t’s no secret that some of the materials and designs used to create our race car’s components come from the aerospace industry, but there are not too many camshafts or pistons that use nuclear tech in their development. If you’re into drag racing it’s likely you’ve seen the mono-barrel carburetor by Pro Systems Racing Carburetors called the SV1, and besides it’s trick look and great performance, what’s interesting also is this is the first car part we’ve heard of to be inspired by systems found on a nuclear reactor. A couple years ago, Pro Systems’ Patrick James was hired by Northrop Grumman to optimize water flow in cooling towers for a nuclear reactor. James came up with a design to reduce the turbulence/flopping in the cooling system to reduce its operational costs. By using what he developed for that project, James came up with a way to apply his idea of fluid management to properly use distribution tubes to atomize the fuel in a carburetor without the “flopping” issues that previous tube designs encountered. Flopping is when the fuel will sometimes exit left and then sometimes exit right around a circular object. This causes fuel distribution issues and loss of power and increased drag in the venturi. A handful of patents later, the SV1 is the carb of choice for six national champions and eight world and national records only one year after it’s release.
When Pro System’s SV1 carburetors came out they definitely raised eyebrows and many gearheads were skeptical, but it didn’t take long for racers to start seeing the benefits. Although the addition of the SV1 carb has been a success for James, he admits the traditional four-barrel carbs will always have their place in racing and hot rodding as a good low cost performance option. We contacted James one afternoon in the fall to get the scoop on this trick looking carb, its’ design and potential benefits for the drag racer.
The first thing one notices about the SV1 is the obvious single barrel, but that’s not the only difference between the SV1 and a conventional carb. “The only reason why they went with four barrels in the first place was for drivability. You see back in the old days, no one could generate good low speed signal,” James said. So they would essentially split the carb in half, then you could get it going on the primary barrels before the secondary barrels opened up. “With the SV1 signal is not a problem, we incorporated emerging technologies and advancements in metering, moved some things around in the fuel circuits and simplified the way the fuel is directed and off it went.” He continued, “Another thing we did is, instead of employing pressed in boosters like on a standard 4150 and 4500 series, the SV1 boosters float on o-rings, to dampen booster vibrations and seal up tight.” In James’ testing with NHRA Pro Stock, he found the benefits of reducing vibrations in the carb, which can add complications when tuning. This dramatically increased the air-to-fuel ratio consistency and sealing them with o-rings increased low speed signal and sped up shift recovery compared to a press fit booster design that always leaks a little. The boosters can be changed easily too. You don’t even need to unbolt the carb to change them out. They just slide out the front. “I built the SV1 tuner friendly, so you can make pretty big changes without messing things up,” he said.
Idle Quality/Thermal Balancing
One thing that wasn’t a planned benefit of the SV1 carb when James designed it was how well they idled on even the most radical engines. He knew it would idle better, just not this much better. You see, on a regular four-barrel, air comes in both the front side of the throttle blades and the rear side of the throttle blades. But only the front side of the blade supplies the fuel, the rear side of the blade on a four-barrel carb only supplies air. So you rarely end up with even fuel/air distribution at an idle with a four-barrel. This unevenness effects the engines operation at both an idle and as it travels down the race track as the engine will be thermally unbalanced (has hot and cold cylinders) before the run down the track even starts and will have a loss in power due to this uneven distribution of fuel at an idle and the cylinder temp variations this creates. The Professor of Pro Stock, Warren Johnson, was
very enthusiastic concerning this discovery and he and Mr. James are stressing this importance to the NHRA. This in an effort to get the design legal for NHRA Pro Stock racing as it would allow the Pro Stock teams to even up their timing on their cylinders at the starting line. By employing the SV1’s they would no longer have to compensate for uneven thermal balancing that requires them to advance or retard individual cylinder timing to compensate for the hot/cold cylinder issue that four-barrel carbs create. Because with the SV1, the fuel is distributed evenly throughout the whole perimeter of the blade, all of the air entering the engine with an SV1 is exposed to a fuel port for atomization and distribution to the cylinders. The blade then acts like a big booster to atomize the fuel, it evens up the cylinder temps and as James explained, the engine is thermally balanced. This reduces problem cylinders during a run and allows the owner to stand on the tuneup harder and the idle quality is amazing as a result. It will ‘freak you out’, it will idle so low and smooth. James also mentioned that a specific customer of his with a very radical, big-block with an aggressive roller cam (that should’ve idled at 1,300 rpm), was scratching his head when it happily and cleanly idled at 750 rpm with the SV1. Another customer employed an SV1, making the swap right at the track to replace a four barrel carb on an engine that was experiencing uneven fuel distribution. The SV1 with its better booster atomization design and idle quality, straightened the engine right up and he went on to set a Drag Radial record that day as a result of the swap (Matt Mungall @ 4.917).
Making more horsepower is great, but according to James, these carbs don’t necessarily make tons more power; it’s really all about the instant response to demand and shift recovery. “Quicker shift recovery and response to sudden changes in airflow is one of the biggest reasons why our carbs are making cars run quicker,” James said. “And the way I did that was simplify the way the fuel circuits are routed and to simplify the distribution of this fuel.” In the past, James would sometimes solve a fuel problem by moving or adding a circuit in the metering block, but he soon found if it’s too complicated, the fuel becomes too busy by these added circuits and shift recovery and response time slows and the car won’t accelerate as well. This is because during a demand change (like a gear shift or sudden launch), the busy fuel needs to “catch up” to the demand, and if there’s a complex route the fuel has to travel, it takes more time to get the fuel into the engine and that little bit of lag has been known to be worth a tenth in e.t., and to a racer, that’s as good as gold. Once again proving, that Albert Einstein was correct, “Simplicity reigns supreme”.
Pro Systems Carburetors