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Which Brake Fluid?

A Fluid Answer

Curt Schneck; via CarCraft.com: I have a ’70 Pontiac LeMans Sport and I am adding a disc brake setup that I built with stock spindles, stock calipers, stock master cylinder, cross-drilled rotors, and performance pads. I am also, at the same time, replacing all the brake lines with stainless steel lines, stainless steel braided hoses, the proportioning valve, and new, rear-wheel cylinders for the rear drums. I would like to know what brake fluid to use when doing this conversion: DOT 3, 4, or 5? The whole system will be new, so I don’t have to worry about purging the system to use silicone brake fluid. This car sees the street and really does not see the track. I know DOT 3 brake fluid absorbs moisture. Since I live in the northeast where the car sits in a non-climate-controlled garage, is that an issue? What are the differences between DOT 4 and DOT 5? Are there any performance advantages/disadvantages between them, besides the boiling point? Keep up the great work guys—Car Craft is the only real-world car mag!

Jeff Smith: These are great questions, Curt. All common brake fluids are generally referred to as hygroscopic, which means they have a tendency to absorb water. That is why all master-cylinder covers use a rubber liner between the fluid and the outside atmosphere. It is also why the brake fluid container should always be stored with the lid tightly closed. What is less well known is that while stock flexible-rubber brake lines do a great job of keeping the fluid in, the brake fluid can still absorb water through these lines, as implausible as that may seem. How the car is used helps to determine the kind of brake fluid you should choose. Let’s start with the basics. The difference between DOT 3 and DOT 4 fluids is, as you suspected, more than just the boiling point. The DOT standard for a wet boiling point is 3 percent water. This may not sound like much, but check out these boiling points as listed on Amsoil’s website in the chart below. Note how both the DOT 3 and DOT 4 Amsoil fluids drop a greater percentage of the boiling point compared with the DOT standards when subjected to 3 percent of water mixed with the fluid. This is a typical negative to pushing the dry boiling point higher. DOT 3, 4, and 5.1 fluids are polyglycol ethers, while DOT 5 is silicone based. As you’re probably aware, normal brake fluid is an excellent paint remover, but silicone-based fluid is not, which makes choosing DOT 5 a great idea for show cars. The downside to DOT 5 fluid is that it is compressible. That means as the fluid gets hotter, the brake pedal becomes spongy, which is not what you want, especially if this fluid were used in a car driven on road courses or other situations in which the fluid could see extreme temperature. The plus side to DOT 5 silicone fluids is that they have a low affinity for water, which makes them much better for use in cars like yours that are subjected to humidity. However, water can still exist in a brake hydraulic system with silicone fluid; it tends to collect at the bottom of either the brake master or calipers, where it may be troublesome to remove. It appears that DOT 5 might be a better fluid for a car like yours that is parked for long periods of time.

For performance cars on which the brakes are abused at track days or autocross events, the best choice is the DOT 4 fluid. We’ve used the Amsoil DOT 4 with no problem in our ’65 Chevelle road-race car, but we change the fluid after two events, completely flushing the system front and rear. We learned that Raybestos now offers a new Super Stop Super High Performance DOT 3 brake fluid with a rated dry boiling point of 550 degrees F that sells for $5.99 per can.

More Info

Amsoil; Superior, WI; 715/392-7101; Amsoil.com

Phoenix Systems; St. George, UT; 435/673-0777; BrakeBleeder.com

Raybestos; McHenry, IL; 815/363-9000; Raybestos.com

DOT 3 STD AMSOIL DOT 3 DOT 4 STD AMSOIL DOT 4 DOT 5 STD DOT 5.1 STD
DRY 401 535 446 580 500 518
WET 284 313 311 410 356 374

*All temperatures are listed in degrees Fahrenheit

Timing Issues

Dominic Magrini; Manalapan, NJ: Regarding your tech answer on timing in the Jan, ’12 issue, I, too, am having a similar problem with the initial timing on my stroked 340 Mopar motor. It is now 416 ci with a HR226/345-251-10IG Crane Cam, 10.5:1 flat-top pistons, an Edelbrock 800-cfm carb, an Edelbrock RPM cylinder heads, and a Procomp Electronics ignition. I was told by a mechanic to power-time the motor to 35 degrees at 3,000 rpm. This leaves my initial timing at 8 degrees, and the car idles very poorly and is very hard to start. Where should I go from here?

