I have an '87 Corvette that has now clocked 110,000 miles. I have owned the car for about four months, and it is my daily driver. I read about the Bosch Platinum +4 spark plugs and decided to give them a try. Changing the plugs on the driver side was a snap, but the passenger side took a little longer due to some really tight places. According to my owner's manual, on models equipped with aluminum heads it is essential that the spark plug be coated with a small amount of antiseize compound and torqued to 12 pounds. These plugs are factory set, and so there is no need to adjust them. The great thing about these plugs is they do what they say they do. I immediately noticed smoother acceleration from start and greater response when punching the throttle. They cost a little more, but you do get what you pay for.
John Schmidt, Via e-mail
Glad to hear about your experience. A number of people have expressed doubt about the power increases we saw on the dyno after installing Bosch Platinum +4 plugs in place of the original ones, but the improvements are real. To me, it's a no-brainer. Back in the day, we used to file the ground electrode of conventional plugs back so it covered less than half of the center electrode. This practice repeatedly showed power increases of 5+/-horsepower (because it unshrouded the spark kernel which leads to improved combustion efficiency). The design of the Platinum +4 plugs provides the same advantage of unshrouding the spark, so it stands to reason these plugs will provide a measurable performance improvement. The only drawback to these, or any other platinum plug, is they're not suitable for turbo or supercharged applications. The center electrode is too small in diameter to handle the temperatures and pressures encountered in a pressure-boosted engine.
I've also noticed a performance improvement after installing MSD coils in place of the factory coils. I haven't had an opportunity to do a comparative dyno test, but I'm not so sure there will be a big difference in peak horsepower. What I did notice is that the engine runs smoother and is more responsive in the lower-rpm range, and drivability is unbelievably good, even with a camshaft that's a bit over the top for a street-driven car.
36 Doesn't Always Equal 36
I'm planning to do a heads-and-cam swap on my '04 six-speed. I understand that I'll also have to install larger injectors, but I keep getting different stories on the size I need. Some people say I need 36-pound injectors, others say that size is too big, and somebody else told me that a 30-pound injector is all I need because it will put out more fuel when it's installed in my LS1 engine. That doesn't make any sense. Can you point me in the right direction?
Jim, Via e-mail
It's a pretty safe bet that when you ask five different people about anything related to a Corvette, you'll get at least four different answers. Obviously, you haven't gotten the one I'm going to give you, so here's number five.
I have no idea what size injector you need because you haven't provided any information about your proposed camshaft and cylinder heads. What I can tell you is that injector flow rate is fairly easy to figure-based on actual power output. Without getting into too much minutia, a naturally aspirated engine runs at a Brake Specific Fuel Consumption (BSFC) of approximately .5, which means it consumes approximately a half pound of fuel per hour for each horsepower (measured at the crankshaft) it produces. If your proposed modifications will result in 450 hp, the injectors must be capable of delivering 225 pounds of fuel per hour. Your engine has eight injectors, so each injector has to deliver just over 28 pounds of fuel per hour. But it's not advisable to operate an injector at 100-percent duty cycle, so target maximum duty cycle is about 80 percent. That being the case, a 28 lb/hr injector will only deliver 22.4 lb/hr. You'll need an injector rated at 36 lb/hr to reliably deliver 28 pounds of fuel. These guidelines are just that, so they can be fudged a bit, but it's always best to err on the side of higher capacity than required.
The amount of fuel an injector will flow is also dependent upon system fuel pressure. Port fuel injectors (as opposed to those installed in a throttle body) are typically rated at 43.5 psi (3 bar), but LS1, LS2, LS6, and LS7 fuel systems operate at 58 psi (4 bar). So an injector rated at 36 lb/hr at 43.5 psi is rated at 41.5 lb/hr at a system pressure of 58 psi. (These rates do not include the 80-percent duty cycle adjustment.)