I take it you are grinding your very own cams for this project? If so, what was the biggest variation as far as the lift/duration between the original cams and new cams? Have you tried any variations to perform better at higher RPMs or are you just focused on making the most out of low end and mid range RPMs?
Scottie
Hi Scottie,
We are not grinding cams for this project because the auto-decompressor system is located inside the exhaust cam, and that complicates the cam-making procedure. And we don't want to delete the auto-decompressor because that protects the electric starting gear system from damage.
We plan to address the lift and breathing issues in a different way with this engine, and leave the original cams in place, along with the auto-decompressor.
However, for the older Iron Barrel engines we had cams ground for us called "Ace Magnum Cams" which have about .040" higher lift, and about 8 degrees longer duration, compared to the stock cams. And the opening/closing timing points are different than stock, and the ramps and lobe shapes are different than stock. These things are determined by the flow characteristics of the ports, so that we can make the most out of the flow, without putting any higher stress than necessary in the valve train components. These cam figures might not sound all that impressive for an increase, but it must be viewed in the context that we are flowing about 30% more through the ports on average, because of our head work.
On the Fireball, we focused on a wide torque curve, with an upper-rpm range raised to about 6000 rpm, and peaking horsepower relatively near the max rpm of the engine. This gave a good result for street use, and still allowed a good higher rpm power, and the ability to get a top speed of over The Ton.
We have good understanding of cam design, and so we can apply that to our needs, whether they be higher rpm power, or low rpm torque, or whatever. In the end, the cams are basically the "traffic cop" of breathing, and ultimately it is the flow capacity and the flow characteristics in the head which will determine the power potential and power range of the engine.
With the Bullet, the long stroke is a limiting factor in rpms, so the max rpms are not really going to get very high. So with the normal 90mm stroke that all the Bullet engines have, we consider 6000-6500rpm to be about the safe limit for a street rod, while keeping engine longevity in mind as one of the goals. Generally we aim for 6000 rpm limit, and give a few hundred extra rpms for a useful extra "cushion" if needed for some reason on occasion.
With this approach, we can get a nice power level at the higher rpms, without objectionable losses down there in the lower rpms, and good street tractability, good fuel economy, and a good expectation of longevity.