Chevy Nova: Put That Rat on Steroids
Ron Shagool; Bardstown, KY: I am in the process of restoring the first car I ever owned—a 1970 Chevy Nova that I was lucky enough to hunt down and purchase. As with most people in this economy, I am trying to stretch every dollar. Over the years I have been able to collect/accumulate a number of big-block Chevy engines, and feel I should use what I have on hand to save some money. Most of these are 396ci engines.
I found a website that specializes in stroker kits and located one kit that claims to increase a 396ci motor to 434 ci. It comes with a 4.00-inch nodular iron crank, forged rods, and hypereutectic pistons for $1,350 or $2,200 for a steel crank and forged pistons. Do you know much about these motors after such a stroker kit is installed?
My second question concerns the factory 049- and 781-casting-number, cast-iron, oval-port big-block Chevy Nova heads. I know many articles have been written about the good flow numbers of these heads and engines that have been built utilizing them. But I have never heard of anyone building a 396-based engine using these heads. Most people use the closed-chamber 396 heads that came out on these motors (215, 290 casting numbers). I would rather use a set of the open-chamber 454 heads for my Chevy Nova (I have both 049 and 781 castings). I have been told I must be careful with not putting too large a valve in the heads and using them on a 396 motor due to the smaller bore versus using them on a 427 or 454 motor. Is this true? I have also been told that the 049 would be the better head for a 396 and the 781 head would be better on a 427 or 454 motor. Is this true, or are there any differences at all in the two castings?
When the motor is finished, my Chevy Nova will be used for street cruising and the occasional trip down the dragstrip. I would like to build a motor using as many of the factory parts as possible but upgrade them with some of the later technology, such as a hydraulic roller cam, roller rockers, an aluminum intake, headers, and so on. Should I even pursue these heads, or should I just order new ones? I have seen Patriot aluminum big-block heads advertised for $1,350 to $1,400. I have no predetermined horsepower figures I have to meet or rules I have to live with to race in a particular class. I have already built a 200-4R overdrive transmission and currently am rebuilding the 12-bolt.
Jeff Smith: You have a stack of good questions, so let’s get started. To begin with, the classic car-crafter approach with engines is to start with what you have. The limitation with a 396 block is its small bore diameter at 4.094. Even the 0.030-over 402 barely pushes the bore to 4.125. The stock 396 engine stroke is 3.76 inches, so adding a 4.00-inch stroke to the oversize 4.125-inch bore delivers 427 ci. The 434ci effort you mentioned is attained by stretching the bore to 4.155. While the bore increase helps, the question comes down to increasing inches with a stroker crank assembly to push it up to 427 or 434 inches. But at the same time, it might be easier (and cheaper) to find a usable stock 454 short-block and start there. Staffer John McGann just came back from a local boneyard hunt where he found three complete 454 engines for $399 each. If you bought just the short-block, you might get it for $350 or less but then need to invest $600 to $800 in machine work and $400 in pistons and rings, after which you’d have a larger-displacement engine for the same price as the stroker 396 package and would still have to invest in machine work. The advantage of the 454 block is its larger 4.250-inch bore and stock 4.00-inch stroke crank. Punch the bore another 0.060 and you have 467 inches while retaining the stock crank and rods. I found a 0.060-over Sealed Power hypereutectic piston in the Summit catalog for $355 with an 11 cc dome that would make 9:1 compression. Milling the 118cc heads down to 110 cc would bump the compression to 9.5:1, which is about the limit on pump gas with a mild cam.
