k24madness

iTrader: (6)

I have a Rotrex powered car and wonder how vacuum/boost can be consistent around the track given it's producing boost most of the time.

I don't see any FI people complain about it so maybe I am over thinking things.

chpmnsws6

iTrader: (12)

You can get 2-3 good hits of the brake before you lose the booster. Any time you let off the throttle/decel, you are pulling 24+ inches of vacuum into the booster. As long as you keep the check valve in place, you are over thinking it.

bbundy

Have you actually tried setting up a Miata to run boosterless? I’m not convinced comments like this aren’t too far off of things coming from Miata.net similar to things like you must have 1/2 degree more camber in the rear for your car to be balanced.

EP Miata’s smoke most of the turbo Miata crowd on the track. Most of the top level prepped ones don’t have boosters in there braking system.
A few blips of the throttle and some downshifts in a significant braking zone often times will have a significant effect on the amount of assist you get from the booster even with a darn good driver it can compound the inconsistency’s.

Bob

Alta_Racer

iTrader: (4)

Removing the booster gave my car much more consistant braking, not boosted.

buffon01

iTrader: (9)

Doesn't the booster maximize the pressure applied to the system?

bbundy

The booster acts like a force assist on the pedal. The problem is its power supply is an inconsistent source, Manifold vacuum is not consistently available at the same level and the vacuum reservoir is not big enough in some cases usually associated with racing situations. Maybe a secondary vacuum canister would increase the system capacity or maybe use an electric vacuum pump. But I think on a light car like the Miata setting up the system to work without assist would still work the best.

Bob

Joe Perez

iTrader: (8)

Disclaimer: I have never driven my Miata on a proper track.

That being said, I would think that most of the times when you are pressing the brake pedal, you are not also pressing the throttle with the intention of accelerating the car in gear (eg: heel-toe shifting through a corner does not count.)

If true, I can't see how the system would be unable to recover sufficient vacuum to keep the brake booster working at a fairly consistent level. At worst, you might need to add an external vacuum reservoir teed off from a point between the check valve and the brake booster, which could be as simple as a piece of large-bore PVC pipe with both ends capped off and a nipple installed in one end.

k24madness

iTrader: (6)

I spoke to one of the local racers this afternoon. He stated all of his race cars do not use boosters. Consistent pedal and feel were the reasons he cited.

bbundy

Since I think most the people never experienced the difference and don’t really realize how inconsistent a vacuum boosted system is I suspect there are very few people qualified to make statements about it.

I’d like to know what the best setup is for dual master cylinder boosterless so I can copy it.

Bob

hf-mx5t

my one way valve failed at the track.. that caused a few nervous moments.. full throttle then actually put positive boost into the booster when slamming on the brakes, the pedal was hard as a rock, for almost a second, at close to 130mph. the 3rd gear 90degree right hander came up mighty quick..

other than that, never had any issues with the booster for track use.

Savington

iTrader: (31)

Which local racer, what kind of car, etc?

Pretentious much? It's your job to convince us that a boosterless setup is better, Bob - we aren't going to accept a new idea with no testing just because you think it might be good, and you sure as hell don't get to dismiss/insult someone just because they haven't tried it.

Have you measured the vacuum in the booster line during downshift blips? Do you have any evidence to prove that boosters cause inconsistent braking beyond "I think they do"? I like to think that I can wheel a Miata around a road course and get close to its ultimate potential, and I have never once driven a booster setup that I thought was overboosted or inconsistent in braking zones.

I'm not going to argue for or against boosters either way, but I have a huge problem with you being a pretentious dick and assuming that they are better with nothing but speculation and off-application examples to back up the claim. (Plenty of reasons EP cars would ditch the booster - shave weight, not enough vacuum pulled due to high-overlap cams, etc.)

I would love to see you do the pressure testing (I might throw a MAP sensor behind the check valve myself at the next track day). Even better, I'd love to see brake line pressure comparisons with and without a booster, although that data is a little pricier to obtain. I think that both of my Miatas have pretty consistently bitchin brakes (Sport master/boosters and 1.38" Wilwoods), so it's going to take a little bit more than "It would be better in theory" to get me to spend a penny or a second to switch them.

Stein

iTrader: (46)

Going way out on a limb here, but if it truly WAS a problem, why couldn't you install a smallish vacuum canister between the booster and the check valve to add a bit of "vacuum reservoir" to ensure enough vacuum is available and to moderate out any real or perceived "inconsistency". An Accusump for vacuum. A Vaccusump?

Alta_Racer

iTrader: (4)

What I found dropping the booster, was better padal feel, and the ability to regulate braking better in situations where I had previously locked up one or more tire(s). The pedal effort, yes a little more, but I now dont even notice it jumping from my race car to my street car(power assisted). Trail braking is much more consistant, or should I say predictable, and I can "feel" the reaction of the pedal much better.

