Take A Brake - Wilwood Brakes master Cylinder
Gerald Lum, Rolling Hills Estates, CA: Many of the cars in Car Craft and other mags show brake systems sans the vacuum booster. I think they do it for a cleaner, better-looking engine compartment. But how well does this stop the car?
Jeff Smith: Great question, Gerald. The common misconception is that disc brakes require a booster to make sufficient line pressure to actuate the brakes. While it is true that discs require more line pressure to squeeze the pads against the rotor compared with drum brakes, it is possible to generate sufficient line pressure with a nonassisted master cylinder. The concept is very simple. A smaller master cylinder bore diameter will generate more output pressure in pounds per square inch (psi) than a larger piston version given the same amount of pedal effort. As an example, let's exert a force of 50 pounds directly to a 1-inch-diameter piston master cylinder. By calculating the area of the piston (Pi x radius x radius), we come up with an area of 0.7854 square inch. Divide the force by the area (50/0.7854) and the result is 63.66 psi of hydraulic pressure. Now let's do the same math with a 7/8-inch (0.875-inch) master cylinder (Pi x 0.4375 x 0.4375 = 0.601 square inch of area). Divide the 50 pounds of force by 0.601 and we get 83.19 psi, or a whopping 30 percent increase in line pressure. For the record, there is also a significant ratio gain from the pedal of usually around 6:1, so 50 pounds of force on the pedal quickly becomes 300 pounds of force applied to the master cylinder. If we divide 300 pounds by that same 0.601-square-inch area, we get 499 psi of line pressure with a 7/8-inch piston.
Of course, there's no such thing as a free lunch, especially with hydraulics. The price we pay with the smaller master cylinder piston is moving a reduced volume of fluid for a given piston stroke. In other words, converting to a smaller master cylinder piston requires moving the piston a greater distance to displace the same volume of fluid. If the entire braking system is sized properly, this usually isn't a problem, but it is an important point that can't be overlooked. As an example, we recently replaced a 1-inch iron master cylinder on our Orange Peel Chevelle with a 7/8-inch-diameter piston Wilwood Brakes aluminum master to save some weight. Many years before, we had converted the Chevelle over to disc brakes and mistakenly routed the brake lines with the front master cylinder piston connected to the rear brakes and the rear piston routed to the front discs. When we bolted on the Wilwood Brakes master, the rear master cylinder piston displaced insufficient fluid volume to move the front brake caliper pistons and pads against the rotors. As a result, the brake pedal just fell to the floor as if there were massive air in the system-which there wasn't. In most GM master cylinders, the front (or forward) piston assembly is designed to move a greater fluid volume to accommodate the generally larger pistons used in most disc brake calipers. Because we had routed the lines backward, total pedal travel created insufficient volume to move the calipers' pistons, and as a result, we had no pressure, even though there was no air in the system. Once we rerouted the brake lines, we had a very firm pedal. The first testdrive also revealed far less pedal effort necessary to generate the same braking force.
Another important point is that anytime you change master cylinder piston diameter, it will require changes to the brake proportioning valve. Let's assume for a moment you have discs in the front and drums in the rear and have just changed to a smaller master cylinder diameter. If the car is not equipped with an adjustable brake proportioning valve, this is a perfect time to add one. Do not rely on a factory proportioning valve to work if any modifications have been made to the car or brake system. As an example, just changing rear tire diameter will have a drastic impact on how much rear brake balance is necessary. A taller tire requires less brake pressure than a shorter tire. This is just one of dozens of examples of changes that can affect brake balance, which is why an adjustable proportioning valve is critical for modified cars. One point that many enthusiasts don't know is every adjustable prop valve has a minimum setting that allows a certain amount of brake pressure to pass through the valve. This means even when the valve is set at its lowest level, there will still be a given amount of pressure transferred to the rear brakes.
We spotted this AMC Hornet with junkyard-fresh writing on the window. Looks like it escaped cash for clunkers.
