Wilwood big brakes, 914-4 brakes |
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Wilwood big brakes, 914-4 brakes |
Freezin 914 |
Jan 21 2024, 09:22 PM
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#1
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Senior Member Group: Members Posts: 871 Joined: 27-July 14 From: Wisconsin Member No.: 17,687 Region Association: Upper MidWest |
I figure some here will have more info on this, but Wilwood is advertising it has a big brake available for 914-4s. Just in case anyone would be interested. I haven’t even looked it up yet, but seen the ad in Excellence.
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technicalninja |
Jan 22 2024, 05:44 PM
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#2
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Senior Member Group: Members Posts: 1,290 Joined: 31-January 23 From: Granbury Texas Member No.: 27,135 Region Association: Southwest Region |
Maybe I have the rear pressure accumulator backwards...
A real proportioning valve (that has both front and rear circuits into the unit) hits a knee point that proportionally reduces the rear pressure. As the front pressure goes higher the rear pressure also increases but at a slower rate. The 914 valve only sees rear pressure and it merely shuts it off at a spring-loaded point. Once you hit that point the rear pressure doesn't change in any way, it doesn't drop or gain until you release the brakes at which point the pressure drops off and the accumulator section dumps its load back into the master. This non-knee point is why I don't like them. It can be "tuned" with spring changes, but it is not proportional in any way. The way I understand it is if you lower the spring rate on the accumulator section you lower the pressure it activates at and instead of the stock 525 you see something less. OMG are you right on basic OEM brake set ups. They should always put heavy bias to the front. Morons can deal with front lock up SO MUCH BETTER than rear. As the CG of the car moves rearward this gets more important. I just read your second post... The puppy that Porsche installed looks like a simple accumulator to me. I've worked with shitloads of these (automatic transmissions!). Normally they accumulate extra volume/pressure and are released to make something happen faster. I don't think you will ever see any higher pressure in the rear system than what the valve operates at. Now, I'm going to have to take one apart to investigate further. A bit of search led me here. https://tiltonracing.com/wp-content/uploads...ning-Valve_.pdf That is COOL! the one line only Tilton valve definitely has a knee point. You can adjust when it happens, but you cannot adjust the percentage of proportion. Still way cool! The Tilton valve does NOT look like an accumulator, but the Porsche part does... Thanks @GregAmy just the tidbit about how the Tilton valve works was worth it! I'm big on balance bar dual masters but that link has shown a deficiency in my thought process. I'll be adding one of those to the 916 clone... |
GregAmy |
Jan 22 2024, 06:19 PM
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#3
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Advanced Member Group: Members Posts: 2,311 Joined: 22-February 13 From: Middletown CT Member No.: 15,565 Region Association: North East States |
The 914 valve only sees rear pressure and it merely shuts it off at a spring-loaded point. Once you hit that point the rear pressure doesn't change in any way... I did find this that implies it works the same as the knee valves (with disassembly photos). https://forums.pelicanparts.com/porsche-914...-revisited.html QUOTE As the CG of the car moves rearward this gets more important. My Dodge race cars (L, G, and P bodies) as well as the minivans had a prop valve mounted on the chassis with a lever arm attached to the solid rear axle via a spring; as the car braked the rear end came up, the rear axle would drop relative to the chassis, and the spring would pull on the prop valve, reducing rear brake pressure. We'd cheat in Showroom Stock by modifying/replacing that rear spring to get the bias we wanted... (IMG:style_emoticons/default/aktion035.gif) - GA EDIT P.S. These days, brake bias is managed 100% with electronics via the ABS system. That's been the case for a large percentage of the market since the mid-00s if not earlier. Manufacturers are no longer mechanically limiting rear brake bias, they're managing it via the ABS/TCS systems. We ran into this when we built an '08 Civic Si into a race car for a series that required us to disable the ABS; first time we drove the car (Daytona) we flat-spotted 3-4 rear tires before I drove to Home Depot and bought my add-on aftermarket rear brake bias limiting adjusters to get through the weekend...hey, "brake lines are free" per the regs... |
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