Boosterless Brakes?

[BeirBrennerE30]

I recently removed my brake booster and fabbed up a dual master setup. I have never driven the car with it but I am nervous my braking is going to suck. Either to stiff or to much movement of the pedal. The car is mostly a street car so I kinda want stockish to a slightly firmer pedal.

I would like it to pass the "girlfriend test" i.e. You could put your girlfriend behind the wheel and , assuming she is a decent driver, she wouldnt rear end someone/go flying into a ditch.

set-up specs:
I changed the pedal ratio from ~4:1 to 6.2:1
Front brakes are 332mm rotors with 4 piston calipers 44mm and 36mm pistons
Rear brakes are 299mm rotors with 4 piston calipers 30mm and 28mm pistons
OE Porsche pads

are there any other options to running a remote mount booster? I dont want to run linkage all over the engine bay and a hydroboost system seems overly complex and I have head gives very weak brake feedback. I like the idea of boosterless, its simple, adjustable, fits in a small space(underdash). I just fear poor pedal feel. All the math works out but I have no real world expirence with this. Tilton has been less than helpful.

Thanks guys

[Jean]

The stiffer the pedal the better right? Subscribed to find out your results :)

[z31maniac]

Paging iflytii........

[lifeiskaos]

I have also done the booster delete mod, but have not driven the car yet. From what I've read, there is a very fine line between choosing the right pedal ratio and the right MC size(s). You can easily either have too much travel, or too stiff of a pedal. If you've gone with what tilton has recommended, then I'd definitely try that out first.

If it's too stiff, you can either lower the pickup point on the pedal, or decrease the MC size. If there is too much travel, move the pickup point up, or increase the MC size. If both cases are true.... start working out your right leg :D

[BeirBrennerE30]

The stiffer the pedal the better right? Subscribed to find out your results :)

well up to a point. There is a point where you have to push so hard on the pedal to stop that its a pain in the ass/ not be able to generate enough force

on the other hadn you can make the pedal so limp that it will go to the floor and not move enough fluid to press the pads hard enough against the rotors.

[bejbis]

Im assuming you've done all the math involving the brakes on a stock e30? how does that compare to the setup you have now? i may have missed it, but you forgot to add your master cylinder bore.

[Mike325]

Check this thread out.

http://www.r3vlimited.com/board/showthread.php?t=78855&highlight=Euro+Brake+Booster&page=7

[2002maniac]

What size master cylinders are you running? You'll want them small to ease the pedal pressure (travel will be longer)

I experimented with a 7:1 pedal ratio and stock sized master cyl and it was definitely way too stiff to pass the girlfriend test.

I might give it another try with a 19mm porsche master.

Here's what I came up with:

[BeirBrennerE30]

Check this thread out.
http://www.r3vlimited.com/board/show...Booster&page=7

yeah I have read that thread cover to cover about 4 times now. I talked to Mike. B and he isnt making the DTM setup anymore.

As for as master size. I know what the equations tell me I should run. I am waiting for Tilton to confirm it... But they say that are too busy. Thats a whole different story though.

if some one wants to do a sanity check on my math here it goes... I made some assumptions so please correct them if they are wrong.

Weights: Last time a weighed the car with me and full fluids it was around 2900lb. I am assuming a 53/47 weight balance to the car front to back with an s54. I have no data to confirm that. Thats 1537lb on the front axel static and 1363lb on the rear. I am guesstimating that the CG height is 18" from the road surface. I measured it before but it was with the m20 still(2001) and the car has changed a lot since then.

Cars wheelbase is 101"

Tire rolling diameter for a 205/40-17 is 23.5" or 1.96'

Brake pad coef or friction... just guessing .4 here. Cant find much data on this.

Max decel rate... I have no idea... 1.25g???

Weight transfer during braking = total weight * decel rate *( CG height / Wheelbase)
= 645.4lb

Dynamic front weight = static + transfer
=2182.4lb (this seems high to me... but its erring on the wrong side i guess)

Dynamic rear weight = static - transfer
=717.6lb

Torque requred to stop the front = (Dyn Front / 2 wheels)* (Tire dia / 2) * decel
=1335.6 ft-lb

torque rear = 439.16 ft-lb

Front brake pressure needed to stop = torque front / ( piston area on one side of caliper * effective rotor radius in feet ~ rotor radius -1in * pad coef of friction * 2 side of the caliper)
= 1011.2psi

rear circuit pressure
= 732.6psi

no assuming I use a .625" bore for the front master and a .75" bore for the rear (these are as small as tilton masters go for the front)

force needed for each master = front pressure * master bore area
= 310.2lb

rear force = 323.7lb

The balance bar averages these out and i would need a little front bias on the bar if these numebers are right. but if you add them I need to generate 633.9 lb for force with the pedal.

with a 6.2: pedal ratio thats 102.2lb I would need to generate to stop my e30 at the quickest rate possible.

102lb seems like a lot of force. Thats more than half my body weight. Assuming the girlfriend test and a 110lb girl thats almost her entire weight on the pedal to stop the car at the max rate. Now granted every stop isnt an emergency stop or going into the corkscrew at Laguna but is this something I want to deal with??? discuss...

[Massive Lee]

Get small MCs. No more than 18-19mm (3/4")
And don't forget that with a race set-up, you need race pads with a high friction coefficient. ;-)

[BeirBrennerE30]

Get small MCs. No more than 18-19mm (3/4")
And don't forget that with a race set-up, you need race pads with a high friction coefficient. ;-)

you really think I would need race pads Lee? what do you think about this set-up? Is it streetable? what does it feel like?


I did some more calculations....

Prior to ripping up everything in my car I had a 25mm master with the same brakes and an e21 booster

still trying to get 1011.2 brake pressure the 25mm master requires 769.4lb of force. With a 4:1 pedal ratio thats 192lb. Anyone know what the multiplication factor of the e21 booster is? if its 2:1 we may be in business. If its 5:1 I am basically screwed.

Conversely I had these brakes with a stock e30 master and booster and I thought the brake pedal was too spongy.

[BeirBrennerE30]

more data... I found this from the Highway Safety Research Institute that did a study on brake pedal force.

An experiment was conducted to provide distributions of foot force for U.S. drivers in order to derive guidelines for the maximum force requirement for actuation of an automobile service brake. The results of this study are compared with three others conducted at about the same time. Since the 5th percentile female maximum brake pedal force is about 400 newtons, it is recommended that no more than this force be required to attain near maximum braking capability from a passenger car.

400n is ~90lb not too far off from my original calculation of 102lb...

[payney8]

subscribed

[b*saint]

Why would you want to remove the booster?

[TwoJ's]

You just subscribed to a thread that hasn't been posted in for over three months...


Eh, forget that. I had a very similar problem to this one that was given to me by a potential employer. I have the scans of the written-out shit I did. I'll post them in a little while to see if they are of any use.