The BasicsMike Ritter, via CarCraft.com: I am a new subscriber and new to the car-hobby scene. I'm looking for a referral for books or information on how engines work and the parts involved. I've looked on the Internet, but I've found nothing so far. I read your magazine from cover to cover monthly. I'm not even sure what it means when you bore and stroke an engine. I think it has to do with the cylinder size (bore) and the crank (stroke). Help! Any help or point in the right direction is appreciated.
Jeff Smith: Hey, Mike, we all have to start somewhere, right? This will sound self-serving, but one of the best ways is to read this magazine every month. At first, there will be a bunch of stuff you don't understand. But after a while, it will begin to make sense as you appreciate how all the individual components of an engine and chassis work together. The other great way to learn is to dive in there and get your hands dirty on a car. It really doesn't matter what kind of car; pick one you will enjoy working on and from which you will get some self-satisfaction by completing a task. It's the best way to learn. We'd also suggest reading any other magazines and books that will help you learn.
As for the Internet, we've run across a site called hotrodders.com that spans the entire knowledge base from beginner to the esoteric, and it's a great place to ask questions and get quick answers. Unfortunately, the responses you get will not always be accurate. Be prepared to sift through a lot of b.s. to get the right answer. At first, ask lots of questions, read everything, and keep asking. You'll notice in most forums there will be one or two guys who are always on the site and offer excellent knowledge on most subjects. They are the ones to follow.
As for your question on bore and stroke, let's introduce the basics. Let's look at a one-cylinder engine. As you guessed, it will have a bore, the diameter of the cylinder, and a stroke, which is the entire length the pistons travels from the bottom to the top. If you remember high school geometry, volume of a cylinder (displacement) is calculated by multiplying the area of the cylinder by its length. Let's assume we have a cylinder with a 4.00-inch bore (diameter) and a 3.00-inch stroke (length). Radius is defined as half the bore diameter.* Piston area = pi (3.1417) x radius x radius* Piston area = 3.1417 x 2.0 x 2.0 * Piston area = 12.567 square inches
Now we multiply piston area by the stroke, and that gives us the displacement of the cylinder* Cylinder volume = piston area x stroke * Cylinder volume = 12.567 x 3.00 * Cylinder volume = 37.70 cubic inches
Multiply that one cylinder by eight, and we have a Ford or Chevy V-8 that displaces 301.6 ci. Ford and Chevy rounded this off to 302 ci. This is referred to in later-model Mustangs as a 5.0L engine, which is the metric equivalent of 302 ci. There's a bunch to learn if you really get into the technology of cars, Mike, but don't let all this intimidate you. You'll be amazed at how quickly you can pick this stuff up.
Twin-Turbo TerrorChris Cerce, Taunton, MA: I'm building an '86 Camaro with a twin-turbo small-block. I made my own headers, and I'm using two T04 turbos with Turbonetics wastegates along with an intercooler. The only piece of the puzzle I can't figure out is the carb. I have a back issue of Car Craft where a kid built an S-10 with two turbos and said he used a Holley 750 but modified it. I wish I knew what he did to it so I could do the same. I want to run 7 psi of boost and don't have $850 to spend on a CSU carb. There was also a back issue with a twin-turbo Camaro with a big-block, but I lost that issue.
Jeff Smith: There is an increasing amount of information on blow-through carburetor applications that are not just for turbochargers. If you think about it, the carburetor really doesn't care what device creates the boost, so the modifications for a blow-through carb will work regardless of the application.
We did a story in the Oct. '05 issue called the "Guide to Blow-Through Superchargers" in which our pal Tim Moore built an ATI ProCharger centrifugally supercharged 540ci big-block Chevy using a blow-through carburetor. We learned some very important things from that engine that will help you dial in your package.
