460HP, 5.3L Engine Combo
Tucker Ryals; Gainesville, FL: I'd like to pose a question regarding an article Jeff Smith wrote on the Chevy 5.3L motor "Bolt On a Cam and Heads and Add 120+ HP" (April '08). I read the article with great interest, as I am planning on a budget motor build, utilizing a Gen III or IV Chevy V8. I plan to install the motor and a T-56 into a second-gen RX-7 and use the car for open track days, HPDEs, and time trials. I would like to piece together a package using various off-the-shelf parts to create a motor that is willing to spin pretty high but still have a nice, wide powerband. I'd be willing to sacrifice some low-end torque to pick up some higher-rpm power.
While I don't have a stated financial limit, I would really like to put together the package as inexpensively as possible, mixing and matching parts across the engine family if necessary. For instance, some folks claim a 4.8L crank in a 6.0L block yields a spin-happy motor while others pooh-pooh the idea, claiming driveability issues. Given those stated goals, I would welcome your recommendations on a workable recipe.
Engine swapping is high Car Craft art. This is a carbureted 4.8L truck motor in our orange
Jeff Smith: Wow, we could go on for days on this subject, Tucker. Let's try and narrow it down to a few essential truths. I like the idea of a strong V8 in a lightweight car, and I hear this is a popular swap for the RX-7. Before we get into the specific details, let's hit a couple of basic engine ideas that may help color your decision. The first thing we should discuss is displacement. The easiest way to make power is with displacement. Given a relatively non-restrictive induction and exhaust system and camshaft, a bigger engine will make more torque and more horsepower than a smaller engine. It's that simple. So starting with a 6.0L engine might make more sense than swapping parts around to build a 5.3L or 5.7L engine. But it appears you are looking to spin this engine a little higher in the rpm range for a road-race-style application, so we need to address the factor of rpm as well. High rpm and long-stroke engines are generally not compatible unless you spend big money on quality parts. So let's assume we will be using a shorter-stroke engine. As we all know, we can calculate horsepower based on the torque created by the engine at a given rpm. The formula is very simple: (torque x rpm) / 5,252 = HP. From this, it's simple to see that if an engine makes 400 lb-ft of torque at 5,252 rpm, then it makes 400 hp. But by modifying the engine design, we could make that same 400 lb-ft of torque at 6,000 rpm. Plug that into the equation, and now this engine makes 457 hp. We're making the same torque, but because it occurs at a higher engine speed, the engine makes more horsepower. Good-flowing heads and a big camshaft are required to make this kind of torque. Big-displacement engines often rely on a long stroke to create that larger engine size, which means the piston now has to travel a greater distance at these higher speeds. This creates very high g-force loads on the piston and connecting rod. This is the main reason short-stroke engines are considered "rpm" engines. The pistons travel a shorter distance and therefore place less stress on the rotating assembly, which includes the crankshaft. Engine speed also affects the valvetrain, as those valves, springs, and lifters also have to travel at greater speeds and are impacted by increasingly greater loads directly caused by rpm. So if we decide to build a road-race-style engine that will see 6,500 to 7,000 rpm, we have to decide how big the engine will be and how much money we are willing to spend to ensure its durability.
Let's go a little deeper into the 5.3L engine story you mentioned. That combination was a stock short-block 5.3L engine with a Comp Thumper camshaft (227/241 degrees at 0.050 with 0.563/0.546-inch lift with a 109-degree LSA), a carbureted, single-plane intake manifold, and a set of West Coast Racing Cylinder Heads–ported Edelbrock heads. The cylinder heads increased intake- and exhaust-port airflow (267-cfm intake flow at 0.500 lift), and this, combined with the longer-duration cam, pushed the peak-torque rpm point up to 5,600 rpm (from the baseline engine's 4,200 rpm). Generally speaking, most engines will create a powerband of around 1,500 rpm. We define the powerband as that rpm spread between peak torque and peak horsepower. In this 5.3L engine's case, peak torque was at 5,600 rpm and peak horsepower occurred at 6,800 rpm for a powerband of 1,200 rpm. The engine did make a strong 460 hp, but we had to spin it to 6,800 rpm to achieve that number. We didn't get into engine durability in that story, but the reality is that cast pistons and those spindly, stock connecting rod bolts would probably fail within a couple of hours (perhaps minutes) of running this engine at 6,800 rpm. The g-forces on those components increase geometrically as engine speed increases. While those stock parts might live a relatively long time (at 6,500, for example), they will fail within a very short time at 6,800 rpm—a mere increase of 300 rpm. The 5.3L engine was designed as a truck engine, and it's fair to say that the GM engineers never intended this engine to spin anywhere near 6,800 rpm for long periods of time.
