Hemi Vs. Viper!

As far as we’re concerned, there is only one certainty in the fast-car hobby—talk is cheap. Everybody brags about 500 horsepower 440s and 10-second cars they swear are driven to work daily. We prefer to put our stock in the great equalizer—the DynoJet Chassis Dynamometer, where the bull stops and the rollers do the talking. The chassis dyno makes honest people out of everyone.

Net versus Gross

Back in the early ’70s, horsepower ratings fell through the basement seemingly overnight. Ever wonder why? There were several factors involved, including reductions in compression ratios on all engines (some so small it’s hardly worth mentioning, others considerable), and ratings taken at different rpm than previous years. However, the biggest reason for the dramatic changes was that starting in 1972 auto manufacturers adopted a “net” system of rating engine power, as opposed to the “gross” figures they had published in years past.

Simply put, the gross rating system was a measurement of an engine’s power, at the flywheel, taken without any restrictions on the engine’s ability to perform. Engines were set up on a dyno and the measurements were taken with no air cleaners in place, no alternator or other engine-driven accessories, and very often with tubular headers. Mufflers? No way! That changed in ’72, partly in an effort to “under rate” a car’s performance capability and mollify the insurance industry, and partly to give a fairer “real world” estimate of what kind of power buyers could expect from their car. Net horsepower ratings were taken with all the crank-driven accessories in place, a functioning air cleaner, and factory exhaust manifolds. As an example of what the new ratings did to advertised engine performance, the gross horsepower rating for a ’71 383 4bbl engine, with 8.5:1 compression, was 300hp at 4800 rpm. Its net rating was 250.

So when the venerable 426 Street Hemi was rated at 425hp, it was impressive. When the Viper came out and was rated at 400 horses, we all “ooo-ed” and “ahhh-ed” over it because it was the most powerful engine to come out of Detroit in over 20 years. But it still didn’t have the numbers of the Hemi. Or so we thought. In fact, it was more impressive, because that 400 horses was a net power rating, compared to the Hemi’s 425 horse gross rating! When the Viper V-10’s ratings got upped to 450 a couple of years later, the raw numbers showed an engine that had finally surpassed the published ratings of the legendary Elephant.

The Test

We’ve always wanted to compare the two generations of super motors head-to-head, on an even playing field. That would mean bolting engines to a dyno and winding them out, both with all driven accessories affixed, stock exhaust in place, and the air cleaners on. However, full-resto Hemi engines don’t grow on trees, and we hadn’t won the lottery yet so we couldn’t buy a new Viper and yank its engine for our little comparo. Besides, the thing about an engine dyno that we don’t like is that it never tells you how much power is getting to the ground, which is ultimately the only place it matters. Certainly a drag strip test would offer insight, but the wide disparity in rubber meeting the road is also a concern.

Our only option—a chassis dyno. The DynoJet would give us real world power comparisons between a stock Hemi-powered car and a Viper, and that’s what we wanted. But there were still two problems: Even on a concours restored Hemi the owner will often slip in a bigger cam or change the compression ratio. At the very least the jetting in the carbs and the ignition timing are different. And even if we did find one that was stone stock so many of these original Hemi cars never see the road; we didn’t think we’d ever find one with an owner who would let us strap it to a chassis dyno and air it out, so our idea seemed like it never would be more than a “wouldn’t it be neat to...”

Then we went to Atlanta a year ago to visit Jeff Dodson at Six Packs To Go, and over the course of bench racing for two days we told him about our little idea, and lamented about how it would never come to light for the previously discussed reasons. That’s when Jeff told us about his friend Steve Simmons and his ’67 Hemi Belvedere II 4-speed car. “He drives the car a lot, and as far as I know, it’s stock. He’d probably do it,” said Jeff. This sounded great to us, but when Jeff said that Steve drives his car a lot, we figured the engine had been modified, at least a little bit. But we really wanted to see this thing happen, and called Steve to pitch our idea to him. Much to our surprise and delight, Steve said he’d love to. All that remained was the scheduling!

He’s Da Man!

Our number came up in the press pool Viper rotation last August, and Chrysler sent us a shiny red ’99 Viper R/T 10 for a few days, which was promptly floorboarded up to Atlanta Chassis Dyno in Duluth, Georgia—about 20 miles north of Atlanta. On the morning of the shootout, we were running about ten minutes late and felt bad when we pulled into ACD’s parking lot and saw that Steve already had his car off the trailer, meaning he’d been there for a while. Then we noticed there wasn’t a truck and trailer anywhere in sight. We also noticed Steve’s “ONE OF 3” license plate. “Where’s your trailer?” we asked him. “I don’t have one. I drove it up here this morning. It’s over an hour each way—I stretched it out a bit and took the back roads, though.”

Ladies and gentlemen, all we can tell you is that Steve’s car looks like a trailer queen, even up close. When we saw the license plate and learned it was one of only eight ’67 Hemi Belvederes, and one-of-three equipped with a 4-speed, we naturally assumed that “driven a lot” meant to the burger stand on Friday nights and in the country on Sundays—if it wasn’t raining. How wrong we were! Steve told us he drives the car very often, including to shows several hundred miles away, local cruises, club meetings, you name it.