Part of the problem with choosing the smaller-bore 396—even after boring it to 4.155 inches—is that the large, open-chamber 049 heads hurt the compression, even if you go with a 4.00-inch crank. With the stock 118cc chamber, you’re looking at 8.4:1 compression, which limits power and only works if you want to run 87-octane fuel. Milling the heads to 110 cc will push the compression up to 8.96:1. This assumes an 11cc domed piston, a 0.015-inch deck, and a 0.042-inch-thick head gasket. The whole idea behind the 454 is not only the added torque and cubic inches but also the hidden value of the larger bore that will help even those oval-port heads to breathe better. Over the years, you might recall that I’ve done several oval- versus rectangle-port big-block head comparisons. The oval-port heads always win. A fair number would be an average of 12 to 15 lb-ft of torque and 10 to 14 hp increase with the oval ports, especially with a smaller-displacement engine like a 454. If you go the 454 route, remember that it’s an externally balanced engine, while the 396/402/ 427 engines are all internally balanced.
From what I’ve found, there is very little difference between the 049 and 781 casting-number heads. If you go the smaller bore route, I suggest you retain the stock 2.06/1.72-inch valve sizes since the larger valves will deliver a minimal power improvement considering the investment. If you decide to go the bigger-bore 454 route, I would recommend bumping the valve sizes up to original 2.19/1.88 dimensions on the rectangle-port heads. More than likely, the stock valves will be worn anyway, so this is a great reason to upgrade. Also, you have the opportunity to use smaller, 11⁄32-inch (0.3415-inch-diameter) stem valves that save weight over the stock 3⁄8 (0.3715-inch) stems. This requires different guides, but the price of replacing them with smaller ones should be the same. The larger-intake valves require grinding the seats larger, which is a benefit on older heads where the valve seat has likely seen prior work. The larger diameter moves the short-side radius location, which improves the midlift flow on these stock heads. All of this will help midrange torque and throttle response. As the least expensive aluminum head will cost roughly $1,400, you should be able to rebuild the stock oval-port heads with high-quality valves and good machine work for less than $800. Not only that, but the heads on a 467ci Rat would make excellent torque. So unless the benefit of the lighter-weight aluminum heads is important—along with their wow factor—you might stick with the iron oval ports. There would be few good reasons to put an expensive set of aluminum heads on the smaller-displacement stroker 396, as the flow advantage would be limited with the smaller-bore engine.
As for a camshaft, I like your idea of going to a hydraulic roller. This is where you will spend some money, but I think this is also where the return on the investment (dollar per horsepower or dollar per lb-ft of torque) really pays off. On the big-block, oval-port cylinder head test we did back in the Mar. ’08 issue (“Big-Block Cylinder Head Test”), we chose a Comp XR276HR cam for our 496ci engine. That cam delivered fantastic torque, making as much as 626 lb-ft of torque at 3,900 rpm. Assuming you go along with our 454 suggestion, a slightly smaller cam might be beneficial, since our engine was 50 ci larger. I’d suggest the XR270HR cam with 218/224 degrees of duration at 0.050 tappet lift. This cam still delivers the same 0.510-inch lift as the larger XR276 cam on the intake side, but the shorter duration will make more usable torque in the midrange for your smaller engine. I’d suggest a set of 1.7:1 roller rockers and the same valvespring used on our dyno test—the 933-16 Comp hydraulic roller spring worked very well controlling those heavy big-block valves. Combine all this with an Edelbrock Performer RPM intake and a 750-cfm Holley carb, and you will have a muscular street 454 that could easily make 530 to perhaps 550 lb-ft of torque. That’s what you’ll feel in the seat of your pants when you stomp the throttle. The oval ports should also make enough steam to push your 454 to between 475 and 500 hp. Those are good numbers for a stock iron-headed budget Rat. Hit it, maestro!
Comp Cams; Memphis, TN; 800/999-0853; Compcams.com
The Competitive Advantage
Name Withheld Upon Request: I am a student at UTI and we have many classes, but there are three classes that most people want: Hot Rod 1a, Hot Rod 1b, and Super Street. Super Street is mostly computer tuning, but the Hot Rod classes include getting a Summit 350 Chevy short-block, taking measurements, and then modifying it. While I subscribe to CC, I have no idea about Chevy 350s because I am mainly a Ford guy. I was wondering if you could give me some pointers so I could be ahead of my class—or in other words, so I can cheat. I am not too sure how the class will be carried out, but from what I have heard we put the stock engines in a T-bucket and do a chassis dyno pull and compare it with the modified one. I know we can either have a large shot of nitrous or a Roots-type supercharger and a small shot. What would you suggest? I know that it will change depending on engine setup, cam, piston, head, intake manifold, and carb setting, but I don’t have those figures yet. If you could tell me how to get the extra horsepower and torque out of a 350 by doing small things—clearances, timing and so on—that would be awesome.
