Technical Info from Roush development of Ford GT (40)

[Tom F&L GoR]

Roush Industries (as in Jack Roush the racer/engineer/industrialist) has an SAE (Society of Automotive Engineers) technical paper on their site at

http://www.roushind.com/news_downloads/tech_papers/2004-01-1252.pdf

which was up yesterday but seems to be down as I write this. The title is "2005 Ford GT Powertrain - Supercharged Supercar."

Anyway, there are little information nuggets like it takes 80 hp to drive the supercharger, and also that when they calculate connecting rod stresses, they ignore the combustion gas loads because they are insignificant relative to the inertial forces. If the site doesn't come back soon, I'll send it to you.

 

[GR8_ASP]

The last statement is not true in general(at least in my experience). In general a rod is designed to obtain about a 30% safety factor for both compressive (power) and inertial (speed) factors. They act differently as the cap and cap mounting are very important in the inertial and not a factor in compression. But, if a very heavy piston is required for the compression forces, the resulting inertial aspects could be overwhelming. Lots of design variables to play with to affect the result in both directions. Trying to make a long stroke engine into high speed would have the type of result mentioned though.

 

[Tom F&L GoR]

Well, Mr. Roush could be wrong. I tend to believe it (assuming decent rod bolts) because compression loads go up proportionately (linearly, I would assume) with MEP and inertial loads get larger faster with speed (probably a squared function.) A little more power is easy, a little more RPM is a potential problem.

According to the paper, that engine is at 100HP/L, has a 0.85 bore/stroke ratio (oversquare) and the analysis for designing the con rod was at 7000 RPM.