Pierce Peck, via CarCraft.com: It's time to take off the gloves and put together a shootout between the Edelbrock dual-quad Air-Gap combo (Glad) and the proposed Victor Jr./750 carb combo (Smith). It's fine to dyno both combinations, but why not go the extra step and drop it into a '65 to '69 Chevelle, optimize each combination (converter and gears), and run them down the quarter-mile, similar to the crate motor shootout published in the Oct. '08 HRM?
I realize the single-plane intake will likely make more horsepower, but I'm also t-hinking with that mild Comp cam (2-647-5) and relatively small heads, the dual-quad Air-Gap combo will have more than enough torque throughout the rpm range to show its taillights to the single-plane combination.
I am building a mild mechanical-roller-cammed, AFR 305cc-headed 496 for my '67 Chevelle and am intrigued by the fairground appeal of the dual-quad intake. This test would give me an idea of what (if anything) I may give up by going with this combo (in my case, Edelbrock PN 2066). Yes, I definitely plan on bracket-racing the car, and my build will be a slightly milder version (Comp 11-772-8 cam) of the one Smith built in the Mar. '07 edition of Car Craft.
Should I go with the dual-quad combo? And understanding that dual-plane-equipped big-blocks like lots of cfm, should I go with the 650-cfm Edelbrock Thunder Series AVS carbs or stick with the 500-cfm units? Let's duel this one out.
Jeff Smith: We'd love to duke 'em out, Pierce, but with the vast number of dyno tests we already have planned, we might get to it sometime in 2012. So let's see if we can shed a little light on all this. To bring everybody up to speed, Edelbrock makes two different twin four-barrel manifolds for the small- and big-block Chevys. The early-style manifolds (PN 5420 for the oval-port Rat motors and 5425 for the small-blocks) are similar to the dual-quad manifolds popular in the '60s. Edelbrock also makes a dual-four Air-Gap manifold for the Rat motor (7520 for oval-port and 7522 for rectangle-port) and small-blocks (7525). The Air-Gap manifolds will make more power than their earlier brethren while the early stuff delivers the nostalgic look that is popular right now. The PN 2066 system you reference is the entire package with an RPM Air-Gap dual-plane intake and a pair of 500-cfm Edelbrock carburetors.
Those are Wheel Vintiques Gasser Alloys on the front. Built one yet?
We made 707 hp with an 850-cfm carb and a stock oil pan with our first 496 back in 2007. W
Comparing a single-plane intake on a 496ci big-block with the Air-Gap dual-quad package is simple enough that we really don't need to run 'em on the dyno. The dual-quad system will make outstanding torque-something you may not need more of with a 496. More importantly, the dual-quad system must sacrifice intake runner length to fit in that second carburetor. The problem back in the early '60s was that big carburetors didn't exist-so adding a second carb was the only way to add more cfm. Today, you can buy a 1,050-cfm 4150-style Holley, so cfm isn't an issue. However, if the appeal of dual quads is what you're looking for-then go for it. Just know that you're probably going to give up 10 to 20 hp compared with the single-plane, and whatever torque advantage the dual-plane offers will be in an rpm range that won't offer much (if any) advantage on the dragstrip.
Based on this and the sacrifice of runner length on the dual-quad Air-Gap, the result will be that a good single-plane like a Victor 454-R would be the wise investment, since you're going to be running brackets. Managing one carburetor will be much easier than juggling two.
You mentioned you'll be using a Comp XR286 mechanical roller. That cam specs out at 248/254 degrees at 0.050 with 0.653/0.660-inch lift with a 110-degree lobe-separation angle. This is a pretty big camshaft, although smaller than the one we used in the Mar. '07 issue (254/260 degrees duration at 0.050 with 0.660/0.666-inch lift). The CC 496 peaked at 707 hp at 6,400 rpm. With a slightly smaller cam, you can expect your 496 to peak at around 6,000 or 6,200 and make power of around 690 or so. We've already discussed in this column how much power is lost with chassis headers (even 2.0-inch primary size), mufflers, a 180-degree water temp, and a full accessory drive system that we didn't run on the dyno at Westech for that test. If you package your big-block in a car with at least a 3,000-stall converter and a little bit of gear, you can expect it to run mid-10s, assuming you can hook it to the starting line.