Jeff Smith: What a great letter. I wouldn’t consider what you are doing cheating—I prefer to look at it as creating a competitive advantage. But it’s a double-edged sword because we’re publishing the letter. You wanted a private response, but as Car Craft has more than a million readers, I would rather share this information with all of them, including anyone who might also be taking the class! I really don’t have enough information to give you a solid, this-will-put-you-at-the-top-of-the-class answer, but I have some generic ideas that can point you in the right direction. Let’s start with a comparison of nitrous with the supercharger.
Setting nitrous fuel pressure must be done dynamically if you want to be accurate. This Ze
If I were the instructor, I’d want the blower and the nitrous choices to be as close in power as possible. It appears this supercharger versus nitrous comparison has occurred in this class before, so I’m assuming the instructor knows what’s going to happen. The reason I’d want both combinations to be close in terms of power is to ensure the winner would be the person who is going to assemble the engine properly and then—here’s the real key—tune it so he or she gets the most out of the combination. The big thing I see among those building high-performance engines is that once they have all the parts bolted on, they think the job is done. The truth is that they’ve taken the process only half way. Tuning to make the most power with what you have is the difference between the winners and the also-rans.
I’m not sure why the blower gets a shot of nitrous, though I’m guessing you’re using a mini-blower that can’t make the power of a typical 150hp shot, so the blower gets tickled with an additional 50hp shot or so. More than likely, both the nitrous and fuel jets will be fixed so you can’t alter them. I would do that to prevent a tuner using too lean a fuel jet in search of a hero horsepower number. Assuming this, I’d choose the straight nitrous setup because it is simpler, as you are managing only one power-adder rather than two. I also am going with the nitrous because while superchargers make positive manifold pressure, they also make heat. The classic mini-blowers such as the Weiand or old B&M blowers are generally not very thermally efficient and tend to put more heat into the inlet air (exceptions to this are the Magnuson and the Kenne-Bell). This reduces air density in the manifold. You will get boost, but the air is hot. Hot air is more prone to detonate, so you have to be careful with ignition timing, assuming you’ll use pump gas.
If you choose the straight nitrous route, there are plenty of tuning issues that can be addressed. For example, make double sure that the bottle you are using is full and up to pressure. Weigh the bottle on an accurate scale and compare the total weight as listed on the bottle label. For example, a full 10-pound nitrous bottle might weigh something like 25 pounds, with 10 pounds of liquid nitrous combined with a 15-pound weight of the bottle. For pressure, most nitrous systems use 900 to 950 psi as a starting bottle pressure. According to a chart listed by Nitrous Supply, a bottle temperature of 85 degrees F will produce 950 psi, while a lower temperature of 80 degrees F will drop the pressure to 865—almost 100 psi lower. Lower nitrous pressure will produce a richer overall air/fuel ratio, as the optimal air/fuel is based on the 950-psi number. If you don’t have an accurate pressure gauge (not one of those 1-inch-diameter gauges) to ensure proper pressure, use an inexpensive infrared temperature gun to measure bottle temperature. I would ensure the bottle pressure is adequate by immersing the bottle in a tank with 100-degree hot water to raise the bottle pressure. Once the pressure is up, keep the bottle warm until it’s time to use it. Never use an open flame like a torch or propane flame to heat the bottle. A full nitrous bottle is under immense pressure, and an open flame can create a crack and cause the bottle to split. It’s happened more than once. Nitrous is not a fuel, but any gas under this much pressure is equal to a small bomb that can cause major damage if not treated with the respect that it deserves.