That means we have to change some components to ensure our little engine will spin that high and survive. The first change should be a switch to a high-quality forged piston. For the sake of discussion, let's look at the idea of adding the 4.8L engine crankshaft to a 6.0L iron-block engine. The idea behind this plan has some merit. The factory 5.3L (325ci) engine uses a relatively small 3.78-inch-bore diameter combined with a 3.62-inch stroke length. You can create almost the exact same displacement by switching to a larger, 4.00-inch bore and the shorter 4.8L engine's 3.26-inch stroke. This creates a 327.7ci engine that, ironically, is almost an exact replicate of the original small-block Chevy 327 with a 4.00-inch bore and 3.25-inch stroke. You could add a few inches by boring the cylinders 0.030-inch oversize, which would create a 332ci engine. There are a couple of advantages to this setup over a stock bore and stroke 5.3L engine. The first is a shorter stroke, which reduces piston friction, and the second is the slight cylinder-head-flow improvement with the larger bore's 4.030-inch diameter. The problem with this approach is finding a 4.030-inch piston and the proper combination of compression height and connecting-rod length that will put the piston at the deck height. Our initial search for a 4.030 piston with 6.100-inch connecting rod and the proper compression height wasn't successful. You could have custom pistons made, but that is expensive. A slightly better idea would be to go with the 5.3L crank stroke of 3.62 with a 4.030-inch bore that will add displacement (369 ci) and also piston speed, and therefore add friction. This combination can still make decent power, since the stroke is not that much longer than that of a typical 350ci small-block Chevy (4.00-inch bore and 3.48-inch stroke), and Lord knows there are tons of these high-rpm road-race applications running. The piston was also difficult to find, mainly because it appears that most of the off-the-shelf pistons are aimed at larger-displacement engines. You could fall back to a 0.020-over 5.3L engine with the stock stroke and good rods. Wiseco offers a forged, flat-top piston for a 6.125-inch rod. While this piston is more than $700, it, along with a good 4340 steel connecting rod, will deliver the durability. Add in the cam and heads we used in the story you referenced, and you would have a 460hp package that would not only live but also deliver excellent power, especially for a relatively lightweight car such as yours. This might be the least expensive way to go, but there will still be significant cost involved with building the engine. It sounds like it will be fun to drive!
Comp Cams; 800/999-0853; CompCams.com
West Coast Racing Cylinder Heads; 818/705-5454; Proheads.com
Wiseco Pistons; 800/321-1364; Wiseco.com
Effective Compression Ratios
Derrick Morris; Pearland, TX: OK, guys, I need to know this information, as I can't find the answer anywhere. Basically, I have a 12:1-compression, 414ci LSX motor using a 6.0L iron-block with a 4.060 bore and 4.00-inch stroke with L92 heads. While the motor was originally intended for carb/nitrous, I want to put boost to it, but I don't want to change pistons. I know my cam is not ideal for a turbo, but it's new, so it's getting put to use. The cam is a Comp hydraulic roller 260/268 at 0.050 0.646/0.646 on a 112 LSA. I've got good parts, including Manley Inconel valves, T&D shaft rockers, and ARP head and main studs. I've also converted to fuel injection with a Victor Jr. intake.
I just came across Ask Anything in my Mar. '12 issue and read the letter titled "Effective Compression." Using the formula: [(boost psi/14.7) + 1] x static compression = ECR, I come up with the following for my engine: 15 psi/14.7 = 1.02 + 1 = 2.02 x 12(compression) = 24.2:1 ECR, which is obviously high. So what ECR is too high? I did some digging and came up with a stout motor from Pro Line in the Lynch/Petty Mustang from June '08 issue of Hot Rod (3,500 hp on 10.5W). They are running 34 psi on roughly 9:1 and using above formula, which comes out to an ECR of 29.8:1.