As for your question about carburetors-assuming we're talking about the single-plane intake now and not the dual-plane-the plan for our new 496 is to start testing with a 950 HP Holley and then try a 1,050-cfm Dominator. There is power with the bigger carb not necessarily because of more cfm but with better mixture distribution from the larger bores of the Dominator carburetor. Plus, the larger carb at max rpm will slow the air speed through the carburetor and allow the air more of a chance to make the change in direction from vertical flow to horizontal flow into the ports after leaving the carburetor. This is why spacer plates work so well at peak rpm, because they help the air and fuel generate a gentler 90-degree turn.
Tire diameter plays a big part in overall gear ratio. On our Orange Peel Chevelle, our str
Charles Wilson, Elmwood, TN: Several years ago, Car Craft had an article on how to figure out some of the math involved in building a street machine. There was a formula to determine rpm, final drive gear ratio, tire size, and mph by knowing three of the variables. I have since lost that issue but would love to know the formula again. Any help would be most appreciated.
MPH = (RPM X Tire Diameter) ÷ (Gear Ratio X 336)
MPH = (3,000 X 26) ÷ (4.10 X 336)
MPH = 78,000 ÷ 1,377.6
MPH = 56.6
RPM = MPH X Gear Ratio X 336 ÷ Tire Diameter
RPM = 70 X 4.10 X 336 ÷ 26
RPM = 3,709
Gear Ratio = (RPM X Tire Diameter) ÷ (MPH X 336)
Gear Ratio = (3,000 X 26) ÷ (70 X 336)
Gear Ratio = 78,000 ÷ 23,520
Gear Ratio = 3.31:1
Tire Diameter =MPH X Gear Ratio X 336 ÷ RPM
Tire Diameter = 65 X 3.31 X 336 ÷ 2,700
Tire Diameter = 26.8 inches
Effective Gear Ratio = (Old Tire Diameter ÷ New Tire Diameter) X Gear Ratio
Effective Gear Ratio = (26 ÷ 28) X 3.55
Effective Gear Ratio = 3.29:1
Jeff Smith: Here are the critical equations that relate to tire diameter, engine rpm, and gear ratio. One reason I never became an engineer was because of the math. That side of my brain suffers from multiple disconnections. So I rely on an HP book titled the Auto Math Handbook written by John Lawlor. You can find it on Amazon.com for around $15. The constant (336) in all these equations simplifies the math by reducing the conversion from hours (in mph) to minutes and miles to inches and also accounts for determining diameter from circumference with Pi (3.1415927).
The part number for the 3M panel adhesive is 8115 for steel and aluminum and sells for $35
Will It Play In Peoria?
Pete Lassen, Peoria, AZ: I was just reading the article on rust repair and had a question. If you cut the floorpans, left a flange for them to rest on, then welded them from the top side, wouldn't that leave a shelf on the bottom exposed to the elements where dirt can collect and start to rust? I know you are in SoCal where, except for the occasional flood, it never rains-but shouldn't you weld it from the bottom, too?
Jeff Smith: The short answer, Pete, is yes. The best plan for welding any two panels together is to butt-weld them, but that requires much greater fabrication skills. To address your question, there are several ways to eliminate this gap. Assuming you can access the backside of the panel, the best procedure would be to weld it closed. However, on a large panel, this would be a long process of a series of short welds to prevent putting excessive heat into the panel, which could easily cause distortion. Before the welding process begins, you should thoroughly clean both surfaces and spray them with a paintable zinc-based weld-through primer. Dupli-Color has a 12-ounce spray can (PN 108, $16.95, Summit Racing) that would work well, and we've also used the 3M primer with excellent results. There still will be some bare metal directly where the weld heat penetration is the highest, but the rest of the area will be protected.