Jeff Smith: There is a fairly simple remedy to your problem, Dominic. Depending on the distributor you are using, it might take only a few minutes. The information you received about power-timing the engine is correct. What you are doing is setting the total ignition timing at the rpm at which the engine should have achieved its maximum advance. Just make sure to set this with the vacuum-advance hose disconnected from the distributor. The fact that you have only 8 degrees of initial timing means that the distributor is delivering 27 degrees of mechanical advance (8 initial + 27 mechanical = 35 degrees total). The engine is hard to start and lazy at low engine speeds because the longer-duration camshaft (226/230 degrees at 0.050) wants more timing at low engine speeds to compensate for weak cylinder pressure (dynamic compression). A good place to start would be 12 to 16 degrees of initial timing. Unfortunately, 16 degrees of initial timing would put your total advance at 43 degrees, which is way too much. I would suggest setting the initial timing at 14 degrees and driving the car around for a short time at light throttle to see if it helps driveability and restarts. Do not go to WOT during this drive, as the engine will almost certainly detonate. What you’re trying to determine is how the engine responds to part throttle and if it feels crisp. If it does, you know you will need to reduce the mechanical timing by 6 degrees.

You didn’t mention the kind of distributor you have in your engine. Stock Mopar distributors place the mechanical-advance mechanism underneath the pickup plate. This requires you to remove the vacuum-advance pod and the points or the electronic pickup plate to access the advance mechanism. This is a pain, especially if you have to do more than one change to get the curve correct. Essentially, all the mechanical-advance systems work the same way. The usual method involves a pair of eccentric weights that are forced outward with increasing engine speed. A pair of springs is used to determine the rate at which these weights move outward. As the weights move outward with rpm, they are tied to a single plate that uses a pin inside a slot. The diameter of the pin and the length of the slot determine the amount of mechanical advance. So in your case, the easiest way to limit timing would be to reduce the length of the slot. Most old-school tuning shops used a torch and braze to effect this change. To establish the length, you’ll need to shorten the slot; you might try measuring the length of the pin travel and then dividing that length by the amount of mechanical advance (27 degrees). This figure will be a rough estimate of the degrees of advance for the given distance. For example, if the pin travel is 1.00 inch in length and the total mechanical advance is 27 degrees, then the pin is moving roughly 0.037 inch for every 1 degree of mechanical advance. So, if you wanted to limit the mechanical advance to 20 degrees, you would need to shorten the slot by 0.259 inch or roughly a quarter of an inch.

If you have an MSD distributor, you are in luck. The advantage to the MSD distributor is that it places the mechanical-advance mechanism directly underneath the rotor, as in a GM-style distributor, where it is easy to access. Even better, rather than adjusting the length of the slot, MSD supplies different bushings that fit over the pin. The smallest bushing is red and allows 28 degrees of advance, the silver is 25 degrees, the blue limits to 21 degrees, and the largest, black bushing allows only 18 degrees. For your application, the blue would probably be best, since it would allow you to set the initial timing at 14 degrees before top dead center and still deliver 35 degrees of total timing. If you don’t have a dial-back timing light or a degreed balancer, reading total timing can be problematic. MSD offers timing tapes that glue to the balancer to indicate total timing (PN 8985; $4.95, Summit Racing). The tapes come on a single sheet with several tapes specific to the diameter of the balancer. This should solve your timing problem and make the engine much more fun to drive.

More Info
Autotronic Controls Corp. (MSD); El Paso, TX; 915/857-5200; MSDPerformance.com

Watts My Line?

Jay Mandernach; Cucamonga, CA: I’ve heard there is a way of automatically shutting off the alternator at WOT. How do you do it? I’m running a big-block in a first-gen Camaro and need about two-tenths to hit the 10s. Do you think this change would get me there?

Jeff Smith: For a short question, the shorter answer is: No. But because abbreviated answers rarely help, let’s run through some numbers to take the mystery out of what we’re talking about. My handy power-conversion chart tells me that 1 hp equals 750 watts. We measure watts by multiplying voltage by amperage. So let’s assume our car requires 50 amps to run down the track. That’s a little higher than normal, but play along with us. Fifty amps at 14 volts pulsing out of our alternator equals 700 watts, which comes pretty close to 1 hp worth of electrical power. Assuming it takes another horsepower to drive the alternator both from losses due to heat and beltdrive, we’re at a grand total of 2 hp. That’s not going to be nearly enough to cut two- or three-tenths of a second from your elapsed time, especially as a typical drag Camaro probably requires less than 30 amps to make a pass down the track, assuming a gnarly CD ignition system and a big electric fuel pump. The classic rule of thumb is that 10 hp is worth 0.10—and 1 mph is not far off in your case. We simulated a big-block Camaro running 10.77 at 129.8 mph and added 10 hp to the simulation, and the result was 10.71 at 130.5 mph, so 10 hp is worth about 0.06 second and 0.7 mph. It appears you’re going to need more than 20 hp to knock 0.2 second off your current times.