Obviously, we are dealing with cylinder pressure and staying away from detonation, so my short version of the question is whether there is such a thing as too much ECR? I know why guys are running lower static compression when running boost, as the higher the compression, the lower the boost, and you can make more power with lower compression and higher boost. Obviously, you want as much compression as you can get, and I realize there is a point at which you can only run so much. But if motors are staying together with ECR of 29.8:1, and since they say in that article that they were going to step it up to 40 psi, and that there are higher ECRs out there, it all comes down to my 12:1 motor. Can I shove 15 psi into it or not? What about 20 psi that would generate a 28.3:1 ECR? Thanks!
Compression height is the distance from the centerline of the wristpin to the top of the p
Jeff Smith: It appears your question has really more to do with octane rating, avoiding detonation, and high-quality race fuels than about effective compression. It would probably not be a good idea to place too much faith in that formula. I think it's more useful as a comparator than anything else. But having said that, I recently applied that formula [(boost in psi /14.7) + 1] x static compression ratio to a 1,200hp, 4.8L LS engine in our sister book, Hot Rod. That engine had a static compression ratio of 9:1, used a whopping 25 psi of boost, and came up with an ECR of 24.3:1. That engine ran on 118-octane race gas and had no detonation issues, at least on the dyno, where there is good control over most variables. On the dragstrip or the street, many different variables come into play. For example, on the dyno, load is constant as is the acceleration rate of the engine, while both are completely different in the car.
Let's start with boost. In this equation, it's used as an indicator for cylinder pressure, and there are several problems with that. In this case, boost--or pressure in pounds per square inch (psi)--is merely an indication of a restriction to flow. Part of the ECR equation computes something engineers call pressure ratio. This is merely the calculation of psi divided by 14.7. That means 15 psi of boost represents a pressure ratio of 1.02--exactly what you calculated in the first part of the ECR equation.
The problem is that pressure ratio is merely an efficient way to express pressure that is above atmospheric levels. What it does not tell us is how hot the air becomes on its way to creating that ratio. There are ideal gas laws (called Boyle's Law) that relate pressure to volume. In an ideal situation, raising the pressure of air will result in a rise in temperature (this is referred to as 100 percent adiabatic efficiency), which means this is the minimum temperature rise (without aftercooling). Turbochargers are generally about 75 percent efficient when it comes to creating pressure. That means that by creating pressure (boost), our turbocharger also inevitably inputs heat into that pressurized air. When air is heated, it loses density because the molecules are more active and space themselves farther apart. So a cubic foot of air at 200 degrees F is less dense than a cubic foot of air at 100 degrees F at the same pressure. In other words, cooler air is always better. When it comes to horsepower, the real reason we increase boost (pressure ratio) is to shove more oxygen into the combustion chamber (that's how nitrous works--by adding oxygen). The equation uses pressure ratio to compare with static compression but doesn't take into account the discharge temperature, so we have a huge variable here. And this is just one variable; it would take the rest of the year for this column just to touch on the hundreds of variables that also have an effect on combustion efficiency.
So really, we're talking about the ability of the fuel to resist detonation (among other things) that will allow us to build an engine that makes more cylinder pressure and not detonate. In the Hot Rod story, that 1,200hp engine ran on 118-octane race gasoline. This is where chemistry begins to cloud the issue of combustion. So perhaps a better question should be, what kind of fuel would help me achieve my goals? The two major rating forms for octane are Research (RON) and Motor (MON). Of the two, Motor is far more important to a race engine, as that rating takes into account how the fuel deals with heat and temperature in a real engine. The anti-knock index (AKI) is rated by adding the Motor and Research Octane numbers together and dividing by two: (R + M) / 2. One critical factor we uncovered researching this answer was that the closer the two octane numbers are, the more stable the fuel. So for a stable, 100-octane fuel, we might see the Motor number at 96 and the Research number at 104. A less stable fuel could exhibit numbers such as 90 and 110. As an example, VP's C-16 leaded race gasoline has a MON of 117 and a RON of 117 with a R+M/2 AKI (referenced sometimes as pump octane number or PON) of 117. Clearly, this is a highly stable fuel with excellent anti-detonation characteristics. In your search for a high-quality fuel, choose the one with the higher MON number.
