Pedal boxes

[Theo]

Hi Keith, I had seen the OBP product range and considered them, only reason I'm leaning towards Wilwood is that there's a relativly local supplier so I can go and look at the pedal box before buying it. I did contact OBP asking for a drawing of the bulkhead mount box but they couldn't supply one.

[Theo]

I ended up buying a Wilwood pedal box from Rally Design. Fitting it is progressing nicely - it needs welding in but you get the idea. My friend fabricated a nice frame out of steel box section which picks up on the body shell in several places. I forgot to photo this, shame as it's the bit which requires a bit of thought.





Geoff - would you be able to post up, or pm me the calculations you made for sizing the master cylinders please? I'd be interested to play around with a few variables and see what impact they have.

[Dan318-is]

If any of you guys are interested i have a spreadsheet that will help you work out your sizing for hydraulic brake circuits.

[billgatese30]

I'd be interested in that Dan if you don't mind.

[UweM3]

If any of you guys are interested i have a spreadsheet that will help you work out your sizing for hydraulic brake circuits.

you still have my email address???

[UweM3]

Looking good Theo! Do not skimp on the sheet thickness. My M/C bracket is 5mm thick and I could still see the bulkhead flexing when I stomped on the pedal to test it.

[Dan318-is]

PM me your email address' guys, il fly it over. Its a university one and is quite proper, was written by my dynamics teacher, it is a useful tool.

[GeoffBob]

Nice work Theo. 'Can just make out the underside of that frame you were talking about in the top section of your second photo. Looks properly rigid, I think you're onto something there. It really is a big advantage that these type of pedal sets mount that way.

Geoff - would you be able to post up, or pm me the calculations you made for sizing the master cylinders please? I'd be interested to play around with a few variables and see what impact they have.

Will do. I'll see what I can post up during my lunch time tomorrow. My method is basically identical to that PDF you posted a link to earlier. I'll include some values to help make it a little more understandable.

[Theo]

Yes the frame is nice and rigid. It's welded to the shell in several places, the bulkhead piece shown in the picture is just to make things look nice and tidy. The E30 throttle linkage needs some tweaking so that it doesn't interfere with the clutch pedal, but that shouldn't be too difficult. I really need to get some master cylinders and set the pedal height so I can sort out things like return springs and the brake switch.

Will do. I'll see what I can post up during my lunch time tomorrow. My method is basically identical to that PDF you posted a link to earlier. I'll include some values to help make it a little more understandable.

Geoff, if you could do that I would be very grateful. If you're ever back in Tunbridge Wells I'll gladly buy you a beer!

[billgatese30]

PM me your email address' guys, il fly it over. Its a university one and is quite proper, was written by my dynamics teacher, it is a useful tool.

its in my sig mate

much appreciated

[GeoffBob]

Geoff, if you could do that I would be very grateful. If you're ever back in Tunbridge Wells I'll gladly buy you a beer!

'Might take you up on that offer some time, many thanks.

Took more work to type up those calculations than I expected, and I'm buggered if I'm going to post them all as images here, so I've written them up with an explantion in a PDF document that you (or anyone else interested) can download here

You can also download a spreadsheet in which I have implemented all the calculations here
All values in yellow are values that you can play with. The rest are calculations and should be left alone.

All values in both the PDF document and the spreadsheet are specific to your E30 with the SR20DET engine (or as best as I can estimate). Others will have to estimate values for their own cars (or have them measured). You can expect the larger 6-pot engines to have a slightly higher forwards weight bias than those with 4-pots.

Hope this helps.
Geoff

[Dan318-is]

I'd be interested in that Dan if you don't mind.

Email sent

[Theo]

Geoff, if you could do that I would be very grateful. If you're ever back in Tunbridge Wells I'll gladly buy you a beer!

'Might take you up on that offer some time, many thanks.

Took more work to type up those calculations than I expected, and I'm buggered if I'm going to post them all as images here, so I've written them up with an explantion in a PDF document that you (or anyone else interested) can download here

You can also download a spreadsheet in which I have implemented all the calculations here
All values in yellow are values that you can play with. The rest are calculations and should be left alone.