What is less obvious is what happens when the alternator is disabled. A typical battery is fully charged at 12.6 volts. The alternator maintains voltage at a much more efficient 14.3 volts. This is the voltage used to push amperage to all your electrical components. If you disable the alternator, the voltage drops quickly to around 11.8 volts. This reduced voltage doesn’t really affect the ignition, since most CD systems will fire the plugs down to as low as 10.5 volts. But your electric fuel pump output will be drastically reduced at lower voltages, and that could be a problem. When we asked Brady Basner of Powermaster about this subject, he agreed, adding that lower voltage can also contribute to run-to-run inconsistencies that are the opposite of what you want for bracket racing. Our recommendation is to keep that alternator charging and look somewhere else to pick up those couple of tenths. You’ve probably already put your Camaro on a diet, but remember that 100 pounds is a tenth of a second. A buddy of mine said he was able to cut 20 pounds off of his race car by replacing all the steel sheetmetal bolts with aluminum fasteners. That’s a great idea. Also, rather than focusing on peak horsepower improvements, consider enhancing the torque in the middle. This will drastically improve acceleration all the way down the track. Nobody said it would be easy! Especially when you’re trying to break into the 10s.

Push Me, Pull Me

Norman Neal; via CarCraft.com: I’m pretty sure you’ve run a tech article in the past about cooling fans. I’ve got a ‘49 Chevy pickup with a healthy 496 big-block Chevy and an aluminum radiator using a pull-type electric fan. I’ve never had a heat issue with it. With my it’s-not-broke-but-I’m-going-to-fix-it-anyway approach, I’m going to put a 6-71 huffer on it and will need to change the fan to a pusher mounted to the front of the radiator. I’m looking for an answer that will explain the exact difference in effectiveness between the pusher and the puller mountings.

Jeff Smith: We asked a Ford cooling-system engineer this exact question several years ago, and he said that a pull-style fan is generally about 10 percent more efficient than a pusher fan. While that’s a very generic answer, it’s clear that using a puller-style fan will move more air than the same-size pusher fan. However, you might not be able to just remount the fan in front, since most fans are designed specifically as either pushers or pullers (most fan companies will specify if the fan can be used in either direction). This means if you reposition a puller as a pusher and then just switch the leads on the fan, the setup may result in less than favorable results. We spoke with Dave Heutmaker at Flex-a-lite, and he says that with most Flex-a-lite fans, you can remove the fan from the electric motor, flip it over, and then reverse the leads to the electric motor to turn the fan into a pusher. When mounting the fan to the front of the radiator, you can improve performance by placing the fan very close to the radiator and carefully sealing the area around the radiator core to prevent air from bypassing the radiator core.

In terms of choosing an electric fan, size matters. A pair of smaller-diameter fans will do a better job of moving air than one large fan because the two can cover more area. Twin-fan packages are also often mounted in an offset pattern to squeeze a pair of slightly larger blades. It’s not accurate to use amperage draw as an indicator of fan efficiency, as electric motor quality can vary wildly. A more efficient motor will pull fewer amps than its less-efficient cousin. Fan design also makes a difference. Straight-blade fans are generally noisier and will move more air than a curved blade, but Heutmaker says current S-blade designs are often more efficient than even the straight blades, so that might be worth additional consideration.

Radiator thickness also affects fan performance. Most fan companies don’t recommend using a pusher assembly on a four-core radiator because the added core thickness makes it difficult for air to push through. This is a tough enough job for a puller fan.

Beyond the question of proper positioning, it’s also important that the fans be wired professionally. Each electric fan should use a dedicated relay. Relays allow you to use a light-duty switch to control high-current-draw fans. We’ve worked with the guys at Hollister Road, a small company that makes a nice wiring package that combines relays, circuit breakers, and a wiring harness to control a pair of fans. The switch is set up to turn the fans on at 210 degrees and off at 185 degrees. You can also order an additional switch so you can control the first fan to come on at 185 and the second fan to come on at 210 degrees. This would put less load on the alternator, as the second fan would only come on is when it is really needed.

For applications in which a pull fan will fit, Hollister Road also offers relay kits for giant Lincoln Mk VIII, Taurus, and T-bird fans that you can buy new for a great price. The Lincoln fan is generally found as a two-speed fan, and Hollister Road sells a relay controller that will run the two speeds in a similar method as described above. A ’95 T-bird fan can be purchased for $72 through Rock Auto, so there’s no reason to go searching through the junkyard when you can buy a new one that is this inexpensive. We covered this issue in more in detail in our Junkyard Builder story in the Nov. ’11 issue. You can also find the story online. What’s good about this fan is that it moves some serious air, perhaps even more than a pair of smaller fans. Check it out.

