Modern 305 Cubic-Inch Sprint Cars: Less Can Be More

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Photo By Scott Frazier

How to Choose the Best Internal Engine Parts for 305 Sprint Cars

Sprint Cars are some of the coolest dirt racing machines on the planet. They also can be some of the most expensive, and it’s easy for the local racer to be priced out of competition by the high-dollar teams competing in 360c.i. and 410c.i. classes. This is where the 305c.i. option comes in. Not only does the 305 provide a platform for open-wheel enthusiasts to compete in the high-stakes, lightning-fast world of Sprint Car racing, it also allows him or her to do so with a variety of relatively inexpensive off-the-shelf components and limited rules.

Sanctioning bodies like RaceSaver provide specs that allow for a state-of-the-art engine to be bought for around $18,000, a far cry from the $40,000 or more that a 360 or 410 team might spend on a power plant alone. Since 305 engines require specifically mandated parts to keep prices down, valve train companies around the country are looking for ways to help engine builders make the most on a limited budget and rules. It turns out there is a lot of compromise.

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Photo By Scott Frazier

While these companies design parts for high-end machines winning races and championships in the World of Outlaws, ASCS, the National Sprint League and others, they also provide parts any hobby racer can afford for classes where many stock, off-the-shelf options are mandated. The trick is knowing how they work together.

Due to the limited rules of 305 Sprint Cars, engine builders have found the ability to create a wider torque curve and make more rpm and horsepower by going to a slower, less-aggressive lobe profile, which promotes valve train stability. A slightly less aggressive cam also make the springs last longer because the valve is not being hit as hard.

“What we have found – by using chassis dyno technology – is that we can make much more torque with the gear selection than with the cam profile,” explains COMP Cams Performance Account Manager Jay Adams.

RaceSaver 305 Sprints are limited to a single spring, as opposed to the dual or conical versions that might be found in the upper levels of Sprint Car racing. They also must run a flat tappet camshaft with stock-diameter .842-inch solid lifters. Any duration or lobe separation on the cam is legal, but the valve lift, when measured at zero lash, cannot exceed .510 inches on the intake and .535 inches on the exhaust. Any cam lobe lift and rocker ratio that ends up with that valve lift, or less, is acceptable. These series also often have very limited cylinder head rules, a 3/8-inch diameter rocker arm stud, spec valve weights, and any other variety of cost-saving measures.

At first, builders tried to make all the torque they could using fast ramp profiles, but they were hard to control with the limited valve spring, and fatigued it as well.

Initially, it was thought that the legal valve weights and cam rules make the natural rpm potential of a 305 Sprint around 7,200 to 7,400. This has been far surpassed, some eclipsing the 8,000 RPM mark. And, while it’s possible to simply put a fresh set of springs and other parts on an engine for a performance advantage, just like four new tires, very few racers in 305 series have the budget to do that.

As a result, less aggressive profiles to save springs are a viable option. It sounds counterintuitive to what a racer usually likes to hear, but in this case, it’s true that sometimes less really is more for better valve control in the higher RPM range.

“The ideal valve train is one that has found that happy place where the valve train is provides adequate power but is still in control,” says longtime Crane Cams account manager Allan Bechtloff. “Sometimes that place isn’t always easy to find. With a big-budget NASCAR team, it can be found with a lot of expensive dyno and Sprintron testing. But in the case of a budget racer, the trial and error method is reality. So, the communication between the racer, engine builder, and camshaft supplier become very important. Everyone needs to be taking careful notes and reporting what works and what doesn’t.”

Since the rules packages in 305 Sprints are so limiting, it’s a necessity to be creative to get the most from these engines.

“The rules are very good at boxing you into a corner,” Bechtloff says. “It becomes a management challenge. The best idea is to keep the engine components as compatible to one another as possible to get as much consistency out of the engine as possible and increase its longevity.”

Adams explains it wasn’t until he and engine builders began testing cars on the chassis dyno instead of the engine dyno that they finally realized it was the optimum way to tune a 305. Otherwise, racers would be looking at replacing springs every four nights of racing or so, counterintuitive to a class designed to cut costs.

