Increasing rear brake bias without a bias controller?

[rossint]

Throw some super aggressive rear pads in it. That willl help the rear do more.
Have tested it on my car, and you definitely have to adjust the prop valve.

Depending on how involved the EBD wants to get aggressive rear pads might not have much affect? Anyone played around with F/R compounds on an EBD car?

[SKYHI]

Ok, so I've now determined I can fit a prop valve in the engine bay, but even after reading a number of threads over different forums, the jury still seems to be out on whether or not it'll work on the SE with EBD

Time to email some "experts" and see what they say.

[rossint]

It appears to be one of the worlds great unanswered questions, report back with any findings.

[RS2000]

Ok, so I've now determined I can fit a prop valve in the engine bay

If you're talking about an abs/ebd car with a willwood valve next to the master cylinder, then you could physically place it in the front OR rear line. But you will only be able to reduce the pressure between the relevant m/c piston & the abs block.

[greenMachine]

Ok, so I've now determined I can fit a prop valve in the engine bay

If you're talking about an abs/ebd car with a willwood valve next to the master cylinder, then you could physically place it in the front OR rear line. But you will only be able to reduce the pressure between the relevant m/c piston & the abs block.

The valve needs to be on the front line(s), to move the bias to the rear.

Do you mean the valve will not affect the line pressure post-ABS block? If you do mean that, it then follows that the ABS block can both pulse for ABS, and somehow (undetectably?) modulate line pressure for more subtle adjustments. This latter function would be news to me (on NB8B). It would also require a sophisticated pressure monitoring function across all three lines, which I rather doubt our rather agricultural ABS is capable of. As far as I know, the only sensing that happens is wheel speed.

I have read the 'EBD' references here to be along the lines of 'the ABS acts like an EBD insofar as it limits the amount of rear braking at the point of rear lock-up'. I have not noticed any 'EBD effect' at low levels of braking, nor can I see much advantage to it beyond evening out F/R pad wear.

The upshot is that I believe a Wilwood valve on the front line out of the master cylinder (and before the ABS) would work to shift the brake bias rearwards. Not having tried this, I can't 'prove' it though. However, the prop valve my now-defunct racecar, in the rear line after the ABS, worked.

[SKYHI]

I am happy to put the prop valve either pre or post ABS, and anywhere in the brake system as long as I can get the desired affect.

[RS2000]

Ok, so I've now determined I can fit a prop valve in the engine bay

If you're talking about an abs/ebd car with a willwood valve next to the master cylinder, then you could physically place it in the front OR rear line. But you will only be able to reduce the pressure between the relevant m/c piston & the abs block.

The valve needs to be on the front line(s), to move the bias to the rear.

Do you mean the valve will not affect the line pressure post-ABS block? If you do mean that, it then follows that the ABS block can both pulse for ABS, and somehow (undetectably?) modulate line pressure for more subtle adjustments. This latter function would be news to me (on NB8B). It would also require a sophisticated pressure monitoring function across all three lines, which I rather doubt our rather agricultural ABS is capable of. As far as I know, the only sensing that happens is wheel speed.

I have read the 'EBD' references here to be along the lines of 'the ABS acts like an EBD insofar as it limits the amount of rear braking at the point of rear lock-up'. I have not noticed any 'EBD effect' at low levels of braking, nor can I see much advantage to it beyond evening out F/R pad wear.

The upshot is that I believe a Wilwood valve on the front line out of the master cylinder (and before the ABS) would work to shift the brake bias rearwards. Not having tried this, I can't 'prove' it though. However, the prop valve my now-defunct racecar, in the rear line after the ABS, worked.

All I'm saying is that the w/w valve can only reduce pressure downstream in the line it is installed in, because upstream is already at m/c pressure. I'm not getting into what happens post abs block.

You would think that installing the valve in the front line at the m/c would allow bias shift to the rear. But, if it does work, you are reducing front braking to achieve it!

[Magpie]

https://www.racedatasystems.com/products/bosch-motorsport-abs-m4-clubsport-kit

https://www.worldtimeattack.com/index.php/motorsport-abs-why-you-need-it/

[greenMachine]

What has happened - the post I wrote last night has disappeared

Basically, I was saying that providing you can still lock the fronts with ABS off (fuse pulled, or handbrake light on), reducing the front line pressure has only had the effect of increasing pedal pressures (ignoring for the moment the effect of increased line pressure in the rear lines).