All values in both the PDF document and the spreadsheet are specific to your E30 with the SR20DET engine (or as best as I can estimate). Others will have to estimate values for their own cars (or have them measured). You can expect the larger 6-pot engines to have a slightly higher forwards weight bias than those with 4-pots.

Hope this helps.
Geoff

Wow, great stuff. I can't thank you enough for taking time to write that up and post it here Geoff. Interesting stuff, and nice to have actually learnt something! I look forward to corner weighting the car and seeing how accurate your estimations are, that's several weeks away though.

I'm still waiting to find out what the clutch pedal ratio on the 200sx is so I can get the right master cylinder for that

Next step is to shell out for some master cylinders I suppose, AP, Tilton and Wilwood all have suitable offerings, all of which are more expensive than the girling type which I was originally thinking I'd use.

[GeoffBob]

Hi Theo, glad I could help.

Don't count on my estimations being too close. I'm afraid I did the best I could under the circumstances so that you would at least have some numbers to work with. I also wish I could be more helpful with regard to tyre traction data - I'm sure there are graphs out there somewhere for Toyo 888's. If I can find those graphs, and if you know your corner weights, I can tell you exactly how many g's of braking you can expect before you start to slide (for a given surface condition). Once you know how many g's of braking you are aiming for, you can plan your cylinder sizes accordingly to make sure you get that amount of deceleration without having to stomp the brake pedal through the floor, or one end of the car breaking traction before the other end has even started to bite! 'You get this right, and you'll have a certain advantage going into corners.

BTW, there's a substantial write-up on an SR20DET engine transplant from a 200SX into a Nissan Silvia in Paul Morton's book "How to Drift".



It's not the most well written book imo, but the SR20DET info may be useful to you and plus you get to learn how to drift. I seem to recall he discusses the clutch pedal in detail since the donor Silvia he used was an Auto, and hence he had to install his own.

More info on the book here

Regards
Geoff

[Theo]

Well I've emailed Toyo to see if they can supply tyre traction data. I also had a search for info on Michelin Pilot Sport Cup as I have a set of those in the garage, but again didn't come across any data.

I've been told that the Nissan pedal ratio is 5.1, so I'm thinking a .813 master cylinder will be ideal. (.625 x 1.25 = .78125)

Thanks for the tip on the book, sounds like it's worth a read although I do find these people who obsess over drifting rather odd. Maybe I should write a book about the art of understeer based on my findings in my track car when it had a 3.5 fitted?

[e21Jason]

Theo

I have several books on suspension and handling, and Geoff has done a very good job of writing up the calcs (top effort by the way) but before Geoff posted I was going to recomend this book as I cannot be botherd to trascribe the calcs.



Gives the calcs for brake setups and is also one of the best i have read for salon cars as most of the other Mcbeath/Stainforth/etc tend to focus on single seaters and double whishbones.

Also if you want a good book on aero



Jason

[GeoffBob]

Thanks for the tip on the book, sounds like it's worth a read although I do find these people who obsess over drifting rather odd. Maybe I should write a book about the art of understeer based on my findings in my track car when it had a 3.5 fitted?

Inclined to agree. Thought the SR20DET bit might be of interest to you, although a transplant into a Silvia is hardly a challenge. Hopefully the lighter SR20 will have solved some of that understeer for you.

I have several books on suspension and handling, and Geoff has done a very good job of writing up the calcs (top effort by the way) but before Geoff posted I was going to recomend this book as I cannot be botherd to trascribe the calcs.

Thanks Jason. 'Will hopefully be of use to a few people. That's not a book I have in my collection yet, I'll look out for that one, Ta.

[Theo]

Is my logic flawed with regard to increasing clutch master cylinder size by the same amount as change in pedal ratio?

This was posted on a nissan forum where I asked about pedal ratio, and I don't really understand anything he says.

Fluid displaced is proportional to length of stroke times cylinder diameter squared. To displace the same fluid with the shortened stroke, you need a 11.8% wider cylinder. 111.8% wider in one direction * 111.8% wider in the other direction = 125%.

.625 * 1.118 = 0.69875

So you could get a .687 (11/16") clutch master cylinder. It'll be 3.3% short. The .75's action will be 15% longer than standard, but that might be a good thing if you're going for an uprated clutch later.

[Jhonno]

Is my logic flawed with regard to increasing clutch master cylinder size by the same amount as change in pedal ratio?