Then we asked him what deviations from stock the engine had. “I changed the mechanical cam to hydraulic lifters, but it has the exact same specs. Otherwise, everything else is stock, even the jetting and metering rods in the carbs and the ignition timing. It’s good enough to get me around town just like it came.” The factory-delivered compression ratio is still intact, but is made usable with premium pump gas and octane booster. We’re talking stock, right down to the proper Hemi mufflers and small-ish diameter exhaust pipes, complete with kinked bends and all. Hardly an optimal package by today’s standards, but that’s exactly what we wanted. The only other concessions to modern driving are the red line radial tires.

As for the Viper, anyone who’s ever driven one knows that it’s really a race car. Sure, they sell it to the public, it has a heater, A/C, and a radio, and Team ORECA sells an official race version, but when it comes down to it, the Viper is a race car. Features of note include cold air induction, tuned factory exhaust manifolds, mandrel-bent large diameter exhaust tubing, and low-restriction mufflers and catalytic converters. With an advertised 450 horsepower (net) from its all-aluminum 488ci engine, we felt kind of guilty—like we were leading the lamb into the lion’s den.

The Results

Steve displayed no fear as the guys from Atlanta Chassis Dyno rolled his car onto the DynoJet and strapped it down. He didn’t do anything more than smile when we had him sign the cover-our-butt release form. He was excited because he’d never done anything like this, and was genuinely curious to see the results his beast would register. For the test, all the belts were left in place, the exhaust was left bolted on, and the hood was closed to better simulate real world driving conditions. Oh yeah, did we mention this all took place during one of the hottest weeks Atlanta has seen in years?

The same procedure was used when we put the Viper on the rollers, including closing the hood, which would give the Viper an advantage right out of the gate due to its fresh air induction versus the Hemi’s closed element air cleaner sucking hot underhood air. Another advantage the Viper has over the Hemi are reflective heat shields on the exhaust manifolds that theoretically keep underhood temps a little lower. And tuned intake runners, dual throttle bodies, a roller cam—the list goes on.

After running both cars, the results were predictable: The Viper made more rear wheel horsepower and torque than the Belvedere. What was impressive was that the Belvedere made 315 rear-wheel horsepower at 4,900 rpm and held it, table flat, past 5,500 rpm. Torque was nothing short of stump pulling, with a peak reading of 354 lb/ft at 4,200 rpm, and never dropping below 300 lb/ft between 2,000 and 5,500 rpm. Power specs for the Viper were more peaky, with a max horsepower reading of 362 achieved at 5,600 rpm, but it fell off from there as quickly as it climbed. The V-10’s torque curve was relatively flat, with a range of 370-380 lb/ft between 2,700-3,600 rpm, which then peaked to 410 lb/ft at 3,750 rpm, dropping off from there, with another small climb in the 4,400-4,700 rpm range. After that, it fell off pretty steadily. The raw numbers: The Viper’s V-10 bested the Belvedere’s 426 Hemi by 47 peak horsepower and 56 lb/ft of torque.

Spin Doctoring

When the results were in, the crew at Atlanta Chassis Dyno, ourselves, and Steve were all impressed with the stock Hemi’s power. The ACD crew probably more so than any of us, because they had never been around Hemis that much. We were all surprised that in 30 years, the power gap wasn’t more substantial. Of course, bench racing ensued, and we speculated that if all things were equal, meaning the Hemi was given a performance tune, the carbs and ignition were optimized, and the thing was allowed to breathe, the results would have been different. Just imagine what the Hemi could do with nothing more than an open element air cleaner, headers, mandrel bent pipes, and a decent aftermarket exhaust system! And we could probably pick up a little something on the top end if we swapped back to the solid lifter cam, too. Better yet, equal things up with a roller cam! But that’s not for this story.

So we were impressed with the performance of the stock Hemi, and we felt very lucky that we were able to do the story. But it wasn’t until three days later, back at the office talking to others about the results, when we made perhaps our biggest observation, and one that seems obvious now: The Viper, at 488 cubic inches, has the advantage of pure displacement over the Hemi to the tune of 62 cubic inches! Obvious, sure, but that got us wondering about the efficiency of the engines, on a per-cubic-inch basis. A quick evaluation with a $3.99 calculator revealed that the Hemi made .470 rear wheel horsepower per cubic inch of displacement. The Viper chugged out .473hp per cube. That’s only a .003hp difference—equal to 0.43 percent. The two degree change in temperature could account for that! Differences in torque per cube were even closer, with the Hemi making .838 lb/ft per cubic inch and the Viper recording .840 lb/ft per cubic inch, for a difference of only .002 lb/ft-cubic inch—0.24 percent. Like the patriots at the battle of Bunker Hill, who didn’t shoot until they saw the whites of their eyes and kept it up until they were out of ammunition and had to retreat, the Hemi may have lost the battle when you look at the bottom line, but it was unquestionably a moral victory when you tally the numbers and consider what 32 years of technology has really offered.