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86GT3.4DOHC
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APR 04, 04:33 PM
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All standard engines maintain (if operating properly) about -9PSI at idle, -6PSI at cruise and ~0PSI at WOT. A SC/Turbo engine is just the same, with the exception that they go to above 0 PSI at WOT and heavy acceleration, they will still stay at -9 idle and ~-6 cruise, if they didnt you would get really really bad gas mileage as the ECM would constantly be in full enrichment mode. While I have no way of confirming, I would speculate that the boosters would maintain and check in as much vacum as possible, IE the -9PSI on all models, though the larger area would take longer to evacuate, if you turn your car off and pump the brakes you can get 2-3+ full pumps out of them before they go rock hard, so I again would speculate that there would be plenty of air available, and unless you are slamming on the brakes while holding WOT you should be fine. What I dont like about the setup is modifying the pushrod, I hesistate to change anything that could result in a catastrophic brake failure, such as that coupler's threads sheering or the rod bending or what not. I also dont really see a need as I can lock the brakes on all of my Fieros without too much effort, even with 12" vette rotors, but I guess thats the same deal as the power steering. If you think you need it, go for it. Fundamentaly this install seems sound. ------------------
Boost is like Venereal Disease, one night of passion can result in weeks of pain (and work.)
Its not always about who gets to the finish line first, its who looks good when they get there. 'Course it doesnt hurt to have both.
http:\\www.myspace.com\keeptherubbersidedown
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Phil
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APR 04, 04:44 PM
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| quote | | Originally posted by Quickster: But I have a revelant question.........Does replacing the Master Cylinder with a Bigger one have an affect on the pedal? I replaced my M/C with a Bigbore and the brakes haven't been the same since! Now,...if I replaced the Booster with the aforementioned S-10 option,...would that help my "soft Pedal" problem? |
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A bigger M/C will definately affect your pedal feel, for the same amout of foot pressure you will get less brake line pressure . If you are still using the stock Fiero calipers you will have to push the pedal harder to get the same braking force at the rotors. I'm not sure what you mean by "soft pedal"
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Phil
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APR 04, 04:48 PM
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| quote | | Originally posted by 86GT3.4DOHC: ........What I dont like about the setup is modifying the pushrod, I hesistate to change anything that could result in a catastrophic brake failure, such as that coupler's threads sheering or the rod bending or what not. I also dont really see a need as I can lock the brakes on all of my Fieros without too much effort, even with 12" vette rotors, but I guess thats the same deal as the power steering. If you think you need it, go for it. Fundamentaly this install seems sound. |
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The push rod ends up being exactly like the stock Fiero pushrod. If you had the proper tools you could take the pushrod out of the Fiero booster and put it in the S10 booster.
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Pyrthian
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APR 04, 04:53 PM
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| quote | | Originally posted by Quickster: But I have a revelant question.........Does replacing the Master Cylinder with a Bigger one have an affect on the pedal? I replaced my M/C with a Bigbore and the brakes haven't been the same since! Now,...if I replaced the Booster with the aforementioned S-10 option,...would that help my "soft Pedal" problem? |
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sounds like you need to do some bleeding. the MC should have been "bench bled" before installed, then the whole system heavily bled. your pedal should be harder, not softer. in fact, thats what this whole thread is about.
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86GT3.4DOHC
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APR 04, 04:58 PM
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Oh, ok I didnt read that far into It, I just saw the coupler dealy on the one pic But yea Ditto the bleeding. If you have the car off, pump the brakes, once they firm up, they should go rock solid and hold by 1/2 pedal travel, if not you have air in the system or bad hoses that are flexing and expanding.
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kcfiero85
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APR 04, 06:21 PM
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all, I work at GM on Brake Apply systems.... Some General comments on Boosters,,,, Im not familar with the two booster sizes.
Bigger Booster does have more Total Boost Assist ( once Vacuum levels stabilize )
Bigger Booster will take longer to reach Max Vacuum Level Bigger Booster will typically have a lower system response ( assuming simular Booster Design ) Bigger Booster typically has more can deflection ( assuming common Can Design, you can see the can deflect under higher pedal forces) Also the the pedal feel will be softer / mushy with a larger booster ( if the internals of the booster are the same, spring rates etc) Larger Diameter Master will generate Less Pressure with a given input force
There may be some internal differnces or improvements in a 96 S10 booster so the feel improvement may not be size alone. modern boosters over time have improved force/travel losses,,,,,,
my two cents....
