1986 C4 Corvette Solo 2

This is the Corvette that Dave Hill and his Corvette engineering staff don't want to know about. The C4s, built from early 1983 (as an '84 model) 'til mid-1996, were former chief engineer Dave McLellan's creation, while Hill gets credit for the '97 and newer C5s. Some folks inside at GM have told us that McLellan deserves more credit for the C5 than he's been given, but that's another story entirely.

Autocross, or Solo 2 in SCCA, is a unique form of competition. You have to drive around on an artificial course that's usually set up in a giant parking lot. You're racing against the clock, not against other cars, and a lap lasts less than a minute. If you think of an autocross as a qualifying lap in racing, you're pretty close. There's no chance to relax and very little opportunity to think about what you're doing. 

Driver ability and a good handling car are the important things for winning in autocross. It also helps for your engine to have a lot of low-end torque and to be hooked to a solid-shifting automatic transmission. When you're driving through cones on narrow courses, wide cars and long wheelbases are hindrances to getting the best time. Early ('84-90) C4s are 176.5 inches long and 71 inches wide on a 96.2-inch wheelbase, while C5s are 179.6 inches long and 73.6 inches wide with a 104.5-inch wheelbase. The same width and long wheelbase that makes a C5 roomy inside and exceedingly stable at high speeds makes it awkward and unwieldy on a tight and twisty autocross course.

The old '85 to '87 Corvettes seem to rule the autocross courses around the United States. These old C4s flat beat everything that's come out of Chevrolet since the mid-'80s. When you look at the SCCA National Championships, you'll always find some of these old torque monsters in the standings.Roger Johnson's yellow '86 is one of the best of these unbeatable autocross Corvettes. It's so competitive that a couple years ago some members of the Corvette engineering team invited Roger and his '86 to the Milford (Michigan) Proving Grounds so their boss could see a real, winning autocross Corvette. Some of the team thought it might be useful if they could get a handle on why this old C4 was able to blow away the brand-new C5s. Of course, it blew away the new Corvettes, right on Chevrolet's home turf.

This yellow '86 is a legend amongst the autocross fraternity. While no one is sure if it's the driver or the car that is great, Johnson's driving ability is something that every Corvette owner who's ever run an autocross aspires to. On the other hand, most autocrossers would like to have his car.

There are several reasons that the '85-87 C4s make wonderful autocross cars. The old L98 just can't be matched for bottom-end torque-it'll damn near pull stumps out of the ground. The LT1s, LT4, LT5s, LS1s, and LS6s are all great horsepower engines, but each and every one of them lacks the raw low-end grunt of the old Tune-Port Injection 350. Fifteen years of technology has produced some great engines, but none of 'em can match the low rpm power of a well-tuned L98.

Roger's car, which he bought brand new, only has about 5,000 miles showing on the odometer. The first thousand or so was on the street. The rest is a lot of Solo 2 runs, a whole lot if you consider that the average run is usually well under one mile, and lots of times closer to a half-mile.

In late 1987 the folks at Chevrolet convinced Roger that the new '88 Corvette with its re-designed, zero-scrub-radius front suspension would be the way to go. He even put the yellow beast up for sale while he prepped a new '88 version. Roger was serious about the '88's prep, so the car was sent to C4 performance guru Kim Baker for special attention. The late John Lingenfelter was made sure that all was perfect within the engine.

There was only one problem. The brand new 1988 Corvette couldn't match the times of the old '86. Nothing that Roger did would make the '88 Corvette competitive with the yellow '86. If Roger Johnson, Kim Baker, and John Lingenfelter's combined expertise couldn't make the '88 run as fast as the older car, all hope was gone. Fortunately, no one had come up with the required cash to purchase the "old car" so the "For Sale" signs were taken off the '86 and placed on the '88. It was back to Old Yellow.

Roger has tried C5s but feels that they have major limitations for competitive autocrossing. A great many other Corvette autocrossers apparently agree with him, as you seldom see a C5 at autocrosses, other than Corvettes-only events. Some have tried, but few have succeeded, except with Z06s, at the SCCA level of competition.

The one thing that Roger Johnson has proven is that if you start off with the "right" car, stick with that car, and develop it, you can have a winner. While most of us try the latest trick part of the week, or maybe even the trick car of the month and stay also-rans, Roger just keeps running up the miles on his old yellow '86, and keeps right on winning.

Here's an interview that someone else did with Roger Johnson. Very interesting. He talks about how all of his Corvette engines were blueprinted. 

This article was originally published in Vette magazine around 1999.