My next step, will most certainly be a dual master setup. I want this for better control of front/rear bias, and the saftey aspect of 2 isolated systems, in case of hydrolic failures.

Add to all this, a cupple of pounds saved, and less things to go wrong, master and lines further away from heat, I'm happy.

The car will be boosted this year, but I am currently building a LARGE cam, 14:1, IRTB, high rev motor, that will be in the car for next season. I dont expect to make a lot of useable vacume, and dont want to mess with brakes at that time.

chpmnsws6

iTrader: (12)

Never a Miata, but I've setup a few other cars with booster-less masters. I've never once been impressed with the feel. Some things ARE better left in the 50's. To me, its not worth the few pounds saved to have a brake pedal 3x harder then stock (like I've seen on the other cars). I've heard people say you can adjust the pedal ratio which is a bit of rubbish, as you can effectively adjust the ratio by changing the MC bore size while keeping the rod angle to a minimum. I tried changing the bore sizes also with no luck. I like Stein's idea on adding volume to the system to decrease the effects of pedal usage.

*Edit*- I will add that the cars I was converting to booster-less were around 1,000 pounds heavier.

k24madness

iTrader: (6)

Currently he has a late model mustang with Chevy LS Motor turning low 1:50's to High 1:40's over the top at thunderhill. He runs and owns the American V8 Iron series. He has been club racing for years with various cars. I don't want to post any more info without his permission but with the above you can figure it out.

I don't have enough seat time in my Miata to know if the booster causes any inconsistencies. I was looking for feedback from the more seasoned FI drivers. Based on your statements it's a non issue.

bbundy

You know your wheel bearings will blow up unless you run the factory offset of 45mm

Yes my car has awesome brakes and I don’t have much problem being pretty quick in the car with them. I am pretty use to how they work.

I am also pretty certain there are situations where you get varying levels of assist with the system.

A quick transition from acceleration to braking without a downshift gives you less vacuum assist than if you downshift and generate more overrun vacuum than since the last instant you were off the gas while not on the brake pedal on the track. The difference in braking per pedal force is more than just due to added engine braking I’m pretty sure.


Occasionally in braking Zones and I don’t fully understand what’s going on here for sure there are combinations where you can get on the gas and brake at the same time (Inconsistent heal tow error?) and loose vacuum in your booster and the only way to get it back is let off the brake and gas with the car in gear for an instant. Usually though the response is to just press the brake pedal harder to get the level of braking you want.

There is little doubt in my mind that eliminating vacuum from the intake manifold in the equation will make things more consistent especially for an inconsistent race driver. What the difference will be I’m only guessing. But so are the guys popoing the Idea holding religious beliefs that there stock boosted brake setups are the best it can or needs to be. I don't think any of the FI guys have fully investigated anything about this.

Bob

ZX-Tex

iTrader: (15)

I think the Joe/Stein suggestion of a larger vacuum reservoir would be interesting to try. It is really easy to do if built like Joe hinted at. Like, get a 2-3" piece of PVC, cut it 1-2 ft long, cap it, tap one end for a hose barb, tee it into the brake booster line (booster side of the check valve), stash it in the cowl tray area (where the wipers are) and viola. And a simple in-line ball-valve would make a back-to-back, hell even a lap-to-lap reservoir versus no reservoir test pretty easy to see if it makes a difference.

Vaccusump, ha! Love it. Get a lawyer on retainer now for the Canton infringement lawsuit.

I have definitely felt the inconsistent brake pedal travel phenomenon and have wondered if it came from varying vacuum levels from differing throttle/brake transients. At the very least it hinders heel/toe shifting. In fact I was very close to trying a larger bore master cylinder to help alleviate the problem somewhat. The Vaccusump would be an easier, cheaper option.

FWIW I have tested my booster and check valve and they are both OK.

bbundy

I think as you become faster the amount of time spent in transient between throttle and braking periods becomes much smaller. This is one of the main things you are trying to minimize in order to lower lap times. A vacuum booster requires being off throttle and off brakes simultaneously for an instant to get a full vacuum charge in the system. In trying to drive faster you are really trying to minimize this. I also think peak vacuum charge pressure varies with how much engine overrun you have since the prior brake application. You would never notice it on the street, cruising steady state for any period of time you got a good vacuum charge usually the same every time. On the track however even driving consistent I suspect I’m feeling different amounts of boost assist in different corners. You actually adjust for it pretty easily though. On the track your never driving steady state if possible your accelerating braking or using throttle maintenance in a turn. Even shifting is done quick as to not reach a steady vacuum.

Bob

Stein

iTrader: (46)

LOL, I missed that when I read through. Didn't try to steal Joe's idea.

Savington

iTrader: (31)

Because it's not our job to investigate your ideas. You should probably go and gather some vacuum data on the booster in various situations, maybe compared against TPS/MAP/RPM, instead of insulting anyone who dares to question you.