A good alternative would be to use some type of high-quality seam sealer to fill the gap on the back side seam. We've used 3M's Heavy Drip Check with great results on our trunk floor installations. This stuff looks like a tube of silicone but in fact is much stronger and basically the same material used on older cars for panel installations with overlapping seams. If you are working on something like a quarter-panel on an El Camino where there is no easy access, it's possible to use a pressure gun with a long snout that can access the backside of the quarter-panel from the taillight opening. We found a rust-proofing kit from Eastwood (PN 50369ZP, $119.99) that includes the gun along with antirust and undercoating material. This gun has a long wand that will shoot undercoating or rust-proofing material into hard-to-access areas.
Finally, there is an alternative to welding. The 3M company makes a panel bond adhesive that allows even the backyard sheetmetal worker to adhere two nonstressed body panels together without a welder or heat. According to our sources, the OEs have been using this adhesive for several years on new cars. The idea is to overlap the pieces like in a quarter-panel, for example, and use this two-part adhesive to glue them together. We asked 3M about using this to glue the trunk floorpan on our '64 Olds, but because a potentially 120-pound gas tank hangs from these panels, it's probably not a good idea. But if you wanted to adhere a small repair to your door, this would be an excellent alternative to welding.
We're not sure what this is, but it has a '65 Chevelle front end and an LS swap.
A quick way to tell a high-volume pump from a standard one is to compare pump bodies. A hi
Oil is Well
Unidentified CC reader, Somewhere in the Midwest: I spent last weekend at the World Series of Drag Racing in Cordova, Illinois. During a time out for cleanup, I engaged in an argument with another person who thought he knew it all. He voiced the old wives' tale about restricting oil to the heads so as not to fill the valve covers with oil. I countered that it was impossible to pump that much oil with large drain-back areas, and besides, lots of oil was required to cool the valve-springs. He says he reads all the magazines. How about it? Was I correct?
Jeff Smith: In a way, you're both right. Several decades ago, drag racers were obsessed with windage and thought restricting oil to the top end of the engine would decrease the amount of oil draining back. This would mean with less oil hitting the crank, horsepower would improve. All those experiments proved was it's easy to kill valvesprings by eliminating oil to the top of the engine since the oil keeps springs cool. Too much is not good, but too little is worse.
I had a conversation with Kurt Urban of Urban Performance regarding this point and he told me the GM LS-series engines are particularly susceptible to pumping the pan dry because the crank-driven gerotor oil pump is very efficient. This may be accentuated by the fact that these engines are purposefully designed to only drain oil back in the corners of the engine rather than down over the top of the camshaft like Gen I small-block Chevys and most engines built in the '60s. To combat this situation, we discovered that Comp Cams builds oil-restricting pushrods with half-size 0.050-inch lube holes that reduce the volume of oil to the top of the engine. These Comp pushrods are available in 5/16-inch diameter in various lengths for GM LS-series engines. This lesson apparently evolved out of GM's Corvette road race experience.
Older engines are less likely to experience this situation since they have excellent drain-back capabilities, but these engines can also experience a flooded top end if the engine is equipped with a high-volume oil pump. While there may be a need for a high-volume pump in certain situations, virtually all popular street engines we deal with have no need for high-volume pumps. You may recall we just did an oil pump evaluation ("The Great Oil Pump Test") in the Nov. '09 issue and found that the standard small-block Chevy oil pump came out on top in terms of power and was worth 8 hp peak and almost 5 average horsepower over a high-volume version of the same pump. So those are very good reasons to invest your money somewhere else instead of buying some trick oil pump that really isn't necessary-at least for a small-block Chevy. While this is off the subject somewhat, the 351C and 429/460 Ford engines feed the mains and rods through the lifters, so with these engines, higher pressure and perhaps a higher-volume pump would be of some benefit.