The first and perhaps most important item is the fuel-delivery system. Even with 7 psi of boost, you're looking at making some serious horsepower, and it's likely that if your combination is successful, double-digit boost will not be long in coming. This will require a high-volume fuel-delivery system. We recommend a full-flow system with a return. This will require a pump with the capacity to feed a minimum of 600 to 700 hp. We had excellent success with an Aeromotive A1000 pump (PN 11101) that's capable of up to 1,100 hp in a forced-air condition. Next, you'll need a boost-referencing fuel-pressure regulator, such as the PN 113105. Both the main fuel-feed line and the return line should be no less than 11/42 inch in diameter, and the return line cannot be smaller than the feed line to prevent backpressure problems. If the return line is too small (especially on a carbureted application), it effectively reduces the fuel pressure the pump can supply to the carburetor. Be sure to return fuel to the tank in an opposite corner from the inlet so there are no fuel-aeration problems near the fuel pickup. This is important with a high-volume system where a majority of the fuel is returned at low engine speeds.
We're going to assume you will use a fuel hat on top of your carburetor rather than a full enclosure for the carburetor. Either way, the fuel-pressure regulator must be able to boost-reference. When the boost pressure is applied to the carburetor, the float bowls are subjected to this same pressure. That means the pressure regulator must increase fuel pressure in a 1:1 ratio for every psi of boost pressure created by the turbo. For example, if the turbo creates 7 psi, and under normally aspirated conditions the carb sees 5 psi of fuel pressure, at 7 psi of boost, the actual fuel pressure at the float bowls will climb to 12 psi (5 + 7 = 12). Effectively, however, the fuel pressure in the bowl is still only 5 psi, which ensures adequate fuel pressure and fuel volume to the carb. This is important and cannot be stressed enough if the package is to be successful.
As for the carburetor, it's actually quite simple. We learned much of this from our friends at Quick Fuel Technology. According to Quick Fuel's Marv Benoit, the key to success with a blow-through carb is to use a smaller-cfm carb with annular-discharge boosters. The trick is supplying enough fuel to feed the potential airflow. On our 540ci Rat motor, Quick Fuel supplied a 750-cfm carb with annular-discharge boosters, and we had excellent luck making 977 hp with virtually out-of-the-box jetting and only 11.75 psi boost. Everyone who witnessed our combination thought the carb was too small to make this kind of horsepower, but Benoit says this smaller size generates higher air velocity through the carb, which pulls more fuel from the annular-discharge boosters. We think this is the key. You might be able to get away with a standard downleg booster with low boost levels, but be prepared to run very large jets-on the order of high 90s-and you will probably have to drill out the power valve channel restrictors again to increase fuel flow. Smaller high-speed air bleeds may also be necessary to increase fuel flow at higher engine speeds.
If it's possible to find a used, annular-discharge booster, Holley carb that would work, we'd suggest sending it to Quick Fuel to let them tweak it for you. That might keep the cost down. Another important point is that regardless of the carb you use, you should seal those pressed-in brass cups Holley uses on cast metering blocks with epoxy. Under boost pressure, it's possible for these cups to push out, which would spray pressurized fuel all over the engine compartment and would instantly cause a fire. These plugs were never intended to have pressure applied to them and could push out under boost pressure. A boost-referencing plate to prevent fuel from pushing out past the throttle-shaft seals is also a good idea. A diagram of this plate can be found in the Hugh MacInnes book, Turbochargers, from HP Books. It's available on amazon.com for $12.82. We'd like to thank Ken Crocie for bringing this to our attention. It's an excellent point.
Internal-Regulator ServiceRichard Ramsey, Princeton, MN: My son and I have a '69 Camaro we are restoring. We want to eliminate the old voltage regulator and go with the internal regulator type. I'm not sure what to do as far as rerouting the wires to get rid of the regulator. It has four wires-one large, red, fusible link, one brown, one white, and one blue. Also, directly below the regulator is some type of relay. There are six wires to this box, one of which goes to the horn. I know there is a way to bypass the old regulator but would rather delete it altogether if possible. Sure hope you can help, thanks.
Jeff Smith: You're going to like the answer to this question, Richard. The swap is incredibly easy. M&H Electric Fabricators makes a slick conversion kit that adapts an SI- or CS-style alternator to early Camaros, Chevelles, and all other early external-regulator GM cars and trucks to an internal regulator alternator. On the alternator side, there is an adapter that adapts between the original harness connector and the new alternator with no cutting required. Then, you merely unplug the four-wire harness that connects to the external voltage regulator located next to the radiator and connect the M&H plug. This allows you to eliminate the regulator altogether. Internally, this plug connects the blue field wire to the brown wire in the harness that is used as the energizer wire when the key is turned to "on."
