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  #16  
Old July 10th 2009, 15:40
RuleO9 RuleO9 is offline
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New pics of today!
Chassis is ready!





Adaptors for the boxster calliper..
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  #17  
Old July 11th 2009, 05:28
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Is this primarily a competition car? I notice that your brake bias is heavily to the front (assuming a 19/19 master cylinder) the Kersher rear brakes don't help with the small single pot calipers and solid discs.

Clive
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  #18  
Old July 11th 2009, 07:02
RuleO9 RuleO9 is offline
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No it's just a street car.. It's also a bigger master cilinder

Do you mean that my front brakes are to big against the rear brakes?
Grtz Roel
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  #19  
Old July 11th 2009, 09:00
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The front brakes will be 4 piston and the rear is shown as a single piston. A bug requires near to a 50/50 brake bias. That is to say that the braking power should be about the same front and rear because of the heavy rear weight bias transfers forward under braking. On a front engined car with a weight bias of 55% front and 45% rear the brake bias will be around 75% front and 25% rear to take care of the weight transfer under braking.

The way to calculate your current bias is to compare the total front caliper piston area/front master cylinder piston area with the total rear caliper piston area/rear master piston area. Also, the brake disc diameters will moderate the final figures but I am assuming that the front and rear discs are about the same diameter?

You say that the master cylinder is larger - why? The smaller the master cylinder the more power you can apply to the brakes as the hydraulic advantage = total caliper piston area/master piston area. The downside of the smaller master piston is the longer pedal travel but generally this is minimal on a well set system. The bug 19/19 master cylinder is usually big enough for almost all applications and it will be only where massive caliper piston areas are used will you need a larger master cylinder to compensate.

Clive
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  #20  
Old July 11th 2009, 09:27
RuleO9 RuleO9 is offline
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The diameter is the same.. You're the first to say that the brake bias isn't correct with these calipers..
So i need? Bigger rear calipers or smaller had the front?
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  #21  
Old July 11th 2009, 10:20
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You do need the same piston area or thereabouts at the front and rear if you are running a plain bore master cylinder. Alternatively, you could use a balance bar set up on the brakes so that you can run the same calipers as you have but i suspect that the difference in the master cylinder bores would be almost unobtainable. Another problem you have is that the rear disc is solid that restricts your options on calipers dramatically. You were much better off using the 944 rear disc as many of the standard Porsche alloy calipers fit. I have the 944 set up with 928S4 4 pot calipers on the rear that would complement your front set up perfectly.

I suspect the Kersher rear brakes were to match the standard disc fronts not a Porsche 4 pot units. If you want to retain some sensible brake balance you will need in my opinion to change the rear discs and calipers for a Porsche set up with 4 pot calipers. Obviously, if you can fit the same set up to the rear that you have as the front that would be ideal. I would (have) fitted a brake bias valve in the rear circuit when you have matching front and rear or more powerful rear brakes so that you can finely balance the car. For a road car the front brakes must just lock before the rear to maintain optimum control and maximum braking effort.

Clive
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  #22  
Old July 13th 2009, 07:50
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Looking very nice!!

What paint did you use on the chassis of the car?
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Blitzem with Type 4 power
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  #23  
Old July 14th 2009, 11:39
RuleO9 RuleO9 is offline
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First the chassis was metalised..

After that i sprayed coating on the chassis...


The same i did with the frame..
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  #24  
Old July 14th 2009, 16:11
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Quote:
Originally Posted by evilC View Post
The front brakes will be 4 piston and the rear is shown as a single piston. A bug requires near to a 50/50 brake bias. That is to say that the braking power should be about the same front and rear because of the heavy rear weight bias transfers forward under braking. On a front engined car with a weight bias of 55% front and 45% rear the brake bias will be around 75% front and 25% rear to take care of the weight transfer under braking.

The way to calculate your current bias is to compare the total front caliper piston area/front master cylinder piston area with the total rear caliper piston area/rear master piston area. Also, the brake disc diameters will moderate the final figures but I am assuming that the front and rear discs are about the same diameter?

You say that the master cylinder is larger - why? The smaller the master cylinder the more power you can apply to the brakes as the hydraulic advantage = total caliper piston area/master piston area. The downside of the smaller master piston is the longer pedal travel but generally this is minimal on a well set system. The bug 19/19 master cylinder is usually big enough for almost all applications and it will be only where massive caliper piston areas are used will you need a larger master cylinder to compensate.

Clive
All of the above is VERY true. Took me a while to actually get to know the real world data against the 'theory'. The theory is rather off, but the above is spot on.
Just take really good notice of what he said Roel ;-)
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  #25  
Old July 15th 2009, 19:00
RuleO9 RuleO9 is offline
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I can't use these rear brakes? Also with a balance bar set up on the brakes?
Because these disc and calipers are new.. and my pockets are almost empty after 2 $$$ years...
Than i have to change the discs and calipers.. An other 1000$
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  #26  
Old July 15th 2009, 23:16
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Rule,
I think what they are trying to do is to let you know that you have built an amazing car, and that they want you to fully understand the setup that you have and the way you have it setup.
It's important to know that if you run the setup you have, you can get into a scary braking situation. You have built your system (very well) however with a possible error in the configuration. Can you drive the car as it sits? Yes, just do so carefully. And at the earliest opportunity I would advise a brake upgrade in the rear. Why did you decide not to run the 944 arms and calipers? I mean I know the wheel was to wide but why not run small offsets (wheel spacers this lets you run a bit wider fender in the rear, and who doesn't like a little wide ass-end). that would allow you to maintain the 4 pot rear caliper setup. And when you do upgrade that way, make sure you cut a brake balancer into the rear brake line.

Sick build great pics.
thanks for sharing, and drive safely.
jmd
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  #27  
Old July 16th 2009, 02:10
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Yes, its more like jmr says, spot-on actually.
Just run it as is, it will be fine, but if you want more total brake action and less locking up the front tires, another possibility that just costs about 50-100 euros is to use a 944 brake master cylinder. Those have 23mm cups for the front brakes and that will lessen the front brake action somewhat, so bias will improve and pedal travel will be even less.
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  #28  
Old July 16th 2009, 05:44
RuleO9 RuleO9 is offline
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@jmd my rear fender are 6cm wider..
The rear rims were 4cm to wide each side.. That 8cm in total..
My option were smaller wheel or what i did..
If i have on 1 day other wheels i can change the 944 suspension back..

@ Wally.. My master cilinder is from csp and it was order by Frank from franky's vw service after he know witch brake set-up i have on my bug.


I'm gonna wait and look how the bug drives and brakes..
I'm going to be carefull.. And maybe in the future change some parts..

Thx
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  #29  
Old August 3rd 2009, 13:33
RuleO9 RuleO9 is offline
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My engine is ready, i'm gonne pick him up tommorow...

162hp on 5600rpm
227nm on 4500rpm

On 3000rpm i have 220nm

Next week is my bug ready to drive..
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  #30  
Old August 4th 2009, 11:16
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