Quote:
Originally Posted by mmartin762
Do you have any experience with cam in block engines with non-variable valve timing? I wish to know about advancing the cam. I have a double roller timing chain set with 3 keyways: 4* advance, 0*, 4* retard. I am told a 4* advance brings max the torque point down in the rpm range. Will this hurt my fuel mileage as a side effect? I cant seem to get a straight answer. I know most camshafts have a degree built in. If it will hurt my fuel economy, i simply wont do it.
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I've had more experiences with OHC engines but I never tried advancing or retarding stock cams. Anyway, simply setting the peak torque point down in the RPM range won't do any "miracle" efficiency-wise, unless those torque figures are higher enough to justify running at a higher gear with a lower engine RPM. You may know, as a rule of thumb the gear ratio means not just how many times the engine must spin for the wheels to do a complete turn, and it's also how many times the torque is going to be multiplied. So, let's consider two engines with the same displacement, one rated at 250lb.ft. at 3000 RPM and the other rated at 300lb.ft. at 2500 RPM, the one with the lower torque rating at a higher RPM would not just spin 20% faster but also require a lower gearing to keep the same effective torque at the wheels while driving at the same speed.