This was posted on a nissan forum where I asked about pedal ratio, and I don't really understand anything he says.

Fluid displaced is proportional to length of stroke times cylinder diameter squared. To displace the same fluid with the shortened stroke, you need a 11.8% wider cylinder. 111.8% wider in one direction * 111.8% wider in the other direction = 125%.

.625 * 1.118 = 0.69875

So you could get a .687 (11/16") clutch master cylinder. It'll be 3.3% short. The .75's action will be 15% longer than standard, but that might be a good thing if you're going for an uprated clutch later.

Simple maths Theo (area and volume..)

[Theo]

Well it's very simple as far as I'm concerned. His post makes pretty much no sense though. Diameter squared means nothing to me? Maybe he means pi r squared? Then he mentions 111.8% wider? Does he mean 111.8% of the original?

Perhaps you could clarify this simple maths...

[GeoffBob]

Theo, his post does makes sense. Area=pi*(r^2)=pi*((d/2)^2) where r is the clutch MC radius and d is the clutch MC diameter. Therefore, it is acceptible to say that area is proportional (note, not equal) to both radius squared or diameter squared.

The point is, you need to increase the clutch master cylinder's working area in proportion to the change in pedal ratio.

Going from a 5:1 Nissan pedal to a 6.25:1 Tilton pedal you need to increase the area of your clutch MC piston by a factor of 6.25/5=1.25, or 125%, as he said.

Thus, you need to increase the radius (and thus diameter) of the MC by a factor = squareroot(1.25) = 1.118.

So, to keep your clutch pedal stroke the same as the standard Nissan clutch pedal, simply multiply the size of the standard Nissan clutch MC by a factor of 1.118.

My suggestion, however, is to go one further and choose the next size clutch cylinder up from that. But that's based on personal preference and if you don't wan't a short-stroke clutch, don't do it. I am running an uprated clutch from a diesel truck with my Toyota engine, but then I am lucky enough to still have a left leg strong enough to push the pedal and my leverage is very good due to my seating position. My preference may change as I get older.

[GeoffBob]

Simple maths Theo (area and volume..)

"By stating it is simple is showing off in my opinion.."

Just kidding Jhonno No offense intended

[Theo]

Once again Geoff, thanks for putting me straight - bit of a schoolboy error by me.

.700 to keep the travel the same or .750 to make it 13% shorter, I'll have another drive in my mates Silvia before deciding, but i'll probably go with the .750.

[GeoffBob]

Just re-read his last sentence and agreed, that part makes no sense.

So you could get a .687 (11/16") clutch master cylinder. It'll be 3.3% short. The .75's action will be 15% longer than standard, but that might be a good thing if you're going for an uprated clutch later.

If the Silvia uses a 0.625" (5/8") clutch M/C then, agreed, the next size up, 0.687" (11/16") will about give you the same pedal stroke as the Silvia (assuming you have the same slave cylinder/clutch arrangement etc). However, going one up on that to 0.75 (6/8") as I suggested will shorten your stroke, not make it longer as he stated.

Sorry, I missed that bit first time around.

Agreed, however, that a 0.75" clutch cylinder will do the trick without making the clutch too hard or too short (just don't forget to adjust the pedal stop!). And even if you should decide to swap it out later on, every track enthusiast running this setup needs to have at least one 0.75" MC in their collection. I'd aim, eventually, to have about five MC sizes (at least) so that you can chop-and-change them between brakes and clutch for various applications. Hill-climbs, for example, demand a slightly different brake setup quite simply because gravity very kindly shifts your static weight to the rear when your cars nose is pointing upwards (depending on how steep the hill is of course).

[Theo]

He has since corrected his typo regarding the master cylinder sizes, and explained his inital post in much the same way you did.

What's your opinion on running an adjustable proportioning valve in the rear brake line as well as having a remote adjuster for the balance bar?

