Tips For Selecting The Proper Circle Track Cam - Engine Builder Magazine

Tips For Selecting The Proper Circle Track Cam

This isn’t always your fault, but this is often followed by the racer selling the cam to a fellow racer who thinks it’s the best cam he ever ran. Why did this cam work so well for one racer and not for another? The reasons can be many. The following are some tips for selecting the proper cam for circle track applications.

• Longer duration cams require tighter lobe separation to have any power off the corner (not usually a preferable combination in 2 bbl classes). Shorter duration cams with wider lobe separations usually yield much flatter torque curves. Longer rod engines seem to prefer shorter durations and wider lobe separation.

• Stock exhaust manifolds or a highly restricted exhausts usually respond well to shorter exhaust duration and wider lobe separation. Power increases are most evident at higher rpm where exhaust back-pressure is greatest and reversion is most prevalent.

• Most unported heads approach 85 or 95 % of peak flow at .400? to .450? lift and do not need or want a maximum valve lift over .540? to.555?. Often a low cam lift with 1.65 or 1.7 ratio rockers is very helpful on the intake side as long as lift is kept to about .550?. Exhaust is less critical with 1.5 or 1.55 being the most popular. Dyno testing doesn’t test drivability or throttle response of the engine.

• The important numbers on a dyno sheet are about a thousand RPM above and below peak torque and peak horsepower. Peak numbers are for bragging purposes and high peak numbers do not win races.

• The benefit of high ratio rockers is faster valve movement and the added lift is frequently detrimental in unported heads. It often helps to utilize a lower cam lift with high ratio rockers.

• Changing the valve lash is a good way to get an indication of which way to go for your next cam change. You won’t hurt anything by going too tight but too loose will let the valves slam shut causing damage to valves and seats. .004? to .006? loose is usually OK.

• Look at the “major intensity” numbers to get an idea as to how radical the profile is (major intensity is the difference between the .020? duration and the .050? duration). Lower numbers are more radical but anything less than 26 or 27 degrees may be very hard on the valve train. CamCraft’s 24 degree XTLZ profiles are a notable exception to this.

• Camshaft intensity is a measurement term coined by Harvey Crane to compare ramp characteristics of camshafts.

– Hydraulic Intensity is the difference between .004? duration and .050? duration.

– Minor intensity is the difference between .010? duration and .050? duration.

– Major intensity is the difference between .020? duration and .050? duration

• Lower numbers indicate more radical profiles, but too low can be too radical and lead to noisy valve train and even to broken parts.

–Tech Tip courtesy of Camcraft Performance Cams

You May Also Like

Crank Balancing Update

If there’s anything all of us in this industry have come to understand, it’s that you can never be certain someone else did the job correctly – and when it comes to crankshafts and crank kits that you or a customer might purchase, it’s imperative to ensure a proper balance job was performed and not just trust that it was because it says so.

As performance, technology and ultimately horsepower have continued to increase over the years, engine builders have needed to evolve along with it. That means being able to control increased horsepower to create livable and workable horsepower. 

Obviously, pistons still go up and down and cranks go round and round, but the technology involved in the entire engine has allowed performance to reach new heights. All that increased horsepower has to go through the crankshaft – aka the heart of the engine. If that crank/heart is unhappy, everybody’s unhappy. Enter crankshaft balancing.

EFI Timing Control & its Advantages

No one can overstate the fact that EFI timing control has radically changed the ability for anyone to fully, and correctly, optimize an ignition timing curve, assuming they are interested in investing the time.

Rebuilding Chevrolet’s Gen VI Big Block Engine

Following Chevy’s introduction of its popular small block V8 in 1955, the OEM needed something larger to power its medium-duty trucks and the heavier cars that were
on the drawing board at the time. Enter the big block!

Shop Solutions July 2023

Engine and machine shop tips and tricks.

Shop Solutions June 2023

Engine and machine shop tips and tricks.

Other Posts

Pennzoil and API on Developing Motor Oil Standards

For more than 90 years, Pennzoil has worked alongside the American Petroleum Institute (API) to ensure Pennzoil products meet – and often exceed – the stringent requirements of motor oil specifications implemented to best help protect the performance of your engine. Related Articles – Nitrous Update – Heavy-Duty Diesel Engines, Equipment and Replacement Parts – Diesel Piston

Nitrous Update

The use of nitrous oxide in diesel engines is not a new concept. In fact, it has been used in drag racing for decades. However, it is only in recent years that it has gained widespread popularity in the worlds of diesel truck pulling and drag racing. Now, it seems as if almost everyone in the competitive scene is using it. 

Heavy-Duty Diesel Engines, Equipment and Replacement Parts

Relying on OE manufacturers like Caterpillar, Cummins, Detroit Diesel and Waukesha has always been an option, but diesel equipment owners are now more than ever seeking the aftermarket as a more viable solution for replacement parts.

Diesel Piston Technology

Diesel and heavy duty go hand-in-hand. There’s no way around it. High compression causes high cylinder temperatures, with peak cylinder pressure often as high as 2,700 psi (or higher). This high pressure and high heat only have one thing in mind, to beat relentlessly on the first thing to get in the way – the pistons.