The next nitrous tuning tip is to carefully set the working fuel pressure. Many newbie nitrous users make the mistake of setting fuel pressure with the pump dead-heading into a closed fuel solenoid. The problem with this approach is that when the fuel solenoid opens, the pressure drops well below the static setting. This is really bad because low fuel pressure means less fuel is delivered to the solenoid and the nitrous/fuel ratio becomes lean, which can burn a piston in a matter of seconds. Most nitrous systems are designed to have a pressure regulator feeding the fuel solenoid. To accurately set the fuel pressure, you need to measure and set it dynamically. Zex makes a very cool tool that does this, but an enterprising car crafter could replicate the design. The concept is to disconnect the fuel line that runs to the fuel solenoid. You should place an accurate fuel-pressure gauge (with a range of 0 to 15 psi) in a T that then leads to a fitting that incorporates the fuel jet you will be using. Place the end of the hose with the jet in a gas can. With all fittings tight, turn on the fuel pump and fuel will flow through the jet into the can. The fuel jet becomes the restriction in the delivery system and will produce a pressure on the gauge. Most nitrous systems are designed to operate at 5 or 5.5 psi of fuel pressure. You should do some research on the kit you are using to determine what the nitrous manufacturer recommends. Set this pressure at the regulator and then turn the system off. After reconnecting all the lines back to the plate and the solenoid and checking for leaks, you will see that the dead- head pressure will be higher. This is normal. When the nitrous is engaged, the pressure will be correct. Ignition timing is another important factor. If this is a 150hp shot, all nitrous companies would recommend retarding the timing. The general numbers are 4 to 6 degrees to prevent detonation. However, we just looked up NOS’ newly revised tuning instructions and found that for a 150hp shot with a middle-of-the-road combustion chamber like the small-block Chevy’s, it recommends only 27 degrees of total timing with a 100-octane fuel. That sounds very conservative, but you have to be careful because too much timing can cause the engine to detonate, and then it’s game over because that could cause major engine damage.
I spoke with NOS’ Jay McFarland and he told me the company recently adjusted its standard kit-jetting recommendations by reducing the size of the fuel jet, which it says will make the system work more efficiently. We found an older recommendation for a 150hp Cheater NOS system that spec’d a 0.63 nitrous jet and a larger 0.071 fuel jet. For that same 150hp Cheater system, Holley’s newest information now specifies 0.063 nitrous and 0.063 fuel jets. Note how the fuel jet is eight steps smaller. McFarland says this actually improves engine durability, as NOS’ testing indicates that excessively rich mixtures could be contributing to engine problems. This is with a typical 5-psi fuel pressure, and McFarland says the kits have not really changed other than this new recommendation, so guys with older kits might see a mild power increase by going to a leaner jet. You can find the NOS tune-up recommendations for each kit on Holley’s website. Other important points relate to the ignition system. New spark plugs, good wires, and sufficient spark energy from the distributor are all critical issues for any engine with a power-adder, because as cylinder pressure rises, it places a greater voltage load on the secondary (high-voltage) side of the ignition. You might consider narrowing the spark plug gap to perhaps 0.030 inch. This reduces the voltage requirement. With either power-adder, go with a four to seven steps colder spark plug with a short ground strap to prevent pre-ignition. Finally, when assembling the engine, make sure you add a little extra ring gap to the top ring so it doesn’t butt due to the extra heat from the nitrous and/or blower. We’d shoot for 0.022 inch on a 4.030-inch bore. Armed with all this information, you should be able to do well enough to impress your instructor—good luck!