There are actually three different GM alternators you can use to do this conversion. We're assuming you're using the most common, '69-'84 SI internally regulated alternator that is identifiable by the multiple ribs on the rear half of the alternator case. The second type is the GM CS alternator with the smaller, more compact design that was used in GM cars and trucks from '84 to '99. M&H offers bolt-in kits to convert each of these two alternators for your '69 Camaro. The SI alternator kit is PN 27555, and the CS alternator kit is PN 37787, and both are priced at an affordable $19.
If you have not chosen an alternator yet, the later-model CS alternators offer more output at lower engine speeds, which may be an advantage if your Camaro is equipped with any combination of electric cooling fans, electric fuel pump, or a high-output stereo that pulls lots of amps. The total output may be similar to the older alternators, but the newer models produce a greater percentage of their output at idle speeds, where you need them the most.
Here's another tip. Once the alternator is connected and working, use a voltmeter to check voltage output at the back of the alternator at idle. Let's say it reads 14.5 volts. Now check the voltage at the battery. If the reading is 13.9 volts or fewer, there is a significant voltage drop in the output circuit somewhere between the alternator and the battery. Start with the small wire that runs from the positive terminal on the battery to the junction block on the radiator-core support. This is usually the culprit. The spec of 0.5-volt drop is acceptable for this circuit.
Rat's Head SoupMike Myhrvold, Virginia beach, VA: I have been a reader of your magazine for more than 25 years. As magazines come and go, Car Craft has remained the best, and I should know, I have subscribed to all of them. Now that the niceties are completed, I have a request.
I have a set of big-block Chevrolet cylinder heads casting number 3993820 on which I have been trying to get specifics, such as port volume, for some time. I was wondering if you could add them to your cylinder-head database for testing or just throw me a bone. I know I should have measured them myself when I was building the engine, but they were assembled, and the short-block was calling my name. They came on a '72 402 engine (that's now a 414ci) and have 119cc combustion chambers. The engine is installed in a '70 Chevelle. Looks damned good if I say so myself. I have installed 2.19/1.88 valves in them, but they originally came with small valves. No one else can find the info.
Thanks in advance. Don't worry, I will still subscribe even if I don't hear back from you.
Jeff Smith: We don't have access to a set of those heads, Mike, so we can't measure the port volume, but we can come pretty close. These heads were used in '71 402 and 454 big-blocks, and as you mentioned, are oval-port castings. Stock valve size for these heads is 2.06/ 1.72, so you were wise to open them up to the larger 2.19/1.88-inch diameters. According to Alan L. Colvin's book Chevrolet by the Numbers: The Essential Chevrolet Parts Reference 1970-1975, this head had redesigned intake and exhaust valve seats, and the spark-plug seat was changed to a tapered design as opposed to the older gasket-sealing style. According to Colvin, who had unprecedented access to the GM archives for his information, the combustion-chamber size was 113 cc-not 119 cc as you said. That will be worth some additional compression. But if you measured the chambers at 119 cc, then believe that number, since production variations were common.
As for port volume, we can only go by similar heads, since Chevrolet never published port volumes for any of its heads. This is a marketing-generated number created to quickly identify different aftermarket heads. The problem with port volumes is they don't tell you the whole story about an intake port. This is especially true with Rat motors because there are two good ports and two bad ports in each head. The good ports aim the intake charge toward the center of the cylinder, while the bad ports shoot the intake port more toward the cylinder wall.
We looked at several heads in our cylinder-head database, and the closest is the 049 head that also is an open-chamber, oval-port head. This head measured 253 cc and also came with the same smaller valve sizes. Our estimate would be that your heads will measure very close to this same volume.
Hopefully, you opened up the throat area underneath the valve seat when you added the larger valves to these heads. Generally, the throat area underneath the intake will be roughly 75 percent of the diameter of the valve-so a 2.06 valve would have a throat diameter of around 1.55 inches. When the machine shop increased the valve diameter to the larger 2.19-inch intake, the throat area became restrictive at roughly 70 percent of the diameter of the valve. Most cylinder-head porters we talk to agree that 85 to 90 percent throat diameter compared with the valve diameter is a good number, and under no circumstances should the number exceed 91 percent. Using a conservative 89 percent, that means the throat diameter underneath those new 2.19-inch intake valves should be 1.949 inches-a solid 0.040 inch larger. I realize the heads are already on the engine, but the next time you have an opportunity to increase valve size, take a look at the throat diameter as well. It might really be worth increased flow that will pay off with more horsepower. For information on how to do pocket porting correctly, check out Car Craft's past porting how-to stories, like the Vortec porting story on the Car Craft Web site under Technical Articles.