Exhaust Headers

All of our cars have exhaust manifolds. Some of us are even using the stock manifold that came on the car when it was new. Others have spent thousands of dollars on the latest and greatest header system. Before you get your checkbook out you need to think about a few things. Am I spending all this money to go faster? Or, am I concerned about what people think when I open the hood? Maybe it’s a little bit of both.

Materials: We have a number of choies here. About eighty per cent of all aftermarket headers are coated mild steel. Stainless steel though is becoming a popular replacement material for exhaust headers. Just keep in mind that not all stainless is the same. The folks at Burns Stainless point out that technically, Stainless Steel is a trade name applied to what are known as corrosion-resistant steels. They believe that “It is a fabulous material that outperforms mild and alloy steels in so many different applications in racing that no other material can match it.”

A three-digit system is used to identify stainless steel but we need to focus on what is called the 300 series. Type 304 is a popular choice for exhaust systems. It’s also the least expensive. Another good choice is stainless 321. Jim Browning of Ultimate Headers (ultimateheaders.com) prefers the 321 because it’s about fifty per cent stronger than the 304. This means you can use a thinner sidewall thickness and save some weight. Weight is always a big deal with racecars.

A number of firms have recently started using 400 series stainless. You want to avoid any of the 400 series products.  These are simply not as durable or as resistant to corrosion as the 300 series. You can do a really quick test with a small magnet. A magnet will not stick to anything in the 300 series. It will though stick to the 400 series. You can practice this test on your barbecue grill.

One advantage that stainless has over mild steel is heat retention. Stainless steel will hold the temperature of the exhaust gases in the primaries much longer. We want to keep as much of the heat inside the exhaust manifold pipes as we can.

Inconel 625 is another popular choice for exhaust manifolds. Although the name "Inconel" is a registered trademark of Special Metals Corp., the term has become something of a generic reference to a family of austenitic nickel-chromium-based super alloys which have good strength at extreme temperatures and are resistant to oxidization and corrosion. Inconel's tensile strength and toughness at elevated temperatures allows for a very thin sidewall. This means your exhaust manifold is lighter.

  

All Formula 1 cars and a number of Sprint Cup teams use Inconel for their headers because of the weight savings. Some NASCAR teams are routinely using headers made from 0.020-inch wall Inconel tubing. One problem is that these header walls are so thin that you can easily damage them during installation. Given that Inconel is incredibly expensive I don’t think we’ll see a lot of Inconel header is vintage racing.

The Flange: This is the part of the exhaust manifold that goes right up against the cylinder head. We have some compromises to deal with here. The thicker the flange is the better the seal is. A thicker flange will simply be more durable over time. A thicker flange though means more weight. Even worse is that this extra weight is up high. Exactly where you don’t want extra weight.

Years ago everyone built header systems with a 1/4-inch flange. Today everyone is building headers with a 3/8-inch flange. The one exception is if you’re running a turbocharger. In that case a ½-flange is usually used. The best material seems to be an investment cast stainless steel flange.

Wraps: We want to keep all the heat inside the exhaust system as long as possible. Hot exhaust gases have greater velocity because they are not as dense. As the exhaust temperature cools the velocity slows. These wraps allow you to maintain the temperature of the exhaust gas.

Actually the wraps do the same thing as the high-tech ceramic coatings. They just do it a lot more cheaply. They do have one huge downside. They don’t look period correct.        Presentation is very important in vintage racing and a lot of people just don’t think that exhaust wraps look all that good. While we seldom worry that the inside of our engine is period correct we do spend a lot of time making sure that at least the engine compartment looks period correct.

Coatings: If you decide that a wrap doesn’t look all that period correct on your vintage racer you can coat the exhaust manifold to keep the heat inside the pipe. Remember though that there are two very different types of coatings.

First we have the cosmetic coatings. The only thing they do is make your exhaust header look look shiny. These low-tech coatings are nice looking but they do very little to insulate the exhaust or increase your power. You want a thermal barrier that keeps the energy in the header. Keeping the heat in the pipe lowers the temperature in your engine compartment and more importantly it keeps exhaust gas velocity high. These thermal coatings are usually about 0.15-inch thick as opposed to the cosmetic coating, which are seldom more than 0.002-inch. Swain Tech Coatings (swaintech.com) has a ceramic coating that normally reduces radiant heat by about fifty-five percent.

Most people feel you can skip the internal coatings. It’s virtually impossible to prepare the internal surfaces of a pipe to receive a thermal coating and these coatings can easily become detached. Even a thin paint can reduce the available flow area by up to 2% giving rise to reduced engine performance. You just need to worry about the exterior of you exhaust system.

               Originally Published in