The power output of an engine is what is leftover after all the “losses.” — Mark Cronquist, head engine builder at Joe Gibbs Racing
Continuing, Cronquist says it’s easier to make power by saving more of the power already made. At least, that’s what Cronquist would likely had shared with the Advance Engine Technology Conference on Tuesday had he been on the podium. A family emergency, however, kept Cronquist at home, so his former Joe Gibbs colleague — the always entertaining Lake Speed, Jr. — filled in.
Continuing with the theme of finding hidden horsepower, Speed focused on a number of engine functions that can rob horsepower. While revealing the results of a government study that showed where the parasitic losses occurred in a typical internal combustion engine, Speed noted that losses through pistons, valvetrain and bearings can account for 15 percent of IMEP (indicated mean effective pressure).
In addressing the valvetrain, Speed says some of today’s robust pushrods have a wall thickness equal to the entire pushrod diameter in years past.
“Think of a pole vaulter’s pole and how it bends,” adds Speed. “It’s like a second spring in the valvetrain, and the motion of a pushrod can contribute to valve bounce. Once you get the valve under control, then you can back off the valve-spring mass.”
Here are some other observations from Speed’s wide-ranging talk:
- Thermal control — Keep the temperature stable and even as possible.
- Engine break-in — Cylinder surface finish is a major factor, and many builders didn’t realize honing changes may be required when switching to compact graphite iron (CGI) blocks. Speed says, “You need to get the stones and coolant right, and you’ve got to measure surface roughness. Get a profilometer.”
- Other surface finishes: “When you decrease the surface roughness, you increase the load-carrying capacity,” says Speed, noting the increased use of DLC on some components and micro polishing on others, like crankshafts. “It’s expensive, but the benefits are there.”
- Tighter bearing clearances: Allows engine builder to run lower viscosity oils.
- Oil control: NASCAR engines are pulling 24 inches of vacuum out of the pan, which includes sucking out oil vapors. Sections in the dry-sump pans also improve scavenging efficiency and keep oil droplets from robbing horsepower.
“All these small things,” concludes Speed, “add up.”