JT's M20 Build Thread

[digger]

Thanks for pointing me in this direction.

Looking through a number of posts, I think we can safely say peak brake pressures are under 2000PSI. In fact, looking at pressure traces under track conditions peak system pressures seem to be around 1100PSI. Overall this is good news (for me) because it means I should be able to get a not-undrivable pedal feel with dual 0.625" MCs and stock rotors. At 70lbs I will be around 800PSI on the two circuits, and 100lbs at the pedal would put me at the 1100PSI peak range. If I absoloutely had to, I know I could put 200lbs on the pedal, which takes me to over 2000PSI.

Those numbers are all with a 50/50 balance bar. Adjusting for a front bias (some spec e30 numbers lead to me believe a roughly 2/3rd pressure delta is what we see above 300psi with the factory setup) means that at 70lbs I should see over 1000psi on the front circuit. I may even be able to get away with a 6.1 pedal ratio, which would reduce pedal travel.

I think I am going to give it a shot. I really want to dump that ugly ass booster.

you sure at 100lb you are over 1100psi?

i couldnt upoad the XLS file but here is the next best thing. i need to check the FR vs RR circuit pressures

unsure if the pressures are just force / total FR + RR MC areas meaning the pressure will be the same in both circuits and hence the bias is only adjusted with the adjustable bias lever not MC piston size but i do not believe this is the case. My calulations use the ratio of areas to work out the pressure in each FR and RR line

[JehTehsus]

Finally got around to taking a stab at degreeing my cam.

Was having some issues getting the dial micrometer properly lined up, anyone have any recommendations where I should rest the pointer?



Further, I decided to quickly check duration (cam is supposed to be a 284/280). Just a rough check, knowing my micrometer probably wasn't perfectly positioned, I was getting 245 degrees or so valve open on the exhaust and 315 on the intake.

Ok, what the fuck?

Oh...



Don't bend the shit out of your degree wheel, kids.

So anyway, I have yet to degree the cam.

[JehTehsus]

Ranger (doesn't post here much anymore) did a bunch of analysis on the stock e30 braking system for his Spec e30. I have read many posts about it from him, might be worth searching out those posts (here and I want to say it was Bf.c). IIRC he had put gauges on both F/R, noted the pressures, leak downs with/without bias valve etc.

Thanks for pointing me in this direction.

Looking through a number of posts, I think we can safely say peak brake pressures are under 2000PSI. In fact, looking at pressure traces under track conditions peak system pressures seem to be around 1100PSI. Overall this is good news (for me) because it means I should be able to get a not-undrivable pedal feel with dual 0.625" MCs and stock rotors. At 70lbs I will be around 800PSI on the two circuits, and 100lbs at the pedal would put me at the 1100PSI peak range. If I absoloutely had to, I know I could put 200lbs on the pedal, which takes me to over 2000PSI.

Those numbers are all with a 50/50 balance bar. Adjusting for a front bias (some spec e30 numbers lead to me believe a roughly 2/3rd pressure delta is what we see above 300psi with the factory setup) means that at 70lbs I should see over 1000psi on the front circuit. I may even be able to get away with a 6.1 pedal ratio, which would reduce pedal travel.

I think I am going to give it a shot. I really want to dump that ugly ass booster.

[ForcedFirebird]

Ranger (doesn't post here much anymore) did a bunch of analysis on the stock e30 braking system for his Spec e30. I have read many posts about it from him, might be worth searching out those posts (here and I want to say it was Bf.c). IIRC he had put gauges on both F/R, noted the pressures, leak downs with/without bias valve etc.

[JehTehsus]

one thing im not sure of is if you put 1000lb into the stock 22.20/17.46 MC what is the pressure you in the FR and RR lines. is it apportioned inversely proportional to area? are the two pistons in linked on common shaft of is there just a spring coupling them? Anyone pulled the guts out to rebuild one?

my thoughts are with 1000lb in the force is common on the stock as probably just a spring coupling them.

where as with dual M/C the force gets split as the displacement is common assuming balance bar is adjusted equally

Most diagrams I have seen show springs between the two pistons internally. Which to my mind makes sense, if you did have a slow leak in one circuit having a spring may mean the difference between getting a single stop done with partial brakes from that circuit vs it not contributing at all. That said I have no idea what BMW did, and I don't have a spare MC around to check.