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kcfiero85
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APR 04, 06:52 PM
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One more thing,,, and prob the most important. Booster 's have what is called a Reaction Ratio / Gain Ratio Which is simply THE RATIO OF INPUT FORCE / OUTPUT FORCE , AT A GIVEN VACUUM LEVEL (SLOPE OF THE CURVE) THIS IS DETMERINE BY BOOSTER DESIGN,, THERE IS AN AIR VALVE INTERNALLY TO THE BOOSTER THAT CONTROLS HOW QUICKLY BOOST IS APPLIED ( THE RATE IN WHICH ATMOSPHERIC AIR IS RELEASED INTO THE BOOSTER ) YOU CAN HAVE THE SAME SIZE BOOSTER WITH TWO DIFFERENT GAIN RATIO'S. IF YOUR NOTICING AN IMPROVED ABILITY TO LOCK UP THE BRAKES,, MY GUESS IS THAT THE REACTION RATIO OR GAIN RATIO IS HIGHER FOR THE 96S10 BOOSTER. AND YOU COULD GET AWAY WITH A HIGHER RATIO SINCE THE VOLUME OF THE BOOSTER IS LARGER (SO IT TAKES LONGER TO DEPLET VACUUM ). I HAVE SEEN GAIN RATIOS RANGING FROM 5-10.... SORRY,,, I KIND OF WENT ON TOO MUCH,,,,,,
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ltlfrari
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APR 04, 08:31 PM
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fierogt88
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APR 04, 10:39 PM
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Thats a great link.
Added to favorites.and thanks kcfiero, I knew it had to be more complex than just simple diaphragm size. So -9PSI is all the vacuum we have? On the internet I'm seeing GM boosters listed as either 8" or 9" in diameter (there may be more, this is just one web site). If the fiero is an 8" that sounds like ~50 lbs of assist and if the s10 is 9" that sounds like ~64 lbs of assist. So it's going to remove ~14 lbs of foot effort and that sounds worthwhile. It also sounds a little low, so I'm still scratching my head on that one... I always imagined engines producing more vacuum than that. But, the naysayer in me would still be happier if Phil could measure the vacuum inside his s10 booster so I could compare it to the stock one.
I know you posted 18" of merc on the engine, but I'm not sure off the top of my head what that refers to in PSI, and I would love to see the same number show up inside the booster itself... Of course, maybe kcfiero can shed one more piece of light on this: The check valve. Is it just a one way valve that grabs the most vacuum it can from the engine? Or is it a limiting one way valve that will limit the amount of vacuum in the canister? My guess, now that I've perused the internet for a length of time and we've got some numbers on the vacuum engines produce, is that it's just a one way valve that gets as much as vacuum as it can. I can't see putting a limiter on there if the engine itself only produces -9PSI. That's not much at all...
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theogre
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APR 04, 11:23 PM
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Exactly how was the bracket connected to the booster? Was I reading correct you said 4 rivets? My first concern at the moment is long term strength of the bracket. It was built to have the 4 rivets. There is a chance that long term the bracket may not hold up if you have only two connection points and nothing to reinforce. My next concern whenever I see this sort of thread... A "larger" brake booster can help brake performance. I'm not arguing that. The issue is that many people that might do this, and see a performance increase, are compairing apples to oranges. IE compairing a defective OE part to a new or better condition used part. This happens allot when people compair OE rubber suspension parts to polyurethane aftermarket parts. I'll mostly skip over the chronic caliper problems that most people have and never actually fix. Fiero brakes for most driving are not bad design, even with all solid rotors. Yes there are times where the brakes require upgrades but allot of people that are doing this on otherwise stock or lightly modified cars could be simply hiding major system malfunctions. Malfunctions that left hidden will simply get worse until there are no brakes at all. My last item is this... The Fiero brake pedal is a 4:1 lever. At least one of the links above might make you think it is a 3:1 lever, which it is not. 100 pounds on the pedal is 400 pounds on the MC/Booster rod. It is very easy to put over 1000 pounds of force onto that rod. A strong person might even make a solid ton or more. Any modification to the brake rod MUST be able to handle that load or it will fail. Likely with no warning at all and at the worst possible time. IE... Epoxy is not a viable solution. I'm not sure anything less than welding, likely with some splinting on the weld, is safe. The rod can and likely does flex some under high load. A modification that can't deal with that will eventually snap like a twig. The correct fix is to see if the Fiero brake rod can be transfered to the alternate booster. These rods are usually held by some snap ring etc that is fairly easily removed. It's been a long time since I had to replace a booster so my mind is a bit fuzy on details. ------------------
Dr. Ian Malcolm: Yeah, but your scientists were so preoccupied with whether or not they could, they didn't stop to think if they should.
(Jurasic Park) The Ogre's Fiero Cave (It's also at the top of every forum page...)
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