The Wheel Deal

Tim DiMasi; San Diego, CA: I’d given up on something until John McGann’s piece on wheel widening (Dec.’11) renewed my interest. I’ve got a white ’10 Dodge Challenger R/T with 20-inch wheels and 45-series tires. Its color and simplicity of design scream for ’60s-era steelies, Mopar dog-dish hubcaps, and 60-series tires. I figure an 18-inch-diameter wheel will do the trick. I’ve located a supplier that says it can handle an adapter to take the 5x115mm bolt pattern to the traditional Mopar 5x5-inch pattern, but this is as far as I can get. Those younger guys who missed the days of bare- bones Coronets stuffed with 383s and Max Wedges think I’m nuts. Maybe I am, but I still want my steelies. Whatchathink?

Jeff Smith: I discussed this with staffer McGann, and he remembered seeing steel space-saver wheels in some late-model Charger LX-platform cars. Most spares are 17 inches, but a few are 18-inch wheels, depending the brake size of the car they go with. He did a search and found one on eBay that mounts a tiny 135/90-17 tire for the “buy now” price of $95, though the highest bid at the time was only $35. We learned that this wheel has the same 5x115mm bolt pattern as your Challenger. So your next step could be to purchase four space-saver wheels. But before you make this step, take the time the measure the caliper clearance around a 17-inch wheel. The ’10 Challenger uses a 12.6-inch-diameter rotor, which pretty much eliminates using a 15-inch wheel, but you should measure caliper clearance to make sure a 17-inch wheel will fit. If it does, you can go forward on deciding the width of the new wheels. The factory rims are 9 inches wide, so that’s a great place to start. Then you can have a shop like Pico Wheel cut the centers out of the space-saver wheels and mount them in 17-inch hoops of the proper width. Once the width is determined, you can look for a tire that is roughly the same diameter as the original Challenger tires. The stock tires on your Challenger are 245/45ZR20 Goodyear RSA tires that are tall rascals at 28.7 inches. On the Tire Rack website (TireRack.com) we found a 255/60R17 tire that is 29.1 inches tall, which is around 0.4 inch taller. This will affect your speedometer readout by about 1 to 2 percent. To make the car look right, you need a decent performance tire, so we dug a little deeper and found that General makes a Grabber UHP tire in the 255/60R17 size that has a cool, aggressive tread pattern. General recommends mounting this tire on anywhere from a 7- to 9-inch-wide wheel.

You will also need to specify the amount of backspacing you want on these custom wheels. Since the new 17-inch tires are 20 mm, 0.787 inch wider, it might be best to move the wheel inboard slightly. The best thing to do is measure the amount of clearance available with the Challenger’s current wheel and tire package. If you have more inboard than outboard clearance, add the appropriate amount of backspacing. Let’s say you have 3⁄4 inch of clearance on both the inboard and outside sides of the tire with the current wheel/tire package. Since the new tire is 3⁄4 inch wider, that’s 3⁄8 inch wider on both sides. To simplify our example, let’s assume the backspacing on the 20x9-inch factory wheel is 4.5 inches. The easy thing to do is to duplicate that with the new wheel with a zero offset. In the front, you will need to pay attention to clearance at full lock, but more than likely, it will clear as well. It would be best to compare the overall section width of the tire you choose for the new 17-inch wheels against the section width of your factory tires. While overall diameter for tires is generally consistent, we’ve seen a difference of as much 3⁄8 inch in overall width in same-size tires from different manufacturers. Section width is the measurement of the widest part of the tire when mounted on a given wheel. For example, the 255/60ZR17 General UHP Grabber tire mounted on a 7.5-inch wheel generates a 10.2-inch section width. We looked at the section width for the Goodyear, Dunlop, and Pirelli tires of the same size and they all had the same section width, but it is something that warrants attention.

Finally, space-saver wheels don’t appear to be able to mount the Mopar dog-dish hubcap. But that just means you will have to be creative. We’ve seen guys use an aluminum spacer that screws onto the stud drilled and tapped on the other end for a 10x32 panhead screw. Locate the position of this spacer to the hubcap and drill a hole in the cap, perhaps in a dark or painted area where it will be less obvious. The machine screw could be painted black to make it nearly disappear, and the hubcap would be secured.

More Info

General Tire; Fort Mill, SC; 800/847-3349; GeneralTire.com

Pico Wheel & Tire: North Hollywood, CA; 818/982-0375

Ask anything— We’ve got solutions!

CarCraft@CarCraft.com

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El Segundo, CA 90245

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