Has someone analyzed which configuration gives the best end results? Especially when looking at turbocharged eco and sports engines where you want to have
high specific output but still a broad torque curve. Do you get the broadest torque curve with 5 valves or 4 valve with VVL (seeing as you can’t have VVL with 5 valves currently)?
I realize I could test this myself but there are so many variables I’d like to hear from what others have found about this first. Thanks!
4 valve vvl has a broader range but 5 valve has better airflow and less weight per valve which allows higher revs and more top end power. In terms of just economy I’d say it goes 4 valve-5valve-4valve vvl. After that its mostly user’s preference as there are pros and cons between vvl and 5valve, like reliability, weight, service costs, torque, economy… Its about what kind of character you want your engine to have.
Edit
VVL also has plenty of variation just in itself, you can have a very abrupt kick in or you can make a broad smooth curve. If you are looking for a economic turbo car I’d say vvl, you can get nice flat torque curve with the right set of cams, and turbo setup. 5 valve turbos can make lots of top end power but with more lag, it’s a lot harder to make the turbo both spool quick and still rev high with only 1 can profile.
5 valve: recommended for race engines that doesn’t had much power and torque at bottom RPM, and is designed to perform at high RPM.
4 valve+ VVL: recomended for road cars, because you can select 2 cam profiles to make a smooth, progressive and a flatten torque and lineal power delivery at all RPM.