So if you wanted to build an engine that would have 15 psi of boost and a 12:1 compression ratio (ECR = 20:1), you would want it to run on gas that has a strong octane rating but also one with Motor and Research numbers as close together as possible. My recommendation would be to sneak up on this combination. Start with relatively conservative boost numbers with a high-quality fuel, and see how that works. Then gradually increase the boost and use careful evaluation of the spark plugs to get an idea of what is happening in the combustion chamber. Unfortunately, if something goes wrong, the first indication will probably be a piston that begins to disintegrate. The hint earlier in this discussion was all about temperature. The lower your inlet air temperature, the more power you will make, and the engine will be much happier. Alcohol is a good fuel for this type of application, as its cooling effect is dramatic. E85 is a bit less aggressive with 85 percent ethanol and 15 percent gasoline, and it enjoys an increasingly strong following. The general consensus is that pump-gas E85 hovers around 105-octane. E98 (or 98 percent ethanol) is around 115-octane. One disadvantage to pump E85 is that you don’t really know the actual percentage ratio of ethanol to gasoline or the quality of gasoline that is added to the ethanol. According to Tim Wusz at Rockett Brand Racing Fuel, because ethanol has such a great octane rating, pump gas tends to be mixed with low-grade gasoline, which would push the RON and MON numbers farther apart. On the other side of the technology coin is E85’s excellent cooling effect. This is called latent heat of vaporization. An example of this process is when you spread a small amount of isopropyl alcohol on your skin and notice that as the alcohol evaporates, it pulls heat away from your skin, creating a cooling sensation. When used in an engine, alcohol boils (evaporates), and its physical state changes from a liquid to a gas, which removes heat and cools the inlet charge. We see this when using E85 in draw-through supercharged engines in which the discharge temperature of the pressurized inlet is radically lower than that of a similar engine running on gasoline. The point of this discussion is that as the inlet air temperature becomes lower, the engine becomes less sensitive to detonation. A 10-degree reduction in inlet air temperature is a big move. If you’ve ever driven an engine that is overheating, it will detonate like crazy because the entire engine is hot and this heats the inlet air temperature and contributes to the engine rattling.
This has been another long walk off a short pier, but as you can see, there are plenty of variables that contribute to engine detonation—and we’ve only just begun to dig into this topic. Combustion-chamber shape, quench-area effectiveness, piston-to-head clearance, mixture distribution in the combustion space, piston-ring sealing, oil contamination, and a few dozen other variables all contribute to the witches’ brew that constitutes the combustion process. As you have added injectors to a Victor Jr. intake, are you aware that injector placement within the induction system appears to be very critical? I’m not privy to any in-depth research, but it’s clear that the farther upstream you can place the injectors, the more time the fuel will have to cool the incoming air.
This answer has probably created more questions than answers, but I would caution you to move slowly and carefully and encourage you to call the tech people at VP Racing fuel and Rockett Brand Racing Fuel for more specific application questions.
Rockett Brand Racing Fuel; 714/694-1286; RockettBrand.com
VP Racing Fuels; 512/621-2244; VPRacingFuels.com
Anthony Guy; via CarCraft.com: I’ve been reading Car Craft since I first started driving in the mid ’70s. It was an article written during that time that showed the basics of airbrushing in the height of the kustom van craze that got me into airbrushing. I currently have a two-wheel-drive ’94 S-10 pickup that had some serious body lean in the corners. I installed a rear antisway bar that flattened out the roll problem, but now it has some very noticeable oversteer. I don’t have a garage, so any projects I take on have to be completed during daylight hours over a weekend. Eventually, I’d like to lower the body a couple of inches, so I haven’t tried replacing the shocks for fear of having to replace them twice. Is there an easy solution to this oversteer problem, or will I just have to deal with it? Thanks.
Jeff Smith: You should never just “deal with it,” Anthony. Improving the handling not only makes your truck more fun to drive but also makes it immensely safer. To simplify this somewhat, when you added a rear sway bar, you increased roll resistance in the rear of the vehicle. So in the middle of a corner when you try to accelerate, the stiffest end of the car (in your case, the rear) will break free, causing the oversteer condition you described. Let’s take a basic look at both the front and rear suspensions and then we can figure out a way to reduce the body lean, improve your handling, and make your little S-10 pickup a hoot to drive.
