From Bad To Really Bad

The coolest thing about a Dodge Viper is its unique blend of old-school musclecar and new-world road car. Just for that reason, "sporty car" types hate it, saying it's "too unrefined." Guys like us say, "Right on! I can work on that thing!" Not all of us can have an exotic ride like a Viper, but we have to give it respect. After all, it's the most powerful American car on the road and its tail-out driving habits make for fun driving and watching. They're just cool.

It's the ease of repair, access, and over-built structures that have serious muscle fans, with the means, of course, ordering new Vipers and scouring the insurance reports trying to find crashed cars for a value. Top Fuel racer and mail-order guru Doug Herbert is one such guy (he should know about the "crash" part, as he bought back his totaled '96 R/T for a profit). Doug figured he could bolt-on 100 hp to his '99 GTS by using the right selections from the aftermarket, all the while doing it without screwing up the integrity or reliability. As you'll see from this tech story, he was right.

Though you can make a ton more power by changing the heads, cam, and intake manifold, Doug and his "Team B" IHRA Top Fuel squad (the NHRA guys were out on the road) didn't want to take the car off the road for more than a day or two (look for Herbie to get serious with his ride in months to come, likely on these pages). So, they bought the common sense bolt-ons, like headers, exhaust, air boxes, throttle bodies, a shifter, and roller-rockers. Along the way, they uncovered a few easy-to-remedy situations, like odd valve geometry, heavy retainers, and necessary fabrication, but none of these were deals that couldn't be handled with a couple more mail-order parts and some thought.

Follow along as we look into a 100hp bolt-on buildup with some cool guys and a serious musclecar of our time. We found that the lessons learned and examples in play are just plain solid automotive tech for late-model vehicles--the principles are valid on so many other rides.

Don't believe the hype: Viper headers come off pretty easily--just remember to number the spark plug wires before you pull them off. The starter and the heater box need to come off, too. Once we had the stock system off, we laid it out and made a comparison to the Borla T-304 stainless-steel system, to make sure we had all of the bends and pieces correct from left to right. This sounds silly, but you'll have a lot of parts floating around. Because we were using new headers and not the stock exhaust manifolds, we had to cut the cats at the inlet and weld them back into the "new" stock location (this is important for street-legal status). That was a no brainer, and the exhaust kit simply bolted on without a worry.	This is the part that had the V-8 guys feeling funny--oh yeah; this thing has a couple of extra cylinders!	The CARB-approved Edelbrock T.E.S. headers (PN 6606, for '92-1/2 through '99 Vipers) arrived with its Pro-Tech coating in place.
This means any use of header wraps could mar the finish and void the warranty (use only soap and water to clean them, too. No chemicals).	Though we couldn't test these parts individually on the chassis dyno, we expected to see a gain of 25 hp with just the replacement of the stock exhaust manifolds.	The stock airbox features baffles to keep water from entering the intake under severe conditions, so don't be fooled into spending a fortune on a carbon fiber system that doesn't offer the same protection. Though this one has trick dual inlets, there's always room to improve.
To avoid that water issue, Herbert kept the front half intact and added Hennessey Motorsports' Upgraded Rear Airbox Section (about $400), which incorporates larger, 2 7/8-inch air outlets. This was another no-brainer install.	This mod shouldn't see much of a gain on the chassis dyno, since the Viper is sitting still, but Hennessey tells us the benefits come at around 50 mph--and when do you think Herbert will drive this thing at less than 50 mph?	K&N supplies Hennessey with its air filter elements, and this one that came with the kit is specifically chosen. Compared to stock, you should expect a 5 to 10hp increase with only this two-minute swap.
When you do the Rear Airbox Section, Hennessey recommends you do these PowerTubes at the same time (about $100). This comparison tells the tale, going up to a 3-inch tube. These sections of silcon hose, attached to stainless tubing, won't collapse under heavy intake loads and are oh-so-easy to swap out.	The stock throttle bodies on a GTS are 58mm units, and the Team Viper guys surely got it right in the first place. However, when you swap out for bigger airboxes and the like, you'll need bigger diameters to take advantage of the overall increase. These Billet Aluminum Throttle Bodies (about $900) come in a pair and are polished to the hilt.	These are 65mm units, but 70mm examples are available and come recommended if you go as far as tweaking the intake, cam, and heads (a stroker kit would also force the necessity, too). When you install them, remember that there is a left and a right, and you need to remove the throttle position sensor (TPS) from the originals and install it on the new versions. Timing the shafts can be tricky, so call Hennessey (like we did) if you have issues. As if you own a Viper!
With the exhaust and intake revisions complete, it's time to dig into the valvetrain. The stock valvetrain, though it does make famous power, is really pretty weak for a big money deal like this. The stamped rockers, weak springs, and forged retainers need to go!	We yanked off the stock 1.5:1 ratio rockers and bolted up a set of 1.7:1 shaft rockers from T&D (just like they use on the ORECA GTS-R that runs at Le Mans). This makes for a little more lift and duration, and is both stronger and easier than pulling the water pump and the front cover. The rocker swap literally took less than two hours and should be worth about 10 ponies. What's cool here, hence that Le Mans reference, is that when Herbert gets the courage to take apart his expensive Viper and bolt on an intake or revised cylinder heads, these will still be the rockers of choice.	Before getting the rockers off, we used this Moroso Stud Mount Valve Spring Changer (PN 62370) to get rid of the stock springs and that heavy retainer without having to remove the heads. This cool tool can be used with either 3/8-inch-24 or 7/17-inch-20 rocker arm studs, so it's pretty universal.
Herbert reminded us of a great tech tip, too: Use a compression checker, like this Snap-on unit straight out of the Top Fuel trailer, and pressurize the cylinder to keep the un-retained valve from falling into the cylinder!	We got Crower's spring and titanium retainer set, specific to the GTS, knowing that it would take a ton of weight off the tip of the valve and help Herbert's Viper rev up quicker. Man, we were right. We checked on the scale, and found that it was nearly 40 percent lighter!	One thing to be careful about, however, is spring pressure. These stock springs made about 175 pounds on the seat, installed at 1.900 inch. That was about 35 pounds more than stock, and can be a little hard on the lifters--be sure to start the car and let it idle for awhile before revving 'er up.
One obvious thing you have to do here is get new pushrods, as you can't start jacking with a two-tenth change in rocker ratio and not expect to have to change the pushrods--you'll need longer examples, not bigger or stronger necessarily.	Voila! Here's the finished product in the valvetrain department, before and after.	Though we did all of these mods at once, we can just about guarantee that this little swap was worth a lot of the gains we saw.