If that condition is met, then the next step would be to play with the prop valve to get the rears and the fronts to trigger the ABS as close together as possible. If that still leaves you wanting more rear bias (ie still can't get rear ABS activation close enough to front activation even with prop valve fully 'on') then changing rear pads is the only option left.

Thanks for those links Magpie (so pleased that Bosch have at last introduced a budget ABS kit ), there is also a thread on MT.net on a Teves ABS unit. This appears to be out of a BMW, and from my reading is both 4-channel and somewhat (at least) tuneable. Since I am now in 'post-racecar' mode, I have not read it closely. There is also a thread on here from some time ago (which I can't find), but IIRC it was largely focussed on the debate over whether to use ABS or chuck it, rather than how/where to use it.

[SKYHI]

So contacted Trackspeed and 949 via email with the following message:

I have a 2004 NB SE (Australian version of the MSM), that I run in Time Attack events here. It’s a lightly tuned version with about 220rwhp, and runs on the Yokohama AD08R tyres. Because of class regs, it also retains the standard brake calipers, but runs slotted rotors, road/track pads and braided brake lines. It’s become pretty obvious that the front brakes are doing the majority of the work on track, so I’m looking to adjust the bias and get the rears to work a bit harder. I’ve looked into the prop valves, like the ones you guys sell, but no one seems to be able to tell me for certain whether or not they’ll work with our cars given that they have ABS and EBD.

These are their responses, Trackspeed:

Unsure. I have no experience with the NB2 EBD ABS systems. I know that prop valves have been used with those systems, but I think the systems are typically disabled first.

Thanks,
Andrew Kidd

949:

Hello Paul,

The prop valve kit we offer is ABS compatible.

Cheers,
Sales
949 Racing - Supermiata

Neither of them really shed any further light on the existing confusion

[RS2000]

https://supermiata.com/wilwood-brake-prop-valve.aspx

The text line under the Willwood Brake Proportioning Valve heading, reads "Maximum line pressure reduction is 57% with this valve".

They don't mention proportioning ratios, because it is a simple, 2 port, pressure reducing valve, that can't proportion.

I'd guess that those using it on ABS/EBD systems, have uprated the rear brakes until there is a lot more rear bias. Then they install the w/w valve in the rear line, to reduce the pressure down, to give the front/rear balance they want with the car setup they have.

There's good info on ABS re road & track use in that 2nd link posted by Magpie. Cheers

[greenMachine]

For clarity, the SE does NOT have EBD. It does have ABS .

You may have confused Andrew with that reference ...



ETA: RS, just seen your post. That 57% is the maximum line pressure reduction the prop valve achieves. The minimum is significantly less, and the handle adjusts the line pressure reduction between the maximum and minimum values - I call that proportioning, certainly it adjusts the bias F/R. It does not act like a switch, with only an off or an on.

[RS2000]

ETA: RS, just seen your post. That 57% is the maximum line pressure reduction the prop valve achieves. The minimum is significantly less, and the handle adjusts the line pressure reduction between the maximum and minimum values - I call that proportioning, certainly it adjusts the bias F/R. It does not act like a switch, with only an off or an on.

Yes gM, I agree it does all that, I have one on my nb8a, & it definitely adjusts bias. But it does so by adjusting the pressure in one line, using a pressure reducing valve. A proportional hydraulic valve reads the pressure from one line & adjusts the pressure accordingly in the other line.

The factory proportional valve (non abs cars) adjusts the rear pressure according to what front brake pressure (m/c pressure) it sees.
Up to about 570psi m/c pressure, the rear pressure is the same (1:1 ratio) . This point is called the knee point. After this point, the rear pressure is adjusted at a different ratio, & the rear pressure doesn't increase at the same rate as the m/c (front brake) pressure.
The factory prop valve is non adjustable, & you can't get up to max m/c pressure in the rear line, & that's why people remove it & put in the w/w valve.

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[rossint]

The Wilwood valve actually adjusts the knee point based on the pressure it sees rather than just restricts flow through the valve across the board, It is a proportioning valve.
Here’s a guy who actually tested the valves performance.
https://wilhelmraceworks.com/blog/brake ... ning-valve

[rossint]

For clarity, the SE does NOT have EBD. It does have ABS .

From what I’ve seen and read SEs don’t have a prop valve by the master cylinder, you can call the system it uses EBD, ABS or voodoo it’s clearly a different ABS system from other NB2 cars that employ a prop valve