Cammed Up and No BrakesChuck McGeorge, Livonia, MI: I have a '68 Chevelle with a 427ci, 435hp big-block that had great brakes until a couple of years ago when I decided to put in a larger cam. The specs for the cam are 0.575 inch lift with 305 degrees of duration at 0.006 inch tappet lift. The part number is a Crane 11-214-4. I also had the heads redone with 125 pounds of seat pressure at 1.88 inches of installed height with 315 pounds at 1.280 inches open spring pressure. I also changed over to roller rockers. The rest of the package consists of a TH350 with a 3,800-rpm Cohan stall speed converter and a 12-bolt with 4.11 gears.
While I was doing all this, I also changed my brakes to disc up front and left the drums on the rear. I used a smaller, dual-chamber vacuum booster that came with the brake upgrade and also a dual-reservoir master cylinder.
The car hasn't stopped very well since I did all this. With such little vacuum (7 inches of vacuum at idle) coming from my cammed-up motor, I put on a 12-volt vacuum pump that gives me 16 inches, which still isn't enough.
People have suggested putting an adjustable proportioning valve on it, but why would I restrict the flow to the rear when there isn't enough flow now? I have heard of a hydraulic-assist pump that works off my power steering, but I haven't looked into that yet.
Oh, the proportioning valve is located on top next to the master cylinder. I had to remove the line lock because it would not hold the front brakes for burnouts.
I would like to drive the car more, but since it doesn't stop very well, I am afraid to take chances.
Jeff Smith: We're going to have to make a couple of assumptions to answer your question, Chuck. First, we're going to assume that when you say your Chevelle doesn't stop very well, that you have to apply a lot of pedal pressure and the car still requires too much distance to stop. You mention that you installed the disc-brake conversion at the same time you bolted in the larger cam. It also sounds like the brake kit was not optimized, even if you had not chosen the larger cam, and the lower-idle vacuum certainly didn't help. The good news is that the fix is easy and not that expensive.
You're right that changing the proportioning valve will not help your problem. The proportioning valve only reduces hydraulic line pressure to the rear drum brakes when used in conjunction with front disc brakes. Drums require less line pressure than disc brakes, and even rear discs on a four-wheel, disc-brake-equipped vehicle require less line pressure in most cases because anytime the brakes are applied, dynamic weight transfer occurs, which shifts weight off the rear tires and onto the front tires. This means that less pressure to the rear brakes will prevent the rear tires from locking up under hard braking. This leads us to what may be your problem.
It sounds like the kit you purchased is using a master cylinder with too large a piston diameter. In any hydraulic system, there is a direct relationship between master-cylinder piston diameter and the size of the piston on the caliper. The smaller the master-cylinder piston, the more pressure it will make. Increasing the master-cylinder piston diameter will reduce the amount of pressure given the same amount of pedal effort. What the larger piston delivers is more fluid, but at a lower pressure. Add to this your reduced-manifold vacuum, which reduces the effect of the vacuum-assist booster. You said a vacuum pump didn't help much, which also reinforces the concept that the master-cylinder piston diameter is too large.
I'm going to go out on a limb here and guess the master-cylinder diameter is somewhere in the area of a 111/416-inch-diameter piston. What I've found works well, even in manual four-wheel disc-brake applications, is a master cylinder with a 151/416-inch-diameter piston. The tradeoff with this smaller piston is that it will require more brake-pedal movement to displace the same amount of fluid as the larger piston.
Let's do some simple math and see what the difference in pressure will be between a 111/416 (1.0625 inches) and a 71/48 (0.875 inch) master cylinder. We're going to assume 50 pounds of brake-pedal effort, a brake-pedal ratio of 6:1, and a front-brake caliper with two pistons, each with a diameter of 1.5 inches.