[GeoffBob]

First off, lose the pressure regulating valve in your rear brake hydraulic line (EDIT: sorry, I should have been clearer here, that is to say - lose the stock E30 valve). I think it goes without saying that it is not suited to use with a dual M/C brake setup (although this statement will likely spark some debate that I may have to defend). If you find that you are in the habit of locking your rear wheels without one then, obviously, your bias is incorrect, which is why one should get this right from the word go. In the event that you do apply the brakes hard enough to break traction, you ideally want to break traction on all four wheels at the same time. Well actually you don't want any wheel breaking traction, what I mean is, you need to know that all four wheels are working equally hard (per the given load that each wheel carries)

In other words, its all or nothing. You don't need some nanny acting on your rear wheels when you are trying to brake as hard as possible. You will, inevitably, just lock your front wheels (ring any bells?) in an effort to rapidly slow down.

Now, placing a proportioning valve in line with your rear hydraulic line has its place when and where, under certain conditions, you need to reduce your rear braking torque.

However, be aware that placing a simple restricting tap in line with your rear hydraulic circuit simply slows/restricts the flow of fluid to your rear brakes. That is to say, it does not regulate the fluid pressure. Thus, it functions to slow down the onset of the rear brakes. If you still push the pedal down for long enough the rear caliper pressure will rise and the rear brakes will work just as hard as without the valve. This type of valve must of course be accompanied with an unrestricted one-way valve (in parallel with the tap) else you rear brakes will also come off slowly. Not good!

The preferable option (EDIT: preferable to a flow restrictor that is) is to fit an adjustable pressure regulator in line with your rear hydraulic circuit. This works in such a way that (just like the E30 pressure regulating valve) it caps the pressure to your rear calipers at some value according to the position that you have adjusted the regulator handle. If you now attempt to push the brake pedal harder the hydraulic pressure before the regulator will build and you will feel this as the force applied via the pedal to the rear M/C. So, any increase in pedal force goes to the front M/C since the force at the rear M/C is, essentially, locked by the regulator. In other words, fitting an adjustable pressure regulator will not only limit your rear brake torque, but will also increase your front brake torque if you attempt to push your pedal harder in order to overcome the regulator. Thus, fitting a pressure regulator in your rear hydraulic line also has the effect of adjusting your brake bias (and is a technique that I have seen abused by some who got their M/C sizes wrong in the first place).

My recommendation therefore goes to the remote balance-bar adjuster. It achieves exactly what you require it to without having to fit a complicated and expensive mechanism in line with your rear brakes. I would however suggest that anyone attempting what you are doing size their brake M/C’s correctly in the first place before relying upon a balance-bar adjuster to correct any design woes. The remote balance-bar adjuster is, however, a very useful tool to have in your car for when you need it.

[Theo]

Another very interesting read Geoff, thanks for posting. I hadn't actually considered using my old adjustbale proportioning valve until it was suggested to me in another thread on this forum* I had assumed that the balance bar would give all the adjustability needed, which you seem to be confirming.

*http://www.e30zone.net/modules.php?name ... 8&start=25

[UweM3]

GeoffBob I am little bit confused after reading your last post. You are talking about a adjustable pressure regulator for your rear brake line as preffered option. But your description below it is exactly what a prop valve does.

taken from AP's website


AP:
The screw type proportioning valve CP3550-14 offers infinite adjustment within the limits of normal brake operation. With the cap screwed fully in no reduction in output pressure occurs, with the cap screwed fully out, output pressure is reduced to approximately 1/3rd of input pressure

[GeoffBob]

Agreed Uwe, they are the same device. These type of devices go by a range of names including proportioning and apportioning valves. The point I wanted to make, however, was that in the event of fitting an aftermarket device that claims to be a proportioning valve, fit the pressure regulating type, which is why I use the term pressure regulator in my description. Don't simply fit a flow restrictor. The pressure regulating type is preferable to a simple flow restrictor.

I realise that this point may seem redundant to some, but you'd be surprised what some shops sell and what some people fit.

Theo, from your last post it sounds as if you have have a proportioning valve? So long as its a quality aftermarket pressure regulating type then fit it! As described in my last post it not only works to reduce your rear brake torque, but will increase your front brake torque (as a result of the balance of forces at the pedal). In other words, it will adjust your brake bias. Thus, you will not need a remote balance bar adjuster. We will, however, have to look at resizing your M/C's to work with the valve. Post specs if you can (or maybe its the same as the one Uwe posted? Thanks Uwe).

[UweM3]

I realise that this point may seem redundant to some, but you'd be surprised what some shops sell and what some people fit.