I wonder if anyone here has actually checked brake pressure on the stock lines? Maybe it is closer to 800PSI on the front and rear circuits under moderate braking. I haven't really seen brake line pressures listed online above 1500psi for panic stops, but it isn't clear to me with our caliper setup how the line pressures correspond to actual braking force and feel. I also can't imagine BMW designed in excessively high line pressures for some reason, but I don't have a working setup to check.

As it is, right now I *may* be boned if those numbers as I have them are roughly correct. i.e. I do not think it is safe to run any combination of dual MCs with the stock calipers because of their smaller piston areas, unless I can get really tiny MCs. Seems like a better plan is to change the calipers, but I don't want tot think about touching that until I have the engine running again. I was looking at it last night, I realized that one of the advantages to having AN fuel lines and connections everywhere is that I could probably get away with leaving the booster in for now if I just don't plumb the E85 sensor and associated Y fittings and bypass hose. I do need to mount everything else though and jiggle some stuff around before I am sure that will work.

[digger]

Ok, I have tried actually putting together a calculator for comparison purposes.

Running the numbers like this it does seem obvious there is an issue... in fact, I am kinda hoping I am buggering up my math. But I think originally I was assuming that at 70lbs pedal force, both MCs would be seeing 70lbs, whereas in reality they only see 35 (with 50/50 balance).

Essentially, stock brakes with vacuum assist (and ignoring proportioning valve), I am getting roughly 4500lbs at each front caliper pad and 2000 at each rear caliper pad, for a total of 13000lbs. Realistically it will probably a little higher because the proportioning valve will introduce a pressure imbalance, and high front caliper pressure but lower rear caliper pressure will equal more overall caliper grip force in lbs due to larger area of front pistons. That being said, rotor diameter, weight transfer, grip etc. all come into play so these numbers are for reference comparison only.

Now, if I run the exact same calculations with dual masters @50/50 balance, 0.75" bore, 70lbs of human effort and a 6.9 pedal ratio... I get 1515lbs for each front caliper and 675 for each rear, i.e. ~4400lbs total, or basically 30% braking force at the rotors for equivalent human effort. Sweeeeeet.

What really sucks, is if I run the same numbers but with 0.625" MCs front and rear, and a 50% front bias, I am getting still only around half the equivalent force of the stock setup. Bringing pedal force up to 140lbs brings me into the right neighborhood, but I am not sure I am comfortable with that kind of effort repeatedly. Certainly with 0.75's front and rear I would need to be putting 200lb on the pedal. Yes, I can do a one legged squat of my 200lb fat ass, but I am sure as hell not doing that all day.

Now, all this goes out the window once you start moving to larger calipers. With something closer to 3.5sq inch front caliper area (say, 1.5" bore dual piston wilwoods), at 70lbs pedal force and 50% bias you see 2780lbs at the calipers. If you are also running larger diameter rotors I would not be at all surprised if this translates into a really good brake feel.

Anyway if someone wants to check my math so I can throw all those numbers out, that would be wonderful:

https://docs.google.com/spreadsheets...it?usp=sharing

one thing im not sure of is if you put 1000lb into the stock 22.20/17.46 MC what is the pressure you in the FR and RR lines. is it apportioned inversely proportional to area? are the two pistons in linked on common shaft of is there just a spring coupling them? Anyone pulled the guts out to rebuild one?

my thoughts are with 1000lb in the force is common on the stock as probably just a spring coupling them.

where as with dual M/C the force gets split as the displacement is common assuming balance bar is adjusted equally

[JehTehsus]

Ok, I have tried actually putting together a calculator for comparison purposes.

Running the numbers like this it does seem obvious there is an issue... in fact, I am kinda hoping I am buggering up my math. But I think originally I was assuming that at 70lbs pedal force, both MCs would be seeing 70lbs, whereas in reality they only see 35 (with 50/50 balance).

Essentially, stock brakes with vacuum assist (and ignoring proportioning valve), I am getting roughly 4500lbs at each front caliper pad and 2000 at each rear caliper pad, for a total of 13000lbs. Realistically it will probably a little higher because the proportioning valve will introduce a pressure imbalance, and high front caliper pressure but lower rear caliper pressure will equal more overall caliper grip force in lbs due to larger area of front pistons. That being said, rotor diameter, weight transfer, grip etc. all come into play so these numbers are for reference comparison only.

