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Cam Shaft Specifications for Maximizing Fuel Economy

I am in the process of having a 22R engine rebuilt for my '87 Toyota 1/2 Ton Pick-Up. (Standard Carb.) I have asked the guys at the machine shop to either get or have machined a new cam shaft that would maximize fuel economy. What (generally) would the cam specifications (or profile) for maximizing fuel economy? I generally drive the vehicle for getting from Point A to Point B and only occasionally actually use it as a truck for actually hauling stuff. Thanks!

Comments

  • edited August 2008
    For most older domestic truck engines, there is the "RV Cam" which maximizes low end torque, and fuel economy. There may be a similar option for your truck. Of course you'd lose top end power as well. You're driving a 20 year old 4 banger pickup truck. It was about the most fuel efficent small truck when it was new. It'll be hard to improve on it.
  • edited August 2008
    I agree w/daddy-stock cam would be hard to beat. Also, do you have a shop that can reliably grind a cam for you? I thought that took some special skills....
  • edited August 2008
    Chevrolet just came out with their Cobalt XFE model that improved highway mileage from 33 to 36 mpg for 2008 and 37 for 2009. As I understand, they changed the camshaft profile, reprogrammed the computer, revised the transmission and final gear ratios, removed the spare tire and replaced it with a sealant kit and an inflator pump for reduced vehicle weight and also used low rolling resistance tires.

    My guess is that the camshaft revision is a small portion of the 3 or 4 mpg improvement. You can take it from there.
  • edited August 2008
    You just about have it right now. I do understand that improvement is possible but it's not very likely that anybody would know just where to make the changes. Narrow tires might help.
  • edited August 2008
    I'm not really sure if a mild cam designed for low rpm torque is really what you want for best fuel economy. I can think of several motorcycles that got lower mpg after the factories retuned the engines for better mid and low rpm torque. Also, Toyota's variable valve timing (VVT)used to switch from advanced intake valve timing for low rpm torque to retarded intake valve timing for high rpm power at a certain rpm. Today's intelligent variable valve timing (VVTi) switches modes not just on rpm but also throttle position. When the engine idles with the throttle closed, the cam is in the retarded position that the older dumb VVT only had the cam in during high rpm. That retarded intake timing kills the manifold vacuum because the valve waits until the piston goes up the cylinder a ways before closing and lets the piston return a portion of the charge back to the manifold.

    What's going on here? I think that engines that are tumed to make maximum low and midrange torque also make maximum intake manifold vacuum when the throttle is closed. The pistons having to fight against that manifold vacuum during the intake stroke causes the engine to have to do a lot of work just to pump the air through it during low power use.
    BTW, what most people call "compression braking" is really pumping loss braking. Two stroke engines nearly freewheel when you close the throttle (compared to four strokes) and they have a compression stroke every revolution. The compression stroke is like a hill in the road, you slow down going up it but the hill speeds you right back up going down it. The energy is returned. On the other hand, the vacuum of the intake stroke is like a hill that only goes up.

    I also remember a how-to article in a hot rod magazine that showed how to improve the horsepower of the engine used in the Ford Pinto by retarding the cam a few degrees for better high rpm power. A curious side benefit was a few more mpg.
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