First we have to calculate the area of the two different master-cylinder pistons. We have to convert these piston diameters into square inches of area. The formula is as follows:* Area = radius squared x pi (3.1417)-let's simplify that to:* Area = diameter x diameter x 0.7854* 1.0625 x 1.0625 x 0.7854 = 0.887 square inches of piston area* 0.875 x 0.875 x 0.7854 = 0.601 square inches of piston area
We also have to calculate the area of two, 1.5-inch-diameter caliper pistons used in our typical two-piston brake caliper. The formula here is to calculate the area of each piston and add them together.* 1.5 x 1.5 x 0.7854 = 1.77 square inches of area for one piston plus another 1.77 square inches for the second piston, which equals a total of 3.54 square inches of caliper piston area.
To calculate the line pressure created by the master-cylinder piston area, we'll use this formula:* Pedal force x pedal ratio / piston area = line pressure (psi)* Big piston master = 50 pounds X 6 / 0.887 = 338 psi* Small piston master = 50 pounds x 6 / 0.601 = 499 psi
From line pressure alone, you can see the advantage of the smaller piston. But now that advantage is multiplied by the diameter of the caliper piston. The larger the caliper piston, the more pressure is multiplied. In our example, the two-caliper pistons generate a total of 3.54 square inches. Hydraulic pressure (in psi) created by the master-cylinder piston now multiplies the pressure times the area of the brake-caliper piston.* Big-piston master cylinder = 338 psi x 3.54 sq. in. = 1,196 psi of pad force* Small-piston master cylinder = 499 psi x 3.54 sq. in. = 1,767 psi of pad force
The force difference on the caliper pad between the big and small master-cylinder pistons is 47.6 percent! The smaller master-cylinder piston creates almost half again as much caliper force. With the larger 111/48-inch-diameter master-cylinder piston, your car won't stop without a ton of pressure on the brake pedal. It's possible a 1-inch master cylinder will also work well in your application. Either way, you can see it's critically important to properly match brake components.
I can't take credit for the math involved with this answer (if you saw my high school algebra grades, you'd know why). For this information, I referenced the HP Trade title Brake Handbook by Fred Puhn that unfortunately is out of print. If you're interested, used copies of this book are still available at amazon.com, but the prices are a bit steep at around $50 a copy. HP does have a current book titled Brake Systems by Mike Mavrigian and Larry Carley that sells on amazon.com for cheap.
HindsightKen Hunter, via CarCraft.com: I have a '71 Chevelle, and now I am looking to do the rearend. Right now, I have a 10-bolt, one-tire-fire with 3.73 gears, and I want to put a 12-bolt posi with 4.10s. I found a '72 Buick Riviera in a junkyard with a 12-bolt rearend for $180, but I noticed there was a weird-looking rear axle yoke I have never seen before. Can I take that 12-bolt out and put it in my Chevelle? Would I have clearance and backspacing issues? Can I put the same wheels and tires on with no problems? What are my options?
Jeff Smith: The '72 Buick Riviera is what GM calls a B-body car, which is the next-size-larger vehicle in the GM scheme compared to a Chevelle that is referred to as an A-body car. The rear axle assemblies for the B-body cars are not the same as for the A-bodies and do not interchange. Worse yet, the 12-bolt you refer to is an odd-ball housing that does not share internal components with the typical Chevelle or Camaro 12-bolt, right down to the oddball pinion yoke. So this rear-axle assembly won't interchange on several levels.
The question then becomes whether to attempt to build up the existing 10-bolt or step up to a the stronger but more expensive 12-bolt. The answer lies in how much power you plan to make. If your current combination is a small-block that makes less than 450 hp, then the current 8.2 10-bolt would probably be sufficient. You mention that it's a "one-legger", which can be cured with a performance limited-slip differential, also called Posi-traction, which was GM's term for a limited-slip unit. The good news is there are two limited slips, including an Auburn cone-type and a clutch-type that is similar in design to the original GM unit. We researched the Drive Train Specialists (DTS) catalogue and found a U.S. Gear clutch-type posi for $385.02 (PN US01-082728) that would work fine. DTS also offers several Auburn limited slips including PN AU5420108 for $363.00.