Kurt Urban Performance
Commerce, MI; 248/345-8169
Simi Valley, CA
With the advance mechanism removed, it's easy to see how the two small pins (arrows) move
Advancing the Spark
Joe Pacheco, via CarCraft.com: I seem to have a timing problem I just can't figure out, so I thought I would ask your opinion. About two years ago I bought a new Mallory 85-series street HEI distributor. I have an '82 Trans Am with a 327 small-block and a World Class T5 trans. When I was setting the timing, I noticed only 8 degrees of mechanical advance at 3,600 rpm. The car is currently running 18 degrees base timing, so if you add 8 degrees mechanical, I am only getting 26 degrees of total advance. I did some research on these particular distributors and found the amount of total advance built into these units is 36 degrees. The distributor came with a spring set to adjust the mechanical or centrifugal advance, so I tried the lightest springs in hopes that they would increase the amount of total advance. No luck-the advance just came in sooner. I have pulled the cap and checked the rotor for binding and found nothing. When I turn the rotor by hand, it looked like I have about 1/2 inch of advance, so the weights are not binding. I am stumped. Do you know if these distributors had issues with the advance? Once in a while, the car will run really well with a lot more pull, but most of the time it is not running to its potential, which leads me to believe I am getting the correct advance. Please help.
Jeff Smith: I spoke with the Mallory people and they say the 85-series HEI is the standard replacement version of the HEI. It sounds like the advance mechanism might have a small burr or some obstruction left over from the stamping process that might be preventing it from advancing the timing. We've included a photo of the stock-type HEI advance system for reference. In the photo, we've removed the rotor, the weights and springs, and even the inner tab that fits over the posts so you can see the advance slots. Note that an HEI distributor uses two slots as opposed to a single one used with the older GM point-type distributors. It's possible that there is a small burr or obstruction in this slot or perhaps somewhere on the top of this mechanism where the weights move across. I know you mentioned the rotor seemed to move easily, but that may be with your assistance, and the system may bind when left on its own. This also fits in with your statement that lighter springs only brought the minimum advance in quicker. Plus, you state that every once in a while the car seems to run much better. This could be the result of the weights actually advancing as they should-but something is holding them back from doing that consistently.
It would be worth the effort to remove the distributor and take it to a shop with a distributor machine so you can watch the weights move with the rotor removed. Also check the relationship of the center piece to the two centrifugal weights. This might be the best way to determine exactly how much advance the distributor is delivering. If the advance mechanism indeed binds, then you've discovered your problem and can now fix it. Carefully disassemble the entire advance system and smooth any sharp edges or stamping flash that may exist on the weights, plates, or in the slots. If you can see a sharp edge in one of the advance slots, you will have to drive out the roll pin that positions the distributor gear on the shaft. Once the gear is off, the shaft can be removed, which will allow easier access to the two slots. This will also give you access to the plate underneath, as that might be part of the problem as well. Once everything moves freely, lightly lube the area with Lubriplate and reassemble the distributor.
The distance the pins move inside the slots determines the amount of mechanical advance available with this distributor. That 36 degrees sounds excessive, and if so, you will need to limit the travel so you can add some initial timing. Some HEIs may come with bushings over these pins that limit the amount of available travel. These bushings can be exchanged for smaller (more advance) or larger (less advance) bushings to custom-tailor the total advance. You mentioned you currently have 18 degrees of initial timing. After repairing the distributor, you should shoot for total centrifugal advance of something like 22 to 24 degrees. This will allow you to set the initial at 12 degrees, and with 24 degrees centrifugal, this will create a total of 36 degrees. Remember to always disconnect the vacuum advance hose from the distributor while you're checking the centrifugal and initial timing.
A substantial amount of combustion chamber cooling can be accomplished by directing a stream of oil at the bottom of the piston. Look closely and you can see the oil squirters just above the main bearing cap in this aluminum Ford GT engine block. These 5.4L engines are the ultimate version of the Mod motor. Look for more Mod stuff coming next month.
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Car Craft Mag
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