Agree with you about that. I haven't come across any other devices than pressure limiting prop valves so far. But I am sure if you are after a bargain...

I have decided NOT to fit a balance bar/twin master cylinder (yet...) for various reasons.

-- space
-- already have a new twin M/C
-- was happy with the "old" setup (twin M/C, stock limiter valve)
-- never locked the rear wheels, but the fronts

Also a balance bar setup has one downside compared to a prop valve/limiter setup IMHO , it will only work at it's optimum under FULL braking (or wherever the user has dialed it in). That is fine for a race application but in less than racing driving conditions your rear brakes will not be used to their full potential.

Therefore I have decide to give the old tandem cylinder another go and if that is working I have saved myself a lot of trial and error and some £££.

Of course it can also turn out to be shite and I have to strat all over with a pedal box.

PS I haven't seen a pedalbox AND prop valve setup at the same time. Was under the impression you either have one or the other.
Feels like having "a bracket to fit a bracket" if you get my drift.

[GeoffBob]

Also a balance bar setup has one downside compared to a prop valve/limiter setup IMHO , it will only work at it's optimum under FULL braking (or wherever the user has dialed it in). That is fine for a race application but in less than racing driving conditions your rear brakes will not be used to their full potential.

Agreed. I initially responded to Theo's last post last night with an explanation as to why a proportioning valve is not required with a dual M/C setup, since the front and rear M/C's should be chosen to put the car right on the edge of its traction limits. And then, if you plan to win races, this is where you should always brake. Well, that's pretty much how the Barber school of racing teaches you how to brake. I then realised what a hornets nest that would stir up and deleted my post. I think the truth is that a pressure regulating valve (whether fully, partially or non self-adjusting) has its place motorsport. Pulling a maximum g braking manoeuvre (threshold braking) before every single corner is not for everyone (especially during track days and other fun outings)

I plan to post more on this topic later after I have crunched some numbers. I'll see if I can hi-light the actual difference in braking performance when a proportioning valve is added to a dual M/C setup.

[Theo]

[quote="GeoffBob"Theo, from your last post it sounds as if you have have a proportioning valve? So long as its a quality aftermarket pressure regulating type then fit it! As described in my last post it not only works to reduce your rear brake torque, but will increase your front brake torque (as a result of the balance of forces at the pedal). In other words, it will adjust your brake bias. Thus, you will not need a remote balance bar adjuster. We will, however, have to look at resizing your M/C's to work with the valve. Post specs if you can (or maybe its the same as the one Uwe posted? Thanks Uwe).[/quote]

I've got a Wilwood lever type adjustable proportioning valve. It has 6 positions ranging from 0 to 57% reduction in line pressure. I don't have any preference in using this instead of a remote balance bar adjuster, unless it somehow means that I wouldn't need such a large (7/8") rear master cylinder, as this would give me a few more choices.

[GeoffBob]

I've got a Wilwood lever type adjustable proportioning valve. It has 6 positions ranging from 0 to 57% reduction in line pressure. I don't have any preference in using this instead of a remote balance bar adjuster, unless it somehow means that I wouldn't need such a large (7/8") rear master cylinder, as this would give me a few more choices.

I'd need to work it out for you, but you'd most likely require a smaller rear brake master cylinder in order to get your rear line pressure up. That is to say, shift the bias to the rear in order to improve rear brake torque while executing a less than maximum braking manoeuvre. Then, as you increase the pedal force (approaching the point of threshold braking) the rear pressure will be capped and the bias will swing forwards (as required during threshold breaking).

Do you have a part number for that Wilwood valve? I cannot work out the correct M/C sizes to work with it unless I have a graph of P_in vs P_out (similar to the one Uwe posted), otherwise I'd recommend you leave it out.

[Theo]

Very annoyingly I seem to have thrown away the packaging the valve came in, which included the relevant graph as I remember. I've had a quick look on the net for the graph but not found it thus far. The Wilwood part number is 260-8420.

[GeoffBob]

OK, I found the part on the Wilwood site. Unfortunately their PDF download does not include that graph - I'd suggest you contact them and get a copy if you want to use it. In the mean time I'm just going to use the numbers from the graph Uwe posted. Once you have the data from Wilwood I can just change the numbers - otherwise you may have to buy an AP valve