“What we found was that we could make up for a great deal of torque deficiency with the gear,” Adams says. “We could make more upper end horsepower by slowing the ramp speed down on the cam lobe and maintaining better control of the valve, as well as prolong valve spring life.”

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Photo By Scott Frazier

While some smoother and more seasoned drivers can get away with more aggressive valve train packages, the compromise in sacrificing aggression for control has been a performance-enhancing and cost-saving discovery for many racers.

In addition to finding a valve train setup that is easier on components, Adams says setting up the car is also important because a really good 305 engine will truly make around 500 horsepower at most.

“You have to keep in mind that these motors don’t make near the torque or power of that of a 360 or 410,” he explains.

“That being said, setting these cars up ‘free’ almost to the point where they are on the verge of stepping out on you is where they tend to make the most speed. You get a 305 car just a bit too tight, and it will kill lap times. They just don’t have the torque to overcome a tight set up, especially when the track is locked down either heavy or taking on rubber.”

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Photo By Scott Frazier

He notes that a dyno is great for comparing and testing different components back to back, provided all of the elemental inputs are the same. A chassis dyno allows you to get an idea of how the car will react to certain changes. But to really know how the engine’s valve train package is going to complement the driver’s preferences, nothing beats track time.

“Knowing the driver’s preferences on car set up, being familiar with torsion bar rates, tire compounds, track surface, the fueling system, as well as the locations relative to sea level and so on all become vitally important to making these cars fast,” Adams says.

The staff at Lunati, LLC is also heavily involved in the 305 scene. The company designs not only valve train components, but rotating assembly pieces as well. The concept is the same, however, that components are tested both on the dyno and the track.

Lunati’s Kirk Peters explains many of his company’s cams are custom-ground to fit within the limited 305 engine rule packages.

“Getting a cam that matches the needs of the racer is easy as pie,” Peters says.

Peters also notes Lunati has a rotating assembly package perfect for the 305 engine combination. It is built around the company’s budget-priced Voodoo Series, and includes a Voodoo Crankshaft, Voodoo Connecting Rods and Flat Top ICON Pistons.

“Getting the rotating assembly as light as possible within the rules is so important,” Peters notes.

Allan Bechtloff of Crane Cams believes the idea of 305 Sprint Cars fits right into the wheelhouse of what his company’s namesake always hoped to accomplish in the circle track world.

“Harvey Crane always preached that you had to finish the race to win the race,” Bechtloff says. “He was very much into trying to learn what was really going on and how to increase horsepower and still keep control of the valve train. It’s a balancing act, more aggressive designs make more power, but then how do you keep that advantage and survive the race event? The learning curve has been continuance. And along the way you push things too far, but hopefully you learn were the edge is design-wise.”

Jay Adams of COMP Cams is a racer himself and says while it is of course possible to spend high dollars on 305 Sprint Cars – as it is with any race car – on average, he spent less than $230 per night on a 305 Sprint than when campaigning with his 360. When you consider purses in 305s have grown substantially throughout the class’ two decades of existence, it actually is a pretty good return on investment.

For some, 305 racing is about racing on a budget; for others it’s about sharpening skills; and for many it’s both.

“The focus of this 305 class is much more about ‘work on the chassis,’ ‘work on your driving techniques’ and less about making more horsepower,” Bechtloff says. “Have fun, grow the sport, and move up the ranks as your knowledge and abilities increase.”

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Photo By Scott Frazier


Choosing the Proper Oil for a 305 Sprint Car

Along the lines of limited engine rules, changing oil types and grades is a major area for improving performance. For instance, going from a conventional 20W-50 to a synthetic 10W-40 is worth up to 10 horsepower. Companies like Driven Racing Oil have spent weeks on an acceleration dyno studying which components and formulas help an engine accelerate faster.

This is particularly important in the 305 division where horsepower and torque is limited. Driven has found synthetic oils like its XP9 option provide quicker acceleration rates in 305 engines compared to mineral-based 20W-50 oils. Faster acceleration means quicker lap times, so it’s important racers do their research to determine which oil work best for their specific needs.


 

About the author

Dan Hodgdon

Dan is a long-time contributor to the OneDirt magazine. While he is passionate about circle track racing, he also appreciates street rods, classics, and late model vehicles.
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