Quote:
Originally Posted by sixto
Can going from 1.6 to 1.7 ratio rockers improve cruising mpg in a '93 351W EFI? I found an article with aircooled VW dyno tests comparing 1.1 to 1.4 ratio rockers. The 1.4s made more power from 3500 and allowed the engine to rev higher. No torque charts. If the same results apply to a 351W, will that help mpg?
Sixto
87 300D
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A change of 1.1 to 1.4 is a MUCH bigger change than 1.6 to 1.7. The first is about a 22% change and the second is only about a 6% change.
That aside, there are MANY variables involved. I personally wouldn't bother with such a modification unless I were in the midst of an engine build and buying parts anyway.
On the American V8's, it has been shown numerous times that going to full roller rockers will have almost as much effect as the ratio change due to friction loss. The REAL benefit of full roller rockers is lowered oil temperature.
Another benefit if high lift rockers, is in a situation where you are reaching some valve train geometry stumbling blocks that are putting you in a situation where an increase would make for a short lived cam and lifter combination which made me think of something:
Isn't that a roller cam version of the 351W? If so, already being set up for a roller cam opens up some possibilities. Even so, IF you could wangle any fuel economy improvement, it would be fractional and would take a LONG time to recoup the modification cost.
The biggest factors in fuel economy are weight and aerodynamics. In you vehicle it won't be easy to address either of these situations. Those are good trucks, but they've NEVER been known as economy vehicles.