Springs are designed to support the weight of the vehicle. Entering a corner places greater load on a given side of the suspension. In a left-hand turn, weight transfers from the lefthand side of the vehicle to the right with more weight moving to the front as the vehicle enters the corner. Stock suspensions always involve a compromise between ride quality and handling. Generally, production spring rates are decidedly on the soft side to improve ride quality. Given a softer spring rate, the spring will compress more under load when you negotiate a corner. The spring compresses until the force stabilizes, creating excessive body roll, which dramatically affects the front suspension geometry (and to a lesser extent, the rear). Pickup trucks add another variable into this equation, as they are designed to carry a given payload in the bed. This means the rear springs will be a significantly higher rate compared with the spring rate of a similar-sized passenger car. For example, a ’94 S-10 has a load-carrying capacity of 1,500 pounds. Even with a spring rate of 300 pounds per inch (300 lb-in), the rear suspension will drop 5 inches with that amount of load in the bed. Even if the leaf-spring rate is closer to 250 lb-in, that’s still a very stiff rear spring rate for the vehicle when there is no load in the bed. Adding a rear sway bar increased the effective spring rate (by adding resistance to roll) when entering or exiting a corner. So it’s no wonder that your S-10 wants to oversteer. If you want to reduce body roll by retaining a sway bar, there are a couple of options. First, reduce the diameter of the rear sway bar. Next, reduce the rear spring rate by removing one or possibly two leaves from the springs. This will soften the spring rate and reduce the tendency to oversteer. Of course, this will reduce the load capacity of the bed as well. It’s all a compromise.
For the sake of tuning (and because this topic is so much fun!), let's take this a little bit further. The rate at which weight transfer occurs in a corner is directly affected by the shock absorber. If we use an adjustable shock absorber, we can change the rate at which the shock (and therefore the suspension) compresses. If we stiffen the shock valving to reduce the rate at which the shock compresses, we can use the handling feedback to tell us what the car wants to improve the handling. Several companies offer adjustable shocks that can be used to help tune the car for superior handling. I spoke with Eric Norrdin from Global West Suspension, and his recommendation was to go with a double-adjustable rather than a single-adjustable shock. Norrdin says that single-adjustable shocks such as those from QA1 or Koni are rebound adjustable, but because of valve design, any increase in valving to the rebound also affects the rate of compression. The ideal way to fine-tune your suspension is to make one change at a time. This is why double-adjustable shocks are superior to singles--you can make separate adjustments to the compression, for example, without that change affecting the rebound adjustment. This makes tuning much easier and quicker. Of course, there's no free lunch in the performance world, and double-adjustable shocks are not cheap. The QA1 double-adjustable Stocker Stars for the front of your S-10 are part number TD505 and will run $227.95 each, while the rear shocks are TD901 and will cost $229.95 each (Summit Racing). That's over $900 for a set of four, but these shocks are rebuildable, which means they can potentially last a lifetime.
For a tuning procedure, let's say you install a smaller rear sway bar, remove two leaves from the rear suspension, and add double-adjustable shocks on all four corners. Let's take your truck to an autocross course. After several baseline runs, we increase the compression stiffness in the front shocks. If the truck responds with improved corner-entry handling, the spring rate in the front is probably too soft, as we're using the shock valving to crutch the front spring rate. We can increase the front spring rate, which will reduce body lean, and then reduce the shock-absorber compression valving to control the rate of weight transfer. Generally, the most efficient process is to improve the front suspension so corner entry is acceptable and then tune the rear suspension to help with corner exit. Most likely with your S-10, there is so little weight on the rear axle (compounded by a stiff rear spring rate) that any amount of added stiffness (such as the sway bar) will make the rear end of the truck step out on corner exit--which is classic oversteer. While this procedure is described for an S-10, it will work with any rear-wheel-drive vehicle.
This is a great question, as we're working on an S-10 of our own that we intend to put on an autocross course as soon as we get that small-block and five-speed bolted in place. The front suspension on the S-10 is very similar to a G-body ('88 Monte Carlo, for example). Global West offers upper and lower tubular control arms, front coil springs, and QA1 shocks for S-10 pickups, which, when combined with a taller spindle and bigger disc brakes, dramatically improve the truck's handling. The taller spindle is available with the 12-inch rotor disc brake conversion kit (DB-2312, $1,065.90). The taller arms produce a negative-roll camber package that really plants the front tires in a corner, which produces a remarkable improvement over the stock front suspension. Addco sells a 11?8-inch front sway bar for the S-10 (PN 739, $224.95; Summit Racing) that will also help. All this costs money, but the beauty is that you can upgrade the system one part at a time as your budget allows.