Now, if I run the exact same calculations with dual masters @50/50 balance, 0.75" bore, 70lbs of human effort and a 6.9 pedal ratio... I get 1515lbs for each front caliper and 675 for each rear, i.e. ~4400lbs total, or basically 30% braking force at the rotors for equivalent human effort. Sweeeeeet.

What really sucks, is if I run the same numbers but with 0.625" MCs front and rear, and a 50% front bias, I am getting still only around half the equivalent force of the stock setup. Bringing pedal force up to 140lbs brings me into the right neighborhood, but I am not sure I am comfortable with that kind of effort repeatedly. Certainly with 0.75's front and rear I would need to be putting 200lb on the pedal. Yes, I can do a one legged squat of my 200lb fat ass, but I am sure as hell not doing that all day.

Now, all this goes out the window once you start moving to larger calipers. With something closer to 3.5sq inch front caliper area (say, 1.5" bore dual piston wilwoods), at 70lbs pedal force and 50% bias you see 2780lbs at the calipers. If you are also running larger diameter rotors I would not be at all surprised if this translates into a really good brake feel.

Anyway if someone wants to check my math so I can throw all those numbers out, that would be wonderful:

https://docs.google.com/spreadsheets/d/1HgsvKMWmHsRS0U1TAcTCXZ_7MEarS7WT9j1ftFkRTqI/edit?usp=sharing

[JehTehsus]

you could estimate the assist assuming the diaphragm is 10" OD and 5" ID

Pressure x area

7.5 psi x pi/4*(10^2-5^2) = 440 lbf (1,960 N)

equivalent to 110 lb at pedal with 4:1

not sure what the internal spring stiffness is this counteracts the assist

So taking those numbers I am getting ~1000psi pressure from the stock E30 master cylinder @70lb human effort. Which is what I thought originally (used 400lbs for the booster in my estimates when selecting cylinders). I wonder then if the issue is the fact that there are now two masters, even though they are now split across the front and rear? I will take a look at the actual leverage ratios all the way to the disk using whodwhos numbers above and see what it works out too.

I wonder if there is a comfortable set point with the stock brakes. A 0.625 and 0.7 already seem pretty small.

[digger]

Do you have any idea what sort of assist the E30 brake booster provides? It would be great if I had something more definite for comparisons, random googling yields boosters providing anywhere from 400-1000+ pounds of assistance. I suppose we could try and calculate based on diameter and vacuum pressure, but I am far from an expert on whether there is more to it than that or not.

you could estimate the assist assuming the diaphragm is 10" OD and 5" ID

Pressure x area

7.5 psi x pi/4*(10^2-5^2) = 440 lbf (1,960 N)

equivalent to 110 lb at pedal with 4:1

not sure what the internal spring stiffness is this counteracts the assist

[JehTehsus]

Not sure on the fluid vs mechanical advantage, both will cost travel for advantage but not sure on the % each

From notes (not 100% sure on accuracy of MC and Caliper bores)



E30 48/33 Caliper
E30 M3 23mm MC 54/38mm Caliper
328 23.81/22.20? MC 54/38mm Caliper
E36 Ti 23.81/20.64 MC 54/34 Caliper
E36 54/36mm front to rear ratio of 2.25:1
E36 M3 25.40/20.64 MC 60/40mm Caliper front to rear ratio of 2.25:1
E46 330 23.81/22.20 MC 57/44 Caliper

Do you have any idea what sort of assist the E30 brake booster provides? It would be great if I had something more definite for comparisons, random googling yields boosters providing anywhere from 400-1000+ pounds of assistance. I suppose we could try and calculate based on diameter and vacuum pressure, but I am far from an expert on whether there is more to it than that or not.

[whodwho]

thanks for the clarification, so here's a dumb question is changing the effective pedal ratio equivalent to changing the bore size (assuming the % change was equal) or does one avenue provide more force advantage with less additional travel in the real world? my concern over the 5/8 was the pedal travel and it was suggested that 3/4" with 7:1 would be a decent baseline if the pressure limit valve was deleted.

