I was all ready to tear into the engine and advance the cam timing 5 to 7 degrees. The rational was since the engine in turning 10% slower than stock due to the large tires, that advancing the cam would allow allow me to lug the engine more. This would reduce frictional losses, since they are proportional to rpm squared, reduce pumping losses since I'd be lugging at open throttle and move the bsfc minimum point down, however after researching Google on the subject I am not sure if advancing is the right way to go.
TDI diesels and Cummings turbo diesels seem to respond to advancing cam timing with better low end power and better mpg, 2 mpg for the truck.
Ford 460 engines are reportedly peppier and have better mileage with the cam advanced 5 degrees. Many chevy 350 enthusiasts advance cam timing for street use.
AndyMan on the other hand has has retarded cam timing on 4 Hondas with favourable results.
Toyota Hybrid engine has a modified Atkinson cycle.
Analysis:
1) Diesels are not limited by pre-ignition.
2) Large low compression engines, 8.6:1 probably benefit from advanced cam timing.
3) When warm, my sc1 engine knock sensor is actively retarding the timing at low rpm and full throttle so the reduction in effective compression ratio due to late intake closing would not effect mean effective cylinder pressure.
4) Opening the exhaust valve later could increase efficiency or increase pumping losses.
5) On the highway, at 65 mph, the 2 liter engine is at 2040 rpm and on flat ground very little throttle is needed, due to the aerodynamic improvements (
http://ecomodder.com/forum/showthrea...ods-15529.html) so retarding the cam timing should reduce pumping losses.
6) The right way to would be to mill the head to increased compression ratio and retard cam timing, but Saturn engines are a bitc_ to work on with the timing chain cover, not simple like old Honda engines. I may take a trip to the junk yard and scavenge a head.