get a ratio of about 5 to 1 for the manual system.
I would also note that 85 lbs load applied to the pedal is a very conservative loading.
Davew

Like Dave said.
Liquids don't compress, so lets just call it a ratio.
Mostly folks talk about pedal ratios. By moving the attachment closer to the pivot, you will be compensating for the loss of assist. Just need to make sure you have enough travel to fully apply the brakes without bottoming out the pedal.

It is much easier to find larger bore mazda masters than smaller. Seems they used that size on nearly everything that is compact. However, if you find you need a smaller bore because the effort is too great, a late 80s ford festiva master has the same size fittings (m10-1.0) and has a 3/4 bore.

_________________
Miata UBJ: ES-2074R('70s maz pickup)
Ford IFS viewtopic.php?f=5&t=13225&p=134742
Simple Spring select viewtopic.php?f=5&t=11815
LxWxHt
360LA 442E: 134.5x46x15
Lotus7:115x39x7.25
Tiger Avon:114x40x13.3-12.6
Champion/Book:114x42x11
Gibbs/Haynes:122x42x14
VoDou:113x44x14
McSorley 442:122x46x14
Collins 241:127x46x12

DaveW and Miata8, thank you both for all of your help with this. I'll go ahead and start off with your recommendation on moving the M/C up by either an inch or two and go from there on lowering it until I get a spot that feels "correct". If I still can't get it to where I want it at I'll try a smaller bore sized M/C.

When moving the MC and push rod up to change the pedal ratio, you need to address the travel arc of the push rod. You do not want the brake pedal arm swinging pass center. Which will actually start to reduce the leverage. Just keep that in mind. You may have modify or make a new push rod, depending on how you designed your hanger bracket for the brake pedal. As mentioned before, try to keep the push rod within a 7* input angle into the MC.
Davew