Do you know what size pistons are stock FR and RR stock and the M3 FR you have? numbers i found are 48.0 mm & 33.0 mm for stock but not sure.

based on my calcs the stock pedal box ratio is ~4:1 and the Lee's linkage is 1.7:1 and 1.5:1 which gives the 6:1 and 7:1 settings. Sound about right? i figure maybe i should do some actual calculations before installing

Not sure on the fluid vs mechanical advantage, both will cost travel for advantage but not sure on the % each

From notes (not 100% sure on accuracy of MC and Caliper bores)

The lever in the twin MC booster delete kit (pedal box) has two positions. The mounting point closer to the 1" balance bar multiplies the original pedal ratio by 1.52 while the mounting point further away has a multiplier of 1.73

On an e30 with the original pedal ratio being 4:1, it translates into either 6.1 :1 or 6.9:1
On an e36 with the original pedal ratio being 4.3:1, it translates into either 6.4 :1 or 7.2:1
On an e46 with the original pedal ratio being 3.8:1, it translates into either 5.7 :1 or 6.5:1
Most racing pedal boxes you get from AP, Tilton, Wilwood etc have a pedal ratio of around 6:1

19mm MCs (3/4") is a baseline when using calipers with a single Ø60mm piston or multiple 1.625" pistons

E30 48/33 Caliper
E30 M3 23mm MC 54/38mm Caliper
328 23.81/22.20? MC 54/38mm Caliper
E36 Ti 23.81/20.64 MC 54/34 Caliper
E36 54/36mm front to rear ratio of 2.25:1
E36 M3 25.40/20.64 MC 60/40mm Caliper front to rear ratio of 2.25:1
E46 330 23.81/22.20 MC 57/44 Caliper

[JehTehsus]

FWIW, my Nuke cam gear is pretty much dead on to the cam specs (Enem Z45 turbo) when the "zero" marks are lined up.

I don't expect to have any issues, but doing a fairly quick and rough cam profile isn't too much work so I figure I may as well check.

[mikey.antonakakis]

FWIW, my Nuke cam gear is pretty much dead on to the cam specs (Enem Z45 turbo) when the "zero" marks are lined up.

[digger]

Sorry that is a bit confusing, I was running behind and a little too quick to reply. 8^(

I meant bigger size in general, without a lot of mechanical advantage the pedal is too hard and no modulation. Even with the max leverage setting on this bracket (7:1) it was still not good for me with the .700 and .625 MCs and the stock calipers. When I went to the M3 brakes the fluid ratio of those MCs and the M3 calipers made it usable again. I ended up using a .750 and .625

thanks for the clarification, so here's a dumb question is changing the effective pedal ratio equivalent to changing the bore size (assuming the % change was equal) or does one avenue provide more force advantage with less additional travel in the real world? my concern over the 5/8 was the pedal travel and it was suggested that 3/4" with 7:1 would be a decent baseline if the pressure limit valve was deleted.

Do you know what size pistons are stock FR and RR stock and the M3 FR you have? numbers i found are 48.0 mm & 33.0 mm for stock but not sure.

based on my calcs the stock pedal box ratio is ~4:1 and the Lee's linkage is 1.7:1 and 1.5:1 which gives the 6:1 and 7:1 settings. Sound about right? i figure maybe i should do some actual calculations before installing

[JehTehsus]

is the input fitting to the rail a sharp angle bend like the one coming out to the FPR or a radius one?

I knew the cast log manifold was good for something.....

I have another 90 degree swivel fitting I am putting on the feeder end of the fuel rail. It is going to point towards where the brake booster currently is. The plan is to mount the flex fuel sensor below the brake master cylinders, of course sensor is not very big so I have a Y splitter that takes the 8-AN fuel lines down to two 6-AN, one of which goes through the flex fuel sensor and the other as a bypass. Then another Y fitting, and 8-AN hose to the fuel rail right angle fitting. All of this is fed by the fuel filter, which is just a bit after the hardline adapters. Return line is going to be running directly from the bottom of that FPR back to the hardlines.

*edit: Wanted to note, if you are thinking fuel pressure drop due to the 90 degree bends is a major concern, I think because of the size of the 8-AN fittings I am seeing very minimal loss... I was just using an online calculator to check though (https://www.gates.com/us/en/knowledg...alculator.html) but it makes sense with my understanding, where smaller lines are much more sensitive to bends than larger lines. That said, I understand the fuel has momentum and it does not want to change direction, which certainly makes mounting my FPR directly after a 90 less than ideal, but at this point I am somewhat boned on where to put it. As LowR3vin noted, it is a bit of a piglet.

I could mount it on the other end of the rail (*maybe, there is not much more room there), but I would have to flip the feeder end around. That said I don't expect I will see issues; if I do I can certainly move it at that point and cut a couple new hoses.