Holley Performance Products (NOS); Bowling Green, KY; 270/781-9741; Holley.com
Nitrous Supply; Huntington Beach, CA; 714/373-1986; NitrousSupply.com
Zex Nitrous; Memphis, TN; 888/817-1008; Zex.com
We Got it—Backward
It's a simple matter to spin the stock intake around 180 degrees. On our 5.3L motor in our
Mike Smith; Crystal Lake, IL: In the Dec. ’11 issue of Car Craft, you responded to a reader wanting to put an LS truck engine in a kit car. The reader was looking at using an LS1/LS6 intake to avoid “cutting a hole through the back window,” to clear the tall truck intake. The reader appeared to be talking about a mid-engine application. Your advice on changing the accessory-drive system, while valid and helpful in a front-engine setup, is a little off point in a mid-engine application because it will bring the induction piping into the cockpit next to the driver’s ear. The reader could save money by using the existing truck accessory drive if it clears his firewall. Then, what we do at Schwartz Performance is pull the intake manifold and valley cover, remove the oil-pressure sending unit located at the rear of the engine and saw or mill the stand flush and drill, tap, and plug the hole (be careful not to tap too deep). Then move and adapt the sending unit to the small two-bolt cover above the oil filter. Once you’ve reinstalled the valley cover, the Corvette/Camaro LS1/LS6 intake, along with the fuel rails and throttle-body, can now be bolted on backward using the factory torque specs and sequence. The induction piping and/or air filter will now fit nicely above the bellhousing and transaxle. It makes more sense when you see the pictures of the Ultima and GTM car projects at SchwartzPerformance.com. Car Craft is a great magazine, I read it cover-to-cover every month.
This is the twin-turbocharged setup used in the Schwartz Ultima with the reversed intake m
Jeff Smith: This is a great idea, Mike. We mocked up an LS6 manifold on our 5.3L engine to see how this works, and it bolts right up. The reason you can reverse the intake is because the intake ports are symmetrical, unlike the original small-block Chevy. It’s another reason to like the LS-series engines.
Schwartz Performance; Woodstock, IL; 815/206-2230; SchwartzPerformance.com
Jeff Lee; Phoenix, AZ: I just read your article on building the 400 SBC where the cam went flat (“How To Build a 400ci SBC Torque Monster for $2,500!” May ’11, pg.26). The machine shop I use for my race Stock & Super Stock ’70 AMX has a proprietary coating that has been tested extensively with 100 percent success rate. Even on square lobe Stock Eliminator camshafts.
With this coating applied to both the lifters and camshaft, you can load them into your block with race springs installed (not the light-duty break-in springs). fire the engine up, and let it idle. Yes, no high-rpm cam break-in and no more replacing valvesprings after the 2,500-rpm, fast-idle cam break-in procedure. Thus far testing has only been done to 480 pounds of open pressure.
Jeff Smith: Thanks for the information, Jeff. We talked with Bud Yancy at MACH Development in Maricopa, Arizona, a company offering a new coating process called Anealon, an antiwear coating designed for the bottoms of lifters as well as cam lobes. Yancy described it as a proprietary ceramic coating developed by Tech Line Coatings, and MACH Development is a certified installer. Yancy said that on his 428ci Stock Eliminator engine, he coated both the lifter bottoms and the cam lobes and was able to use valvesprings with 260 pounds of seat pressure and 500 pounds over the nose and from initial startup allowed the engine to idle without any special break-in procedure. He says you can coat the cam lobes alone ($125), but it might be a good insurance do the normal break-in procedure as well. Once lifters are installed on the cam lobes, pressure and heat from the interface activate the coating, preventing micro-galling, which is the process of moving metal from one surface, like the cam lobe, to the lifter face, allowing the two wear surfaces to create a long-lasting mating surface.
Yancy also said Anealon can be applied to more than just camshaft lobes and lifters. He has successfully used this coating on a ring-and-pinion set with excellent heat-reduction results. It could also be used on tapered roller bearings and races, manual transmission gearsets, and steel connecting rods at the wristpin.
MACH Development; Maricopa, AZ; 602/278-1200; MachDevelopment.com
Tech Line Coatings; Murrieta, CA; 972/775-6130; TechLineCoatings.com